Albert Einstein imagined the universe as something like the wave pool at a hugely popular amusement park. On Thursday, researchers announced a major new step to prove this is true.
About a century ago, the theoretical physicist imagined that the largest structures in the universe could warp and warp spacetime. On smaller scales, the gravity of planets like Earth can hold back large objects like the moon. But gnarled structures like black holes are massive and common enough to create a series of gravitational footprints throughout the fabric of space-time, continuously rippling through time. Einstein theorized that the lump sum of these strong gravitational impressions creates a series of waves that reverberate throughout the universe.
The new work appeared in the magazine on Thursday science, the next big step is to prove the collective existence of these undulating motions, called the gravitational-wave background. The new technique described in the study could help astrophysicists write an exciting new chapter in astronomy.
What’s new – Just seeing the gravitational wave background would be incredible. But aside from proving Einstein right once again, this technique would help answer questions about the dynamics of the universe, such as how big black holes are when they collide and our knowledge of how galaxies grow substantiate
“Gravitational waves are funny because they have a tremendous amount of energy, but they don’t really do anything,” says Matthew Kerr, an astrophysicist currently working at the US Naval Research Laboratory The opposite. Kerr has been part of the Fermi Gamma-ray Space Telescope research community since the late 2000s and is one of the authors of the study.
Gravitational waves come from powerful objects like black holes and distant pulsars, but they don’t announce themselves to us as large perturbations. Until these waves reach Earth, the waves are weak and detecting them requires intelligent techniques and sensitive instruments. That’s why the ingenuity of LIGO — short for Laser Interferometer Gravitational-Wave Observatory — wowed the astrophysics community back in 2017, when it discovered a twist in spacetime that stretched through our planet by a tiny amount and two high-density objects millions of light-years away violently crashing into each other.
The new study comes from a project with Fermi, a telescope about the size of two refrigerators that was launched in 2008. In the paper, scientists announced they had pooled 12 years of Fermi data to use pulsar timing arrays to form a new gravitational-wave hunting technique.
How it works – Fermi is tuned to gamma rays, which are the most energetic form of light. Kerr and his colleagues are searching for low-frequency gravitational waves from supermassive black holes that have merged across the universe and are filling space with their waves — waves that are currently too subtle for LIGO to detect.
Until now, scientists have used radio waves to look for evidence of the gravitational-wave background. But Fermi has several unique advantages.
For one, it’s “looking at all that stuff all the time,” Kerr said, thanks to a wide field of view capable of seeing one-sixth of the sky at any given time. “It’s really useful for us because we can see a large number of pulsars at any given time, and that’s key to this work where we’re looking for gravitational waves.”
Pulsars are gifts from heaven, Kerr said. “They’re like little lighthouses, and every time they point to Earth, we see a pulse from them.”
They are what happens when a large star collapses on itself after its demise. This after-death material eventually spins with great precision due to the tight shutter, creating jets from the poles of the star corpse. As they sweep the sky in our general direction, we can observe them as evenly timed intervals of energy.
Why it matters – Pulsars are the steady clocks of space. For this reason, astrophysicists use pulsars in the Milky Way as precisely timed beacons. Their pulse timing could hypothetically change if something shortens or lengthens the distance between the pulsar and Earth. Scientists have already detected slight delays and speeding using radio wave arrays.
Now they are working to definitively prove that these perturbations are caused by black holes twisting and bending the fabric of spacetime. This would turn space-time into something like a loose bed sheet, distorting the distance it takes for the pulsar signal to reach Earth.
Fermi’s gamma-ray detection is valuable because it provides powerful data to confirm radio waves. According to Kerr, gamma rays are less dirty than radio waves.
“When light from pulsars comes to Earth, it’s affected by the space between us and the pulsar,” says Kerr. “Space is mostly empty, but there are some things out there — hydrogen atoms and electrons and bits of dust — and when radio waves pass through that, they actually get refracted, much like light goes through a prism.”
“People who have done this work have an idea of how to do this and factor that into their analyses, but there are still some unknowns about what kind of residual effects this propagation of radio waves through space might have.” he adds.
But Fermi will come to the rescue. “Gamma rays will not have this problem at all. They’re high-energy light, they just go straight through from the pulsar and arrive here on Earth at the Fermi Space Telescope with no extra bending.” T
This is a separate way to do the measurement; By comparing the two, researchers can see if radio waves are pointing to a gravitational-wave background or if the models need repairs.
The new study announces that the Fermi-pulsar timing array technique has now “achieved a sensitivity to gravitational waves that is about 30 percent better than what we can currently achieve with radio telescopes,” according to Kerr.
That means Fermi is already almost as sensitive as football field swaths from radio telescope arrays, which cover much more area than that of a double-fridge-sized space telescope. This efficiency also inspires astrophysicists.
What’s next – Fermi is now on par with the radio studies that are currently being conducted, Kerr said. And Fermi’s gravitational-wave detection capacity could increase over the next three to four years.
Alternatively, Fermi could simply show that these changes in pulsar signals are caused by something else. Perhaps black holes don’t merge as frequently as astrophysicists believe. Perhaps they are less massive, and excluding the background could be a way to test other theories of how galaxies grow.
Still, this project will have some lasting impact on the gravitational-wave subfield of astronomy in one way or another.