by Scientists have detected gravitational waves resulting from a merger event with a black hole suggesting that the resulting black hole settled into a stable, spherical shape. These waves also indicate that the combo black hole may be much larger than previously thought.
When it was first detected on May 21, 2019, the gravitational wave event known as GW190521 was believed to be the result of a merger between two. black holes, one with a mass equal to just over 85 suns and the other with a mass equal to about 66 suns. The scientists therefore believed that the merger created about 142 solar mass daughter of a black hole.
However, recently studied space-time vibrations from the black hole created by the merger, flowing out as the void dissolves into a perfect spherical shape, seem to suggest that it is more massive than previously thought. start. Rather than having 142 solar masses, calculations say it should have a mass equivalent to about 250 times that the sun.
These results could eventually help scientists conduct better testing general relativity, Albert Einstein1915 theory of gravity, who first introduced the concept of gravitational waves and black holes. “We’re really exploring a new frontier here,” Steven Giddings, a theoretical physicist at the University of California, San Francisco. 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 dense mass will form their own framework space and time — united as a single, four-dimensional entity called “space-time” — and that “gravity” as we perceive it arises from the curve itself.
Just as a bowling ball placed on a sheet of stretched rubber creates a more extreme “tooth” than a tennis ball, a black hole has more curvature in space-time than a star, and a star has more curvature than does a planet. In fact, a black hole, in general relativity, is a point of matter so dense that the curvature of space-time is so extreme, at a limit called the event horizonNot even light is fast enough to escape the teeth in.
This is not the only revolutionary prediction of general relativity, however. Einstein also predicted that when things accelerate, they should set up the ringed structure of space-time with ripples called gravitational waves. And again, the more massive the things involved, the more extreme the phenomenon. This means that when dense bodies like black holes spiral around each other, constantly accelerating due to their circular motion, the space-time around them ticks like a striking clock, humming with gravitational waves.
These ripples in spacetime carry angular momentum from the spiral black holes, which in turn tightens the mutual orbits of the black holes, pulling them together and increasing the frequency of the gravitational waves emitted. Spiraling closer and closer, the black holes eventually merge, creating a daughter black hole and sending a high-frequency “chirp” of gravitational waves echoing through the cosmos.
But Einstein got one thing wrong about gravitational waves. The great physicist believed that these ripples in space-time would be so weak that they would never be noticed here on. World having traveled across the universe for millions, or even billions, of light years.
But, in September 2015, the two detectors of the Gravitational-Wave-Laser Gravitational Observatory (LIGO) based in Washington and Louisiana proved Einstein wrong. They found GW150914, gravitational waves associated with merging black holes located around 1.3 billion light year taking place. The signal of gravitational waves was detected as a change in the length of one of LIGO’s 2.5 miles (4 kilometers) long laser arms, which is one-thousandth of the width of proton.
It is noteworthy that, since then, LIGO and its fellow gravitational detectors, Virgo in Italy and KAGRA in Japan, have detected many more such events, to the point where they are detecting one gravitational event every week. Although GW190521 stands out even among this gravitational field of detection.
Special gravity event
The merger frequency of the two black holes behind the signal GW190521, located 8.8 billion light years from Earth, was so low that it was only during the last two orbits of the black holes that the frequency became high enough to . reaching the sensitivity limits of LIGO and Virgo.
The team behind this new investigation – which is not part of the LIGO/Virgin Collaboration – wanted to know what information about the violent collision and merger of these black holes could be locked in this signal.
They found that when the black holes collided, the resulting black hole was created with a lopsided shape. Black holes are only stable when they are spherical in shape, meaning that the daughter black hole would have to assume a spherical shape within milliseconds of the merger.
Just as the shape of a bell determines the frequency it rings, the team said, as this new black hole changed its shape and stabilized, the frequencies of the gravitational waves it rang out shifted. The so-called “ring down” gravitational waves contained information about the mass of the daughter black hole and also about the rate at which it is spinning.
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This means that ring-down gravitational waves from such mergers offer scientists another way to measure the properties of merging black holes, in contrast to the traditional method of using the gravitational waves created during the spiral process.
The team found two distinct ring-down frequencies in the gravitational wave signal of GW190521, which when taken together give the resulting black hole a mass of 250 solar masses. That means it is much larger than estimated using the spiral gravitational waves. The detection of these gravitational waves was shocking even to the team behind these results.
“I never thought I would see such a measurement in my life,” said Badri Krishnan, co-author of the research and a physicist at Radboud University.
The team’s research is detailed in a paper published on November 28 in the journal The Physical Review Letters.
