Category Archives: Astronomy

Linking Gravitational Wave Detection to the Rest of the Observable Spectrum

The Laser Interferometer Gravitational-Wave Observatory (LIGO) in the U.S. reported the first ever detection of gravitational waves on 14 September 2015 and, to date, has reported three confirmed detections of gravitational waves originating from black hole coalescence events. These events and their corresponding LIGO press releases are listed below.

  • GW150914, 14 September 2015

https://www.ligo.caltech.edu/page/press-release-gw150914

  • GW151226, 26 December 2015

https://www.ligo.caltech.edu/page/press-release-gw151226

  • GW170104, 4 January 2017

https://www.ligo.caltech.edu/page/press-release-gw170104

The following figure illustrates how these black hole coalescence events compare to our knowledge of the size of black holes based on X-ray observations. The LIGO team explained:

“LIGO has discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). The three confirmed detections by LIGO (GW150914, GW151226, GW170104), and one lower-confidence detection (LVT151012), point to a population of stellar-mass binary black holes that, once merged, are larger than 20 solar masses—larger than what was known before.”

Image credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

On 1 August 2017, the Advanced VIRGO detector at the European Gravitational Observatory (EGO) in Cascina, Italy (near Pisa) became operational, using wire suspensions for its interferometer mirrors instead of the fragile glass fiber suspensions that had been delaying startup of this detector.

On 17 August 2017, the LIGO – VIRGO team reported the detection of gravitational waves from a new source; a collision of two neutron stars. In comparison to black holes, neutron stars are low-mass objects, yet the neutron star collision was able to generate gravitational waves that were strong enough and in the detection frequency range of the LIGO and VIRGO. You’ll find the LIGO press release for that event, GW170817, at the following link.

https://www.ligo.caltech.edu/page/press-release-gw170817

The following figure from this press release illustrates the limits of localizing the source of a gravitational wave using the gravitational wave detectors themselves. The localization of GW180817 was much better than the previous gravitational wave detections because the detection was made by both LIGO and VIRGO, which have different views of the sky and a very long baseline, allowing coarse triangulation of the source.

Gravitational wave sky map. Credit__LIGO_Virgo_NASA_Leo_Singer__Axel_Melli

Unlike the previous gravitational wave detections from black hole coalescence, the neutron star collision that produced GW180817 also produced other observable phenomena. Gravitational waves were observed by LIGO and VIRGO, allowing coarse localization to about 31 square degrees in the sky and determination of the time of the event. The source of a two-second gamma ray burst observed at the same time by the Fermi and INTEGRAL gamma ray space telescopes (in Earth orbit) overlapped with the region of the sky identified by LIGO and VIRGO. An optical transient (the afterglow from the event) in that overlap region was first observed hours later by the 1 meter (40 inch) Swope Telescope on Cerro Las Campanas in Chile. The results of this localization process is shown below and is described in more detail in the following LIGO press release:

https://www.ligo.caltech.edu/news/ligo20171016

The sky map created by LIGO-Virgo (green) showing the possible location of the source of gravitational waves, compared with regions containing the location of the gamma ray burst source from Fermi (purple) and INTEGRAL (grey). The inset shows the actual position of the galaxy (orange star) containing the “optical transient” that resulted from the merger of two neutron stars (Credit: NASA/ESO)

The specific source initially was identified optically as a brilliant blue dot that appeared to be in a giant elliptical galaxy. A multi-spectral “afterglow” persisted at the source for several weeks, during which time the source became a dim red point if light. Many observatories were involved in detailed observations in the optical and infra-red ranges of the spectrum.

Important findings relate to the formation of large quantities of heavy elements (i.e., gold to uranium) in the aftermath of this event, which is known as a “kilonova.” This class of events likely plays an important role in seeding the universe with the heaviest elements, which are not formed in ordinary stars or novae. You’ll find more details on this matter in Lee Billing’s article, “Gravitational Wave Astronomers Hit the Mother Lode,” on the Scientific American website at the following link:

https://www.scientificamerican.com/article/gravitational-wave-astronomers-hit-mother-lode1/

The ability to localize gravitational wave sources will improve as additional gravitational wave detectors become operational and capabilities of existing detectors continue to be improved. The current status of worldwide gravitational wave detector deployment is shown in the following figure.

Source: LIGO

The ability to take advantage of “multi-messenger” (multi-spectral) observations will depend on the type of event and timely cueing of observatories worldwide and in orbit. The success of the GW170817 detection and subsequent multi-spectral observations of “kilonova” demonstrates the rich scientific potential for such coordinated observations

 

Near-Earth Object (NEO) Sky Surveys and Data Analysis are Refining our Understanding of the Risk of NEO Collisions with Earth

It seems that every week or two there is a news article about another small asteroid that soon will pass relatively close to the Earth. Most were detected while they were still approaching Earth. Some were first detected very shortly before or after their closest approach to Earth. That must have made the U.S. Planetary Defense Officer a bit nervous, but then, what could he do about it? (See my 21 January 2016 post, “Relax, the Planetary Defense Officer has the watch”).

While we currently can’t do anything to defend against NEOs, extensive worldwide programs are in place to identify and track NEOs and predict which NEOs may present a future hazard to the Earth. Here’s a brief overview of the following programs.

  • NASA Wide-field Infrared Survey Explorer (WISE)
  • International Astronomical Union’s (IAU’s) Minor Planet Center (MPC)
  • NASA’s Center for Near Earth Object Studies (CNEOS)
  • National Optical Astronomy Observatory (NOAO) NEO sky survey
  • University of Arizona Lunar and Planetary Laboratory

NASA’s Wide-field Infrared Survey Explorer (WISE)

WISE was an Earth orbiting infrared-wavelength astronomical space telescope with a 40 cm (16 in) diameter primary mirror. WISE operated from December 2009 to February 2011 and performed an “all-sky” astronomical imaging survey in the 3.4, 4.6, 12.0 and 22.0 μm wavelength bands. NASA’s home page for the WISE / NEOWISE mission is at the following link:

https://www.nasa.gov/mission_pages/neowise/mission/index.html

NEOWISE is the continuing NASA project to mine the WISE data set. An important data mining tool is the WISE Moving Object Processing System (WMOPS), which has been optimized to enable extraction of moving objects at lower signal-to-noise levels. A comet detection is shown in the following multiple images that have been combined to show the comet in four different positions relative to the fixed background stars.

Comet C/2013 A1 Siding Spring. Source: NASA/JPL-Caltech

To date, the NEOWISE data mining effort has resulted in the following:

  • Detection of ~158,000 asteroids at thermal infrared wavelengths, including ~700 near-Earth objects (NEOs) and ~34,000 new asteroids, 135 of which are NEOs.
  • Detection of more than 155 comets, including 21 new discoveries.
  • Determination of preliminary physical properties such as diameter and visible albedo for nearly all of these objects.
  • Estimation of the numbers, sizes, and orbital elements of NEOs, including potentially hazardous asteroids
  • Results have been published, enabling a range of other studies of the origins and evolution of the small bodies in our solar system.

The output from NEOWISE is delivered to NASA’s Planetary Data System (PDS), which NASA describes as follows:

“The PDS archives and distributes scientific data from NASA planetary missions, astronomical observations, and laboratory measurements. The PDS is sponsored by NASA’s Science Mission Directorate. Its purpose is to ensure the long-term usability of NASA data and to stimulate advanced research. All PDS data are publicly available and may be exported outside of United States under ‘Technology and Software Publicly Available’ (TSPA) classification.”

The link to the NASA Planetary Data System is here:

https://pds.nasa.gov

International Astronomical Union’s (IAU’s) Minor Planet Center (MPC)

The MPC describes itself as the “single worldwide location for receipt and distribution of positional measurements of minor planets, comets and other irregular natural satellites of the major planets. The MPC is responsible for the identification, designation and orbit computation for all of these objects.”

The MPC home page is here:

http://www.minorplanetcenter.net/iau/mpc.html

On this website, MPC lists the following 2017 summary statistics:

Source: MPC

The MPC website offers several short videos that explain the NEO hazard and the challenges of detecting these small objects and determining their orbital parameters with high precision. Key points made in the MPC videos include:

  • The Earth’s cross-section represents only 1/10,000th of the area of the near-Earth region. Earth is a relatively small target area for a NEO.
  • To determine if a NEO is a potential hazard, its orbital parameters must be established with a precision of greater than 1/100th of 1%.
  • There is a “zone of discoverability” (green area in the following diagram) that varies primarily by the size of the object and the aspect of its lighted side to observers on Earth. If an object is outside this rather small zone, then current sky survey instruments cannot detect the object. An example is the 15 February 2013 atmospheric blast that occurred near Chelyabinsk, Russia. This event was caused by a previously undetected NEO that approached Earth at a high relative velocity from the direction of the Sun and vaporized in the Earth’s atmosphere.

            Zone of discoverability (green area). Source: screenshot from MPC video “Asteroid Hazards, Part 2: The Challenge of Detection”

 NASA’s Center for Near Earth Object Studies (CNEOS)

CNEOS is NASA’s center for computing asteroid and comet orbits with high precision and estimating the probability of a future Earth impact. CNEOS is operated by the California Institute of Technology (Caltech) Jet Propulsion Laboratory (JPL) and supports NASA’s Planetary Defense Coordination Office.

The CNEOS home page is here:

http://cneos.jpl.nasa.gov/about/cneos.html

CNEOS is the home of JPL’s Sentry and Scout programs:

  • The Sentryimpact monitoring system performs long-term analyses of possible future orbits of hazardous asteroids, searching for impact possibilities over the next century.
  • TheScout system monitors the IAU’s MPC database for new potential asteroid discoveries and computes the possible range of future motions even before these objects have been confirmed as discoveries.

The average distance between the Earth and the moon is about 238,855 miles (384,400 km), which equals 1 LD. On the CNEOS website, you can view data on NEO close approaches to Earth at the following link:

https://cneos.jpl.nasa.gov/ca/neo_ca_intro.html

By adjusting the table settings and sorting by a specific column heading, you can create customized views of the close approach data. Just looking at data from the past year for NEOs that passed Earth within 1 LD yielded the following results:

  • 48 NEOs passed within 1 LD of Earth.
  • For these NEOs, object diameters were in the range from 1.8 to 83 meters (5.9 to 272 feet). The NEO that caused the 2013 Chelyabinsk blast was estimated to have a diameter of 10 to 20 meters (32.8 to 65.6 feet).
  • Their relative velocities were in the range from 4.02 to 23.97 km/s (8,992 to 53,620 mph). The NEO that caused the 2013 Chelyabinsk blast was estimated to have a relative velocity of 19.16 km/s (45,860 mph).
  • In the past year, the closest approach was by object 2017 GM, which had a “CA Distance Minimum” (3-signa estimate, measured from Earth center to NEO center) of 0.04 LD, or 15,376 km (9,554 miles). After subtracting Earth’s radius of 6,371 km (3,959 miles), object 2017 GM cleared the Earth’s surface by 9,005 km (5,595 miles).

Looking into the future, the CNEOS close approach data shows two objects that currently have values of “CA Distance Minimum” that are less than the radius of the Earth, indicating that impact is possible:

  • Object 2012 HG2: close approach date on 13 February 2047; modest size of 11 – 24 meters (36 – 79 feet); low relative velocity of 4.36 km/sec (9,753 mph)
  • Object 2010 RF12: close approach date of 6 September 2095; modest size of 6.4 – 14 meters (21 to 46 feet); modest relative velocity of 7.65 km/sec (17,112 mph)

So it looks like we have less than 30 years to refine the orbital data on object 2012 HG2, determine if it will impact Earth, and, if so, determine where the impact will occur and what mitigating actions can be taken. Hopefully, the U.S. Planetary Defense Officer is on top of this matter.

National Optical Astronomy Observatory (NOAO) NEO sky survey

On 30 August 2017, NOAO issued a press release summarizing the results of a survey of NEOs conducted using the Dark Energy Camera (DECam) on the 4 meter (157.5 inch) Blanco telescope at the Cerro Tololo Inter-American Observatory in northern Chile.

“Lori Allen, Director of the Kitt Peak National Observatory and the lead investigator on the study, explained, ‘There are around 3.5 million NEOs larger than 10 meters, a population ten times smaller than inferred in previous studies. About 90% of these NEOs are in the Chelyabinsk size range of 10-20 meters.’”

“David Trilling, the first author of the study,…explained…..‘If house-sized NEOs are responsible for Chelyabinsk-like events, our results seem to say that the average impact probability of a house-sized NEO is actually ten times greater than the average impact probability of a large NEO.’”

You can read the NOAO press release here:

https://www.noao.edu/news/2017/pr1704.php

You can read the draft paper, “The size distribution of Near Earth Objects larger than 10 meters,” (to be published in Astronomical Journal) here.

https://arxiv.org/pdf/1707.04066.pdf

University of Arizona Lunar and Planetary Laboratory

In October 2017, astronomer Vishnu Reddy presented data on an intriguing NEO known as 2016 HO3, that is a “quasi-satellite” of Earth. The announcement is here:

https://lbtonews.blogspot.com/2017/10/earths-new-traveling-buddy-is.html

As a “quasi-satellite,” 2016 HO3 is not gravitationally bound to Earth, but its solar orbit keeps 2016 HO3 in relatively close proximity to Earth, but in a slightly different orbital plane. As both bodies orbit the Sun, the motion of 2016 HO3 relative to the Earth gives the appearance that 2016 HO3 is in a distant halo orbit around Earth. The approximate geometry of this three body system is shown in the following diagram, with 2016 HO3’s solar orbit represented in red and the halo orbit as seen from Earth represented in yellow.

Source: www.EarthSky.org

You’ll find a video showing the dynamics of 2016 HO3’s halo orbit on the EarthSky website at the following link:

http://earthsky.org/space/near-earth-quasi-satellite-2016-ho3-confirmation?mc_cid=4d2056208e&mc_eid=19a1fde155

Observations of 2016 HO3 were made from the Large Binocular Telescope Observatory (LBTO), which is located on Mt. Graham in Arizona. You’ll find details on LBTO at the following link:

http://www.lbto.org/overview.html

Key parameters for 2016 HO3 are: diameter: 100 meters (330 feet); distance from Earth: 38 to 100 LD; composition appears to be the same material as other asteroid NEOs. With its stable halo orbit, there is no risk that 2016 HO3 will collide with Earth.

For additional reading on NEO discovery:

Myhrvold, “Comparing NEO Search Telescopes,” Astronomical Society of the Pacific, April 2016

Abstract:

“I use simple physical principles to estimate basic performance metrics for the ground-based Large Synoptic Survey Telescope and three space-based instruments— Sentinel, NEOCam, and a Cubesat constellation.”

http://iopscience.iop.org/article/10.1088/1538-3873/128/962/045004/pdf

S.R. Chesley & P. Vereš, “Projected Near-Earth Object Discovery Performance of the Large Synoptic Survey Telescope,” JPL Publication 16-11, CNEOS, April 2017

Abstract:

“LSST is designed for rapid, wide-field, faint surveying of the night sky ….The baseline LSST survey approach is designed to make two visits to a given field in a given night, leading to two possible NEO detections per night. These nightly pairs must be linked across nights to derive orbits of moving objects…… Our simulations revealed that in 10 years LSST would catalog 60% of NEOs with absolute magnitude H < 22, which is a proxy for 140 m and larger objects.”

https://cneos.jpl.nasa.gov/doc/JPL_Pub_16-11_LSST_NEO.pdf

 

The Event Horizon Telescope

The Event Horizon Telescope (EHT) is a huge synthetic array for Very Long Baseline Interferometry (VLBI), which is created through the collaboration of millimeter / submillimeter wave radio telescopes and arrays around the world. The goal of the EHT “is to directly observe the immediate environment of a black hole with angular resolution comparable to the event horizon.”

The primary target for observation is Sagittarius A* (Sgr A*), which is the massive black hole at the center of our Milky Way galaxy. This target is of particular interest to the EHT team because it “presents the largest apparent event horizon size of any black hole candidate in the Universe.” The Sgr A* event horizon is estimated to have a Schwarzschild radius of 12 million kilometers (7.46 million miles) or a diameter of 24 million km (14.9 million miles). The galactic core (and hence Sgr A*) is estimated to be 7.6 to 8.7 kiloparsecs (about 25,000 to 28,000 lightyears, or 1.47 to 1.64e+17 miles) from Earth. At that distance, the Sgr A* black hole subtends an angle of about 2e-5 arcseconds (20 microarcseconds).

Another EHT target of interest is a much more distant black hole in the Messier 87 (M87) galaxy.

The member arrays and telescopes supporting EHT are:

  • Arizona Radio Observatory /Submillimeter Wave Telescope (ARO/SMT, Arizona, USA)
  • Atacama Pathfinder EXperiment (APEX, Chile)
  • Atacama Submillimeter Telescope Experiment (ASTE, Chile)
  • Combined Array for Research in Millimeter-wave Astronomy (CARMA, California, USA)
  • Caltech Submillimeter Observatory (Hawaii, USA)
  • Institute de Radioastronomie Millimetrique (IRAM, Spain)
  • James Clerk Maxwell Telescope (JCMT, Hawaii)
  • Large Millimeter Telescope Alfonso Serrano (LMT, Mexico)
  • The Submillimeter Array (Hawaii, USA)

The following arrays and telescopes are expected to join the EHT collaboration:

  • Atacama Large Millimeter / submillimeter Array (ALMA, Chile)
  • Northern Extended Millimeter Array (NOEMA, France)
  • South Pole Telescope (SPT, Antarctica)

Collectively, the arrays and telescopes forming the EHT provide a synthetic aperture that is almost equal to the diameter of the Earth (12,742 km, 7,918 miles).

EHT array sizeSource: graphics adapted by A. Cuadra / Science; data from Event Horizon Telescope

Technical improvements to the member telescopes and arrays are underway with the goal of systematically improving EHT performance. These improvements include development and deployment of:

  • Submillimeter dual-polarization receivers (energy content of cosmic radiation is split between two polarizations)
  • Highly stable frequency standards to enable VLBI at frequencies between 230 to 450 GHz (wavelengths of 1.3 mm – 0.6 mm).
  • Higher-bandwidth digital VLBI backends and recorders

In operations to date, EHT has been observing the Sgr A* and M87 black holes at 230 GHz (1.3 mm) with only some of the member arrays and telescopes participating. These observations have yielded angular resolutions of better than 60 microarcseconds. Significantly higher angular resolutions, up to about 15 microarcseconds, are expected from the mature EHT operating at higher observing frequencies and with longer baselines.

Coordinating observing time among all of the EHT members is a challenge, since participation in EHT is not a dedicated mission for any site. Site-specific weather also is a factor, since water in the atmosphere absorbs radiation in the EHT observing frequency bands. The next observing opportunity is scheduled between 5 – 14 April 2017. Processing the data from this observing run will take time, hence results are not expected to be known until later this year.

For more information on EHT, see the 2 March 2017 article by Daniel Clery entitled, ”This global telescope may finally see the event horizon of our galaxy’s giant black hole,” at the following link:

http://www.sciencemag.org/news/2017/03/global-telescope-may-finally-see-event-horizon-our-galaxys-giant-black-hole?utm_campaign=news_daily_2017-03-02&et_rid=215579562&et_cid=1194555

Much more information is available on the EHT website at the following link:

http://www.eventhorizontelescope.org

Radio telescope resolution

An article on the Las Cumbres Observatory (LCO) website explains how the angular resolution of radio telescopes, including VLBI arrays, is determined. In this article, the author, D. Stuart Lowe, states that “an array of radio telescopes of 217 km in diameter can produce an image with a resolution equivalent to the Hubble Space Telescope.” You’ll find this article here:

https://lco.global/spacebook/radio-telescopes/

The Hubble Space Telescope has an angular resolution of 1/10th of an arcsecond (1e-1 arcsecond).

A VLBI array with the diameter of the Earth (1.27e+6 meters) operating in the EHT’s millimeter / submillimeter wavelength band (1.3e-3 to 6.0e-4 meters) has a theoretical angular resolution of 2.5e-5 to 1.2e-5 arcseconds (25 to 12 microarcseconds).

EHT should be capable of meeting its goal of angular resolution comparable to a black hole’s event horizon.

X-ray observation of Sgr A*

Combining infrared images from the Hubble Space Telescope with images the Chandra X-ray Observatory, NASA created the following composite image showing the galactic core in the vicinity of Sgr A*. NASA reports:

“The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow. The inset shows a close-up view of Sgr A* in X-rays only, covering a region half a light year wide. The diffuse X-ray emission is from hot gas captured by the black hole and being pulled inwards.”

This image gives you a perspective on the resolution of Sgr A* possible at X-ray frequencies with current equipment. EHT will have much higher resolution in its radio frequency bands.

NASA Sgr A* picSource: X-Ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

More details on this image are available at the following NASA link:

https://www.nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html

Animation of Sgr A* effects on nearby stars

In my 24 January 2017 post, “The Black Hole at our Galactic Center is Revealed Through Animations,” I reported on how teams of astronomers were developing a better understanding of the unseen Sgr A* black hole through long-term observations of the relative motions of nearby stars that are under the influence of this black hole.

The Black Hole at our Galactic Center is Revealed Through Animations

Evidence is mounting that a supermassive black hole named Sagittarius A* (Sagittarius A star) dominates the center of our Milky Way galaxy. Long-term observations of the galactic center by teams of astronomers are refining our understanding of how stars move in relation to this unseen black hole.

European Southern Observatory (ESO) observations of the galactic center

The ESO, which has many observatories located high in the mountains of northern Chile, has a team involved in observing our galactic center. Two of the ESO optical observatories used in this effort are:

  • New Technology Telescope (NTT), at the La Silla Observatory, has a 3.58 m (11.75 ft) main mirror. In 1989, NTT became the first astronomical observatory with adaptive optics to help correct for atmospheric distortion.
  • Very Large Telescope (VLT), which consists of four Unit Telescopes with 8.2 m (26.9 ft) diameter main mirrors and adaptive optics. The telescopes can work together, to form a giant ‘interferometer’, allowing astronomers to see details up to 25 times finer than with the individual Unit Telescopes.

On 10 December 2008, ESO issued a “science release” entitled, ”Unprecedented 16-Year Long Study Tracks Stars Orbiting Milky Way Black Hole,” which summarized the results of observations made at NTT and VLT from 1992 to 2008. This study mapped the orbits of 30 stars in the region around the galactic center (and did not use VLT’s interferometric capabilities).

 Galactic center_eso0846aStars near our galactic center and the Sagittarius A* black hole. Source: eso0846 Science Release

The eso0846 science release is available at the following link:

http://www.eso.org/public/usa/news/eso0846/

In connection with this study, the ESO team also created a time-lapse video showing star motion around the Sagittarius A* black hole.

“Here, actual images, collected over the past 16 years, have been assembled into a time-lapse video. The real motion of the stars has been accelerated by a factor 32 million.”

This time-lapse video covers the central part of the above color image of the galactic center and shows stars moving around central point that is likely to be the black hole. You can see this animated sequence at the following link:

http://www.eso.org/public/usa/videos/eso0846j/

UCLA Galactic Center Group observations of the galactic center

The mission statement of the UCLA Galactic Center Group is:

“Transforming our understanding of Black Holes and their role in the Universe with high resolution observations of the Center of our Galaxy!”

The Galactic Center Group’s website is a good source of information on black hole science and the technologies employed to observe our galactic center. Their home page is at the following link:

http://www.galacticcenter.astro.ucla.edu/about.html

The W.M. Keck Observatory on Mauna Kea in Hawaii is comprised of two large telescopes, each with 10 m (33 ft) main mirrors and adaptive optics. Currently the Keck Observatory has the largest optical / infrared telescopes in the world. These telescopes have higher resolution than ESO’s NTT and VLT.

Using images taken at the Keck Observatory from 1995 to 2014, the UCLA Galactic Center Group and the W.M. Keck Observatory Laser Team have released their determination of the orbits of stars within the central 1.0 X 1.0 arcseconds of our galaxy, as shown in the following diagram.

UCLA-Keck-2014

The team reported:

“These orbits provide the best evidence yet for a supermassive black hole. While every star in this image has been observed to move since 1998, estimates of orbital parameters are best constrained for stars that have been observed through at least one turning point of their orbits.”

This makes the star S0-2 especially important because it has been observed for more than one full orbital period, which for S0-2 is only 16.17 years. The team estimates that the Sagittarius A* black hole has a mass of 4 million times the mass of the Sun.

The UCLA Galactic Center Group and the W.M. Keck Observatory Laser Team have created a series of animations that demonstrate the motion of stars near the Sagittarius A* black hole. You can navigate to these animations from the home page listed above or use the following direct link:

http://www.galacticcenter.astro.ucla.edu/animations.html

The three animations showing star motions around the Sagittarius A* black hole are:

  • Animation of the Stellar Orbits around the Galactic Center
  • 3D Movie of Stellar Orbits in the Central Parsec
  • Sagittarius A* – IR (infrared)

The importance of adaptive optics is astronomical observations is demonstrated in another animation from the UCLA Galactic Center Group.

“This animation shows observations of the Galactic Center with and without adaptive optics, illustrating the resolution gain. Adaptive optics corrects for the blurring effects of the Earth’s atmosphere. Using a bright star, we measure how a wavefront of light is distorted by the atmosphere and quickly adjust the shape of a deformable mirror to remove these distortions.”

Screenshots from this animation are shown below. The screenshot on the left is with adaptive optics OFF. The image on the right is with adaptive optics ON.

Adaptive optics OFF  Adaptive optics ON

The future

In my 6 June 2015 post, “Three Very Large, New Optical Telescopes are Under Development,” I reported on the Thirty Meter Telescope (TMT), which originally was planned for construction on Mauna Kea, near the Keck Observatory. As the name implies, TMT will have a 30 m (98.4 ft) main mirror and adaptive optics. To illustrate the improved resolution of TMT, the UCLA Galactic Center Group developed an animation showing Sagittarius A* images for the following three cases:

  • Keck telescopes with current adaptive optics (AO)
  • Keck telescopes with “next generation” adaptive optics (NGAO), and
  • The future TMT with adaptive optics.

As you can see in the following screenshot from this animation, the expected results from the much higher resolution TMT quite impressive.

Relative resolution power - Keck & TMT

TMT’s actual construction site is being reconsidered and construction has been delayed. However, ESO has broken ground for the even larger European Extremely Large Telescope (E-ELT), which is being built now at Cerro Armazones, Chile. This giant telescope has a 39 m (128 ft) main mirror and adaptive optics. It will become the largest optical / infrared telescope in the world when it is commissioned as part of ESO’s Paranal Observatory in 2024. Hopefully, time on this great telescope will be allocated to observing our galactic center.

 

 

 

NuSTAR Provides a High-Resolution X-ray View of our Universe

In my 6 March 2016 post, “Remarkable Multispectral View of Our Milky Way Galaxy,” I briefly discussed several of the space-based observatories that are helping to develop a deeper understanding of our galaxy and the universe. One space-based observatory not mentioned in that post is the National Aeronautics and Space Administration (NASA) Nuclear Spectroscopic Telescope Array (NuSTAR) X-Ray observatory, which was launched on 13 June 2012 into a near equatorial, low Earth orbit. NASA describes the NuSTAR mission as follows:

“The NuSTAR mission has deployed the first orbiting telescopes to focus light in the high energy X-ray (6 – 79 keV) region of the electromagnetic spectrum. Our view of the universe in this spectral window has been limited because previous orbiting telescopes have not employed true focusing optics, but rather have used coded apertures that have intrinsically high backgrounds and limited sensitivity.

During a two-year primary mission phase, NuSTAR will map selected regions of the sky in order to:

1.  Take a census of collapsed stars and black holes of different sizes by surveying regions surrounding the center of own Milky Way Galaxy and performing deep observations of the extragalactic sky;

2.  Map recently-synthesized material in young supernova remnants to understand how stars explode and how elements are created; and

3.  Understand what powers relativistic jets of particles from the most extreme active galaxies hosting supermassive black holes.”

 The NuSTAR spacecraft is relatively small, with a payload mass of only 171 kg (377 lb). In it’s stowed configuration, this compact satellite was launched by an Orbital ATK Pegasus XL booster, which was carried aloft by the Stargazer L-1011 aircraft to approximately 40,000 feet over open ocean, where the booster was released and carried the small payload into orbit.

Orbital ATK L-1011 StargazerStargazer L-1011 dropping a Pegasus XL booster. Source: Orbital ATK

In orbit, the solar-powered NuSTAR extended to a total length of 10.9 meters (35.8 feet) in the orbital configuration shown below. The extended spacecraft gives the X-ray telescope a 10 meter (32.8 foot) focal length.

NuSTAR satelliteNuSTAR orbital configuration. Source: NASA / JPL – Caltech

NASA describes the NuSTAR X-Ray telescope as follows:

“The NuSTAR instrument consists of two co-aligned grazing incidence X-Ray telescopes (Wolter type I) with specially coated optics and newly developed detectors that extend sensitivity to higher energies as compared to previous missions such as NASA’a Chandra X-Ray Observatory launched in 1999 and the European Space Agency’s (ESA) XMM-Newton (aka High-throughput X-Ray Spectrometry Mission), also launched in 1999…….. The observatory will provide a combination of sensitivity, spatial, and spectral resolution factors of 10 to 100 improved over previous missions that have operated at these X-ray energies.”

The NASA NuSTAR mission website is at the following link:

https://www.nasa.gov/mission_pages/nustar/main/index.html

Some examples of NuSTAR findings posted on this website are summarized below.

X-ray emitting structures of galaxies identified

In the following composite image of Galaxy 1068, high-energy X-rays (shown in magenta) captured by NuSTAR are overlaid on visible-light images from both NASA’s Hubble Space Telescope and the Sloan Digital Sky Survey.

Galaxy 1068Galaxy 1068. Source: NASA/JPL-Caltech/Roma Tre Univ

Below is a more detailed X-ray view of portion of the Andromeda galaxy (aka M31), which is the galaxy nearest to our Milky Way. On 5 January 2017, NASA reported:

“The space mission has observed 40 ‘X-ray binaries’ — intense sources of X-rays comprised of a black hole or neutron star that feeds off a stellar companion.

Andromeda is the only large spiral galaxy where we can see individual X-ray binaries and study them in detail in an environment like our own.”

In the following image, the portion of the Andromeda galaxy surveyed by NuSTAR is in the smaller outlined area. The larger outlined area toward the top of this image is the corresponding X-ray view of the surveyed area.

Andromeda galaxyAndromeda galaxy.  Source: NASA/JPL-Caltech/GSFC

NASA describes the following mechanism for X-ray binaries to generate the observed intense X-ray emissions:

“In X-ray binaries, one member is always a dead star or remnant formed from the explosion of what was once a star much more massive than the sun. Depending on the mass and other properties of the original giant star, the explosion may produce either a black hole or neutron star. Under the right circumstances, material from the companion star can “spill over” its outermost edges and then be caught by the gravity of the black hole or neutron star. As the material falls in, it is heated to blazingly high temperatures, releasing a huge amount of X-rays.”

You can read more on this NuStar discovery at the following link:

https://www.nasa.gov/feature/jpl/Andromeda-Galaxy-Scanned-with-High-Energy-X-ray-Vision

Composition of supernova remnants determined

Cassiopeia A is within our Milky Way, about 11,000 light-years from Earth. The following NASA three-panel chart shows Cassiopeia A originally as an iron-core star. After going supernova, Cassiopeia A scattered its outer layers, which have distributed into the diffuse structure we see today, known as the supernova remnant. The image in the right-hand panel is a composite X-ray image of the supernova remnant from both the Chandra X-ray Observatory and NuStar.

Cassiopeia ASource: NASA/CXC/SAO/JPL-Caltech

In the following three-panel chart, the composite image (above, right) is unfolded into its components. Red shows iron and green shows both silicon and magnesium, as seen by the Chandra X-ray Observatory. Blue shows radioactive titanium-44, as mapped by NuSTAR.

 Cassiopeia A componentsSource: NASA/JPL-Caltech/CXC/SAO

Supernova 1987A is about 168,000 light-years from Earth in the Large Magellanic Cloud. As shown below, NuSTAR also observed titanium in this supernova remnant.

SN 1987A titaniumSource: NASA/JPL-Caltech/UC Berkeley

These observations are providing new insights into how massive stars explode into supernovae.

 

Severe Space Weather Events Will Challenge Critical Infrastructure Systems on Earth

What is space weather?

Space weather is determined largely by the variable effects of the Sun on the Earth’s magnetosphere. The basic geometry of this relationship is shown in the following diagram, with the solar wind always impinging on the Earth’s magnetic field and transferring energy into the magnetosphere.  Normally, the solar wind does not change rapidly, and Earth’s space weather is relatively benign. However, sudden disturbances on the Sun produce solar flares and coronal holes that can cause significant, rapid variations in Earth’s space weather.

auroradiagramSource: http://scijinks.jpl.nasa.gov/aurora/

A solar storm, or geomagnetic storm, typically is associated with a large-scale magnetic eruption on the Sun’s surface that initiates a solar flare and an associated coronal mass ejection (CME). A CME is a giant cloud of electrified gas (solar plasma.) that is cast outward from the Sun and may intersect Earth’s orbit. The solar flare also releases a burst of radiation in the form of solar X-rays and protons.

The solar X-rays travel at the speed of light, arriving at Earth’s orbit in 8 minutes and 20 seconds. Solar protons travel at up to 1/3 the speed of light and take about 30 minutes to reach Earth’s orbit. NOAA reports that CMEs typically travel at a speed of about 300 kilometers per second, but can be as slow as 100 kilometers per second. The CMEs typically take 3 to 5 days to reach the Earth and can take as long as 24 to 36 hours to pass over the Earth, once the leading edge has arrived.

If the Earth is in the path, the X-rays will impinge on the Sun side of the Earth, while charged particles will travel along magnetic field lines and enter Earth’s atmosphere near the north and south poles. The passing CME will transfer energy into the magnetosphere.

Solar storms also may be the result of high-speed solar wind streams (HSS) that emanate from solar coronal holes (an area of the Sun’s corona with a weak magnetic field) with speeds up to 3,000 kilometers per second. The HSS overtakes the slower solar wind, creating turbulent regions (co-rotating interaction regions, CIR) that can reach the Earth’s orbit in as short as 18 hours. A CIR can deposit as much energy into Earth’s magnetosphere as a CME, but over a longer period of time, up to several days.

Solar storms can have significant effects on critical infrastructure systems on Earth, including airborne and space borne systems. The following diagram highlights some of these vulnerabilities.

Canada Geomagnetic-Storms-effects-space-weather-technologyEffects of Space Weather on Modern Technology. Source: SpaceWeather.gc.ca

Characterizing space weather

The U.S. National Oceanic and Atmospheric Administration (NOAA)Space Weather Prediction Center(SWPC  uses the following three scales to characterize space weather:

  • Geomagnetic storms (G): intensity measured by the “planetary geomagnetic disturbance index”, Kp, also known as the Geomagnetic Storm or G-Scale
  • Solar radiation storms (S): intensity measured by the flux level of ≥ 10 MeV solar protons at GEOS (Geostationary Operational Environmental Satellite) satellites, which are in synchronous orbit around the Earth.
  • Radio blackouts (R): intensity measured by flux level of solar X-rays at GEOS satellites.

Another metric of space weather is the Disturbance Storm Time (Dst) index, which is a measure of the strength of a ring current around Earth caused by solar protons and electrons. A negative Dst value means that Earth’s magnetic field is weakened, which is the case during solar storms.

A single solar disturbance (a CME or a CIR) will affect all of the NOAA scales and Dst to some degree.

As shown in the following NOAA table (click on table to enlarge), the G-scale describes the infrastructure effects that can be experienced for five levels of geomagnetic storm severity. At the higher levels of the scale, significant infrastructure outages and damage are possible.

NOAA geomag storm scale

There are similar tables for Solar Radiation Storms and Radio Blackouts on the NOAA SWPC website at the following link:

http://www.swpc.noaa.gov/noaa-scales-explanation

Another source for space weather information is the spaceweather.com website, which contains some information not found on the NOAA SWPC website. For example, this website includes a report of radiation levels in the atmosphere at aviation altitudes and higher in the stratosphere. In the following chart, “dose rates are expressed as multiples of sea level. For instance, we see that boarding a plane that flies at 25,000 feet exposes passengers to dose rates ~10x higher than sea level. At 40,000 feet, the multiplier is closer to 50x.”

 spaceweather rad levelsSource: spaceweather.com

You’ll also find a report of recent and upcoming near-Earth asteroids on the spaceweather.com website. This definitely broadens the meaning of “space weather.” As you can seen the in the following table, no close encounters are predicted over the next two months.

spaceweather NEOs

In summary, the effects of a solar storm may include:

  • Interference with or damage to spacecraft electronics: induced currents and/or energetic particles may have temporary or permanent effects on satellite systems
  • Navigation satellite (GPS, GLONASS and Galileo) UHF / SHF signal scintillation (interference)
  • Increased drag on low Earth orbiting satellites: During storms, currents and energetic particles in the ionosphere add energy in the form of heat that can increase the density of the upper atmosphere, causing extra drag on satellites in low-earth orbit
  • High-frequency (HF) radio communications and low-frequency (LF) radio navigation system interference or signal blackout
  • Geomagnetically induced currents (GICs) in long conductors can trip protective devices and may damage associated hardware and control equipment in electric power transmission and distribution systems, pipelines, and other cable systems on land or undersea.
  • Higher radiation levels experienced by crew & passengers flying at high latitudes in high-altitude aircraft or in spacecraft.

For additional information, you can download the document, “Space Weather – Effects on Technology,” from the Space Weather Canada website at the following link:

http://ftp.maps.canada.ca/pub/nrcan_rncan/publications/ess_sst/292/292124/gid_292124.pdf

Historical major solar storms

The largest recorded geomagnetic storm, known as the Carrington Event or the Solar Storm of 1859, occurred on 1 – 2 September 1859. Effects included:

  • Induced currents in long telegraph wires, interrupting service worldwide, with a few reports of shocks to operators and fires.
  • Aurorea seen as far south as Hawaii, Mexico, Caribbean and Italy.

This event is named after Richard Carrington, the solar astronomer who witnessed the event through his private observatory telescope and sketched the Sun’s sunspots during the event. In 1859, no electric power transmission and distribution system, pipeline, or cable system infrastructure existed, so it’s a bit difficult to appreciate the impact that a Carrington-class event would have on our modern technological infrastructure.

A large geomagnetic storm in March 1989 has been attributed as the cause of the rapid collapse of the Hydro-Quebec power grid as induced voltages caused protective relays to trip, resulting in a cascading failure of the power grid. This event left six million people without electricity for nine hours.

A large solar storm on 23 July 2012, believed to be similar in magnitude to the Carrington Event, was detected by the STEREO-A (Solar TErrestrial RElations Observatory) spacecraft, but the storm passed Earth’s orbit without striking the Earth. STEREO-A and its companion, STEREO-B, are in heliocentric orbits at approximately the same distance from the Sun as Earth, but displaced ahead and behind the Earth to provide a stereoscopic view of the Sun.

You’ll find a historical timeline of solar storms, from the 28 August 1859 Carrington Event to the 29 October 2003 Halloween Storm on the Space Weather website at the following link:

http://www.solarstorms.org/SRefStorms.html

Risk from future solar storms

A 2013 risk assessment by the insurance firm Lloyd’s and consultant engineering firm Atmospheric and Environmental Research (AER) examined the impact of solar storms on North America’s electric grid.

electrical-power-transmission-lines-united-states-useiaU.S. electric power transmission grid. Source: EIA

Here is a summary of the key findings of this risk assessment:

  • A Carrington-level extreme geomagnetic storm is almost inevitable in the future. Historical auroral records suggest a return period of 50 years for Quebec-level (1989) storms and 150 years for very extreme storms, such as the Carrington Event (1859).
  • The risk of intense geomagnetic storms is elevated near the peak of the each 11-year solar cycle, which peaked in 2015.
  • As North American electric infrastructure ages and we become more dependent on electricity, the risk of a catastrophic outage increases with each peak of the solar cycle.
  • Weighted by population, the highest risk of storm-induced power outages in the U.S. is along the Atlantic corridor between Washington D.C. and New York City.
  • The total U.S. population at risk of extended power outage from a Carrington-level storm is between 20-40 million, with durations from 16 days to 1-2 years.
  • Storms weaker than Carrington-level could result in a small number of damaged transformers, but the potential damage in densely populated regions along the Atlantic coast is significant.
  • A severe space weather event that causes major disruption of the electricity network in the U.S. could have major implications for the insurance industry.

The Lloyds report identifies the following relative risk factors for electric power transmission and distribution systems:

  • Magnetic latitude: Higher north and south “corrected” magnetic latitudes are more strongly affected (“corrected” because the magnetic North and South poles are not at the geographic poles). The effects of a major storm can extend to mid-latitudes.
  • Ground conductivity (down to a depth of several hundred meters): Geomagnetic storm effects on grounded infrastructure depend on local ground conductivity, which varies significantly around the U.S.
  • Coast effect: Grounded systems along the coast are affected by currents induced in highly-conductive seawater.
  • Line length and rating: Induced current increases with line length and the kV rating (size) of the line.
  • Transformer design: Lloyds noted that extra-high voltage (EHV) transformers (> 500 kV) used in electrical transmission systems are single-phase transformers. As a class, these are more vulnerable to internal heating than three-phase transformers for the same level of geomagnetically induced current.

Combining these risk factors on a county-by-county basis produced the following relative risk map for the northeast U.S., from New York City to Maine. The relative risk scale covers a range of 1000. The Lloyd’s report states, “This means that for some counties, the chance of an average transformer experiencing a damaging geomagnetically induced current is more than 1000 times that risk in the lowest risk county.”

Lloyds relative risk Relative risk of power outage from geomagnetic storm. Source: Lloyd’s

You can download the complete Lloyd risk assessment at the following link:

https://www.lloyds.com/news-and-insight/risk-insight/library/natural-environment/solar-storm

In May 2013, the United States Federal Energy Regulatory Commission issued a directive to the North American Electric Reliability Corporation (NERC) to develop reliability standards to address the impact of geomagnetic disturbances on the U.S. electrical transmission system. One part of that effort is to accurately characterize geomagnetic induction hazards in the U.S. The most recent results were reported in the 19 September 2016, a paper by J. Love et al., “Geoelectric hazard maps for the continental United States.” In this report the authors characterize geography and surface impedance of many sites in the U.S. and explain how these characteristics contribute to regional differences in geoelectric risk. Key findings are:

“As a result of the combination of geographic differences in geomagnetic activity and Earth surface impedance, once-per-century geoelectric amplitudes span more than 2 orders of magnitude (factor of 100) and are an intricate function of location.”

“Within regions of the United States where a magnetotelluric survey was completed, Minnesota (MN) and Wisconsin (WI) have some of the highest geoelectric hazards, while Florida (FL) has some of the lowest.”

“Across the northern Midwest …..once-per-century geoelectric amplitudes exceed the 2 V/km that Boteler ……has inferred was responsible for bringing down the Hydro-Québec electric-power grid in Canada in March 1989.”

The following maps from this paper show maximum once-per-century geoelectric exceedances at EarthScope and U.S. Geological Survey magnetotelluric survey sites for geomagnetic induction (a) north-south and (b) east-west. In these maps, you can the areas of the upper Midwest that have the highest risk.

JLove Sep2016_grl54980-fig-0004

The complete paper is available online at the following link:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070469/full

Is the U.S. prepared for a severe solar storm?

The quick answer, “No.” The possibility of a long-duration, continental-scale electric power outage exists. Think about all of the systems and services that are dependent on electric power in your home and your community, including communications, water supply, fuel supply, transportation, navigation, food and commodity distribution, healthcare, schools, industry, and public safety / emergency response. Then extrapolate that statewide and nationwide.

In October 2015, the National Science and Technology Council issued the, “National Space Weather Action Plan,” with the following stated goals:

  • Establish benchmarks for space-weather events: induced geo-electric fields), ionizing radiation, ionospheric disturbances, solar radio bursts, and upper atmospheric expansion
  • Enhance response and recovery capabilities, including preparation of an “All-Hazards Power Outage Response and Recovery Plan.
  • Improve protection and mitigation efforts
  • Improve assessment, modeling, and prediction of impacts on critical infrastructure
  • Improve space weather services through advancing understanding and forecasting
  • Increase international cooperation, including policy-level acknowledgement that space weather is a global challenge

The Action Plan concludes:

“The activities outlined in this Action Plan represent a merging of national and homeland security concerns with scientific interests. This effort is only the first step. The Federal Government alone cannot effectively prepare the Nation for space weather; significant effort must go into engaging the broader community. Space weather poses a significant and complex risk to critical technology and infrastructure, and has the potential to cause substantial economic harm. This Action Plan provides a road map for a collaborative and Federally-coordinated approach to developing effective policies, practices, and procedures for decreasing the Nation’s vulnerabilities.”

You can download the Action Plan at the following link:

https://www.whitehouse.gov/sites/default/files/microsites/ostp/final_nationalspaceweatheractionplan_20151028.pdf

To supplement this Action Plan, on 13 October 2016, the President issued an Executive Order entitled, “Coordinating Efforts to Prepare the Nation for Space Weather Events,” which you can read at the following link:

https://www.whitehouse.gov/the-press-office/2016/10/13/executive-order-coordinating-efforts-prepare-nation-space-weather-events

Implementation of this Executive Order includes the following provision (Section 5):

Within 120 days of the date of this order, the Secretary of Energy, in consultation with the Secretary of Homeland Security, shall develop a plan to test and evaluate available devices that mitigate the effects of geomagnetic disturbances on the electrical power grid through the development of a pilot program that deploys such devices, in situ, in the electrical power grid. After the development of the plan, the Secretary shall implement the plan in collaboration with industry.”

So, steps are being taken to better understand the potential scope of the space weather problems and to initiate long-term efforts to mitigate their effects. Developing a robust national mitigation capability for severe space weather events will take several decades. In the meantime, the nation and the whole world remain very vulnerable to sever space weather.

Today’s space weather forecast

Based on the Electric Power Community Dashboard from NOAA’s Space Weather Prediction Center, it looks like we have mild space weather on 31 December 2016. All three key indices are green: R (radio blackouts), S (solar radiation storms), and G (geomagnetic storms). That’s be a good way to start the New Year.

NOAA space weather 31Dec2016

See your NOAA space weather forecast at:

http://www.swpc.noaa.gov/communities/electric-power-community-dashboard

Natural Resources Canada also forecasts mild space weather for the far north.

Canada space weather 31Dec2016You can see the Canadian space weather forecast at the following link:

http://www.spaceweather.gc.ca/index-en.php

4 January 2017 Update: G1 Geomagnetic Storm Approaching Earth

On 2 January, 2017, NOAA’s Space Weather Prediction Center reported that NASA’s STEREO-A spacecraft encountered a 700 kilometer per second HSS that will be pointed at Earth in a couple of days.

“A G1 (Minor) geomagnetic storm watch is in effect for 4 and 5 January, 2017. A recurrent, polar connected, negative polarity coronal hole high-speed stream (CH HSS) is anticipated to rotate into an Earth-influential position by 4 January. Elevated solar wind speeds and a disturbed interplanetary magnetic field (IMF) are forecast due to the CH HSS. These conditions are likely to produce isolated periods of G1 storming beginning late on 4 January and continuing into 5 January. Continue to check our SWPC website for updated information and forecasts.”

The coronal hole is visible as the darker regions in the following image from NASA’s Solar Dynamics Observatory (SDO) satellite, which is in a geosynchronous orbit around Earth.

NOAA SWPC 4Jan2017Source: NOAA SWPC

SDO has been observing the Sun since 2010 with a set of three instruments:

  • Helioseismic and Magnetic Imager (HMI)
  • Extreme Ultraviolet Variability Experiment (EVE)
  • Atmospheric Imaging Assembly (AIA)

The above image of the coronal hole was made by SDO’s AIA. Another view, from the spaceweather.com website, provides a clearer depiction of the size and shape of the coronal hole creating the current G1 storm.

spaceweather coronal holeSource: spaceweather.com

You’ll find more information on the SDO satellite and mission on the NASA website at the following link:

https://sdo.gsfc.nasa.gov/mission/spacecraft.php

 

Emergent Gravity Theory Passes its First Test

In 2010, Prof. Erik Verlinde, University of Amsterdam, Delta Institute for Theoretical Physics, published the paper, “The Origin of Gravity and the Laws of Newton.” In this paper, the author concluded:

 “The results of this paper suggest gravity arises as an entropic force, once space and time themselves have emerged. If the gravity and space time can indeed be explained as emergent phenomena, this should have important implications for many areas in which gravity plays a central role. It would be especially interesting to investigate the consequences for cosmology. For instance, the way redshifts arise from entropy gradients could lead to many new insights.

The derivation of the Einstein equations presented in this paper is analogous to previous works, in particular [the 1995 paper by T. Jacobson, ‘Thermodynamics of space-time: The Einstein equation of state.’]. Also other authors have proposed that gravity has an entropic or thermodynamic origin, see for instance [the paper by T. Padmanabhan, ‘Thermodynamical Aspects of Gravity: New insights.’]. But we have added an important element that is new. Instead of only focusing on the equations that govern the gravitational field, we uncovered what is the origin of force and inertia in a context in which space is emerging. We identified a cause, a mechanism, for gravity. It is driven by differences in entropy, in whatever way defined, and a consequence of the statistical averaged random dynamics at the microscopic level. The reason why gravity has to keep track of energies as well as entropy differences is now clear. It has to, because this is what causes motion!”

You can download Prof. Verlinde’s 2010 paper at the following link:

https://arxiv.org/pdf/1001.0785.pdf

On 8 November 2016, Delta Institute announced that Prof. Verlinde had published a new research paper, “Emergent Gravity and the Dark Universe,” expanding on his previous work. You can read this announcement and see a short video by Prof. Verlinde on the Delta Institute website at the following link:

http://www.d-itp.nl/news/list/list/content/folder/press-releases/2016/11/new-theory-of-gravity-might-explain-dark-matter.html

You can download this new paper at the following link:

https://arxiv.org/abs/1611.02269

I found it helpful to start with Section 8, Discussion and Outlook, which is the closest you will find to a layman’s description of the theory.

On the Physics.org website, a short 8 November 2016 article, “New Theory of Gravity Might Explain Dark Matter,” provides a good synopsis of Verlinde’s emergent gravity theory:

“According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime……

According to Erik Verlinde, there is no need to add a mysterious dark matter particle to the theory……Verlinde shows how his theory of gravity accurately predicts the velocities by which the stars rotate around the center of the Milky Way, as well as the motion of stars inside other galaxies.

One of the ingredients in Verlinde’s theory is an adaptation of the holographic principle, introduced by his tutor Gerard ‘t Hooft (Nobel Prize 1999, Utrecht University) and Leonard Susskind (Stanford University). According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct—part of the information in our universe is contained in space itself.

This extra information is required to describe that other dark component of the universe: Dark energy, which is believed to be responsible for the accelerated expansion of the universe. Investigating the effects of this additional information on ordinary matter, Verlinde comes to a stunning conclusion. Whereas ordinary gravity can be encoded using the information on the imaginary sphere around the universe, as he showed in his 2010 work, the result of the additional information in the bulk of space is a force that nicely matches that attributed to dark matter.”

Read the full Physics.org article at the following link:

http://phys.org/news/2016-11-theory-gravity-dark.html#jCp

On 12 December 2016, a team from Leiden Observatory in The Netherlands reported favorable results of the first test of the emergent gravity theory. Their paper, “First Test of Verlinde’s Theory of Emergent Gravity Using Weak Gravitational Lensing Measurements,” was published in the Monthly Notices of the Royal Astronomical Society. The complete paper is available at the following link:

http://mnras.oxfordjournals.org/content/early/2016/12/09/mnras.stw3192

An example of a gravitational lens is shown in the following diagram.

Gravitational-lensing-galaxyApril12_2010-1024x768-e1481555047928 Source: NASA, ESA & L. Calça

As seen from the Earth, the light from the galaxy at the left is bent by the gravitational forces of the galactic cluster in the center, much like light passing though an optical lens.

The Leiden Observatory authors reported:

“We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.”

These are exciting times! As noted in the Physics.org article, “We might be standing on the brink of a new scientific revolution that will radically change our views on the very nature of space, time and gravity.”

Atacama Large Millimeter / submillimeter Array (ALMA) Provides a Unique Window on the Universe

The Atacama Large Millimeter / submillimeter Array (ALMA) is a single telescope composed of 66 high-precision, 12-meter antennas. ALMA operates at wavelengths of 0.3 to 9.6 millimeters. As shown in the following chart, this puts ALMAs observing range around the boundary between microwave and infrared.

wavelength-spectrum1Source: physics.tutorvista.com

This enables ALMA’s users to examine “cold” regions of the universe, which are optically dark but radiate brightly in the millimeter / submillimeter portions of the electromagnetic spectrum. In that frequency range, ALMA is a complete astronomical imaging and spectroscopic instrument with a resolution better than the Hubble Space Telescope.

The ALMA Array Operations Site (AOS) is located on the Chajnantor plateau (which in the local Atacameño language, Kunza, means “place of departure”), at an elevation of about 5,000 meters (16,400 feet) above sea level in northern Chile.

ALMA_AOSView of the AOS. Source: ESO

On 30 September 2013 the last of the 66 antennas, each of which weighs more than 100 tons, was delivered to the AOS on the giant transporter named Otto (one of two available for the task) and handed over to the ALMA Observatory. The 12 meter antennas have reconfigurable baselines ranging from 15 meters to 18 km. Depending on what is being observed, the transporters can move ALMA antennas to establish the desired array. The transporters carry power generators to maintain the cryogenic systems needed to ensure that the antenna continues functioning during transport.

ALMA_antenna on transporterSource: ESOalma_antennas_nrao04bSource: ESO

ALMA is managed by an international partnership  of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan, together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile.

The ALMA telescope is operated from the Operations Support Facilities (OSF), which is located at a considerable distance from the telescope at an elevation of about 2,900 meters (9,500 feet). The OSF also served as the Assembly, Integration, Verification, and Commissioning (AIVC) station for all the antennas and other high technology equipment before they were moved to the AOS.

The ALMA website is at the following link:

http://www.almaobservatory.org

You’ll find many downloadable ALMA-related documents on the Publications tab of this website. A good overview of the ALMA telescope and the design of the individual antennas is available at:

http://www.almaobservatory.org/images/pdfs/alma_brochure_explore_2007.pdf

ALMA press releases, with details of on many of interesting observations being made at the observatory are at the following link:

http://www.almaobservatory.org/en/press-room/press-releases

An example of the type of remarkable observations being made with ALMA is in the 16 July 2016 press release, ALMA Observes First Protoplanetary Water Snow Line Thanks to Stellar Outburst.”

“This line marks where the temperature in the disk surrounding a young star drops sufficiently low for snow to form. A dramatic increase in the brightness of the young star V883 Orionis flash heated the inner portion of the disk, pushing the water snow line out to a far greater distance than is normal for a protostar, and making it possible to observe it for the first time.”

ALMA was looking in the right place at the right time. An artist’s impression of the water-snow line around V883 Orionis is shown in the ESO image below.

eso1626aCredit: A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)

You can read this ALMA press release and view a short video simulation of the event at the following link:

http://www.eso.org/public/usa/news/eso1626/

No doubt ALMA’s unique capabilities will continue to expand our knowledge of the universe in the millimeter / submillimeter portions of the electromagnetic spectrum. In collaboration with great land-based and space-based observatories operating in other portions of the spectrum, ALMA will help create a more comprehensive understanding of our universe. See my 6 March 2016 post, Remarkable Multispectral View of Our Milky Way Galaxy,” to see how different a portion of the night sky can look in different portions of the electromagnetic spectrum.

 

The Universe is Isotropic

The concepts of up and down appear to be relatively local conventions that can be applied at the levels of subatomic particles, planets and galaxies. However, the universe as a whole apparently does not have a preferred direction that would allow the concepts of up and down to be applied at such a grand scale.

A 7 September 2016 article entitled, “It’s official: You’re lost in a directionless universe,” by Adrian Cho, provides an overview of research that demonstrates, with a high level of confidence, that the universe is isotropic. The research was based on data from the Planck space observatory. In this article, Cho notes:

“Now, one team of cosmologists has used the oldest radiation there is, the afterglow of the big bang, or the cosmic microwave background (CMB), to show that the universe is “isotropic,” or the same no matter which way you look: There is no spin axis or any other special direction in space. In fact, they estimate that there is only a one-in-121,000 chance of a preferred direction—the best evidence yet for an isotropic universe. That finding should provide some comfort for cosmologists, whose standard model of the evolution of the universe rests on an assumption of such uniformity.”

The European Space Agency (ESA) developed the Planck space observatory to map the CMB in microwave and infrared frequencies at unprecedented levels of detail. Planck was launched on 14 May 2009 and was placed in a Lissajous orbit around the L2 Lagrange point, which is 1,500,000 km (930,000 miles) directly behind the Earth. L2 is a quiet place, with the Earth shielding Planck from noise from the Sun. The approximate geometry of the Earth-Moon-Sun system and a representative spacecraft trajectory (not Planck, specifically) to the L2 Lagrange point is shown in the following figure.

Lissajous orbit L2Source: Abestrobi / Wikimedia Commons

The Planck space observatory entered service on 3 July 2009. At the end of its service life, Planck departed its valuable position at L2, was placed in a heliocentric orbit, and was deactivated on 23 October 2013. During more than four years in service, Planck performed its CBM mapping mission with much greater resolution than NASA’s Wilkinson Microwave Anisotropy Probe, which operated from 2001 to 2010.

One key result of the Planck mission is the all-sky survey shown below.

Planck_CMB_black_background_fullwidthPlanck all-sky survey. Source; ESA / Planck Collaboration

ESA characterizes this map as follows:

“The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today.”

The researchers who reported that the universe was isotropic noted that an anisotropic universe would leave telltale patterns in the CMB. However, these researchers found that the actual CMB shows only random noise and no signs of such patterns.

You’ll find more details on the Planck mission and scientific results on the ESA’s website at the following link:

http://www.esa.int/Our_Activities/Space_Science/Planck

You can read Adrian Cho’s article on the Science magazine website at the following link:

http://www.sciencemag.org/news/2016/09/it-s-official-you-re-lost-directionless-universe?utm_source=howtogeek&utm_medium=email&utm_campaign=newsletter

The original research paper, “How Isotropic is the Universe?” by Saadeh, D., et al., was published on 21 September 2016. It is available on the Physical Review Letters website, if you have a subscription, at the following link:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.131302

 

 

Simulating Extreme Spacetimes

Thanks to Dave Groce for sending me the following link to the Caltech-Cornell Numerical Relativity collaboration; Simulating eXtreme Spacetimes (SXS):

http://www.black-holes.org

Caltech SXSSource: SXS

From the actual website (not the image above), click on the yellow “Admit One” ticket and you’re on your way.

Under the “Movies” tab, you’ll find many video simulations that help visualizes a range of interactions between two black holes and between a black hole and a neutron star. Following is a direct link:

http://www.black-holes.org/explore/movies

A movie visualizing GW150914, the first ever gravitational wave detection on 14 September 2015, is at the following SXS link:

https://www.black-holes.org/gw150914

At the above link, you also can listen to the sound of the GW150914 “in-spiral” event (two black holes spiraling in on each other).  You can read more about the detection of GW150914 in my 11 February 2016 post.

On the “Sounds” tab on the SXS website, you’ll find that different types of major cosmic events are expected to emit gravitational waves with waveforms that will help characterize the original event. You can listen to the expected sounds from a variety of extreme cosmic events at the following SXS link:

http://www.black-holes.org/explore/sounds

Have fun exploring SXS.