Black Hole's "Point of No Return" Found

dsinc writes "Using a continent-spanning telescope, an international team of astronomers has peered to the edge of a black hole at the center of a distant galaxy. For the first time, they have measured the black hole's 'point of no return' — the closest distance that matter can approach before being irretrievably pulled into the black hole. According to Einstein's theory of general relativity, a black hole's mass and spin determine how close material can orbit before becoming unstable and falling in toward the event horizon. The team was able to measure this innermost stable orbit and found that it's only 5.5 times the size of the black hole's event horizon. This size suggests that the accretion disk is spinning in the same direction as the black hole. The observations were made by linking together radio telescopes in Hawaii, Arizona, and California to create a virtual telescope called the Event Horizon Telescope, or EHT. The EHT is capable of seeing details 2,000 times finer than the Hubble Space Telescope."

Comments

Editors

[Anonymous Coward]

What in the name of everything you hold holy were you thinking when posting this?

Sure, the news is interesting, but while we're getting used to spelling errors and broken links on the front page, a blatantly mis-formatted link is something new, I think.

Re:Editors

[L4t3r4lu5]

This isn't the event horizon. This is the closest distance matter can achieve a stable orbit. It's approx 5.5x the event horizon radius, where light cannot escape.

Of all of the things the editor got wrong on this post, this is one of the things actually stated in the stub. I can forgive you for not getting that far, though; This post is utterly appalling.

That link cleaned up

[madcarrots]

If you're too lazy to cut and paste. :)

http://news.harvard.edu/gazette/story/2012/10/point-of-no-return-found/

Re:I thought they were both the same.

[madcarrots]

as i understand it, the Event Horizon is the singularity limit from which light cannot escape. the Innermost Stable Orbit is the closest distance a physical object in space can orbit the black hole without being sucked into it.

Re:I thought they were both the same.

[Anonymous Coward]

Nonsense. Light can fall into a stable orbit too! And light, because it's moving, has mass too.

Maybe you meant matter, when talking about the stable orbit.

Ugh. No. Photons have no mass. They have momentum. Relativistic mass isn't actually mass, and in fact, physicists have been trying to get rid of the term, because of the confusion it causes.

Point of no return = distance below which no stable orbit can exist. If you have thrust, you can actually get out of the "point of no return", it's further away than the event horizon. You just can't have an unpowered orbit that won't eventually decay into the event horizon.

inaccurate summary

[bcrowell]

The harvard.edu news article, quoted in the slashdot summary is inaccurate. It says:

For the first time, they have measured the black hole's "point of no return"-- the closest distance that matter can approach before being irretrievably pulled into the black hole.

This reads as a claim that they've resolved the event horizon. That's not true, although there are good prospects for resolving the event horizon of a black hole in the near future.

As is made clear in the rest of the article, and in the abstract of the published paper, what they've really resolved is structure inside the innermost stable circular orbit (ISCO).

In units where G=1 and c=1, the radius of the event horizon is 2M, where M is the mass of the black hole. The radius of the ISCO, for a nonrotating black hole, is 6M, i.e., three times the radius of the event horizon. What they've resolved is structure at 5.5M.

The first author of the paper, Doeleman, seems to post all his papers on arxiv.org, but unfortunately this one doesn't seem to be there yet, and Science has their copy paywalled.