Astronomers revisited the very first black hole ever identified and found it to be at least 50 percent more massive than we thought.
The black hole in the X-ray binary system Cygnus X-1 has been recalculated to clock in 21 times the mass of the sun. This makes it the most massive black hole ever detected without the use of gravitational waves, forcing astronomers to rethink how black holes form.
Cygnus X-1 was first discovered as an X-ray source in 1964, and its status as a black hole became the subject of a bet between astrophysicists Stephen Hawking and Kip Thorne.
Scientists later validated the interpretation of the black hole of the object’s nature and concluded that the X-ray emission was produced by the black hole nibbling at a binary companion.
It became one of the studied black holes in the sky, and astronomers thought it was fairly well understood: an object about 6,070 light-years away, with a mass of 14.8 solar masses, and a blue supergiant companion named HDE 226868 about 24 solar masses.
We were wrong according to new observations.
Astronomers have made new parallax observations of the system and looked at what it looks like as it ‘wobbles’ in the sky as the earth orbits the sun, using the Very Long Baseline Array, a collection of radio telescopes that work together as one continental receptacle.
Eventually, their observations showed that Cygnus X-1 is a considerable distance further than we thought. Which means that the objects themselves are significantly larger.
“We used radio telescopes to measure Cygnus X-1 with high precision – the first black hole ever discovered,” explained astronomer James Miller Jones of the International Center for Radio Astronomy Research (ICRAR) in Australia.
“The black hole is orbit in a few days with a massive companion star. By detecting the orbit of the black hole in the sky for the first time, we have refined the distance to the system and it is more than 7 000 light-years from Earth.
“This implies that the black hole was more than 20 times the mass of our sun, making it the most massive black hole ever discovered without the use of gravitational waves. It challenges our ideas about how massive stars evolve to form black holes. form. “
Previously, M33 X-7, the most massive black hole detected electromagnetically, was 15.65 times the mass of the Sun. At the time of its discovery, even M33 X-7 challenged our black hole-forming models.
Scientists have concluded that since the massive star that would fall to the black hole reached the end of its life, the mass lost more slowly than the models suggested. They believe something similar for Cygnus X-1.
“Stars lose mass to their surrounding environment by star winds blowing away from their surface. But to make a black hole so heavy, we must turn off the amount of mass that bright stars lose during their lifetime,” said theoretical astrophysicist Ilya Mandel said. of the ARC Center of Excellence in Gravitational Wave Discovery (OzGrav) in Australia.
The forerunner of the Cygnus X-1 black hole would have started about 60 solar masses, and blown off its outer material before the core probably collapsed directly into the dense object, bypassing a supernova explosion.
Now it is locked up in an incredibly close, 5.6-day-long orbital dance with its blue supergiant companion, which now also has a revised mass, bringing it to a thick 40 solar masses.
It is massive enough to also one day end up as a black hole, forming a binary black hole similar to that seen in the mergers that generate gravitational waves.
However, it is unlikely that the binary will merge soon. The refined distance measurement also allows astronomers to recalculate other properties of Cygnus X-1. In a separate article, astronomers have found that it rotates almost as fast as the speed of light. It’s faster than any other black hole ever measured.
This is in direct contrast to gravity wave binaries, which are interpreted very slowly or incorrectly. This suggests that Cygnus X-1 followed a different evolutionary path than the black hole binaries we saw merging.
Given the distance between Cygnus X-1 and HDE 226868, the researchers calculated that the pair would probably not merge within a time scale equal to the age of the universe – 13.8 billion years.
Studying the system closely, before the second black hole crash occurs, provides a rare opportunity to understand black hole binaries.
“Observations like these tell us a lot about the evolutionary paths that are possible to make double black holes, some of which are frequently found on ground-based gravity wave detectors such as LIGO and Virgo,” said physicist Ashley Ruiter of the University of New. South Wales Canberra in Australia, which was not involved in the research.
“It’s amazing that we can still capture the binary ‘in action’ with electromagnetic light before it forms a double black hole – it helps to refine our theories about close evolution of binary stars.”
The team’s research was published in Science.