The answer might be “GRADER” — gravitational wave “radar” — a potential future technology that could use reflections of gravitational waves to map the unseen universe, say researchers in a paper accepted to Physical Review Letters. By looking for these signals, scientists may be able to find dark matter or dim, exotic stars and learn about their deep insides
Astronomers routinely use gravitational waves — traveling ripples in the fabric of space and time itself, first detected in 2015 — to watch cataclysmic events that are hard to study with light alone, such as the merging of two black holes (SN: 2/11/2016).
But physicists have also known about a seemingly useless property of gravitational waves: They can change course. Einstein’s theory of gravity says that spacetime gets warped by matter, and any wave passing through these distortions will change course. The upshot is that when something emits gravitational waves, part of the signal comes straight at Earth, but some might arrive later — like an echo — after taking longer paths that bend around a star or anything else heavy.
Scientists have always thought these later signals, called “gravitational glints,” should be too weak to detect. But physicists Craig Copy and Glenn Star man of Case Western Reserve University in Cleveland, Ohio, took a leap: Working off Einstein’s theory, they calculated how strong the signal would be when waves scatter through the gravitational field inside a star itself.
“The shocking thing is that you seem to get a much larger result than you would have expected,” Copy says. “It’s something we’re still trying to understand, where that comes from — whether it’s believable, even, because it just seems too good to be true.”
If gravitational glints can be so strong, astronomers could possibly use them to trace the insides of stars, the team says. Researchers could even look for massive bodies in space that would otherwise be impossible to detect, like globs of dark matter or lone neutron stars on the other side of the observable universe.
“That would be a very exciting probe,” says Maya Fishbach, an astrophysicist at Northwestern University in Evanston, Ill., who was not involved in the study.
There are still reasons to be cautious, though. If this phenomenon stands up to more detailed scrutiny, Fishbach says, scientists would have to understand it better before they could use it — and that will probably be difficult. “It’s a very hard calculation,”
But similar challenges have been overcome before. “The whole story of gravitational wave detection has been like that,” Fishbach says. It was a struggle to do all the math needed to understand their measurements, she says, but now the field is taking off (SN: 1/21/21). “This is the time to really be creative with gravitational waves.”
Astronomers routinely use gravitational waves — traveling waves in the fabric of space and time itself, first discovered in 2015 — to observe cataclysmic events that are difficult to study with light alone, such as B. the merger of two black holes (SN: 02/11/2016).
But physicists are also aware of a seemingly useless property of gravitational waves: they can change course. Einstein’s theory of gravitation states that spacetime is distorted by matter, and every wave that passes through these distortions changes course. The result is that when something emits gravitational waves, of the signal hits Earth directly, but some may arrive later — like an echo — after taking longer paths that bend around a star or something else heavy.
Scientists have always thought that these later signals, dubbed “gravitational flashes,” were supposed to be too faint to detect. But physicists Craig Copy and Glenn Star man of Case Western Reserve University in Cleveland, Ohio, took a leap: Based on Einstein’s theory, they calculated how strong the signal would be when waves scatter through the gravitational field inside a star itself.
“The shocking thing is that you seem to be getting a much bigger result than you expected,” says Copy. “It’s something we’re still trying to understand where that came from — whether it’s believable, even because it just seems too good to be true.”
If gravitational flashes can be that powerful, astronomers could potentially use them to track the interiors of stars, the team says. Researchers could even look for massive bodies in space that would otherwise be impossible to detect, like clumps of dark matter or lone neutron stars on the other side of the observable universe.
“That would be a very exciting probe,” says Maya Fishbach, an astrophysicist at Northwestern University in Evanston, Illinois, who was not involved with the study.
Still, there are reasons for caution. If this phenomenon stands up to scrutiny, Fishbach said, scientists would need to understand it better before they could use it — and that’s going to be difficult.
“It’s a very tough calculation,” says Copy.
But similar challenges have been overcome before. “The whole story of gravitational-wave detection was like that,” says Fishbach. It was a struggle to do all the math needed to understand her measurements, she says, but now the field is taking off (SN: 01/21/21). “This is the time to get really creative with gravitational waves.”
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