Researchers may have witnessed the birth of a black hole

Rodiano Bonacci
Gennaio 13, 2019

Astronomers targeted the aftermath of a fiery supernova explosion and discovered a mysterious black hole or neutron star they've since dubbed "The Cow".

The event, captured on 16 June 2018 by the NASA-funded ATLAS-1 telescope in Hawaii and several other sources, is known to have originated in a star-forming galaxy in the Hercules constellation, some 200 million light-years away from Earth, meaning the event occurred while dinosaurs still roamed the earth.

"Based on its X-ray and UV emission, The Cow may appear to have been caused by a black hole devouring a white dwarf", said Raffaella Margutti, assistant professor of physics and astronomy at Northwestern University and lead author of the study. With the first observations of the formation of a black hole or neutron star in hand, astronomers will be able to better understand what happens in the moments that a star dies, and a unusual new object springs into being. 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. "But further observations of other wavelengths across the spectrum led to our interpretation that "The Cow" is actually the formation of an accreting black hole or neutron star".

Over three days, the Cow produced a sudden explosion of light at least 10 times brighter than a typical supernova, and then it faded over the next few months. After suddenly bursting into being, The Cow depleted most of its energy within 16 days, casting out particles of hydrogen and helium at about 10 percent of the speed of light. Over the course of just a few days, the cosmic flare grew until it was nearly 100 billion times brighter than the sun. "That was enough to get everybody excited because it was so unusual and, by astronomical standards, it was very close by". The star's collapse triggered an ultra-bright explosion that sent radiation racing across the cosmos.

The SOAR telescope, located in Chile, is operated by Cerro Tololo Inter-American Observatory, a division of National Optical Astronomical Observatory, which is operated by the Association of Universities for Research in Astronomy Inc. under a cooperative agreement with the National Science Foundation.

The Cow disappeared as quickly as it appeared.

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".

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

Margutti attributes The Cow's relative nakedness to potentially unraveling this intergalactic mystery.

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. According to Margutti, this timeline is significantly faster than many known stellar explosions, which can take years to flare up and die off.

It also relatively nearby, allowing for a better view.

"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", said Brian Grefenstette, a NuSTAR instrument scientist at Caltech and a co-author of Margutti's paper.

Calculating that the "offending" black hole was between 100,000 to one million times the mass of our Sun, the "tidal disruption event" proponents believe the star that was shredded was a dwarf star only about the size of Earth.

"Being given the opportunity to contribute to something as cutting edge and worldwide as understanding AT2018cow as an undergrad is a surreal experience", Brethauer said.

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