A new study published in the journal Science shows that the well-known X-ray binary system Swan X-1 contains the most massive stellar-mass black hole ever detected without the use of gravitational waves. This discovery provides important information needed to build models of stellar evolution and understand the formation mechanisms of large mass black holes.
Swan X-1 is one of the closest black holes to Earth and by far the best known. The system, located 7,200 light-years from Earth and consisting of a black hole with a companion star, was discovered in 1964 during a suborbital rocket flight launched from New Mexico.
The object was the subject of a famous dispute between physicists Stephen Hawking and Kip Thorne, with Hawking betting that Swan X-1 was not a black hole. In 1990, he had to admit defeat – Swan X-1 was the first proven black hole. And now new observations of this amazing object has again forced astronomers to reconsider their views on the process of stellar evolution.
The authors observed the Swan X-1 system from different angles, using Earth’s position in a solar orbit to clarify the distance to the system and therefore the mass of the black hole. They used an array of very long baselines the size of a continent, consisting of 10 radio telescopes located in different parts of the United States, as their instrument.
“If we can look at the same object from different locations, we can calculate its distance from us by measuring how the object moves relative to the background,” lead author Professor James Miller-Jones of Curtin University is quoted in a press release from the International Center for Radio Astronomy Research (ICRAR), which coordinated the study. – If you put your finger in front of your eyes and look at it with one eye and the other, you will notice that your finger jumps from place to place. It’s exactly the same principle.”
For six days, scientists observed the full orbit of the black hole and then compared it with observations of the same telescope system made in 2011.
“Our new measurements show that the system is farther away than previously thought and that the black hole is much more massive,” Miller-Jones says.
According to the revised data, the black hole in the Swan X-1 system is 21 times the mass of the Sun, 50 percent more than previously thought. To explain the formation of such a massive black hole, scientists had to admit that stars can lose significantly more mass to stellar winds than previously thought.
Such black holes represent the compacted cores of massive stars that collapsed sharply before their shells were ejected in a supernova explosion. Scientists believe that, depending on their initial mass and chemical composition, massive stars are capable of creating black holes up to 100 times the mass of the Sun. So far, the Swan X-1 black hole has cemented its status as the largest known black hole formed from a star in our Galaxy.
Moreover, according to researchers, it continues to feed off a companion star. However, this donor star is also likely to turn into a black hole before it is finally consumed.
But the unusualness of the Swan X-1 black hole doesn’t end there. The authors found that it is also the fastest black hole known to date – its rotation speed is close to the speed of light, and every five and a half days it revolves around its companion star, a supergiant, which is only one-fifth of the distance from the Earth to the Sun.