Gamma-ray burst detected near first observed gravitational wave

Last September, a tiny space-time disturbance produced by two merging black holes roughly 1.3 billion light-years from Earth and detected by NASA’s Laser Interferometer Gravitational Wave Observatory (LIGO) marked the first-ever detection of gravitational waves.

Less than half a second later, a weak and short-lived burst of high-energy light believed to have originated from the same part of the sky was detected by the Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope – a phenomenon scientists at the space agency noted has a paltry 0.2 percent chance of being coincidental.

While the detection of gravitational waves was a big deal, confirming one of the last predictions of Einstein’s theory of general relativity, the detection of gamma-rays emerging from the merger of two black holes would also be a landmark discovery, according to NASA, as black holes were long believed to have merged without producing even the slightest trace of light.

Valerie Connaughton, a GBM researcher at the National Space, Science and Technology Center in Huntsville, Alabama and lead author of a paper on the burst’s detection currently under review by The Astrophysical Journal, called the discovery “tantalizing” and noted that there was “a low chance” that it was inaccurate.

Discovery could help NASA pinpoint the causes of short GRBs

When the discovery of the gravitational wave known as GW150914 was officially announced in February, it confirmed that black holes of approximately 30 solar masses exist and might be even more common than existing theories had predicted, according to Discovery News.

It also marked the first chapter in a new era in astronomy, in which scientists can detect invisible energetic events that product the waves, but without producing electromagnetism, the site added. However, if Fermi did in fact detect light from a gravitational wave source, it may open the door to an improved understanding of this event and others like it.

However, Connaughton warns, “before we can start rewriting the textbooks we’ll need to see more bursts associated with gravitational waves from black hole mergers.” For that, she and her colleagues will rely on Fermi’s GBM, which can observe the entire sky and is sensitive to both X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV).

Given the instrument’s large field of view and wide energy range, the agency said that the GBM is the ideal instrument for detecting light emitted by short gamma-ray bursts lasting no more than two seconds. Such bursts are believed to be produced when black holes or other compact orbiting objects collide – the same events thought to generate gravitational waves.

“With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB,” said Lindy Blackburn, a postdoctoral fellow from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. “There is an incredible synergy between the two observations, with gamma rays revealing details about the source’s energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event.”

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Image credit: Swinburne Astronomy Productions

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