Recently scientist spotted an impossible black hole that should not exist in our Milky Way galaxy clocking in about 70 times the mass of our Sun.
A new method of searching for black hole has just yielded fruit. Astronomers found a stellar mass black hole clocking in about 70 times the Sun’s mass-but its size is impossible, at least in the Milky Way, according to current stellar evolution models.
The chemical composition of the most massive stars of our galaxy suggests that by explosions and powerful stellar winds they lose most of their mass at the end of their lives, before the core of the star collapses into a black hole.
It is expected that the heavy stars in the mass range that could create a black hole would end their lives in what is called a pair-instability supernova that kills the stellar core altogether. And scientists were scratching their heads trying to figure out how the black hole -named LB-1 -got so chonky.
“According to most current models of stellar evolution, black holes of this size should not even exist in our galaxy,” said astronomer Jifeng Liu of China’s National Astronomical Observatory.
“LB-1 is twice as massive as we thought it would be possible. Theorists will now have to take up the challenge of explaining their formation.” The method of detecting the black hole was really tricky.
Black holes are literally invisible, unless they are actively accreting matter, a process that glows across the spectrum in several wavelengths. There is no radiation that we can detect-no light, no radio waves, no X-rays, zip, zilch. But that doesn’t mean we’ve got nothing in our toolkit for detection.
Way back in 1783, the English natural scientist John Michell (the first person to propose the existence of black holes) proposed that black holes could be detected if orbited by something emitting light — like a companion star — that would be tugged around the shared center of gravity of the resulting binary system.
This is now known as the radial velocity method, and it is one of the main ways we are looking for and confirming the existence of hard-to-see exoplanets as they exert a small gravitational influence on their stars. And finding other invisible things, such as black holes, can also be used.
Liu and his colleagues were searching for these wobbly stars using the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in China and got a hit on a blue giant star in the main sequence.
But it took follow-up observations to reveal the amazing nature of what the scientists had found using the powerful Gran Telescopio Canarias in Spain and the Keck Observatory in the US.
The star, about 35 million years old and about eight times the Sun’s mass clocking in, orbits the black hole every 79 days on what the researchers term a “surprisingly circular” orbit.
Another black hole of a similar mass range has been detected, clocking in at about 62 solar masses-it was created as a result of a collision between two black holes in a binary pair-GW150914, the first direct detection ever made by humans of gravitational waves. It’s not in the Milky Way, but there’s one way it can create such a black hole.
But the newly discovered LB-1 still has its binary companion. One scenario might be that LB-1 was formed by the collision of two black holes and then captured the star later-but its companion’s circular orbit causes a problem here. A capture will produce an elliptical orbit that is extremely eccentric. Time might smooth out this orbit, but it would take longer than the age of the star.
However, one possibility could be a fall back supernova in which material ejected from the dying star immediately falls back into it, resulting in formation of a black hole. Under certain circumstances, this is theoretically possible, but there is currently no direct evidence for it.
Maybe this direct evidence could be LB-1, the researchers noted in their paper.
LB-1 has suddenly become one of the most interesting objects in the Milky Way, and a flurry of follow-up observations are likely to occur.
“This discovery forces us to re-examine our models of how stellar-mass black holes form,” said University of Florida’s LIGO Director David Reitze, who was not involved in the research.
“This extraordinary discovery, along with the LIGO-Virgo observation of binary black hole collisions over the past four years, points in our understanding of black hole astrophysics to a revival.”
The research was published in Nature.