A recent study published in the journal Science reveals that the Cygnus X-1 system hosts the most massive stellar-mass black hole ever detected without gravitational wave data.
Cygnus X-1 is a binary system featuring a supergiant star orbited by a stellar-mass black hole. Discovered in 1964 using Geiger counters on a sub-orbital rocket from New Mexico, it was the first clear black hole candidate.
This object famously sparked a bet between physicists Stephen Hawking and Kip Thorne. Hawking wagered in 1974 that it wasn't a black hole; he conceded defeat in 1990.
Astronomers recently refined parallax measurements by observing a full orbit—about six days—using the Very Long Baseline Array (VLBA), a network of ten radio telescopes across the U.S. They compared these with 2011 VLBA data from the same system.
"If we observe the same object shifting position against the background stars, we can calculate its distance—like your finger jumping when alternating eyes," explains James Miller-Jones of Curtin University. "It's the parallax principle."
The analysis shows Cygnus X-1 is farther than previously estimated: 7,200 light-years instead of 6,700. It's also moving faster than any known black hole—near light speed—and significantly more massive.
"This black hole started as a star 60 times the Sun's mass, collapsing tens of thousands of years ago," Miller-Jones notes. "New data confirm it's over 20 solar masses—50% heavier than prior estimates."
Such extreme mass challenges formation models. Stars lose mass via winds, so retaining enough for a 20+ solar mass black hole implies less mass loss in massive stars' lifetimes.
