“Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution.”
In science fiction, nothing is impossible. In science … there’s plenty that seems to be impossible, but items get checked off of that list occasionally. Today is one of those days. Scientists have long accepted that it’s impossible for black holes in the Milky Way galaxy to be more than 30 times the mass of our Sun. That impossibility wall was knocked down recently by Chinese astronomers who discovered a black hole with 70 times the mass of our Sun a mere 15,000 light-years from Earth. How could this be?
“We thought that very massive stars with the chemical composition typical of our Galaxy must shed most of their gas in powerful stellar winds, as they approach the end of their life. Therefore, they should not leave behind such a massive remnant. LB-1 is twice as massive as what we thought possible. Now theorists will have to take up the challenge of explaining its formation.”
In a press release announcing the publication of the paper on his team’s discovery in the journal Nature, Professor LIU Jifeng of the National Astronomical Observatory of China of the Chinese Academy of Sciences (NAOC) explains how his team found the impossible black hole LB-1 using China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Up until recently, black holes were discovered by searching for the X-rays emitted as they consume a star. If they’re not eating, they’re invisible to conventional X-ray telescopes – and, since most aren’t constantly gulping down stars, we don’t know about their existence nor their size.
Accretion of gas onto a stellar black hole from its blue companion star, through a truncated accretion disk (Artist impression). (CREDIT”
YU Jingchuan, Beijing Planetarium, 2019.)
LAMOST changed that by allowing LIU and his team to look for stars that appeared to be orbiting something invisible. Once they found a star in a strange orbit, they used Spain’s 10.4-m Gran Telescopio Canarias and the 10-m Keck I telescope in the United States to determine the physical characteristics of the invisible mass it circled. What they found was a star eight times heavier than our sun orbiting something that was impossible.
“We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68−13+11 solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system.”
That “dark companion” was black hole LB-1, weighing in at over twice the formerly-accepted physical limit of black holes. The star orbiting it is eight times heavier than our Sun and is maintaining a wide berth, which means that this is considered a star-black-hole binary system where the black hole won’t be eating its companion anytime soon.
Is this a big deal?
“This discovery forces us to re-examine our models of how stellar-mass black holes form. This remarkable result along with the LIGO-Virgo detections of binary black hole collisions during the past four years really points towards a renaissance in our understanding of black hole astrophysics.”
LIGO Director Prof. David Reitze from the University of Florida says it’s not just a big deal, it’s a “a renaissance” … at least for astronomers.
For us, it’s another reminder that impossible isn’t always the law and isn’t always forever. Whether you believe in astrology or not, the stars CAN tell you something.
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