Black holes and gravitational waves

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    • Massive celestial bodies, such as stars, stretch and contract space-time to a measurable extent.
    • Astrophysicists have explored the possibility of “sparkling” produced by gravitational waves scattering from the curvature of spacetime.
    • This glow could enable researchers to measure the internal density profiles of white dwarfs and neutron stars.

      Could we one day use gravitational waves to probe distant matter in the universe? Researchers at Case Western Reserve University suggest, through theoretical physics calculations, that it is possible. Their work shows that signals scattered by large objects can reveal what’s inside them.

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      Gravitational waves are very subtle. Detecting ripples that stretch and compress space-time, the combination of time and three-dimensional space, requires highly sensitive and precise instrumentation.

      General relativity predicts that these scattered wave signals should be larger than physicists expect, astrophysicists Craig Copi and Glenn Starkman said in a report published this summer in the Journal. I am writing in my thesis. physical review letter“People are always interested in measuring something new,” Copi says. To tell popular mechanics“This gives us a whole new way of looking at things in space.”

      Electromagnetic waves and gravitational waves both travel at the speed of light and are polarized. Copi says that when you look at gravitational waves, you can see inside most objects that are normally opaque. However, because gravitational waves can be absorbed by black holes, additional steps and analyzes are required to measure the size of black holes.

      Case Western graduate student Klaountia Pasmatiou’s calculations for this study show that when physicists use these equations in combination with data from the Laser Interferometer Gravitational-Wave Observatory (LIGO), stars including white dwarfs and neutron stars It may be possible to measure the internal density profile of A white dwarf is a small, dense star that has contracted and become smaller. Neutron stars form from the collapse of supergiant stars.

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      Researchers can also look at “dark matter clumps,” Kopi says. Dark matter does not reflect, emit, or absorb light. “I can imagine there could be something more exotic. People talk about all sorts of possibilities.”

      Caltech physicist Caterina Chazioannou is working on one of the two LIGO projects and was not involved in the Case Western team’s work. “There are many regions in space that can’t emit light but can emit gravitational waves. You can also emit in a vacuum,” she says. popular mechanics“Gravitational waves propagate freely through matter. We don’t know what’s going on in the core of a star or the core of a supernova,” explains Chatziioannou.

      But Copi and his colleagues found that when gravitational waves scatter from the curvature of spacetime caused by objects, scientists can record faint signals from this echo effect. Scientists previously thought the glow was too weak to be detected.

      “In this paper, we look at effects that exist in general relativity,” says Copi. “It’s not new in that sense, but it’s something people haven’t paid attention to yet. This allows us, assuming general relativity to be correct, to get some signals from the gravitational twinkling out there, so other You may be able to see things you can’t see the other way.”

      How LIGO measures gravitational waves

      Because gravitational waves are difficult to detect directly, LIGO is deployed in remote areas of Louisiana and Washington to mitigate the devastating effects of urban environments. The Washington setup is located at a relatively quiet nuclear waste site.

      Timelapse of the Ligo Laser Interferometer

      In this time-lapse representation, laser beams are sent down two long tunnels at the LIGO facility in Livingston, Louisiana. Instruments in the tunnel can detect wave forces that can deflect a laser as small as a billionth of the diameter of a hydrogen atom.

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      “Gravitational waves … lengthen or shorten the length that the laser bounces,” says Kopi. “You can see that the interference pattern is changing.”

      Measurement requires a precision of 10-18 A meter smaller than the width of a proton, says Chatziioannou. This involves averaging measurements of many photons in the laser. “A laser splits into two of her, bounces off two faces, comes back and recombines. The way it recombines is the distance between where the laser was emitted and where the test mass is. ,” she explains.

      Why are black holes difficult to measure?

      If LIGO researchers want to analyze black holes, it’s not that simple. First, a photodetector measures the voltage from the laser, he says Chatziioannou. The software converts the voltage into gravitational waves and measures its strain. An analytical tool then converts the strain into the mass of the black hole. This process requires a technique called match filtering. In this technique, a computer compares the signal to what the scientist predicted. Researchers employ the general equation of relativity and solve for many parameters of the signal. Removing noise requires a sophisticated approach.

      Scientists have been trying to detect gravitational waves for over a century, ever since Albert Einstein predicted their existence in 1916. Researchers began building the LIGO lab in the 1990s, and finally, in 2015, gravitational waves were detected for the first time at the LIGO site. It was an exciting moment for the physics community.

      For decades, it was unclear whether gravitational waves really existed. Now that scientists can find them, they can explore the stars more deeply. “Stars may disappear and dark matter may not glow, but it cannot hide from gravity,” the researchers wrote in their paper.

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