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Scientists have detected gravitational waves generated by the black hole merger event, indicating that the resulting black hole settled into a stable spherical shape. These waves also reveal that the composite black hole may be much larger than previously thought.
When it was first discovered on May 21, 2019, the gravitational wave event known as GW190521 was thought to have come from a merger between two stars. black holesOne has the mass of just over 85 suns and the other has the mass of about 66 suns. Scientists believe the merger led to the creation of approximately 142 Solar mass Daughter of the black hole.
However, newly studied space-time oscillations from the merger black hole, which ripple outward as the void transforms into a suitably spherical shape, seem to indicate that it is more massive than initially expected. Instead of its mass being 142 solar masses, calculations indicate that its mass should be about 250 times the mass of the Sun. the sun.
These results could eventually help scientists conduct better tests General relativity, Albert Einstein1915 theory gravityWho first introduced the concept of gravitational waves and black holes. “We’re really exploring a new frontier here,” says Stephen Giddings, a theoretical physicist at the University of California. He said in a statement.
Related: How dancing black holes get close enough to merge
Gravitational waves and general relativity
General relativity predicts that objects with mass distort their own fabric space and time – united as a single four-dimensional entity called “space-time” – and that “gravity” as we perceive it arises from the curvature itself.
Just as a bowling ball on a rubber pad causes a more extreme “dent” than a tennis ball, a black hole causes more curvature in space-time than a star, and a star causes more curvature than a planet. In fact, a black hole, in general relativity, is a point of matter so dense that it causes extreme curvature of spacetime, at a boundary called Event horizonEven light is not fast enough to escape the internal dent.
However, this is not the only revolutionary prediction of general relativity. Einstein also predicted that when objects accelerate, they should define the very fabric of space-time, which resonates with waves called ripples Gravitational waves. Again, the more massive the objects in question, the more extreme this phenomenon. This means that when dense objects like black holes wrap around each other, constantly accelerating due to their circular motion, spacetime around them rings like a tolling bell, buzzing with gravitational waves.
These ripples in spacetime carry angular momentum from the spiraling black holes, and this in turn causes the black holes’ mutual orbits to tighten, bringing them together and increasing the frequency of the emitted gravitational waves. The black holes get closer and closer, and finally merge, forming a new black hole and sending out a high-frequency “chirp” of gravitational waves that echoes through the universe.
But there was one thing Einstein got wrong about gravitational waves. The great physicist believed that these ripples in space-time would be so faint that they would never be detected here Land After traveling through Universe For millions or even billions of light years.
However, in September 2015, the twin detectors of… Laser Interferometer Gravitational Wave Observatory LIGO, based in Washington, Louisiana, showed that Einstein was wrong. They detected GW150914, gravitational waves associated with the merger of black holes located about 1.3 billion away. Light year far. The gravitational wave signal was detected as a change in the length of one of LIGO’s long laser arms, which is 2.5 miles (4 kilometers) long, equivalent to a thousandth of the width of the sphere. proton.
Remarkably, since then, LIGO and its fellow gravitational wave detectors, Virgo in Italy, and KAGRA in Japan, have detected many similar events, reaching the point where they are detecting one gravitational wave event every week. Although even among this abundance of gravitational wave detections, GW190521 stands out.
A special gravitational wave event
The frequency of the black hole merger behind the GW190521 signal, located 8.8 billion light-years from Earth, was so low that only during the last two black hole orbits did the frequency become high enough for the black holes to be observed. Reaching LIGO and Virgo sensitivity limits.
The team behind this new investigation – which is not part of the LIGO/Virgo collaboration – wanted to learn what information about the violent collision and merger of these black holes might be obscured in this signal.
They found that at the moment the two black holes collided, the resulting black hole was created lopsided. Black holes are only stable when they have a spherical shape, meaning that within milliseconds of merging, the daughter black hole must take the shape of a sphere.
Just as the shape of a bell determines the frequency with which it rings, the team said that as the shape of this new black hole changed and became stable, the frequencies of the gravitational waves it emits changed. These “bottom ring” gravitational waves contain information about the mass of the daughter black hole as well as its spin rate.
This means that the gravitational waves generated by this merger offer scientists an alternative way to measure the properties of merging black holes, unlike the traditional method of using gravitational waves that arise during the accretion process.
The team found two separate ring frequencies in the GW190521 gravitational wave signal, which, when considered together, give the resulting black hole a mass of 250 solar masses. This means it is much larger than estimated using spiraling gravitational waves. The discovery of these gravitational waves was shocking even to the team behind these results.
“I never thought I would see such a measurement in my lifetime,” said Badri Krishnan, co-author of the research and a physicist at Radboud University.
The team’s research is detailed in a paper published November 28 in the journal Physical review letters.
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