Astronomers have revisited the first stellar-mass black hole ever identified and discovered that it is at least 50 percent more massive than we thought.
The black hole in the Cygnus X-1 binary X-ray system has been recalculated to record 21 times the mass of the Sun. That makes it the most massive stellar-mass black hole ever detected without the use of gravitational waves, and is forcing astronomers to rethink how black holes form.
Cygnus X-1 was first discovered as an X-ray source in 1964, and its black hole status became the subject of a gamble between astrophysicists Stephen Hawking and Kip Thorne.
Later, the scientists validated the black hole’s interpretation of the object’s nature, concluding that the X-ray emission was produced by the black hole eating a binary companion.
It has become one of the most 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 binary companion. called HDE 226868 timing at around 24 solar masses.
According to the new observations, we were wrong.
Astronomers have made new parallax observations of the system, observing how it appears to ‘wobble’ in the sky as Earth orbits the Sun, using the Very Long Baseline Array, a collection of radio telescopes that together act like a collecting dish the size of a continent. .
Ultimately, their observations showed that Cygnus X-1 is at a far greater distance than we thought. Which means that the objects themselves are significantly larger.
“We use radio telescopes to make high-precision measurements of Cygnus X-1, 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 in a few days orbit with a massive companion star. By tracking the orbit of the black hole in the sky for the first time, we refined the distance to the system, placing it more than 7,000 light years from Earth.
“This implied that the black hole was more than 20 times the mass of our Sun, making it the most massive stellar-mass black hole ever discovered without the use of gravitational waves. This challenges our ideas about how massive stars evolve to form black holes. “
Previously, the most massive stellar mass black hole detected electromagnetically was M33 X-7, clocked at 15.65 times the mass of the Sun. At the time of its discovery, even M33 X-7 challenged our hole formation models. blacks.
The scientists concluded that as the massive star that would collapse to form the black hole reached the end of its life, it lost mass more slowly than the models suggested. Create something similar for Cygnus X-1.
“Stars lose mass in the environment around them through stellar winds that recede from their surface. But to make such a heavy black hole, we must reduce the amount of mass that bright stars lose during their lifetime,” he said theoretical astrophysicist Ilya Mandel. from the ARC Center of Excellence in Gravitational Wave Discovery (OzGrav) in Australia.
The black hole’s precursor star Cygnus X-1 would have started at around 60 solar masses, peeling off its outer material before the core likely collapsed directly into the dense object it is today, bypassing a supernova explosion.
Now, it is locked in an incredibly close 5.6-day orbital dance with its blue supergiant companion, which now also has a revised mass, raising it to 40 thick solar masses.
That’s massive enough that one day it will also end up as a black hole, forming a binary black hole similar to those seen in mergers that generate gravitational waves.
However, the binary is unlikely to merge anytime soon. The refined distance measurement will also allow astronomers to recalculate other features of Cygnus X-1. In a separate article, astronomers found that it rotates almost at the speed of light. That is faster than any other black hole ever measured.
This is in direct contrast to gravitational wave binaries, which have very slow or misaligned spins. This suggests that Cygnus X-1 followed a different evolutionary path than the black hole binaries that we have seen merge.
Given the distance between Cygnus X-1 and HDE 226868, researchers have calculated that the pair is unlikely to merge on a time scale equal to the age of the Universe: 13.8 billion years.
Studying the system now, before the second black hole collapse occurs, presents a unique opportunity to understand black hole binaries.
“Observations like these tell us a lot about the evolutionary pathways that are possible to make double black holes, some of which Earth’s gravitational wave detectors like LIGO and Virgo have been finding regularly,” said physicist Ashley Ruiter of the University of New South Wales Canberra in Australia, which was not involved in the investigation.
“It’s great that we can still catch the binary ‘in action’ with electromagnetic light before it forms a double black hole – this helps to refine our theories about the evolution of nearby binary stars.”
The team’s research has been published in Sciences.