Scientists Divided on Whether Blast Was Black Hole's Birth or 'Tidal Disruption'

For the first time, astronomers have observed the formation of a black hole or neutron star

For the first time, astronomers have observed the formation of a black hole or neutron star

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.

Assistant Professor Dr Raffaella Margutti, of Northwestern University, said: "We thought it must be a supernova".

Astronomers believe it is the moment a star collapsed to form a compact object while the stellar debris, approaching and swirling around the object's event horizon, caused a remarkably bright glow. By combining radio waves, gamma-rays, and X-rays, the team suspects the object, officially named AT2018cow and informally called "The Cow", is likely a black hole or neutron star surrounded by swirling stellar debris.

"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".

"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".

For one, the anomaly was unnaturally bright of between 10 to 100 times brighter than a typical supernova. Over the course of just a few days, the cosmic flare grew until it was nearly 100 billion times brighter than the sun.

Prof Margutti added: "We knew right away that this source went from inactive to peak luminosity within just a few days". 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. Meanwhile, others say the explosion may have been caused by a pre-existing black hole ripping apart a white dwarf star.

The team at the Keck Observatory worked with the University of Hawaii Institute for Astronomy and its ATLAS twin telescopes to investigate The Cow.

The Cow's chemical composition was calculated to contain helium and hydrogen.

Margutti's team at Northwestern includes graduate student Aprajita Hajela, postdoctoral fellows Giacomo Terreran, Deanne Coppejans and Kate Alexander (who is a Hubble Fellow), and first-year undergraduate student Daniel Brethauer.

This enabled them to continue studying the anomaly long after its initial visible brightness faded. Plus, there was less than usual amounts of material surrounding The Cow during the event, allowing astronomers to see through it to observe The Cow's "central engine".

Another team of scientists, analysing data from multiple observatories, including NASA's NuSTAR, ESA's (the European Space Agency's) XMM-Newton and INTEGRAL satellites, and the National Science Foundation's Very Large Array, claimed that it is a supernova - a stellar explosion - could be the source of the Cow.

"A "lightbulb" was sitting deep inside the ejecta of the explosion", Margutti said. "But The Cow had very little ejecta mass, which allowed us to view the central engine's radiation directly". "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".

It's relative closeness to earth is also a plus for scientist to get the most amount of data from the event as possible.

"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", study co-author Dr. Amy Lien said, referring to data gleaned from NASA's space-based Neil Gehrels Swift Observatory.

"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.