When two stars collide

This collision created gravitational waves which travelled through the Universe and reached earth, where they were detected on August 17^th 2017 by the LIGO/Virgo interferometers.

Although there have been 4 detections of gravitational waves before, this detection was different as it is the first time astronomers caught a glimpse of light, or electromagnetic radiation, from this collision in their telescopes. A new era of astronomy is born – Gravitational wave astronomy, and UCD astronomers had a part to play in this historic discovery.

Gravitational waves were first detected in 2015. Einstein predicted as part of his general theory of relativity that when heavy bodies such as black holes or neutron stars accelerate, they create a disturbance which stretches space and time and travels at the speed of light.

These waves only move space a tiny fraction – a ruler 13km long would only be distorted by the width of an atom. Therefore the most sensitive detectors ever built are used to detect these waves.

These are the LIGO-Virgo interferometers – a team of 3 detectors containing long arms along which a laser is reflected off mirrors. The gravitational waves affect the length of the arms, therefore distorting the laser signals. Any outside movement, even a car passing by, must be taken into account.

We cannot see collisions of black holes as there is no matter to emit light, however it is thought that the collision of neutron stars could be detected by telescopes here on earth.

The world has waited for LIGO-Virgo to detect colliding neutron stars so we can begin the search for the light from these collisions.

On August 17^th, this finally happened and UCD astronomers were on hand to glimpse this collision using telescopes on the ground and satellites like NASA's Fermi telescope and ESA's INTEGRAL satellite, which both glimpsed a gamma-ray burst 1.7 seconds after the gravitational waves were detected.

Astronomers in the UCD Space Science Group in the UCD School of Physics, where I am a first year PhD student, had a part to play in these discoveries. UCD Professor Lorraine Hanlon and Dr Antonio Martin-Carrillo are members of the INTEGRAL team and Dr Sheila McBreen is a member of the Fermi team.

The observations of a gamma-ray burst soon after the gravitational waves by these satellites proves that short gamma ray bursts, which are bursts of energetic gamma-rays lasting less than 2 seconds, can be created by collisions of neutron stars.

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