Detecting gravitational waves from supermassive black hole collisions using pulsars

Rodiano Bonacci
Novembre 14, 2017

The existence of gravitational waves, which were first predicted by Einstein's Theory of General Relativity about a hundred years ago, was only confirmed only last year. Supermassive black holes have a mass billions of times than that of the sun.

All these occurrences were detected by ground-based facilities like the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO) in the USA, or the Virgo facility in Italy.

In the case of the September 14, 2015, observation which was announced on February 11, 2016, scientists observed gravitational waves produced by the collision of black holes with a mass about a dozen times that of the Sun. This is due to ripples created at a much lower frequency, and a novel research has demarcated where and how to start looking.

Joseph Lazio, co-author of the study said that perceiving low-frequency gravitational waves would be related to being able to perceive bass singers, not just sopranos. Pulsars are dense neutron stars that rapidly rotate, emitting electromagnetic signals like clockwork.

By analyzing the local nanohertz gravitational-wave landscape, researchers were able to forecast that in a 10-year time frame, astronomers will witness the most powerful gravitational waves ever recorded.

These pulsar timing arrays are based on the same principle as LIGO and Virgo.

"If you take into account the positions of the pulsars in the sky, you basically have a 100 percent chance of detecting something in 10 years", Chiara Mingarelli, a research fellow at the Center for Computational Astrophysics at the Flatiron Institute in New York City, and lead author of the study, said in another statement. Using an array of well-known pulsars can help scientists detect even miniscule abnormalities, like gravitational waves from merging supermassive black holes. "And since the pulsars we study are about 3,000 light-years away, they act as a galactic-scale gravitational-wave detector", she added.

In order to predict when and where these mergers will occur, the new study scoured the sky for the most likely candidates.

Ultimately, detecting a gravitational wave generated by merging supermassive black holes could teach us more about how galaxies form and merge, helping us unravel the secrets of the universe. However, the smaller Sombrero Galaxy black holes mergers would offer a 160 million-year window. Of the total of five such detections since, four instances were a result of the merger of black holes, while the fifth - also the strongest - was caused by merging neutron stars.

The researchers hope that the array can also teach us about how galaxies are formed and what happens when they merge - which could be useful information, considering we're now on-course for a collision with our neighboring Andromeda galaxy. Thus the merger of the blackholes happens for a short time.

"By expanding our pulsar timing array over the next 10 years or so, there is a high likelihood of detecting gravitational waves from at least one supermassive black hole binary", says Mingarelli.

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