Birth of a Black Hole or Death?

 

ATLAS is an asteroid impact early warning system being developed by the University of Hawai`​i and funded by NASA. It consists of two telescopes, 100 miles apart, which automatically scan the whole sky several times every night looking for moving objects. ATLAS 2 on Mauna Loa (pictured left) and project placement in Hawai`i (right).  ATLAS will provide one-day’s warning for a small impact or 3-weeks warning for a very large impact to save a nation.

On June 17, the ATLAS survey’s twin telescopes in Hawaii found something not on their primary mission list, as is often the case in experimental science: a spectacularly bright anomaly 200 million light years away in the Hercules constellation. Dubbed AT2018cow or “The Cow,” the object quickly flared up, then vanished almost as quickly.

TWO VIEWS ON WHAT HAPPENED

A New View of a Supernova: Birth of A Black Hole?

After combining several imaging sources, including hard X-rays and radio-signals, the multi-institutional team now speculates that the telescopes captured the exact moment a star collapsed to form a compact object, such as a black hole or neutron star. The stellar debris, approaching and swirling around the object’s event horizon, caused the remarkably bright glow.

screen shot 2019-01-19 at 9.35.10 am
Prof. Dr. Raffaella Margutti, Northwestern University’s Team

This rare event will help astronomers better understand the physics at play within the first moments of the creation of a black hole or neutron star. “We think that ‘The Cow’ is the formation of an accreting black hole or neutron star,” said Northwestern’s Raffaella Margutti, who led the research. “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.”

Using data from multiple NASA missions, including the Neil Gehrels Swift Observatory and the Nuclear Spectroscopic Telescope Array (NuSTAR), two groups are publishing papers that provide possible explanations for the Cow’s origins.

A Black Hole Shredding a Compact Star?

Another potential explanation of the Cow is that a star has been ripped apart in what astronomers call a “tidal disruption event.” Just as the Moon’s gravity causes Earth’s oceans to bulge, creating tides, a black hole has a similar but more powerful effect on an approaching star, ultimately breaking it apart into a stream of gas.

The tail of the gas stream is flung out of the system, but the leading edge swings back around the black hole, collides with itself and creates an elliptical cloud of material. According to one research team using data spanning from infrared radiation to gamma rays from Swift and other observatories, this transformation best explains the Cow’s behavior.

screen shot 2019-01-19 at 9.49.16 amProf. Dr. Amy Lien, University of Maryland’s Team

“We’ve never seen anything exactly like the Cow, which is very exciting,” said Amy Lien, an assistant research scientist at the University of Maryland, Baltimore County and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We think a tidal disruption created the quick, really unusual burst of light at the beginning of the event and best explains Swift’s multi-wavelength observations as it faded over the next few months.”

The University of Maryland/NASA Goddard Team argues that the Cow is a monster black hole shredding a passing White Dwarf star, as pictured below.

Researchers from both teams shared their interpretations at a panel discussion on Thursday, Jan. 10, at the 233rd American Astronomical Society meeting in Seattle.


 

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