Advanced LIGO Gravitational Wave Event GW150914 Follow-up

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Advanced LIGO Gravitational Wave Event GW150914 Follow-up

Post by bystander » Mon Feb 15, 2016 7:14 pm

Results of Search for Visible Light Associated with Gravitational Waves
Harvard-Smithsonian Center for Astrophysics | 2016 Feb 13
Einstein's general theory of relativity predicts the emission of gravitational waves by massive celestial bodies moving though space-time. For the past century gravitational waves have eluded a direct detection, but now the LIGO Virgo Collaboration has announced the first direct detection of gravitational waves, emitted by a merging pair of black holes. Catastrophic mergers of binary systems can also produce brilliant and explosive fireworks of light, so a team of astronomers, including at Harvard, sought evidence of such an visible afterglow. Although none was spotted, this work represents the first detailed search for a visible counterpart of a gravitational wave event. It also will serve as a model for similar event follow-up in the future.

"Our team has been anxiously waiting for the first detection of gravitational waves so that we can rapidly point the Dark Energy Camera at this location and search for the associated visible light," says Edo Berger of the Harvard-Smithsonian Center for Astrophysics (CfA), the Principal Investigator of the follow-up team. "It's one of the most powerful instruments in the world for this purpose."

The joint detection of gravitational waves and light isn't easy, requiring large and wide-fields telescopes to rapidly scan the sky location of a gravitational wave source. The team used the 3 square-degree Dark Energy Camera (DECam) imager mounted on the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. The search program is a collaboration between astronomers from multiple institutions in the United States, the Dark Energy Survey (DES), and members of the LIGO Scientific Collaboration.

The team rapidly observed the sky location of the first gravitational wave source discovered by LIGO within a day of its announced discovery on 2015 September 16. ...

A Dark Energy Camera Search for an Optical Counterpart to the
First Advanced LIGO Gravitational Wave Event GW150914
- M. Soares-Santos et al A Dark Energy Camera Search for Missing Supergiants in the LMC
after the Advanced LIGO Gravitational Wave Event GW150914
- J. Annis et al
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IceCube: Search for neutrinos in coincidence with gravitational waves

Post by bystander » Thu Feb 18, 2016 5:18 pm

A search for neutrinos in coincidence with the first gravitational wave event
IceCube Neutrino Observatory | 2016 Feb 11
[c][attachment=0]GW150914_neutrino.jpg[/attachment][/c][hr][/hr]
The detection of the first gravitational wave (GW) event by LIGO, a hundred years after Einstein’s general relativity theory suggested their existence, represents one of the greatest scientific breakthroughs of recent years. For neutrino hunters, such as IceCube and ANTARES, this discovery is also a great step forward for the nascent field of multimessenger astronomy.

The detection of the first gravitational wave transient, GW150914, occurred in the first three-month-long observation period of Advanced LIGO. We can anticipate a significant number of new GW sources from longer and more sensitive future observation periods. LIGO researchers have identified a merger of two black holes as the most likely source of this GW. Such an event might also emit neutrinos if the black holes are in a gaseous environment from which they can accrete matter.

After receiving the GW alert in September 2015 from the Advanced LIGO detector, the IceCube and ANTARES neutrino telescopes analyzed the data they had recorded at the same time in order to search for neutrinos that might have been emitted from the same event. Neither search identified any neutrinos that could be associated with the burst. These results set the first limits on neutrino emission from a GW transient event. ...

High-energy Neutrino follow-up search of Gravitational Wave Event
GW150914 with IceCube and ANTARES
- LIGO and Virgo Collaborations et al
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CfA: LIGO's Twin Black Holes Might Have Been Born Inside a Single Star

Post by bystander » Tue Feb 23, 2016 8:22 pm

LIGO's Twin Black Holes Might Have Been Born Inside a Single Star
Harvard-Smithsonian Center for Astrophysics | 2015 Deb 23
cfa-2016-05.jpg
On Sept. 14, 2015, LIGO detected gravitational waves from two merging
black holes, shown here in this artist's conception. The Fermi space telescope
detected a burst of gamma rays 0.4 seconds later. New research suggests
that the burst occurred because the two black holes lived and died inside
a single, massive star. (Credit: Swinburne Astronomy Productions)

On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves from the merger of two black holes 29 and 36 times the mass of the Sun. Such an event is expected to be dark, but the Fermi Space Telescope detected a gamma-ray burst just a fraction of a second after LIGO's signal. New research suggests that the two black holes might have resided inside a single, massive star whose death generated the gamma-ray burst. ...

Normally, when a massive star reaches the end of its life, its core collapses into a single black hole. But if the star was spinning very rapidly, its core might stretch into a dumbbell shape and fragment into two clumps, each forming its own black hole.

A very massive star as needed here often forms out of the merger of two smaller stars. And since the stars would have revolved around each other faster and faster as they spiraled together, the resulting merged star would be expected to spin very quickly.

After the black hole pair formed, the star's outer envelope rushed inward toward them. In order to power both the gravitational wave event and the gamma-ray burst, the twin black holes must have been born close together, with an initial separation of order the size of the Earth, and merged within minutes. The newly formed single black hole then fed on the infalling matter, consuming up to a Sun's worth of material every second and powering jets of matter that blasted outward to create the burst.

Fermi detected the burst just 0.4 seconds after LIGO detected gravitational waves, and from the same general area of the sky. However, the European INTEGRAL gamma-ray satellite did not confirm the signal. ...

Electromagnetic Counterparts to Black Hole Mergers Detected by LIGO - Abraham Loeb
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ND: Continuing the Search for Gravitational Waves

Post by bystander » Tue Mar 29, 2016 7:40 pm

Continuing the Search for Gravitational Waves
University of Notre Dame | 2016 Mar 29

In February, the LIGO Scientific Collaboration announced it had detected gravitational waves for the first time, confirming the last prediction of Albert Einstein’s theory of relativity. Somewhat overlooked in the excitement that followed is the fact that scientists don’t know the exact location the waves were coming from. University of Notre Dame astronomer Peter Garnavich is leading a group of researchers who are hoping to more precisely locate where future gravitational waves originate.

Garnavich and the group are using the LBT (Large Binocular Telescope) in southeastern Arizona to search for visible light emission from the event generating the gravitational waves. Notre Dame owns a share of the LBT project, which consists of two 8.4-meter mirrors and is the world’s largest telescope on a single mounting. The team is searching the sky to find the light emitted from supernovae and gamma ray bursts, and now gravitational wave transients. ...
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APS Tip Sheet: More About Gravitational Waves

Post by bystander » Tue Mar 29, 2016 7:51 pm

LIGO and VIRGO Estimate Gravitational Wave Background
Using data from the recent detection of a black hole merger, researchers improve estimates of the background hum of gravitational waves coming from other mergers across the universe.

The gravitational waves recently detected by the LIGO and VIRGO collaborations were generated by a single event known as “GW150914” -- the merger of a pair of black holes with masses ~30 times that of the Sun. But other pairs of black holes, as well as neutron stars, could be merging constantly, creating a faint background of gravitational waves bombarding Earth from all directions. The amplitude of such a background signal could provide information on the formation of black hole and neutron star binaries. The two collaborations have now used details of GW150914 to estimate the strength of this background hum. Their analysis suggests the background could be ten times stronger than previously expected and might be observed in only a few years thanks to improvements in detector sensitivity.

GW150914: Implications for the stochastic gravitational wave background from binary black holes - LIGO and VIRGO Collaborations
Searching for Primordial Gravitational Waves
The combined analysis of data from several gravitational-wave-detection experiments provides insights into the physics of the early universe.

Cosmologists believe that -- a fraction of a second after the Big Bang -- the universe underwent a period of extremely rapid expansion known as inflation. During inflation, quantum fluctuations of the gravitational field would have been amplified, generating a primordial background of gravitational waves. An international collaboration (Australia, U.S., China and Germany) has now pulled together data from several experiments that should carry direct or indirect imprints of this background (such as LIGO, BICEP2 and Planck). The analysis of such data allowed the authors to put stringent bounds on the background’s energy spectrum and to rule out some exotic models of inflation.

Gravitational-wave cosmology across 29 decades in frequency - Paul D. Laski et al
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ESA: INTEGRAL Sets Limits on Gamma Rays from Merging Black Holes

Post by bystander » Thu Mar 31, 2016 2:28 pm

INTEGRAL Sets Limits on Gamma Rays from Merging Black Holes
ESA Science & Technology | INTEGRAL | 2016 Mar 30

Following the discovery of gravitational waves from the merging of two black holes, ESA's INTEGRAL satellite has revealed no simultaneous gamma rays, just as models predict.
On 14 September, the terrestrial Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves – fluctuations in the fabric of spacetime – produced by a pair of black holes as they spiralled towards each other before merging. The signal lasted less than half a second. ...

Two days after the detection, the LIGO team alerted a number of ground- and space-based astronomical facilities to look for a possible counterpart to the source of gravitational waves. The nature of the source was unclear at the time, and it was hoped that follow-up observations across the electromagnetic spectrum might provide valuable information about the culprit. ...

Models predict that the merging of two stellar-mass black holes would not produce light at any wavelength, but if one or two neutron stars were involved in the process, then a characteristic signature should be observable across the electromagnetic spectrum. ...

"We searched through all the available INTEGRAL data, but did not find any indication of high-energy emission associated with the LIGO detection," says Volodymyr Savchenko ...

INTEGRAL upper limits on gamma-ray emission associated with the gravitational wave event GW150914 - V. Savchenko et al
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Fermi Poised to Pin Down Gravitational Wave Sources

Post by bystander » Mon Apr 18, 2016 6:39 pm

Fermi Poised to Pin Down Gravitational Wave Sources
NASA | GSFC | Fermi | 2016 Apr 18
Click to play embedded YouTube video.
Credit: NASA GSFC SVS
On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light. ...

Fermi GBM Observations of LIGO Gravitational Wave event GW150914 - V. Connaughton et al
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Re: Advanced LIGO Gravitational Wave Event GW150914 Follow-up

Post by neufer » Mon Apr 18, 2016 9:03 pm


“But I don’t want to go among mad people,”
Alice remarked.

“Oh, you can’t help that,” said the Cat:
“we’re all mad here. I’m mad. You’re mad.”

“How do you know I’m mad?” said Alice.

“You must be,” said the Cat,
“or you wouldn’t have come here.”
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Re: Advanced LIGO Gravitational Wave Event GW150914 Follow-up

Post by Ann » Tue Apr 19, 2016 12:00 am

The suggestion that a gamma ray burst may be connected with a black hole merger and its resulting gravitational waves is fascinating.

How often can we reasonably expect gravitational wave events to be detected by earthly instruments? There has been nothing since the first detection.

Ann

(Oh, and...yes, I like your cat-less gravitational wave smile, Art.)
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Re: Advanced LIGO Gravitational Wave Event GW150914 Follow-up

Post by neufer » Tue Apr 19, 2016 2:28 am

Ann wrote:
How often can we reasonably expect gravitational wave events to be detected by earthly instruments?
About 5 times.
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APS: Did Black Hole “Mimickers” Produce LIGO Signal?

Post by bystander » Thu Apr 28, 2016 6:24 pm

Did Black Hole “Mimickers” Produce LIGO Signal?
Physics | American Physical Society | 2016 Apr 27

Recently detected gravitational waves might not be a signature of black holes but of other massive objects that lack an event horizon.

In September 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves for the first time. Although the presumed source was a black hole merger, a new theoretical analysis shows that other hypothetical objects, like so-called gravastars, could produce a similar gravitational wave signal. The authors argue that ruling out such black hole “mimickers” will require more detailed observations of the post-merger phase.

The merger of two massive, compact objects produces gravitational waves before, during, and after the event. The post-merger, or “ringdown,” phase corresponds to the relaxation of the merged object from a highly distorted shape to a spherical one. Physicists often assume that ringdown waves are a direct sign that the merger produced a black hole. But Vitor Cardoso from the University of Lisbon, Portugal, and collaborators show that an unbiased ringdown analysis needs to take into account alternative models (for example, gravastar and firewall).

These alternative models deny the possibility of event horizons—the no-exit boundaries that define black holes. However, compact objects within these models would still have a light ring—the relativistic boundary within which photons can be trapped in circular orbits. ...

Is the gravitational-wave ringdown a probe of the event horizon? - Vitor Cardoso, Edgardo Franzin, Paolo Pani
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APS: Did LIGO Detect Dark Matter?

Post by bystander » Thu May 19, 2016 3:26 pm

Did LIGO Detect Dark Matter? - Simeon Bird et al
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GSFC: Possible Link Between Primordial Black Holes and Dark Matter

Post by bystander » Tue May 24, 2016 5:45 pm

Possible Link Between Primordial Black Holes and Dark Matter
NASA Goddard Space Flight Center | 2016 May 24
Click to view full size image 1 or image 2
Image 1: This image from NASA's Spitzer Space Telescope shows an infrared view of a sky
area in the constellation Ursa Major. Image 2: After masking out all known stars, galaxies
and artifacts and enhancing what's left, an irregular background glow appears. This is the
cosmic infrared background (CIB); lighter colors indicate brighter areas. The CIB glow is
more irregular than can be explained by distant unresolved galaxies, and this excess
structure is thought to be light emitted when the universe was less than a billion years
old. Scientists say it likely originated from the first luminous objects to form in the
universe, which includes both the first stars and black holes.
Credits: NASA/JPL-Caltech/A. Kashlinsky (Goddard)

Dark matter is a mysterious substance composing most of the material universe, now widely thought to be some form of massive exotic particle. An intriguing alternative view is that dark matter is made of black holes formed during the first second of our universe's existence, known as primordial black holes. Now a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, suggests that this interpretation aligns with our knowledge of cosmic infrared and X-ray background glows and may explain the unexpectedly high masses of merging black holes detected last year. ...

In his new paper, ... Kashlinsky analyzes what might have happened if dark matter consisted of a population of black holes similar to those detected by LIGO. The black holes distort the distribution of mass in the early universe, adding a small fluctuation that has consequences hundreds of millions of years later, when the first stars begin to form.

For much of the universe's first 500 million years, normal matter remained too hot to coalesce into the first stars. Dark matter was unaffected by the high temperature because, whatever its nature, it primarily interacts through gravity. Aggregating by mutual attraction, dark matter first collapsed into clumps called minihaloes, which provided a gravitational seed enabling normal matter to accumulate. Hot gas collapsed toward the minihaloes, resulting in pockets of gas dense enough to further collapse on their own into the first stars. Kashlinsky shows that if black holes play the part of dark matter, this process occurs more rapidly and easily produces the lumpiness of the CIB detected in Spitzer data even if only a small fraction of minihaloes manage to produce stars.

As cosmic gas fell into the minihaloes, their constituent black holes would naturally capture some of it too. Matter falling toward a black hole heats up and ultimately produces X-rays. Together, infrared light from the first stars and X-rays from gas falling into dark matter black holes can account for the observed agreement between the patchiness of the CIB and the CXB.

Occasionally, some primordial black holes will pass close enough to be gravitationally captured into binary systems. The black holes in each of these binaries will, over eons, emit gravitational radiation, lose orbital energy and spiral inward, ultimately merging into a larger black hole like the event LIGO observed. ...

LIGO Gravitational Wave Detection, Primordial Black Holes,
and the Near-IR Cosmic Infrared Background Anisotropies
- A. Kashlinsky
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