Last year, on June 16, the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Hawaii detected a sudden and powerful explosion in space. The blast — which was dubbed AT2018cow and subsequently became known as “the Cow,” after the last three letters of its official name — baffled astronomers, who couldn’t explain what had caused it.
As the Inquisitr reported at the time, the Cow was between 10 to 100 times brighter than a supernova and lit up the cosmos for three days, then faded away within a few months — lasting considerably less than typical supernovae.
The mysterious celestial outburst was picked up in the region of a far-off galaxy called CGCG 137-068. This galaxy — which is a star-forming galaxy bustling with activity — is nestled some 200 million light-years away in the constellation Hercules. The source of the AT2018cow blast was traced back to “inside or near a star-forming galaxy,” NASA points out — and that’s as close as scientists got to unraveling the bizarre phenomenon.
Now, a pair of new studies presented at the 233rd American Astronomical Society meeting in Seattle has finally offered a possible explanation for the unusual cosmic explosion, the space agency announced yesterday. The two papers unveil the probable origin of AT2018cow, arguing that the blast was produced by either a supermassive black hole in the process of gobbling up a star or by a supernova explosion that birthed a black hole or a neutron star.
Is it a neutron star born of a supernova? Or a black hole ripping apart a white dwarf? Check out this mysterious phenomenon observed by multiple @NASA missions: https://t.co/0SJTKR7e0o #AAS233 pic.twitter.com/lIidUsjIqX— NASA JPL (@NASAJPL) January 11, 2019
Study 1: Black Hole Devouring A Star
One of the two studies suggests that the enigmatic outburst was the result of a monster back hole feasting on a star. This process is referred to as a tidal disruption event and is one of the most violent phenomena in the universe
The paper, available on the arXiv server and due to be published in the journal Monthly Notices of the Royal Astronomical Society, proposes that the peculiar features observed in AT2018cow have the characteristics of such an event. The conclusion is based on data gathered by several telescopes, including NASA’s Neil Gehrels Swift Observatory, which imaged the Cow in X-ray, infrared, and gamma radiation.
“We’ve never seen anything exactly like the Cow, which is very exciting,” said study co-author Amy Lien, a scientist affiliated with both the University of Maryland in Baltimore County and with 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 multiwavelength observations as it faded over the next few months.”
When a massive black hole gobbles up a star, the unwilling victim gets torn apart and shredded into a stream of gas. This gas ultimately gathers in a cloud of material around the black hole — called an accretion disk, as previously reported by the Inquisitr. The gas from the dead star is then siphoned by the black hole, which emits vast amounts of radiation and relativistic jets — beams of ionized particles traveling close to the speed of light.
The video below, uploaded on YouTube by NASA, shows a visualization of what happens when a white dwarf star gets ripped apart by a black hole.
“The Cow produced a large cloud of debris in a very short time,” said study lead author Paul Kuin, an astrophysicist at University College London. “Shredding a bigger star to produce a cloud like this would take a bigger black hole, which results in a slower brightness increase and takes longer for the debris to be consumed.”
Study 2: Newborn Black Hole Or Neutron Star
The second study points to a supernova explosion as the culprit behind AT2018cow. According to this paper, which can be read on arXiv and has been accepted for publication in the Astrophysical Journal, the Cow heralds the birth of a new black hole or neutron star, forged in a massive stellar explosion.
“Based on its X-ray and UV emission, the Cow may appear to have been caused by a black hole devouring a white dwarf. 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,” said study lead author Raffaella Margutti, an assistant professor of physics and astronomy at Northwestern University in Illinois.
In fact, her team believes that AT2018cow marked the exact moment when a dead star collapsed to form a compact object, which could either be a black hole or a neutron star. This makes the 2018 cosmic blast the first time that such an event has ever been observed by astronomers, notes the W.M. 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.”
In support of their interpretation of the Cow event, the scientists cite multiple observations of the perplexing celestial outburst by a host of observatories, such as NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), the European Space Agency’s XMM-Newton X-ray Observatory and INTEGRAL satellites, as well as the National Science Foundation’s Very Large Array.
These telescopes studied the Cow over an even broader range of wavelengths, spanning from radio waves to gamma rays, and found that the signal had “characteristics similar to a compact body like a black hole or neutron star consuming material,” explained Margutti.
For instance, the team shows that the dazzling optical and ultraviolet flare that first put the Cow on the map could have been the final death cry of the original star as it exploded into a supernova. Meanwhile, the X-ray emissions picked up by the telescopes shortly after the outburst signaled the birth of the new object — and were likely generated by radiation coming from the star’s gas as it collapsed to form a black hole or a neutron star.
“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 study co-author Brian Grefenstette, a NuSTAR instrument scientist at Caltech.
“We looked at this object with many different observatories, and of course, the more windows you open onto an object, the more you can learn about it. But, as we’re seeing with the Cow, that doesn’t necessarily mean the solution will be simple.”