Observatories capture “La vaca”, the supergiant flash emitted by a dying star

In June 2018, telescopes around the world captured a powerful blue flash in the spiral arm of a galaxy 200 million light-years away. The outbreak, dubbed “the cow” and cataloged as ‘AT2018cow’, was a brilliant event of unknown origin or FBOT (for its acronym in English).

Now, a team of astronomers led by the Massachusetts Institute of Technology (MIT) has found solid evidence for the origin of that signal. Details are published today in Nature Astronomy.

In addition to a bright optical flash, the telescopes detected a high-energy X-ray pulse. Scientists traced hundreds of millions of these outbursts back to ‘the cow’ and found that they repeated like clockwork, every 4.4 milliseconds, for 60 days.

Based on the frequency of the pulses, the team calculated that the X-rays must come from an object no more than 1,000 kilometers wide, with a mass less than 800 suns, something that, according to astrophysical standards, corresponds to an object compact, like a small black hole or a neutron star.

These findings suggest that AT2018cow was likely the product of a dying star that, upon collapsing, gave rise to a compact black hole or neutron star shaped object.

The newborn object continued to devour the surrounding material, eating the star from within, a process that unleashed an enormous blast of energy.

“We have likely discovered the birth of a compact object in a supernova,” says lead author Dheeraj “DJ” Pasham, a research scientist at MIT’s Kavli Institute for Astrophysics and Space Research.

“This happens in normal supernovae, but we had not seen it before because it is a very complicated process. We believe that this new evidence opens possibilities to find baby black holes or baby neutron stars”, details Pasham.

Powerful flashes

AT2018cow or the “cow” is one of the few dozen known FBOTs, and is one of the few such signals that have been observed in real time.

Upon detection, its powerful flash – up to 100 times brighter than a typical supernova – was observed by observatories around the world.

But where did this source of energy come from?

Pasham wondered if an answer could be found in the X-ray data, and to find out he used X-ray data collected by NASA’s Neutron Star Inner Composition Explorer (NICER), an X-ray surveillance telescope. located aboard the International Space Station (ISS).

NICER began observing the Cow about five days after telescopes picked up the flare and monitored the signal for the next 60 days.

Examining that data to identify the X-ray signals emanating near AT2018cow, they found that the ‘cow’ appeared to be blasting at a frequency of 225 hertz, that is, once every 4.4 milliseconds.

Pasham used the frequency of this pulse to directly calculate the size of what was pulsing and determined that the size of the object was approximately 1,000 kilometers wide.

“The only thing that can be so small is a compact object, be it a neutron star or a black hole., ”Said Pasham.

The team further calculated that, based on the energy emitted by AT2018cow, it should not be more than 800 solar masses, ruling out the idea that the signal came from an intermediate black hole, according to Pasham.

In addition to pinpointing the origin of this particular signal, Pasham believes the study demonstrates that X-ray analyzes of FBOTs and other ultra-bright phenomena could be a new tool for studying infant black holes. (I)