Banner image: a pulsar that emits a plume of energy. (Credit: NASA / HST / ASU / J. Hester et al.)
Scientists have used a ‘galaxy’ in ‘galaxy’ to find possible hints of a unique signal of gravitational waves, or the powerful ripples moving through the universe and distorting the tissue of space and time itself.
The new findings, recently published in The astrophysical journal letters, from a U.S. and Canadian project called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).
NANOGrav researchers have been investigating for more than 13 years the light emitted from dozens of pulses scattered through the Milky Way system in an attempt to detect a “background for gravity wave”. This is what scientists call the steady flow of gravitational radiation, which according to the theory is constantly washing over the earth. The team has not yet determined the target, but it is getting closer than ever before, said Joseph Simon, an astrophysicist at the University of Colorado Boulder and lead author of the new article.
“We found a strong signal in our dataset,” said Simon, a postdoctoral researcher in the Department of Astrophysical and Planetary Sciences. “But we can not yet say that this is the gravity wave background.”
In 2017, scientists at an experiment called the Laser Interferometer Gravitational-Wave Observatory (LIGO) won the Nobel Prize in Physics for the very first direct detection of gravitational waves. Those waves were created when two black holes crash into each other about 130 million light-years from Earth, producing a cosmic shock that spreads to our own solar system.
Graphic representation of the pulse light moving between the gravitational waves towards the earth. (Credit: NANOGrav / T. Klein)
That event was the equivalent of a pelvic collision – a violent and momentary explosion. The gravitational waves that Simon and his colleagues are looking for, on the other hand, are more like the constant buzz of conversations during a busy cocktail party.
It is an important scientific achievement to realize that background noise opens a new window for the functioning of the universe. These waves can, for example, give scientists new tools to study how the supermassive black holes in the centers of many galaxies fuse over time.
“These alluring first tips from a gravitational wave background suggest that supermassive black holes are likely to merge and that we are bouncing in a sea of gravitational waves that are rippling from supermassive black hole mergers across galaxies across the universe,” said Julie Comerford, associate professor of planetary science astrophysics. at CU Boulder and NANOGrav team member.
Simon will present his team’s results at the 237th meeting of the American Astronomical Society during a virtual press conference on Monday.
Galactic Lighthouses
Through their work at NANOGrav, Simon and Comerford are part of a high-interest, albeit collaborative international race to find the background of gravity. Their project joins two others from Europe and Australia to set up a network called the International Pulsar Timing Array.
Simon said that fusing galaxies and other cosmological events, according to the theory, produce at least a steady amount of gravitational waves. They are humungous – a single wave, Simon said, can take years or even longer to pass the earth. Therefore, no other existing experiments can detect it directly.
“Other observatories are looking for gravitational waves that are within seconds,” Simon said. “We are looking for waves that are in the order of years or decades.”
He and his colleagues had to get creative. The NANOGrav team uses telescopes on the ground not to search for gravitational waves, but to observe pulse veins. These collapsed stars are the lighthouses of the galaxy. They rotate at an incredibly fast speed and send radiation currents to Earth in a flashing pattern that remains mostly unchanged over the centuries.
Simon explained that gravitational waves change the steady pattern of light coming from pulses and the relative distances these rays move, draw, or push through space. Scientists, in other words, can detect the background of the gravitational wave by simply monitoring pulses for correlated changes in the timing of when they reach Earth.
“These pulsars rotate just as fast as your kitchen mixer,” he said. “And we’re looking at the deviation of a few hundred nanoseconds.”
Something there
To find the subtle signal, the NANOGrav team strives to observe as many pulses as possible. To date, the group has observed 45 pulses for at least three years and in some cases for more than a decade.
The hard work seems to be bearing fruit. In their latest study, Simon and his colleagues report that they detected a clear signal in their data: A general process seems to affect the light of many of the pulses.
‘We walked through each of the pulses one by one. ‘I think we all expected to find some that are the scraps to throw our data away,’ ‘Simon said. “But then we all came through and said, ‘Oh my God, there’s actually something here. ‘
The researchers can still not say for sure what is causing the signal. They will need to add more pulsars to their data set and observe it longer to determine if it is actually the gravitational wave background at work.
“Being able to detect the background of the gravitational wave would be a big step, but it’s really just one,” he said. “Step two is to determine what is causing the waves and discover what they can tell us about the universe.”
NANOGrav is an American National Science Foundation Physics Frontiers Center. It is co-led by Maura McLaughlin of the University of West Virginia and Xavier Siemens of Oregon State University.