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SagittariusAStar
2011-Jun-30, 06:41 PM
Famous Black Hole Confirmed After 40 Years

by Ken Croswell

Using a vast array of radio telescopes, astronomers in North America are the first to make a direct measurement of the distance to Cygnus X-1, allowing them to conclude that the mass of its dark star is so great it can only be a black hole. They have also discovered that the black hole spins faster than most of its peers.

"There's no doubt about its distance now, and there's not much uncertainty anymore about its mass," says Mark Reid of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "It's definitely a black hole."

Link: http://physicsworld.com/cws/article/news/46362

Buttercup
2011-Jun-30, 08:21 PM
They have also discovered that the black hole spins faster than most of its peers.

Yeah! That's OUR black hole -- go baby go! :)

Romanus
2011-Jun-30, 10:08 PM
Wonderful news!

Next on the list: SS 433. ;)

Cougar
2011-Jul-01, 03:59 PM
...astronomers in North America are the first to make a direct measurement of the distance to Cygnus X-1, allowing them to conclude that the mass of its dark star is so great it can only be a black hole.

How does its distance away from us allow this conclusion?

eburacum45
2011-Jul-01, 08:33 PM
Excellent!
At a distance of 6050 light years, that is right at the edge of explored space in Orion's Arm.

I was just about to do a write-up about that object for the site- I've already made the image
(here)
http://www.bautforum.com/album.php?albumid=3&attachmentid=15189

eburacum45
2011-Jul-01, 08:51 PM
How does its distance away from us allow this conclusion?
As I understand it, the distance allows astronomers to make an accurate estimate of the mass, and the mass is (quite a bit) greater than the upper limit of a neutron star. But someone else will have to explain the details, as I don't really know them.

Romanus
2011-Jul-01, 11:49 PM
I'm guessing that the greater the distance, the greater the mass would have to be to fit the observed period and motion.

ngc3314
2011-Jul-02, 10:04 PM
We can measure the orbital properties of the sort-of-normal luminous blue companion star from changes in its Doppler shift. However, there has been dispute about its mass, given that it's losing material to a compact companion and thus might not be typical with the mass we'd associate with its temperature. If we get its distance accurately, that places it in the HR diagram and constrains its mass even if it has undergone significant mass loss, and thereby narrows down how massive the unseen companion must be for gravity to hold it in the observed orbit.