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Tuesday, December 5, 2023

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Cygnus X-1 is a black hole about 15 times the mass of the Sun in orbit with a massive blue companion star. (Credit: NASA/CXC/M.Weiss)

Black Hole Secrets Revealed

SDSU astronomy professor Jerome Orosz solves the riddles of Cygnus X-1.
By Gina Jacobs

For decades, Cygnus X-1 has been home to the black hole that you read about in textbooks. A black hole by NASA’s definition is “a place in space where gravity pulls so much that even light cannot get out.” 

Though Cygnus X-1 has long been the most referenced example of a black hole, ironically there wasn’t much known about it – until now. 

San Diego State University astronomy professor Jerome Orosz is the author of one of three papers in the December issue of the Astrophysical Journal, which reveals striking new information about Cygnus X-1, piecing together a more defined picture of this deep dark spot in space.

“These new data are a huge improvement over what was previously known about Cygnus X-1,” Orosz said. 

“While it has long been suspected that Cygnus X-1 contains a black hole and not a neutron star or white dwarf, the precise mass of the black hole was not known previously. We now know the distance from Earth, the mass of the black hole and how quickly it spins, all with uncertainties of less than 10 percent.”

Light years away

The first paper authored by researchers at the Harvard-Smithsonian Center for Astrophysics presented observations that allowed an accurate distance measurement to be made. Cygnus X-1 is 6,070 light years away, with an uncertainty of only 400 light years.

“That’s a long way — even by Star Trek standards,” Orosz said. “Ideally, you would want to fly there in a space ship and poke around, but obviously that’s impossible.”

That’s a long way — even by Star Trek standards.

The second paper, of which Orosz was the lead author, calculated the mass of the black hole and discovered it is approximately 15 times the mass of the sun. 

“The precise distance measurement made it possible for us to pin down the black hole mass,” Orosz said. The third paper, also by researchers at the center, details the measurement of the spin of the black hole using X-ray observations from space.

“With the mass determined, we were able to calculate the spin of the black hole which was found to be about 800 revolutions per second,” Orosz said.

In the beginning

Orosz said this finding helps to shed new light on the origin of the black hole in Cygnus X-1.

“The black hole appears to have been formed with high rate of spin. In addition, it may have formed through a direct collapse of the core of a massive star, rather then through a more spectacular supernova explosion.”