For the first time, astronomers have been able to “hear” the cosmic hum of strong gravity waves propagating throughout the cosmos as a result of collisions between black holes.
The discovery might aid in the understanding of cosmological events including supermassive black holes and the frequency of galaxy mergers.
Albert Einstein first hypothesized gravitational waves in 1916; they are space-time ripples that were first observed in 2015.
The waves were discovered by monitoring pulsars, or the dense remains of huge stars’ supernova-erupting cores, across the Milky Way. As they spin quickly and emit radio waves, pulsars resemble star lighthouses and appear to “pulse” when viewed via telescopes on Earth. Since pulsars can spin hundreds of times per second, their precise pulses are as accurate as cosmic clocks. A pulsar’s radio wave timing is messed up when gravity waves travel between Earth and it. According to Einstein’s theory, gravitational waves could expand and compress space as they travelled around the cosmos, impacting the path taken by radio waves. This indicates that some of the pulses arrive at Earth a tiny bit earlier or later than expected.
As a component of the North American Nanohertz Observatory for Gravitational Waves cooperation, often known as NANOGrav, more than 190 scientists set out to identify the gravitational wave frequencies.
The Arecibo Observatory in Puerto Rico (which is no longer in service), the Green Bank Telescope in West Virginia, and the Very Large Array in New Mexico were used to follow the radio waves from more than 60 pulsars over the course of 15 years.
Their findings are presented in a report that was released in The Astrophysical Journal Letters on Wednesday.
The most potent gravitational waves ever measured have just been discovered. They carry nearly a million times as much energy as the solitary events discovered in recent years that were the consequence of black hole or neutron star mergers and were probably brought on by collisions of supermassive black holes.
“It’s like a choir, with all these supermassive black hole pairs chiming in at different frequencies,” research coauthor and NANOGrav scientist Chiara Mingarelli, assistant professor of physics at Yale University, said in a release. “This is the first-ever evidence of a gravitational wave background. A new window for observing the universe has been opened by us.
Ultra-low-frequency gravity waves make up the gravitational wave background, a type of cosmic noise that has long been postulated but never observed. These waves all hum and echo together in the background as black holes collide throughout the universe.
Although gravitational waves move at the speed of light, astronomers understood that the space-time ripple effect meant that only the rise and fall of one of the waves may take years or decades to complete.
According to research coauthor Dr. Scott Ransom, staff astronomer at the National Radio Astronomy Observatory, “We’re using a gravitational-wave detector the size of the galaxy that’s made out of exotic stars (pulsars), which just blows my mind.”
“We knew we had been hearing something based on our earlier data, but we weren’t sure what. We now know that the sound is gravitational universe music. We’ll probably be able to distinguish notes from the instruments performing in this cosmic orchestra as we keep listening,” Ransom added.
The gravitational wave background is mostly attributed, according to scientists, to supermassive black holes. Most huge galaxies have supermassive black holes at their centers. However, as galaxies collide, their black holes eventually start to revolve around one another.
These enormous bodies, which have billions of times our sun’s mass, dance until they crash. When they do, waves leave the host galaxy and ultimately travel to our galaxy.
Millions or maybe hundreds of thousands of pairs of supermassive black holes are thought to exist throughout the cosmos.
According to study coauthor Dr. Luke Kelley, an assistant professor of astronomy at the University of California, Berkeley, and head of NANOGrav’s astrophysics group, “at one point, scientists were worried that supermassive black holes in binaries would orbit each other for all time, never coming close enough together to generate a signal like this.”
However, Kelley added, “Now we have solid proof that many of these incredibly huge and near binaries actually exist. Nothing can prevent the two black holes from merging within a few million years once they are close enough to be observed by pulsar timing arrays.
However, the researchers admit it’s not impossible that the gravitational wave backdrop had more than one origin, just as there are conflicting theories on how the universe came to be. The group will keep examining the gravitational wave backdrop and make an effort to pick out specific sources to ascertain their origins.
The gravitational wave backdrop is almost two times louder than I anticipated, according to Mingarelli. It’s really at the top of the range of what our models can produce with only supermassive black holes. The future is everything. This is just the start.
Similar observations were also reported by scientists using telescopes in Europe, India, China, and Australia on Wednesday. The researchers claimed that combining data from NANO Grav with those from international collaborators can give a more comprehensive view of the gravitational wave background.
“Our combined data will be much more powerful,” said study co-author and NANO Grav cooperation chair Stephen Taylor, an assistant professor of physics and astronomy at Vanderbilt University. We’re eager to learn what insights they will provide into our cosmos.