The First Black Hole Ever Found is More Massive than Once Thought

[Mercury]

by Maria Temming

Cygnus X-1 is about 21 times as massive as the Sun.

Link: Science News

[Ann]

by Maria Temming

Cygnus X-1 is about 21 times as massive as the Sun.

Link: Science News

I remember it well. Mostly I remember it because the reports (from 1990) said that Cygnus X-1 had a partner, which was a blue giant (or perhaps supergiant).

As if I was going to forget a black hole that was waltzing with its blue giant dance partner!

Ann

[Ann]

I have now read Maria Temming's article.

Fascinating. The black hole in Cygnus X-1 weighs about 21 times as much as the Sun, which makes it 1.5 times more massive than previously though. Astronomers have revised the distance to Cygnus X-1 from 6,000 to 7,200 light-years.

Maria Temming wrote:

Astronomers got a new look at Cygnus X-1 using the Very Long Baseline Array, or VLBA. This network of 10 radio dishes stretches across the United States, from Hawaii to the Virgin Islands, collectively forming a continent-sized radio dish. In 2016, the VLBA tracked radio-bright jets of material spewing out of Cygnus X-1’s black hole for six days (the time it took for the black hole and its companion star to orbit each other once). Those observations offered a clear view of how the black hole’s position in space shifted over the course of its orbit. That, in turn, helped researchers refine the estimated distance to Cygnus X-1.

I guess Gaia should confirm the new distance to the partner of Cygnus X-1, right?

Anyway. The new distance to Cygnus X-1 makes the black hole "almost impossibly massive for a stellar-mass black hole":

“Sometimes stars are born with quite high masses — there are observations of stars being born with masses of well over 100 solar masses,” Mandel says. But such enormous stars are thought to shed much of their weight through stellar winds before turning into black holes. The bigger the star and the more heavy elements it contains, the stronger its stellar winds. So in heavy element–rich galaxies such as the Milky Way, big stars — no matter their starting mass — are supposed to shrink down to about 15 solar masses before collapsing into black holes.

Cygnus X-1’s 21-solar-mass black hole undermines that idea.

Oh, and what about the black hole's stellar partner? The new distance estimate suggests that this star weighs 40.6 Suns, and according to Simbad, its spectral class is O9.7Iabpvar. I think the "p" in O9.7Iabpvar means "peculiar" and the "var" means "variable", the O9.7 means that the spectral class of this star is just at the border between class O and B, and the "Iab" means that this is a supergiant, but not the very brightest kind of supergiant (because the brightest ones would get the designation Ia or Ia-0).

But maybe, with the new distance estimation, the partner of black hole in Cygnus X-1 may get its luminosity class upgraded to at least "Ia"?

It certainly is a blue star, although heavily reddened by dust. (And maybe, just maybe, also reddened by the black hole messing up spacetime around it?)

Oh, by the way. I could easily look up the partner of Cygnus X-1, because I remembered its HD designation after all these years: HD 226868.

Ann