Image credit: Pixabay
Until now, no one had seen a star explode as a supernova, giving rise to a black hole. Although we know that these tremendous stellar explosions can generate both black holes and dense remnants in the form of neutron stars, no one had been able to witness this process.
However, a team of international astronomers from institutions as prestigious as MIT (Massachusetts Institute of Technology), the European Space Agency, NASA, the Los Alamos National Laboratory or the universities of Cambridge, Columbia or Southampton, among others , claims to have seen one right in the center of a rare failed stellar explosion.
The work, which is yet to be peer-reviewed, has just appeared on the pre-publication server ‘Research Square’. And if it turns out to be correct, it would be the first time that we have direct evidence of a star collapsing, exploding and giving rise to a new black hole.
Black hole in the center of ‘la Vaca’
In 2018, astronomers detected a new type of stellar explosion in a relatively nearby galaxy, 200 million light-years away. Officially christened AT2018cow, but informally known as ‘The Cow’, the event was much brighter and faster than a normal supernova. In fact, it peaked in just a few days before dimming three weeks later, in a process that defied explanation.
Scientists’ best hypothesis for the cause of that intense light signal was that the interior of a star collapsed to become a neutron star or black hole before a true supernova could form.
The result was what they called a ‘central engine’, a rapidly spinning object within the star’s outer layers that could be either a black hole or a neutron star. Scientists believe that powerful jets of matter from that object pierce through the outer layers of material, making ‘the Cow’ appear extremely bright.
Now, in their article, the researchers claim to have detected precisely that: an object of this type (neutron star or black hole) right in the center of ‘the Cow’. To do this, they observed the light in the form of X-rays emitted during the 60 days after the explosion. And after precisely timing the arrival of the photons from there on Earth, they calculated that the object producing the light was spinning once every 4.4 milliseconds.
X-ray source is compact and small
“This rapid periodicity,” says Brian Metzger, an astrophysicist at Columbia University and a co-author of the study, “suggests that the X-ray source is compact and small.” And since the rotation remained stable and constant at 4.4 milliseconds, even after billions of spins observed, the most likely explanation is that it is a black hole, and not a neutron star. The expected rate of rotation of a neutron star is to decrease with time.
What seems certain is that whatever is producing these X-rays inside ‘la Vaca’ it must be something extremely compact, just a few kilometers long, pointing directly toward a stellar-mass black hole.
Since 2018, other researchers have been able to see up to three events similar to ‘la Vaca’, but none of them so close and bright, making it difficult to compare them. According to Metzger, ‘the Cow’ is a kind of ‘stellar Rosetta stone’, which could be very useful when interpreting these failed supernovae.
“This is a close event that we can hope to understand,” says the researcher. And if it finally turns out that it is a black hole, then every time we see something similar in the distant universe we will know that a new black hole has formed there ”.
Reference article: https://www.abc.es/ciencia/abci-afirman-haber-visto-primera-nacimiento-agujero-negro-202107260914_noticia.html,