Powerful gravitational waves reached the Earth far away from the depths of space. It’s the heaviest black hole merger ever.
Gravitational waves coming from a black hole far away in the depths of space reached three telescopes on Earth. Scientists detected these waves from GW190521 on May 21, 2019, using the twin LIGO detectors located in Livingston, Louisiana, and Hanford, Washington, and the Virgo detector located near Pisa, Italy.
The signal coming from the event lasted just one-tenth of 1 second.
The researchers announced the discovery in two papers published on September 2, 2020, in the journals Physical Review Letters and Astrophysical Journal Letters.
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About 10 billion years ago, two highly spinning mammoth black holes — weighing in at 85 and 66 times the mass of the Sun — merged together, converting about 8 solar masses into pure energy in the form of gravitational radiation.
Scientists consider the larger of the two black holes to be impossible. Astronomers predict that stars that could give birth to black holes with masses between 65 – 130 times greater than the Sun undergo a process called pair-instability. That’s when a star blows apart and leaves nothing behind.
“The mass of the larger black hole in the pair puts it into the range where it’s unexpected from regular astrophysics processes,” said Peter Shawhan, a professor of physics at UMD, an LSC principal investigator and the LSC observational science coordinator. “It seems too massive to have been formed from a collapsed star, which is where black holes generally come from.”
One suggestion is that a previous black hole merger may have created the larger object rather than a collapsing star.
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The new heavy black hole merger happened when the universe was only about seven billion years old. That’s roughly half its present age. Although the signal was short—just four up-and-down wave cycles—the team could still analyze it. Thus, parsing out its amplitude, its shape, and how its frequency changed over time.
“It was very difficult to interpret,” says team member Alessandra Buonanno, director of the Max Planck Institute for Gravitational Physics (Albert Einstein Institute). “We spent a lot of time persuading ourselves to trust what we’d found.”
The merger formed an even larger black hole weighing a whopping 142 times the mass of the Sun. That’s by far the largest black hole ever observed through gravitational-wave observations.
When a black hole is 100 to 100,000 times more massive than the Sun it’s called an intermediate-mass black hole (IMBH). They are heavier than stellar-mass black holes but lighter than supermassive black holes which lie at the centers of galaxies.
The event confirms that the merger of two small black holes can produce an intermediate black hole.
The bottom line is that we’ve just witnessed the heaviest black hole merger ever directly seen, and that led to the first definitive detection of an intermediate-mass black hole.