One of the biggest scientific achievements of this year has been the detection of gravitational waves. While legendary theoretical physicist Albert Einstein had predicted the existence of them a century ago, it was first spotted by the scientists only in 2015.
The waves that have been detected so far by Laser Interferometer Gravitational Observatory (LIGO) and Virgo, Italy, emerged from the merger of two black holes and neutron stars. Now, the experts believe that astronomers won't have to wait much longer to get the first glimpse of one of the biggest types of unions in the cosmos, which will generate gravitational waves and will be much bigger than the aforementioned mergers.
According to a new research, the merger of two supermassive black holes will be detected within 10 years. This study is the first one that compiled real data, instead of computer simulations, in order to predict the time of such an observation.
"The gravitational waves from these supermassive black hole binary mergers are the most powerful in the universe," said the lead author of the study, published in Nature Astronomy, Chiara Mingarelli, a research fellow at the Center for Computational Astrophysics at the Flatiron Institute in New York City. "They absolutely dwarf the black hole mergers detected by LIGO," which had first detected gravitational waves from colliding black holes in February 2016.
The discovery of a supermassive black holes merging would provide fresh insights to the scientists about how massive galaxies and black holes evolve, said Mingarelli.
Supermassive black holes reside in the heart of large galaxies. Even our Milky Way has them and they can be millions or even billions of times the mass of the sun. Just to provide a clear idea as to how big this upcoming unison is going to be - the merging black holes that have been detected so far by gravitational wave detectors have only been a few dozen times the sun's mass.
When two galaxies collide and combine, supermassive black holes of each of the galaxies move to the center of the newly formed galaxy. As per the prediction by the scientists, the supermassive black holes will then close in together and merge over the course of time. This get-together will then produce intense gravitational waves that would ripple through the fabric of space and time.
While those gravitational waves are strong, they lie outside the wavelengths currently observable by ongoing experiments, such as LIGO and Virgo. The new hunt for gravitational waves formed by merging supermassive black holes will make use of the stars, called pulsars. These stars behave like cosmic metronomes. These rapidly spinning stars send out a steady rhythm of radio wave pulses. As passing gravitational waves stretch and compress the space between Earth and the pulsar, the rhythm changes slightly. Those changes are then monitored by pulsar-watching projects on Earth.
"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. The bottom line is that you're guaranteed to select at least one local supermassive black hole binary," said Mingarelli.
If a supermassive black hole merger isn't detected within the 10-years' time span, it could be because the black holes freeze at around three light-years of separation. This conundrum is called the Final Parsec Problem.
The two black holes come close to each other over time, as their orbits deteriorate because of losing energy while generating gravitational waves, however, the process can even take longer than the current age of the universe. As to whether astronomers will detect a supermassive black hole merger, "it'll be interesting either way," concluded Mingarelli.