Humans may have been able to capture and observe the birth of a black hole or a neutron star in real time for the very first time, astronomers said at a recent national astronomical meeting in Seattle, referring to an extremely bright flash in space first spotted in 2018 that has since become one of the most baffling and most studied cosmic events in history.
The mysterious and spectacularly bright glow was first spotted on June 16, 2018, by ATLAS telescopes in Haleakala and Maunaloa in Hawaii. The event garnered international attention but also left astronomers perplexed.
“We thought it must be a supernova,” astronomer Raffaella Margutti of Northwestern University in Chicago said in a release. “But what we observed challenged our current notions of stellar death.”
Astronomers had a "cow" about this big blast https://t.co/lOEz49wwDd A dramatic stellar explosion, witnessed on June 16, 2018 (dubbed AT2018cow) is now one of the most intensely studied cosmic events in history pic.twitter.com/0nW0cmLpyK
— Caltech (@Caltech) January 11, 2019
The cosmic flare was peculiarly 10 to 100 times brighter than a regular supernova or exploding star—at its most brilliant, it would equate to some 100 billion times the luminosity of our Sun. The cosmic flare also vanished within 16 days—much faster than other supernovae.
The extreme flash was dubbed AT2018cow, or now widely referred to as “the Cow.” It was traced to a galaxy 200 million light-years from Earth called CGCG 137-068, in the constellation of Hercules. Since then, more than 100 astronomers have been observing the event using telescopes around the world, as well as in the sky.
Now, some astronomers say the cosmic flare may be a new type of supernova that was created by a massive star that had collapsed to form either a black hole or a fast-spinning neutron star (also known as a magnetar). Meanwhile, others say the explosion may have been caused by a pre-existing black hole ripping apart a white dwarf star.
Black Hole Birth Observed In Real Time?
Researchers from various groups gathered at the 233rd meeting of the American Astronomical Society in Seattle on Jan. 10, to present and discuss the latest data they’d been collecting.
Using data gathered from 16 telescopes around the world, Margutti’s team analyzed data on the Cow over a broad range of wavelengths that spanned from radio waves to gamma rays, as well as hard X-rays, which are 10 times more powerful than normal X-rays.
At first, the cosmic flash looked to her like a black hole ripping up a white dwarf star.
“Our team used high-energy X-ray data to show that the Cow has characteristics similar to a compact body like a black hole or neutron star consuming material,” Margutti, lead author of a multi-institutional research team, said in a NASA release.
“But based on what we saw in other wavelengths, we think this was a special case and that we may have observed—for the first time—the creation of a compact body in real time.”
By “compact,” Margutti refers to a dense body such as a neutron star or even a black hole.
Margutti said in a release from Keck Observatory, “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.”
Quick and Powerful
Astronomer Daniel Perley from Liverpool John Moores University in the U.K. said that due to the Cow being extremely luminous as well as forming and disappearing quickly makes it so unique “that existing supernova models can’t properly explain it.”
Perley and colleagues of the GROWTH project under Caltech University followed the Cow’s aftermath for over a month. Their data showed that the debris from the explosion was ejected at “very high speeds,” which they say may have caused the quick flare—the Cow had reached its peak brightness in two days, whereas the time frame for a typical supernova is two to three weeks.
“It must be a new type of extremely energetic, explosive event,” he said.
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.
A ‘Central Engine’?
As the Cow’s luminosity dwindled, Perley’s team observed irregularities in the optical data rather than a steady decline in brightness that would be typically observed for declining supernovae. Perley said the findings hint at another source of power, like a “central engine” that is propelling the expanding debris with energy.
“Whatever it is, it must involve some form of energetic and very fast explosion interacting with an extremely dense shell of material very close to the explosion progenitor,” Perley said.
Anna Ho, a GROWTH Ph.D. student at Caltech, was observing the Cow using radio telescopes in Hawaii and Chile—the Submillimeter Array (SMA) and the Atacama Large Millimeter Array, respectively.
“This is the first time any transient has been seen to increase in brightness in millimeter waves,” said Ho. “Normally by the time explosions are observed with a millimeter telescope, they are already fading in brightness.”
Radio astronomy expert Tara Murphy, who oversaw Dobie’s research, said their findings pointed to a similar conclusion.
“The fact it was getting brighter with time and particularly in higher frequencies shows there must be something that was still powering the explosion pumping energy into this material,” Murphy told the Australian Broadcasting Corporation.
She added that the radio data suggests that the unique Cow explosion was being continuously energized by either a black hole or a magnetar at its core.
“It wasn’t just this explosion that happened and then was fading away, there must be something that was still there that makes it different from the typical supernova we see.”