Light Burst from a Black Hole Merger Could Narrow Down Source of Gravitational Waves

Wednesday, 20 April 2016 - 11:29AM
NASA
Black Holes
Astrophysics
Wednesday, 20 April 2016 - 11:29AM
Light Burst from a Black Hole Merger Could Narrow Down Source of Gravitational Waves
In September 2015, two LIGO observatories detected gravitational waves emitted from the merger of binary black holes. Now, NASA is getting ready to narrow down the location of those waves, using a burst of light that, by all accounts, never should have existed in the first place.

Further analysis of the data from the gravitational waves detection shows that the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief burst of gamma ray light coming from the same part of the sky less than half a second after the gravitational waves reached Earth. This constitutes powerful evidence that the light was emitted from the same black hole merger that produced the gravitational waves; NASA claims that there's only a .2% chance that the timing and apparent location were a coincidence.
Opening quote
"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," NASA said in a statement. "Detecting light from a gravitational wave source will enable a much deeper understanding of the event."
Closing quote

In light of this new information (no pun intended), we might be able to narrow down the location of the gravitational waves emission. When LIGO detected the waves last year, they were only able to trace the waves to an arc of sky that spanned 600 degrees, but by combining this information with the localization of the light burst, they may be able to decrease the area to only 200 square degrees.

Black hole mergers are not expected to emit any kind of light, because this emission requires excess gas, while astronomers expected any orbiting gas to be sucked into the black holes long before the merger actually occurs. This had led some astronomers to conclude that the burst of light is, in fact, a coincidence, but if it is related, then it could give us more insight into the merger process, and black holes in general, than ever before.

Opening quote
"With a burst better placed for the GBM's detectors, or one bright enough to be seen by Fermi's Large Area Telescope, even greater improvements are possible," NASA wrote. "[But] it will take further detections to clarify what really happens when black holes collide."
Closing quote
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