Birth of black hole ‘captured for first time’

The birth of a black hole may have been captured for first time, say scientists.

The moment captured by multiple telescopes on Earth is thought to herald the birth of a new black hole or neutron star, caught at the exact moment of its creation.

Astronomers believe it is the moment a star collapsed to form a compact object while the stellar debris, approaching and swirling around the object’s event horizon, caused a remarkably bright glow.

The observations give astronomers a rare glimpse into the physics at play during the creation of a black hole.

Last June a sky survey telescope in Hawai’i observed a mysteriously bright glow in a relatively nearby galaxy – only 200 million light years away from our own Milky Way galaxy in the direction of the constellation Hercules.

The international science community were alerted to the sudden appearance of the new object in the sky.

It was similar to a supernova, except that it brightened, and then faded, faster than a typical supernova, and was intrinsically brighter at its peak.

A supernova (from nova meaning “new” star) is a sudden explosion of a massive star which has reached the end of its lifetime, leading to the formation of a black hole or neutron star.

The transient object, assigned the designation AT2018cow, was immediately nicknamed “the Cow” based on the final 3 letters of its name.

The theory was backed by a multi-institutional team after combining several imaging sources, including hard X-rays and radiowaves.

Assistant Professor Dr Raffaella Margutti, of Northwestern University in the US, said: “We thought it must be a supernova.

“But what we observed challenged our current notions of stellar death.”

“We think that ‘The Cow’ is the formation of an accreting black hole or neutron star.

“We know from theory that black holes and neutron stars form when a star dies, but we’ve never seen them right after they are born. Never.”

For one, the anomaly was unnaturally bright of between 10 to 100 times brighter than a typical supernova.

It also flared up and disappeared much faster than other known star explosions, with particles flying at 30,000 kilometers per second (or 10 pe rcent of the speed of light).

Within just 16 days, the object had already emitted most of its power.

In a universe where some phenomena last for millions and billions of years, two weeks amounts to the blink of an eye.

Prof Margutti added: “We knew right away that this source went from inactive to peak luminosity within just a few days.

“That was enough to get everybody excited because it was so unusual and, by astronomical standards, it was very close by.”

The Cow’s chemical composition was also examined finding clear evidence of hydrogen and helium, which excluded models of compact objects merging like those that produce gravitational waves.

Astronomers have traditionally studied stellar deaths in the optical wavelength, which uses telescopes to capture visible light.

The new study viewed the object with X-rays, hard X-rays which are 10 times more powerful than normal X-rays, radio waves and gamma rays.

This enabled the astronomers to continue studying the anomaly long after its initial visible brightness faded.

And because the collapsed star was surrounded by a relatively small amount of debris, the team was able to peer through the debris and get a glimpse of the object’s “central engine.”

The scientists also benefited from the star’s relative closeness to Earth.

Even though it was nestled in the distant dwarf galaxy called CGCG 137-068, astronomers consider that to be “right around the corner.”

Prof Margutti added: “Two hundred million light years is close for us, by the way.

“This is the closest transient object of this kind that we have ever found.”

The findings were presented at the annual meeting of the American Astronomical Society in Seattle, and published in the Astrophysical Journal.

Mysterious radio signals received from a galaxy far, far away

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