A black hole in the Cygnus X-1 binary system is so large that it challenges current stellar evolution models.
An artist’s impression of the Cygnus X-1 binary system. Image Credit: International Center for Radio Astronomy Research.
Cygnus X-1, discovered in 1964, is an X-ray binary system located in the constellation Cygnus.
The primary star, HD 226868, is a hot supergiant that revolves around an unseen compact companion with a period of 5.6 days.
The companion is a so-called black mass hole, a class of black holes derived from the collapse of a massive star.
Cygnus X-1 was the focus of a famous scientific bet between physicists Stephen Hawking and Kip Thorne, while Hawking bet in 1974 that it was not a black hole. Hawking conceded the bet in 1990.
“Stars lose mass to their surrounding environment through stellar winds blowing away from their surface,” said Professor Ilya Mandel, an astrophysicist at Monash University and the ARC Center of Excellence in Gravitational Wave Discovery (OzGrav).
“But to make a black hole so heavy, we need to turn off the amount of mass that bright stars lose during their lifetime.”
“The black hole in the Cygnus X-1 system started a star about 60 times the mass of the sun and collapsed tens of thousands of years ago,” he added.
“Incredibly, it orbits its companion star – a supergiant – every five and a half days at only a fifth of the distance between the earth and the sun.”
Professor Mandel and colleagues observed Cygnus X-1 using the Very Long Baseline Array (VLBA).
Using the new VLBA data and archive observations, they refined the distance to the binary system and found it to be further away than previously estimated, thus increasing the derivative mass of the black hole of the system to 21.2 solar masses. .
“For more than six days, we observed a complete orbit of the black hole and used observations of the same system in 2011 using the same telescope series,” said Professor James Miller-Jones, an astronomer at Curtin University and the International Center for Radiography. astronomy research, said. (ICRAR).
“This method and our new measurements show that the system is further away than previously thought, with a black hole that is significantly more massive.”
“These new observations tell us that the black hole is more than twenty times the mass of our sun – a 50% increase over previous estimates,” Professor Mandel said.
“Using the updated measurements for the mass of the black hole and its distance from the earth, we were able to confirm that Cygnus X-1 rotates incredibly fast – very close to the speed of light and faster than any other black hole found so far. is. Did Xueshan Zhao, a Ph.D. candidate studying at the National Astronomical Observatories of the Chinese Academy of Sciences.
The findings were published in the journal Science.
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James CA Miller-Jones et al. Cygnus X-1 contains a 21-sun mass black hole – Implications for massive stellar winds. Science, published online on February 18, 2021; doi: 10.1126 / science.abb3363