Category Archives: Astrophysics

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:

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

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:

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:

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 First Test of Standard and Holographic Cosmology Models Ends in a Draw

Utrecht University (Netherlands) Professor Gerard ’t Hooft was the first to propose the “holographic principle,” in which all information about a volume of space can be thought of as being encoded on a lower-dimensional “boundary” of that volume.

Stanford Professor Leonard Susskind was one of the founders of string theory and, in 1995, developed the first string theory interpretation of the holographic principle to black holes. Dr. Susskind’s analysis showed that, consistent with quantum theory, information is not lost when matter falls into a black hole. Instead, it is encoded on a lower-dimensional “boundary” of the black hole, namely the event horizon.

Black hole event horizonSource: screenshot from video, “Is the Universe a Hologram?”

Extending the holographic principle to the universe as a whole, a lower-dimensional “boundary,” or “cosmic horizon,” around the universe can be thought of as a hologram of the universe. Quantum superposition suggests that this hologram is indistinguishable from the volume of space within the cosmic horizon.

You can see a short (15:49 minute) 2015 video interview of Dr. Susskind, “Is The Universe A Hologram?” at the following link:

If you have the time, also check out the longer (55:26) video lecture by Dr. Susskind entitled, “Leonard Susskind on The World As Hologram.” In this video, he explains the meaning of “information” and how information on an arbitrary volume of space can be encoded in one less dimension on a surface surrounding the volume.

You also might enjoy the more detailed story in Dr. Susskind’s 2008 book, “The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics.”

Leonard Susskind book cover   Source: Little, Brown and Company

In my 28 September 2016 post, “The Universe is Isotropic,” I reported on a conclusion reached by researchers using data from the Planck spacecraft’s all-sky survey of the cosmic microwave background (CMB). The researchers 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.

More recently, a team of researchers from Canada, UK and Italy, also using the Planck spacecraft’s CBM data set, have offered an alternative view that the universe may be a hologram.  You’ll find the abstract for the 27 January 2017 original research paper by N. Afshordi, et al., “From Planck Data to Planck Era: Observational Tests of Holographic Cosmology,” in Physical Review Letters at the following link:

The authors note:

“We test a class of holographic models for the very early Universe against cosmological observations and find that they are competitive to the standard cold dark matter model with a cosmological constant (Λ CDM) of cosmology.”

“Competitive” means that neither model disproves the other.  So, we have a draw.

If you are a subscriber to Physical Review Letters, you can download the complete paper by N. Afshordi, et al. from the Physical Review Letters site.


Perspective on the Detection of Gravitational Waves

On 14 September 2015, the U.S. Laser Interferometer Gravitational-Wave Observatory (LIGO) became the first observatory to detect gravitational waves. With two separate detector sites (Livingston, Louisiana, and Hanford, Washington) LIGO was able to define an area of space from which the gravitational waves, dubbed GW150914, are likely to have originated, but was not able to pinpoint the source of the waves. See my 11 February 2016 post, “NSF and LIGO Team Announce First Detection of Gravitational Waves,” for a summary of this milestone event.

You’ll find a good overview on the design and operation of LIGO and similar laser interferometer gravity wave detectors in the short (9:06) Veratisium video, “The Absurdity of Detecting Gravitational Waves,” at the following link:

The LIGO team reports that the Advanced LIGO detector is optimized for “a range of frequencies from 30 Hz to several kHz, which covers the frequencies of gravitational waves emitted during the late inspiral, merger, and ringdown of stellar-mass binary black holes.”

First observing run (O1) of the Advanced LIGO detector

The LIGO team defines O1 as starting on 12 September 2015 and ending on 19 January 2016. During that period, the LIGO team reported that it had, “unambiguously identified two signals, GW150914 and GW151226, with a significance of greater than 5σ,” and also identified a third possible signal, LVT151012. The following figure shows the time evolution of the respective gravitational wave signals from when they enter the LIGO detectors’ sensitive band at 30 Hz.

LIGO GW signals screenshot

Source: B. P. Abbot et al., PHYS. REV. X 6, 041015 (2016)

The second detection of gravitational waves, GW151226, occurred on 26 December 2015. You’ll find the 16 June 2016 LIGO press release for this event at the following link:

At the following link, you can view a video showing a simulation of GW151226, starting at a frequency of 35 Hz and continuing through the last 55 gravitational-wave cycles before the binary black holes merge:

GW151226 simularion screenshotSource: Max Planck Institute for Gravitational Physics/ Simulating eXtreme Spacetime (SXS) project

In their GW151226 press release, the LIGO team goes out on a limb and makes the following estimate:

“….we can now start to estimate the rate of black hole coalescences in the Universe based not on theory, but on real observations. Of course with just a few signals, our estimate has big uncertainties, but our best right now is somewhere between 9 and 240 binary black hole coalescences per cubic Gigaparsec per year, or about one every 10 years in a volume a trillion times the volume of the Milky Way galaxy!”

More details on the GW151226 detection are available in the paper “GW151266: Observation of Gravitational Waves from a 22-Solar Mass Black Hole Coalescence,” at the following link:

LIGO releases its data to the public. Analyses of the LIGO public data already are yielding puzzling results. In December 2016, researchers reported finding “echoes” in the gravitational wave signals detected by LIGO. If further analysis indicates that the “echoes” are real, they may indicate a breakdown of Einstein’s general theory of relativity at or near the “edge” of a black hole. You can read Zeeya Marali’s 9 December 2016 article, “LIGO black hole echoes hint at general relativity breakdown,” at the following link:

Second observing run (O2) of the Advanced LIGO detector is in progress now

Following a 10-month period when they were off-line for modifications, the Advanced LIGO detectors returned to operation on 30 November 2016 with a 10% improvement in the sensitivity of their interferometers. The LIGO team intends to further improve this sensitivity by a factor of two during the next few years.

VIRGO will add the capability to triangulate the source of gravitational waves

In my 16 December 2015 post, “100th Anniversary of Einstein’s General Theory of Relativity and the Advent of a New Generation of Gravity Wave Detectors,” I reported on other international laser interferometer gravitational wave detectors. The LIGO team has established a close collaboration with their peers at the European Gravitational Observatory, which is located near Pisa, Italy. Their upgraded detector, VIRGO, in collaboration with the two LIGO detectors, is expected to provide the capability to triangulate gravitational wave sources. With better location information on the source of gravitational waves, other observatories can be promptly notified to join the search using other types of detectors (i.e., optical, infrared and radio telescopes).

VIRGO is expected to become operational in 2017, but technical problems, primarily with the mirror suspension system, may delay startup. You’ll find a 16 February 2017 article on the current status of VIRGO at the following link:

Perspective on gravitational wave detection

Lyncean member Dave Groce recommends the excellent video of an interview of Caltech Professor Kip Thorne (one of the founders of LIGO) by “Einstein” biographer Walter Issacson. This 2 November 2016 video provides a great perspective on LIGO’s first detection of gravitational waves and on the development of gravitational wave detection capabilities. You’ll find this long (51:52) but very worthwhile video at the following link:

Dr. Thorne noted that, at the extremely high sensitivity of the Advanced LIGO detectors, we are beginning to see the effects of quantum fluctuations in “human sized objects,” in particular, the 40 kg (88.2 pound) mirrors in the LIGO interferometers. In each mirror, the center of mass (the average position of all the mass in the mirror) fluctuates due to quantum physics at just the level of the Advanced LIGO noise.

In the interview, Dr. Thorne also discusses several new observatories that will be become available in the following decades to expand the spectrum of gravitational waves that can be detected. These are shown in the following diagram.

Spectrum for gravitational wave detection screenshotSource: screenshot from Kip Thorne / Walter Issacson interview

  •  LISA = Laser Interferometer Space Antenna
  • PTA = Pulsar Timing Array
  • CMB = Cosmic microwave background

See my 27 September 2016 post, “Space-based Gravity Wave Detection System to be Deployed by ESA,” for additional information on LISA.

Clearly, we’re just at the dawn of gravitational wave detection and analysis. With the advent of new and upgraded gravitational wave observatories during the next decade, there will be tremendous challenges to align theories with real data.   Through this process, we’ll get a much better understanding of our Universe.



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:

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:

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:

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.


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:

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:

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:

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.


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:

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:

Another source for space weather information is the 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:

You’ll also find a report of recent and upcoming near-Earth asteroids on the 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:

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:

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:

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:

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:

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:

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:

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:

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.


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 website, provides a clearer depiction of the size and shape of the coronal hole creating the current G1 storm.

spaceweather coronal holeSource:

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


Space-based Gravity Wave Detection System to be Deployed by ESA

The first detection of gravitational waves occurred on 14 September 2015 at the land-based Laser Interferometer Gravitational-Wave Observatory (LIGO). Using optical folding techniques, LIGO has an effective baseline of 1,600 km (994 miles). See my 16 December 2015 and 11 February 2016 posts for more information on LIGO and other land-based gravitational wave detectors.

Significantly longer baselines, and theoretically greater sensitivity can be achieved with gravitational wave detectors in space. Generically, such a space-based detector has become known as a Laser Interferometer Space Antenna (LISA). Three projects associated with space-based gravitational wave detection are:

  • LISA (the project name predated the current generic usage of LISA)
  • LISA Pathfinder (a space-based gravitational wave detection technology demonstrator, not a detector)
  • Evolved LISA (eLISA)

These projects are discussed below.

The science being addressed by space-based gravitational wave detectors is discussed in the eLISA white paper, “The Gravitational Universe.” You can download this whitepaper, a 1-page summary, and related gravitational wave science material at the following link:


The LISA project originally was planned as a joint European Space Agency (ESA) and National Aeronautics & Space Administration (NASA) project to detect gravitational waves using a very long baseline, triangular interferometric array of three spacecraft.

Each spacecraft was to contain a gravitational wave detector sensitive at frequencies between 0.03 mHz and 0.1 Hz and have the capability to precisely measure its distances to the other two spacecraft forming the array. The equilateral triangular array, which was to measure about 5 million km (3.1 million miles) on a side, was expected to be capable of measuring gravitational-wave induced strains in space-time by precisely measuring changes of the separation distance between pairs of test masses in the three spacecraft. In 2011, NASA dropped out of this project because of funding constraints.

LISA Pathfinder

The LISA Pathfinder (LPF) is a single spacecraft intended to validate key technologies for space-based gravitational wave detection. It does not have the capability to detect gravity waves.

This mission was launched by ESA on 3 December 2015 and the spacecraft took station in a Lissajous orbit around the Sun-Earth L1 Lagrange point on 22 January 2016. L1 is directly between the Earth and the Sun, about 1.5 million km (932,000 miles) from Earth. An important characteristic of a Lissajous orbit is that the spacecraft will follow the L1 point without requiring any propulsion. This is important for minimizing external forces on the LISA Pathfinder experiment package. The approximate geometry of the Earth-Moon-Sun system and a representative spacecraft (not LPF, specifically) stationed at the L1 Lagrange point is shown in the following figure.

L1 Lagrange pointSource: Wikimedia Commons

The LISA Pathfinder’s mission is to validate the technologies used to shield two free-floating metal cubes (test masses), which form the core of the experiment package, from all internal and external forces that could contribute to noise in the gravitational wave measurement instruments. The on-board measurement instruments (inertial sensors and a laser interferometer) are designed to measure the relative position and orientation of the test masses, which are 38 cm (15 inches) apart, to an accuracy of less than 0.01 nanometers (10e-11 meters). This measurement accuracy is believed to be adequate for detecting gravitational waves using this technology on ESA’s follow-on mission, eLISA.

The first diagram below is an artist’s impression of the LISA Pathfinder technology package, showing the inertial sensors housing the test masses (gold) and the laser interferometer (middle platform). The second diagram provides a clearer view of the test masses and the laser interferometer.

LPF technology package 1

Source: ESA/ATG medialab, August 2015LPF technology package 2Source: ESA LISA Pathfinder briefing, 7 June 2016

You’ll find more general information in an ESA LISA Pathfinder overview, which you can download from NASA’s LISA website at the following link:

LISA Pathfinder was commissioned and ready for scientific work on 1 March 2016. In a 7 June 2016 briefing, ESA reported very favorable performance results from LISA Pathfinder:

  • LPF successfully validated the technologies used in the local (in-spacecraft) instrument package (test masses, inertial sensors and interferometer).
  • LPF interferometer noise was a factor of 100 less than on the ground.
  • The measurement instruments can see femtometer motion of the test masses (LPF goal was picometer).
  • Performance is essentially at the level needed for the follow-on eLISA mission

You can watch this full (1+ hour) ESA briefing at the following link:


Evolved LISA, or eLISA, is ESA’s modern incarnation of the original LISA program described previously. ESA’s eLISA website home page is at the following link:

As shown in the following diagrams, three eLISA spacecraft will form a very long baseline interferometric array that is expected to directly observe gravitational waves from sources anywhere in the universe. In essence, this array will be a low frequency microphone listening for the sounds of gravitational waves as they pass through the array.

eLISA constellation 1Source: ESAeLISA constellation 2Source: ESA

As discussed previously, gravity wave detection depends on the ability to very precisely measure the distance between test masses that are isolated from their environment but subject to the influence of passing gravitational waves. Measuring the relative motion of a pair of test masses is considerably more complex for eLISA than it was for LPF. The relative motion measurements needed for a single leg of the eLISA triangular array are:

  • Test mass 1 to Spacecraft 1
  • Spacecraft 1 to Spacecraft 2
  • Spacecraft 2 to Test Mass 2

This needs to be done for each of the three legs of the array.

LPF validated the technology for making the test mass to spacecraft measurement. Significant development work remains to be done on the spacecraft-to-spacecraft laser system that must take precise measurements at very long distances (5 million km, 3.1 million miles) of the relative motion between each pair of spacecraft.

So, when will eLISA be launched? The eLISA website currently suggests a launch in 2028. See Science Context 2028 on the eLISA website at the following link:

In the 6 June 2016 LISA Pathfinder briefing, LPF and ESA officials raised the possibility of a somewhat later launch date (2029 – 2032 time frame). Whenever it happens, eLISA will be a remarkable collaborative technical achievement and a new window to our universe.

Remarkable Multispectral View of Our Milky Way Galaxy

Moody Blues cover - In search of the lost chordAlbum cover art credit: Deram Records

Some of you may recall the following lyrics from the 1968 Moody Blues song, “The Word,” by Graeme, Edge, from the album “In Search of the Lost Chord”:

This garden universe vibrates complete

Some, we get a sound so sweet

 Vibrations reach on up to become light

And then through gamma, out of sight

Between the eyes and ears there lie

The sounds of color and the light of a sigh

And to hear the sun, what a thing to believe

But it’s all around if we could but perceive

 To know ultraviolet, infrared and X-rays

Beauty to find in so many ways

On 24 February 2016, the European Southern Observatory (ESO) Consortium announced that it has completed the ATLASGAL Survey of the Milky Way. The survey mapped the entire galactic plane visible from the southern hemisphere at sub-millimeter wavelengths, between infrared light and radio waves, using the Atacama Pathfinder EXperiment (APEX) telescope located at 5,100 meters (16,732 ft.) above sea level in Chile’s Atacama region. The southern sky is particularly important because it includes the galactic center of our Milky Way. The Milky Way in the northern sky has already been mapped by the James Clerk Maxwell Telescope, which is a sub-millimeter wavelength telescope at the Mauna Kea Observatory in Hawaii.

The new ATLASGAL maps cover an area of sky 140 degrees long and 3 degrees wide. ESO stated that these are the sharpest maps yet made, and they complement those from other land-based and space-based observatories. The principal space-based observatories are the following:

  • European Space Agency’s (ESA) Plank satellite: Mission on-going, mapping anisotropies of the cosmic microwave background at microwave and infrared frequencies.
  • ESA’s Herschel Space Observatory: Mission on-going, conducting sky surveys in the far-infrared and sub-millimeter frequencies.
  • National Aeronautics and Space Administration (NASA) Spitzer Space Telescope: Mission on-going, conducting infrared observations and mapping as described in my 1 April 2015 post.
  • NASA’s Hubble Space Telescope: Mission on-going, observing and mapping at ultraviolet, optical, and infrared frequencies.
  • NASA’s Chandra X-Ray Observatory: Mission on-going, observing and mapping X-ray sources.
  • NASA’s Compton Gamma Ray Observatory: Mission ended in 2000. Observed and mapped gamma ray and x-ray sources.

ESO reported that the combination of Planck and APEX data allowed astronomers to detect emission spread over a larger area of sky and to estimate from it the fraction of dense gas in the inner galaxy. The ATLASGAL data were also used to create a complete census of cold and massive clouds where new generations of stars are forming.

You can read the ESO press release at the following link:

Below is a composite ESO photograph that shows the same central region of the Milky Way observed at different wavelengths.

ESO Multispectral view of Milky WayCredit: ESO/ATLASGAL consortium/NASA/GLIMPSE consortium/VVV Survey/ESA/Planck/D. Minniti/S. Guisard. Acknowledgement: Ignacio Toledo, Martin Kornmesser

  • The top panel shows compact sources of sub-millimeter radiation detected by APEX as part of the ATLASGAL survey, combined with complementary data from ESA’s Planck satellite, to capture more extended features.
  • The second panel shows the same region as seen in shorter, infrared, wavelengths by the NASA Spitzer Space Telescope
  • The third panel shows the same part of sky again at even shorter wavelengths, the near-infrared, as seen by ESO’s VISTA infrared survey telescope at the Paranal Observatory in Chile. Regions appearing as dark dust tendrils in the third panel show up brightly in the ATLASGAL view (top panel).
  • The bottom panel shows the more familiar view in visible light, where most of the more distant structures are hidden from view

NASA’s Goddard Space Flight Center also has created a multispectral view of the Milky Way, which you will find at the following link:

Following is a composite NASA photograph that shows the same central regions of the Milky Way observed at different wavelengths.

NASA Goddard multispectralSource: NASA Goddard Space Flight Center

Starting from the top, the ten panels in the NASA image cover the following wavelengths.

  • Radio frequency (408 MHz)
  • Atomic hydrogen
  • Radio frequency (2.5 GHz)
  • Molecular hydrogen
  • Infrared
  • Mid-infrared
  • Near-infrared
  • Optical
  • X-ray
  • Gamma ray

The Moody Blues song, “The Word,” ends with the following lyrics:

 Two notes of the chord, that’s our full scope

But to reach the chord is our life’s hope

And to name the chord is important to some

So they give it a word, and the word is “Om”

While “Om” (pronounced or hummed “ahh-ummmm”) traditionally is a sacred mantra of Hindu, Jain and Buddhist religions, it also may be the mantra of astronomers as they unravel new secrets of the Milky Way and, more broadly, the Universe. I suspect that completing the ATLASGAL Survey of the Milky Way was an “Om” moment for the many participants in the ESO Consortium effort.



NSF and LIGO Team Announce First Detection of Gravitational Waves

Today, 11 February 2016, the National Science Foundation (NSF) and the Laser Interferometer Gravitational-Wave Observatory (LIGO) project team announced that the first detection of gravitational waves occurred on 14 September 2015. You can view a video of this announcement at the following link:

The first paper on this milestone event, “Observation of Gravitational Waves From a Binary Black Hole Merger,” is reported in Physical Review Letters, at the following link:

The recorded signals from the two LIGO sites, Livingston, LA and Hanford, WA, are shown below, with the Hanford data time shifted to account for the slightly later arrival time of the gravitational wave signal at that detector location. The magnitude of the gravitational wave signal was characterized as being just below the detection threshold of LIGO before installation of the new advanced detectors, which improve LIGO sensitivity by a factor of 3 to 10.

LIGO signals

Source: NSF/LIGO

This milestone occurred during the engineering testing phase of the advanced LIGO detectors, before the start of their first official “observing run” on 18 September 2015.

Analysis and simulations conducted on the data indicate that the observed gravitational wave signals were generated when two orbiting black holes coalesced into a single black hole of smaller total mass and ejected about three solar masses of energy as gravitational waves.

In the Physical Review Letters paper, the authors provide the following diagram, which gives a physical interpretation of the observed gravitational wave signals.

Binary black holes merge

Note the very short timescale of this extraordinarily dynamic process. The recorded gravitational wave signals yielded an audible “chirp” when the two black holes merged.

With only two LIGO detectors, the source of the observed gravitational waves could not be localized, but the LIGO team reported that the source was in the southern sky, most likely in the vicinity of the Magellanic Clouds.

Localization of black hole merger Source: NSF/LIGO

The ability to localize gravitational wave signals will improve when additional gravitational wave detectors become operational later in this decade.

For more information on the current status of LIGO and other new-generation gravitational wave detectors, see my 16 December 2015 post: “100th Anniversary of Einstein’s Theory of General Relativity and the Advent of a New Generation of Gravity Wave Detectors.”

100th Anniversary of Einstein’s General Theory of Relativity and the Advent of a New Generation of Gravity Wave Detectors

One hundred years ago, Albert Einstein presented his General Theory of Relativity in November 1915, at the Prussian Academy of Science. Happy Anniversary, Dr. Einstein!

Today, general relativity is being tested with unprecedented accuracy with a new generation of gravity-wave “telescopes” in the U.S., Italy, Germany, and Japan. All are attempting to directly detect gravity waves, which are the long-predicted quakes in space-time arising from cataclysmic cosmic sources.

The status of four gravity-wave telescopes is summarized below.

USA: Laser Interferometer Gravitational-Wave Observatory (LIGO)

LIGO is a multi-kilometer-scale gravitational wave detector that uses laser interferometry to, hopefully, measure the minute ripples in space-time caused by passing gravitational waves. LIGO consists of two widely separated interferometers within the United States; one in Hanford, WA and the other in Livingston, LA. These facilities are operated in unison to detect gravitational waves. The Livingston and Hanford LIGO sites are shown in the following photos (Hanford above, Livingston below):

ligo-hanford-aerial-02Source LIGO Caltechligo-livingston-aerial-03Source: LIGO Caltech

LIGO is operated by Caltech and MIT and is supported by the National Academy of Sciences. For more information, visit the LIGO website at the following link:

Basically, LIGO is similar to the traditional interferometer used in 1887 in the famous Michelson-Morley experiment (–Morley_experiment). However, the LIGO interferometer incorporates novel features to greatly increase its sensitivity. The basic arrangement of the interferometer is shown in the following diagram.

LIGO experiment setupSource: LIGO Caltech

Each leg of the interferometer has a physical length of 4 km and is a resonant Fabry-Perot cavity that uses a complex set of mirrors to extend the effective arm length by a factor of 400 to 1,600 km.

On 18 September 2015, the first official “observing run” using LIGO’s advanced detectors began. This “observing run” is planned to last three months. LIGO’s advanced detectors are already three times more sensitive than Initial LIGO was by the end of its observational lifetime in 2007. You can read about this milestone event at the following link:

You also can find much more information on the LIGO Scientific Collaboration (LSC) at the following link:

Italy: VIRGO

VIRGO is installed near Pisa, Italy, at the site of the European Gravitational Observatory ( VIRGO is intended to directly observe gravitational waves using a Michelson interferometer with arms that are 3 km long, with resonant Fabry-Perot cavities that increase the effective arm length by a factor of 50 to 150 km. The initial version of VIRGO operated from 2007 to 2011 and the facility currently is being upgraded with a new, more sensitive detector. VIRGO is expected to return to operation in 2018.

You can find much more information on VIRGO at the following link:

Germany: GEO600

GEO600 is installed near Hanover, Germany. It, too, uses a Michelson interferometer with arms that are 600 meters long, with resonant Fabry-Perot cavities that double the effective arm length to 1,200 meters.

You can find much more information on the GEO600 portal at the following link:

Japan: KAGRA Large-scale Cryogenic Gravitational Wave Telescope

The KAGRA telescope is installed deep underground, in tunnels of Kamioka mine, as shown in the following diagram.

img_abt_lcgtSource: KAGARA

Like the other facilities described previously, KAGRA is a Michelson interferometer with resonant Fabry-Perot cavities. The physical length of each arm is of 3 km (1.9 mi). KAGRA is expected to be in operation in 2018.

You can find much more information on KAGARA at the following links: