Astronomers find a clever way to find an Einsteinian phenomenon using dead stars

Albert Einstein imagined the universe as something like the wave pool in an extremely popular amusement park. On Thursday, researchers announced an important new step to prove this.

About a century ago, the theoretical physicist envisioned that the universe’s largest structures could bend and distort space-time. On a smaller scale, the gravitational pull of planets like Earth can hold large objects like the moon. But gnarled structures like black holes are massive and general enough to produce a series of gravitational impressions through the space-time fabric, rippling continuously through time. Einstein theorized that the lump sum of these strong gravitational impressions creates a series of ripples that reverberate throughout the universe.

The new work, published Thursday in the magazine Science, is the next big step to prove the collective existence of these undulations — called the gravitational wave background. The new technique described in the study could help astrophysicists write a vibrant new chapter in astronomy.

What’s new – Just detecting the background of the gravitational wave would be incredible. But in addition to 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 bolster what we know about how galaxies grow.

“Gravity waves are funny because they have a huge amount of energy, but they don’t really do anything,” said Matthew Kerr, an astrophysicist currently working at the US Naval Research Laboratory. inverse† Kerr has been part of the Fermi gamma-ray 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 pulsars that are far away, but they don’t report to us as major disturbances. By the time these ripples reach Earth, the waves are weak, and detecting them requires smart techniques and sensitive instruments. That’s why the ingenuity of LIGO — short for Laser Interferometer Gravitational-Wave Observatory — thrilled the astrophysics community in 2017 when it discovered a twirl of space-time extending through our planet at a very small amount, created by two very dense objects forcibly slide into each other at a distance of millions of light years.

The new study comes out of a project with Fermi, a telescope the size of two refrigerators launched in 2008. In the paper, scientists announced that they had pooled 12 years of Fermi data to use pulsar timing arrays to form a new gravitational wave. hunting technique.

Illustration of a pulsar, the dense remnant of a supernova.Shutterstock

How it works – Fermi is tuned to gamma rays, the form of light with the highest energy. Kerr and his colleagues are looking for low-frequency gravitational waves from supermassive black holes that have fused throughout the universe, filling space with their ripples — which are too subtle for LIGO to detect at the moment.

Until now, scientists have used radio waves to look for evidence of the gravitational wave background. But Fermi has several unique advantages.

First, it’s “looking at all things all the time,” Kerr said, thanks to a large field of view capable of seeing one-sixth of the sky at any given time. “This is very helpful 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 heavenly gifts, Kerr said. “They’re like little lighthouses, and every time they point to Earth, we see a pulse of them.”

They are what happens when a great star, upon its demise, collapses in on itself. This afterlife material eventually spins with high precision due to its tight closure, producing rays from the poles of the stellar corpse. When they sweep the sky in our general direction, we can perceive them as evenly timed energy intervals.

Why it matters – Pulsars are the fixed clocks of space. That’s why astrophysicists use pulsars in the Milky Way Galaxy 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 minor delays and speeding violations 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 space-time. This would turn spacetime into something like a loose sheet, distorting the distance the pulsar signal needs to reach Earth.

Fermi’s gamma-ray detections are valuable because they provide solid data to confirm radio waves. Gamma rays are less dirty than radio waves, according to Kerr.

A demonstration of the ripples in space-time through black hole mergers.MARK GARLICK/SCIENCE PHOTO LIBRARY/Science Photo Library/Getty Images

“When light comes to Earth from pulsars, it’s affected by the space between us and the pulsar,” Kerr says. “Space is mostly empty, but there are things out there — hydrogen atoms and electrons and bits of dust — and when radio waves pass through there, they’re actually refracted just like light when it goes through a prism.”

“People who’ve done this work have an idea of ​​how to do that and incorporate that into their analyses, but there’s still some unknown about what kind of residual effects there might be from this radio wave propagation through space,” he adds.

But Fermi comes to his aid. “Gamma rays won’t have that problem at all. It’s high-energy light, they just go straight off the pulsar and arrive here on Earth at the Fermi Space Telescope with no extra bend.”

this is a separate way to perform the measurement; by comparing the two, researchers can tell if radio waves are pointing at a gravitational wave background, or if the models need repair.

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,” Kerr said.

This means that Fermi is already almost as sensitive as football fields of radio telescope arrays, which occupy much more real estate than that of a space telescope the size of a double refrigerator. This efficiency also excites astrophysicists.

What’s next – Fermi is now on par with radio studies currently being done, Kerr said. And Fermi’s gravitational wave detection capacity could increase in the next three to four years.

Alternatively, Fermi could show that these changes in the pulsar signals are caused by something else. Perhaps black holes don’t merge as often as astrophysicists think. Perhaps they are less massive, and then excluding the background could be a way to check other theories about how galaxies grow.

Nevertheless, this project will somehow have lasting effects on the gravitational wave subfield of astronomy.

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