“Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution,” said Liu Jifeng, astronomer at the National Astronomical Observatory of China and first author of a 2019 study of a black hole known as LB-1, discovered lurking at the far side of the Milky Way with a mass that is around 70 times larger than our sun with an orbiting blue monster, a star eight times the size of the sun.. “LB-1 is twice as massive as what we thought possible. Now theorists will have to take up the challenge of explaining its formation.”
Possible scenarios suggested in this study for the formation of such a massive black hole include mergers between lower-mass black holes, and a supernova explosion that does not expel away as much of the mass of the progenitor star as expected.
The research team from the Chinese Academy of Sciences detected the object with the Large sky Area Multi-Object fiber Spectroscopic Telescope (Lamost), based at Xinglong Observatory in China.
Massive Galaxies Host Several Supermassive Black Holes
An even more astounding discovery was reported in 2018 in a study published in the Astrophysical Journal Letters, where researchers from Yale, the University of Washington, Institut d’Astrophysique de Paris, and University College London predict that galaxies with a mass similar to the Milky Way should host several supermassive black holes (SMBH).
The 2018 team used a new, state-of-the-art cosmological simulation, Romulus, to predict the dynamics of SMBHs within galaxies with better accuracy than previous simulation programs, estimating that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe.”
Too Good to Be True?
However, a few weeks later UC Berkeley graduate student astronomer Kareem El-Badry thought the blockbuster discovery was just too good to be true when, on Nov. 27, the day before Thanksgiving, Chinese astronomers reported the discovery of the system with a black hole that was astoundingly large: 70 times the mass of our sun.
“I was suspicious from the beginning,” El-Badry says. “We know of 20 to 30 black holes in binaries, and they are all half as massive, or less than 70 solar masses. It just made me want to read the paper carefully and try to understand what (the researchers) did.”
In an email to The Daily Galaxy El-Badry wrote: “In my opinion, it has been convincingly shown that LB-1 does not contain a black hole at all, much less a supermassive one. Instead, the system is most likely a binary containing two luminous stars that have undergone an episode of mass transfer.” El-Badry published his theory for LB-1 in a paper immediately after the original discovery was announced. This was followed by additional publications casting doubt about the existence of a black hole in the LB-1 system, including a paper by Katholieke Universiteit Leuven (KU Leuven) astrophysicist Tomer Shenar.
The Invisible Galaxy
On March 2, 2019, The Daily Galaxy reported in “The Invisible Galaxy” that astronomers discovered a dozen black holes gathered around Sagittarius A* (Sgr A*), the supermassive black hole in the center of the Milky Way Galaxy, supporting a decades-old prediction. After conducting a cosmic inventory to calculate and categorize stellar-remnant black holes, astronomers from the University of California concluded that there are probably tens of millions of the enigmatic, dark objects in the Milky Way – far more than expected.
Image credit: with thanks to WGBH