Could supernova be a newborn black hole?

13 Janvier, 2019, 04:42 | Auteur: Therese Cote
  • Could supernova be a newborn black hole?

Back in June scientists spotted an unusually bright flare-up that they now think could have been a black hole or neutron star at the moment of its creation. The Cow was first spotted on June 16 after the ATLAS telescope captured an extremely bright anomaly 200 million light-years away in the Hercules constellation. "The Cow [as the burst was nicknamed] started to look very, very different from anything we had ever seen in the X-ray", explained Raffaela Margutti from the Northwestern University in IL, and the new study's leading author. However, seeing as massive stars are known to form either neutron stars or black holes when collapse, the team thinks that the object could be one or the other.

This object was either a black hole or a neutron star - both incredibly dense regions of space - and the stellar debris approaching the event horizon of the object was responsible for the flash. It was as much as 100 times brighter than a normal supernova, and flared up and disappeared much more quickly, flinging out particles so fast that it almost completely disappeared within just 16 days. It also flared and disappeared much faster than other known star explosions; within 16 days the object had emitted most of its power, and the object had very little ejecta swirling around.

"In a universe where some phenomena last for millions and billions of years, two weeks amounts to the blink of an eye", the statement said.

"We knew right away that this source went from inactive to peak luminosity within just a few days", Dr Margutti said. 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.

The phenomena is similar to a supernova, when a dying star results in the formation of a black hole or neutron star.

The team also obtained optical images from the MMT Observatory in Arizona, as well as the Southern Astrophysical Research SOAR Telescope in Chile. Margutti's team was studying the mysterious explosion in space using x-ray wavelengths from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and XMM Newton spacecraft. Because of the X-ray emissions, Margutti and her colleagues suggest the original star in this scenario may have been relatively low in mass, producing a comparatively thinner debris cloud through which X-rays from the central source could escape.

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

The team found that the "ejecta" swirling around "The Cow" was about 10 times less, compared to a typical stellar explosion. This allowed astronomers to see directly through to the object's central engine's radiation. Study coauthor Brian Grefenstette, an instrument scientist at Caltech, explained that "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".

"We thought it must be a supernova", Raffaella Margutti, researcher at Northwestern University, said in a news release.

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.

The team also believes that the star's relative closeness to Earth helped them track the event in detail.

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

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