Published: Sun, January 13, 2019
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Astronomers first recorded birth of a black hole

Astronomers first recorded birth of a black hole

Back in June scientists spotted an unusually bright flare-up that they now think could have been a black hole or neutron star at the moment of its creation. Dozens of telescopes were trained on the exceptionally bright light, situated 200 million light-years away in the Hercules constellation. "Never", Raffaella Margutti, an astrophysicist at Northwestern University in Evanston, Illinois, and lead author of a forthcoming paper on The Cow, said in a statement.

After looking at several images, hard X-rays and microwaves of the object officially known as AT2018cow, researchers determined that their telescopes captured the exact moment a star collapse and a black hole was formed. The debris left from that collapse is swirling around the event horizon of the object and caused the very bright glow seen in the summer sky.

"We think that "The Cow" is the formation of an accreting black hole or neutron star", said Dr Margutti, who led the research. 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.

According to the research team, the burst was about 10 to 100 times brighter than most supernovas.

The shock wave from the explosion traveled at one-tenth the speed of light-about 30,000 kilometers per second-according to University of Sydney Ph.D. student Dougal Dobie, who was observing the Cow with a radio telescope, the CSIRO's Australia Telescope Compact Array in Narrabri.

It peaked within just 16 days, where typically supernovae can last for millions and billions of years. The dwarf galaxy that houses The Cow is around two hundred million light years away, which may seem like a lot, but is pretty close by astronomical standards. These multi-messenger observations give astronomers a rare glimpse into the physics at play during the creation of a black hole or neutron star. With these observations, the researchers found evidence of hydrogen and helium.

The Cow disappeared as quickly as it appeared. They examined the object at different wavelengths, using radio waves, gamma rays, hard x-rays, and soft x-rays (which are much more powerful than ordinary x-rays).

This enabled them to continue studying the anomaly long after its initial visible brightness faded. The team proposes that the bright optical and ultraviolet flash from the Cow signaled a supernova and that the X-ray emissions that followed shortly after the outburst arose from gas radiating energy as it fell onto a compact object.

Fortunately, about 10 times less ejecta swirled around The Cow compared to a typical stellar explosion.

In addition to Chornock, Roth, and Metzger, Margutti's core team also includes Indrek Vurm, senior research fellow at Tartu Observatory, as well as Northwestern CIERA postdoctoral researchers Giacomo Terreran, Deanne Coppejans, and Kate Alexander. "But The Cow had very little ejecta mass, which allowed us to view the central engine's radiation directly".

Margutti's team 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". Study coauthor Brian Grefenstette, an instrument scientist at Caltech, explained that "if we're seeing the birth of a compact object in real time, this could be the start of a new chapter in our understanding of stellar evolution".

"Being given the opportunity to contribute to something as cutting edge and global as understanding AT2018cow as an undergrad is a surreal experience", said co-author Daniel Brethauer, a first-year undergraduate student at Northwestern.

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