Astronomers see the signatures of a newborn black hole or a neutron star


For the first time in history, astronomers have been direct witnesses to the birth of a super-dense object that is outside our galaxy: the emergence of a black hole or a collapsed star in real time. So far, we have only seen these objects many years after they were first formed. But now, we can study this creation in its infancy, giving us a new vision of how these mysterious phenomena look when they first emerge.

The discovery, dubbed "La Vaca", was a pleasant surprise during a routine study of the night sky. Last year, a group of astronomers using the twin telescopes of Keck Observatory in Hawaii were looking for transients: astronomical explosions that suddenly appear with a flash in the sky and then vanish. On June 17, an incredibly bright one appeared, and in only two days it had reached its maximum splendor. The result was a stellar event 10 to 100 times brighter than the explosion of an average star or supernova.

At first, the astronomers were puzzled. Normally they never see supernovas so bright. But after a closer examination, they realized that they had something special in their hands. The radiation from the core of this explosion shone through all the material that had been ejected during the explosion, revealing something incredibly dense that we generally can not see.

The explosions of stars usually create giant bubbles of material around them, blocking what is inside our view. But this time, astronomers could get a signal from the depths of the explosion. "Normally, in a supernova, the compact object that is formed is hidden, this is an unusual event that is really exciting," says Duncan Brown, a professor of physics at Syracuse University and gravitational wave researcher, who did not participate in the study. The edge.

The cow, seen by the Keck observatory
Raffaella Margutti / Northwestern University

It is too early to tell whether the explosion resulted in a black hole or not. It is possible that it formed in a type of star corpse, known as a neutron star, which is also incredibly dense. The good news is that now that we have found it, we can continue to observe it and see it evolve, something we have not been able to do before. And how changes in this creation could help reformulate our theories as to what happens with black holes and neutron stars right after they are created. "We see them thousands of years later, but we do not know anything about what they do at the beginning," Rafaella Margutti, an astrophysicist at Northwestern University who led the research, which will be published in the Astrophysics MagazineHe says The edge.

We have known for a time that black holes and neutron stars are formed as remnants of the explosions of stars. When super mbadive stars run out of fuel, they explode outward and shed their outer layers of material. What lies below is a dense core, something much smaller than our Sun in size, but filled with the same amount of material. We have also seen evidence of this process. When we observe the remnants of supernovas, thousands or millions of years after they occur, we see traces of these dense objects in place. But black holes and younger neutron stars are always hidden from view by the outer layers of the exploding star that shoots outward.

The first big clue that Margutti and her team had something truly unique came when they measured the X rays from The Cow. They found a lot of "hard" X-rays, which are 10 times more powerful than average X-rays. This type of signal is what some astronomers call a "hump", and it is usually badociated with black holes. This signal strongly suggests that something inside the supernova is engulfing material, as black holes often do. "So there's something alive in The Cow that produces these hard X-rays," says Margutti. "That is the crucial message of observation." She adds: "It's something we've never seen in a transient before, it's completely unprecedented." Margutti says The Cow got its nickname because it was designated AT2018cow as part of the team's name scheme.

The location of the cow in its host galaxy.
Image: Dustin Lang

Margutti and her team believe that they could see this object because the star that exploded did not throw a large amount of material in the explosion. That way, there were not so many things to protect the internal radiation from sight. This can also explain why it got so bright so fast. Normally supernovas take weeks to reach their maximum brightness. The fact that it was illuminated in just two days is really strange, and may be because there was less material to block the light from our view. As for why this happened, the team is not sure. It may be because most of the explosion material may have fallen into the black hole or the neutron star. "We speculate about it, but with complete honesty, I do not know," says Margutti. "We do not know it yet".

It also helped that this explosion happened relatively close, in the cosmic scheme of things, only 200 million light-years away. It makes everything a little easier to observe. And to truly understand this event in more detail, astronomers should continue to see it in the coming weeks and months. At this time, it is too close to the Sun in the sky to see. But after next week, I should be back in a good place for a privileged visit.

And the details we collect from this event could inform us about what happens with black holes and neutron stars when they are newborns. How do they change in size? How are they turning? With The Cow, astronomers hope to be closer to answering those questions. "We've seen isolated neutron stars, neutron stars colliding with each other, and we've seen material falling into black holes," says Brown. "This observation may well be that these things are born. That is very beautiful."

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