16 October 2017

Gravitational waves: scientists see binary two neutron stars colliding to form black hole

University of Sheffield scientists are part of the international team who have ‘seen’ gravitational waves for the first time.

Starry sky, a small galaxy is visible

An international team of scientists has today (Monday 16 October 2017) announced they have detected the debris cast off by colliding neutron stars 130 million light-years away – an unprecedented milestone in our quest to understand more about time and space.

The new gravitational waves observation, from a global team of researchers including scientists from the University of Sheffield, is of two binary neutron stars which collided to form a heavier compact object.

Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas.

As these neutron stars spiralled together, they emitted gravitational waves that were detectable for about 100 seconds; when they collided, a flash of light in the form of gamma rays was emitted and seen on Earth about two seconds after the gravitational waves.

Multimessenger astronomy is in its infancy, but the future of this kind of science is surely very bright, and exploitation of gravitational wave detectors will be a source of new insights into the Universe for a long time to come

Dr Ed Daw

Laser Interferometer Gravitational-Wave Observatory (LIGO)

This is the first time scientists have seen gravitational waves, which were predicted more than a century ago by Albert Einstein, from a binary neutron star system.

The collision was witnessed by the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the US.

The lack of a corresponding signal from the Virgo detector in Italy allowed the sky position for the source to be reconstructed with sufficient accuracy to find the source on the sky with optical instruments.

Dr Ed Daw from the University of Sheffield’s Department of Physics and Astronomy has been part of the LIGO team since 1998.

Commenting on the new announcement Dr Daw said: “This is the first detection of gravitational waves from a binary neutron star system.

“It is extra special because as well as gravitational waves, other signals were detected by astronomical groups in partnership with LIGO and Virgo from the same source, yielding optical and gamma ray counterparts to the gravitational wave event.”

He added: “The event announced today was detected by LIGO the same way the other earlier events were - by the vibrations of test masses suspended from wires in the LIGO detectors.

“But, because the signal was so clean, LIGO and Virgo together were able to determine a small enough area on the sky where the event originated that telescopes of various kinds could be pointed at that area of the sky to look for an electromagnetic counterpart.

“Some of these instruments succeeded in identifying a visible, or a gamma ray, signal coming from the source. These detectors did indeed see the source of the gravitational wave, but they only knew where to point because LIGO had narrowed down the sky area they had to search.”

Gravitational waves, which were first detected in September 2015 carry unique information about the origins of our Universe and studying them is expected to provide important insights into the evolution of stars, supernovae, gamma-ray bursts, neutron stars and black holes.

However, they interact very weakly with particles and require incredibly sensitive equipment to detect.

The LIGO Scientific Collaboration comprises of over 1000 scientists from 17 countries, and includes researchers from ten UK universities including the University of Sheffield.

Earlier this month three members of the LIGO Scientific Collaboration, Ranier Weiss, Kip S. Thorne and Barry C. Barish were awarded the Nobel Prize in Physics for the discovery of gravitation waves.

Dr Daw explained what impact this new landmark discovery will have on the world of physics in the future.

“The science payoff of this discovery is immediate and profound. For example, we have the first confirmations that so-called 'kilonova' events and 'short hard gamma ray bursts' are caused by pairs of neutron stars colliding.

“These events have been mysteries in astronomy for years, and though they were suspected of having their cause in neutron star collisions, we can now confirm what was suspected for the first time.

“Multimessenger astronomy is in its infancy, but the future of this kind of science is surely very bright, and exploitation of gravitational wave detectors will be a source of new insights into the Universe for a long time to come.”

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