Scientists have discovered gravitational waves resulting from a black hole merger event; These waves show that the resulting black hole settled into a stable, spherical shape. These waves also reveal that the combined black hole may be much larger than previously thought.
When first detected on May 21, 2019, the gravitational wave event known as GW190521 was believed to be caused by the merging of two species. black holesOne has a mass of just over 85 Suns, and the other has a mass equivalent to about 66 Suns. Scientists believe that the merger took place for about 142 years for this reason. solar mass daughter black hole.
But newly examined spacetime pulsations from the black hole created by the merger, rippling outward as the void collapses into a proper spherical shape, appear to indicate that it is larger than initially predicted. Calculations say that instead of having 142 solar masses, it should have a mass equal to about 250 times that of the Sun. Sun.
These results could ultimately help scientists make better tests general relativity, Albert Einstein1915 theory gravityThe person who first introduced the concept of gravitational waves and black holes. “We’re really exploring a new frontier here,” says theoretical physicist Steven Giddings of the University of California, San Francisco. he said in a statement.
Relating to: How do dancing black holes get close enough to merge?
Gravitational waves and general relativity
General relativity predicts massive objects warp the fabric of the universe space and time—unified as a single, four-dimensional entity called “spacetime”—and “gravity” as we perceive it, arise from the curvature itself.
Just as a bowling ball placed on a stretched rubber sheet causes a more extreme “dimple” than a tennis ball, a black hole causes more curvature in spacetime than a star, and a star causes more curvature than a planet does. In fact, according to general relativity, a black hole is a point of matter so dense that it causes space-time to warp so extreme that event horizonEven light isn’t fast enough to escape the recess inside.
But this is not the only revolutionary prediction of general relativity. Einstein also predicted that when objects accelerate, they should adjust the texture of space-time ringing with waves called gravity waves. And again, the larger the objects involved, the more extreme the event. This means that when dense objects such as black holes spiral around each other, constantly accelerating due to their circular motion, space-time rings around them like a buzzing bell with gravitational waves.
These fluctuations in space-time remove the angular momentum of the spiraling black holes, causing the black holes’ common orbits to narrow, pulling them together and increasing the frequency of the gravitational waves emitted. Spiraling ever closer, the black holes eventually merge, creating a daughter black hole and sending out a “chirp” of high-frequency gravitational waves that echoes through the cosmos.
But there was something Einstein misunderstood about gravitational waves. The great physicist believed that these fluctuations in space-time would be so weak that they could never be detected here. Soil after crossing the street Universe across millions or even billions of light years.
However, in September 2015, twin detectors Laser Interferometer Gravitational Wave Observatory (LIGO), based in Washington and Louisiana, showed that Einstein was wrong. They detected GW150914, gravitational waves associated with the merger of black holes located in approximately 1.3 billion places. light years far. The gravitational wave signal was detected as a change in the length of one of LIGO’s 2.5-mile (4-kilometer)-long laser arms; This is equivalent to one-thousandth of the width of a laser. proton.
Remarkably, since then, LIGO and its other gravitational wave detectors, Virgo in Italy and KAGRA in Japan, have detected many more such events, to the point of detecting one gravitational wave event every week. Although even among so many gravitational wave detections, GW190521 stands out.
A special gravitational wave event
The merger frequency of the two black holes behind the GW190521 signal, located 8.8 billion light-years from Earth, was so low that only during the black holes’ last two orbits did the frequency become high enough. It reaches the sensitivity limits of LIGO and Virgo.
The team behind this new research, which is not part of the LIGO/Virgo Collaboration, wanted to know what information about the violent collision and merger of these black holes might be hidden in this signal.
They found that when black holes collide, the resulting black hole is formed in an unstable manner. Black holes are stable only when they have a spherical shape; This means that within milliseconds after the merger, the daughter black hole should take the shape of a sphere.
Just as the shape of a bell determines the frequency with which it rings, as the shape of this new black hole changes and stabilizes, the frequencies of the gravitational waves it rings also change, the team said. These so-called “ring down” gravitational waves contained information about the mass of the baby black hole, as well as its spin rate.
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This means that ring-down gravitational waves resulting from such a merger offer scientists an alternative way to measure the properties of merging black holes, as opposed to the traditional method of using gravitational waves created during the spiraling process.
The team found two distinct ringing frequencies in the GW190521 gravitational wave signal; Taken together, these give the created black hole a mass of about 250 solar masses. This means it is much larger than predicted using spiral gravitational waves. The detection of these ring-shaped gravitational waves was shocking even to the team behind these findings.
“I never thought I’d see a measurement like this in my life,” said Badri Krishnan, a physicist at Radboud University and co-author of the study.
The team’s research is detailed in a paper published Nov. 28 in the journal Physical Examination Letters.