NASA telescope may point to gravitational wave sources

A brief, weak burst of high-energy light picked by NASA's Fermi Gamma-ray Space Telescope may help pinpoint source of the gravitational waves which were detected for the first time last year, the US space agency said.
On September 14 last year, waves of energy travelling for more than a billion years gently rattled space-time near Earth.
The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in US.
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 the 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 per cent 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.

"This is a tantalising discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we'll need to see more bursts associated with gravitational waves from black hole mergers," said Valerie Connaughton, a GBM team member at the US National Space, Science and Technology Centre.
Detecting light from a gravitational wave source will enable a much deeper understanding of the event.

Fermi's GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). The energy of visible light ranges between about 2 and 3 eV.
The GBM can detect light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together.
These same systems also are suspected to be prime producers of 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 at the Harvard-Smithsonian Centre for Astrophysics and a member of the LIGO Scientific Collaboration.

Currently, gravitational wave observatories possess relatively blurry vision.
This will improve in time as more facilities begin operation, but for the last year's event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by US.