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The first black hole ever discovered is more interesting than expected

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A study recent published in the journal Science reveals that the Cygnus X-1 system contains the most massive stellar mass black hole ever detected without the use of gravitational waves.

Cygnus X-1 is a binary system housing a supergiant star, around which a black hole of stellar mass evolves. Discovered in 1964 thanks to a pair of Geiger counters carried aboard a sub-orbital rocket launched from New Mexico, it is the first clearly identified black hole candidate.

For the record, the object had been the subject of a famous scientific bet between physicists Stephen Hawking and Kip Thorne, Hawking betting in 1974 that it was not a black hole. Finally, the latter conceded defeat in 1990.

Recently, a team of astronomers looked again at the object to get more accurate parallax measurements. To do this, the researchers observed a full orbit of the black hole around the supergiant (about six days) using the Very Long Baseline Array, a radio telescope made up of ten satellite dishes spread across the United States. They then compared this data with that collected during observations made of the same system with the same network of telescopes in 2011.

If we can see the same object in different places, we can calculate its distance from us by measuring how far the object appears to be moving from the background“, Explain James Miller-Jones of Curtin University. “If you hold your finger in front of your eyes and look at it from one eye at a time, you will notice that your finger seems to be jumping from one place to another. It’s exactly the same principle“.

Astronomers have observed the Cygnus X-1 system from different angles using the Earth’s orbit around the Sun to measure the system’s perceived movement relative to background stars. Credits: International Center for Research in Radio Astronomy

Further away, more massive and faster

Thanks to this work, the researchers were able to determine that the system is actually further away than previously thought: 7,200 light years and not 6,700 light years. It also appeared that this black hole was moving faster than any other black hole found to date. Its speed was very close to the speed of light. Finally, it is also much more massive.

The black hole in the Cygnus X-1 system began life as a star about sixty times the mass of the Sun and collapsed tens of thousands of years ago ”, continues the researcher. “These new observations tell us that the black hole is today more than twenty times as massive as our Sun. 50% heavier compared to previous estimates“.

This black hole is also so massive that it calls into question the way they can be formed. The stars regularly lose mass because of stellar winds. To make a stellar mass black hole this heavy, then we need to reduce the amount of mass that bright stars lose in their lifetime.


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