Cygnus X-1 Contains A Surprisingly Massive Black Hole

The image below is an artist's impression of the Cygnus X-1 system, which contains the most massive stellar-mass black hole we have ever detected without the use of gravitational waves. The massive black hole in the system is 21 times the mass of the sun. Cygnus X-1 is one the closest black holes to Earth and was initially discovered in 1964.

The massive black hole was discovered when a sub-orbital rocket was launched from New Mexico with a pair of Geiger counters onboard. Interestingly, this particular black hole was the focus of a bet between physicists Stephen Hawking and Kip Thorne in 1974. In that bet, Hawking put money on the object not being a black hole and was forced to concede the bet in 1990. In the latest work looking at the black hole, scientists used the Very Long Baseline Array, a massive radio telescope, with a clever technique that measures distance in space.

The Very Long Baseline Array was chosen for the study because it is a massive radio telescope array the size of the continental United States made up of ten dishes spread across the country. Researchers on the project said that viewing the same object from different locations allows the calculation of distance away from us by measuring how far the object appears to move relative to the background. Over six days, the team observed a full orbit of the black hole and also used data from observations from the same telescope array in 2011.

Using the new method and measurements, the team found the system is further away than previously believed and that the black hole is significantly more massive than expected. One researcher said the black hole so massive that it was challenging theories on how black holes form. Cygnus X-1 began as a star that was approximately 60 times the sun's mass that collapsed tens of thousands of years ago.

It orbits a companion star every five and a half days at one-fifth of the distance between the earth and sun. With the new measurements, the researchers estimate the black hole is more than 20 times the sun's mass, which is 50 percent more than previous estimates. Measurements also show the black hole is spinning very close to the speed of light, faster than any other black hole discovered so far.