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January 11, 2021
from the University of Colorado at Boulder
Scientists have used a « galaxy-sized » space observatory to find possible clues to a unique signal from gravitational waves, or the powerful waves that travel through the universe, distorting the very fabric of space and time.
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The new findings, recently published in The Astrophysical Journal Letters, come from a US and Canadian project called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).
For over 13 years, NANOGrav- Researchers examined the light from dozens of pulsars scattered across the Milky Way to try to detect a « gravitational wave background ». This is what scientists call the steady flow of gravitational radiation, which theoretically washes itself constantly over the earth. The team hasn’t pinpointed that goal yet, but it’s getting closer than ever, said Joseph Simon, astrophysicist at the University of Colorado Boulder and lead author of the new paper. « We found a strong signal in our data set » said Simon, a postdoctoral fellow in the Department of Astrophysical and Planetary Sciences. “But we can’t yet say that this is the background of the gravitational wave.”
In 2017, scientists in an experiment called the Laser Interferometer Gravitational Wave Observatory (LIGO) received the Nobel Prize in Physics for the first direct detection of gravitational waves. These waves were formed when two black holes smacked into each other approximately 130 million light-years from Earth, creating a cosmic shock that spread to our own solar system.
This event was the equivalent of a basin crash – a violent and short-lived explosion. The gravitational waves that Simon and his colleagues are looking for, on the other hand, are more like the constant hum of conversations at a crowded cocktail party.
Detecting background noise would be an important scientific achievement and would open a new window for the way the universe works, added he added. For example, these waves could give scientists new tools to study how the supermassive black holes at the centers of many galaxies merge over time.
« These tantalizing first indications of a gravitational wave background suggest that supermassive black holes are likely merge and that we’re moving in a sea of gravitational waves splashing from supermassive black hole fusions in galaxies across the universe, « said Julie Comerford, professor of astrophysics and planetary research at CU Boulder and NANOGrav team member.
Simon will be the results of his Introduce teams at a virtual press conference on Monday at the 237th meeting of the American Astronomical Society.
Through their work on NANOGrav, Simon and Comerford are part of a high-level, albeit collaborative, international race for the background of the gravitational wave. Their project, along with two others from Europe and Australia, forms a network called the International Pulsar Timing Array.
Simon said that, at least in theory, the merging of galaxies and other cosmological events creates a steady migration of gravitational waves. They’re humorous – a single wave, Simon said, can take years or even more to pass the earth. Because of this, no other existing experiments can directly detect them.
« Other observatories look for gravitational waves on the order of seconds, » said Simon. « We’re looking for waves on the order of years or decades. »
He and his colleagues had to get creative. The NANOGrav team uses telescopes on the ground not to look for gravitational waves, but to observe pulsars. These collapsed stars are the galaxy’s lighthouses. They spin at incredibly high speeds, sending streams of radiation toward Earth in a blinking pattern that has remained largely unchanged over the eons.
Simon explained that gravitational waves change the steady light pattern of pulsars and the relative distances they travel Move, pull, or squeeze rays through space. In other words, scientists might be able to easily see the background of the gravitational wave by monitoring pulsars for correlated changes in the time they arrived on Earth.
« These pulsars spin about as fast as you do Kitchen mixer, « he said. « And we’re looking at deviations in their timing of just a few hundred nanoseconds. »
To find this subtle signal, the NANOGrav team tries to observe as many pulsars as possible for as long as possible. To date, the group has observed 45 pulsars for at least three years, and in some cases well over a decade.
The hard work seems to be paying off. In their most recent study, Simon and his colleagues report that they found a clear signal in their data: A common process appears to be affecting the light of many pulsars.
« We went through each of the pulsars one at a time. I think we did everyone expected to find a few to throw away our data, « said Simon. « But then we all got through it and said, ‘Oh my god, there is indeed something here.' »
The researchers still can’t be sure what is causing this signal. You need to add more pulsars to your dataset and watch them for longer periods of time to see if it really is the gravitational wave background at work.
« Being able to capture the gravitational wave background is going to be a big one Be a step, but that’s really only the first step, « he said. « Step two is to find out what is causing these waves and what they can tell us about the universe. »
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