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(Phys Org2)   For the first time, astronomers have measured the radius of a black hole, still can't calculate the number of digits in your mom's pi   ( divider line
    More: Interesting, black holes, supermassive black holes, Event Horizon, astronomers, radius, general relativity, extreme environment, Perimeter Institute  
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2852 clicks; posted to Geek » on 28 Sep 2012 at 1:10 PM (5 years ago)   |   Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»

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2012-09-28 11:26:09 PM  
1 vote:
Pretty sure the radius of a black hole is undefined, since it by definition involves that pesky singularity. Maybe you can measure the circumference and divide it by 2π, but that would only give the true radius if the spacetime within were flat.
ZAZ [TotalFark]
2012-09-28 05:47:32 PM  
1 vote:
As a comment on the article says, they measured the radius of the last stable orbit. To determine the size of the black hole itself from that figure you need to know its angular momentum.
2012-09-28 04:01:55 PM  
1 vote:

whatshisname: So what was the radius?

19 billion kilometers, which is over three times the average distance from the Sun to Pluto. The mass of the black hole is 6.2 billion times that of the Sun.

However, the paper isn't about measuring the radius of the black hole. They got that figure from earlier research. Their new result is the radius of the accretion disk (5.5 times wider than the black hole).
2012-09-28 01:51:06 PM  
1 vote:

TheGogmagog: Interesting I always thought the extragalactic jets were from the black hole itself, but it's more matter ejected from the accretion disk's magnetic field. So you could get really close as long as the magnetic force ejecting you exceeded the pull toward the event horizon.

Yes, provided you were either infinitesimally small, or didn't mind having your head and toes pulled in opposite directions by tidal forces that would literally rip every molecule in your body apart.

I was always confused about the hawking paradox (PBS special) as I thought matter did leave the black hole, negating his paradox. The 'some universe exists where matter didn't fall into a black hole' is a stupid cop out though.

Not sure what you mean... The Hawking paradox always assumed that matter left the black hole, and in fact is why there's a paradox:
1. Stuff (like entangled particles carrying information about their quantum state) falls into a black hole and can never escape.
2. Black holes radiate (kinda) Hawking radiation, and as a result, eventually evaporate.
3. Thus, the information is apparently lost, which violates several symmetry laws.
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