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Black Hole Found Inside Globular Cluster
acidrain writes "Contrary to the prediction of some computer models, scientists have found a black hole resting peacefully in a dense nest of stars called a globular cluster. Previously discovered black holes are either similar in size to a large star, or super massive holes which are millions of times bigger than a star is able to remain stable. This finding indicates there may be an intermediate size range of holes residing within these star clusters."
IANAAP, but i think it refers to the size of its event horizon; it could refer to its mass, but from what i understand mass and event horizon size are pretty well directionally proportional.
The singularity is a point but the Schwarzchild radius around it is directly proportional to mass. One earth mass is equivalent to something like a few cm of Schwarzchild radius.
Inside the Schwarzchild radius everything falls into the hole regardless of velocity, no exceptions.
According to General Relativity, the passage of time at a location depends on the gravitational field there. So, for instance, if the sun were to collapse into a black hole, there would be no change in the passage of time here. You would have to pass within a few Schwarzschild radii to see an effect (The Schwarzschild radius for the sun is about 3 kilometers, while Earth is 150 million km from the sum)
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As far as I remmember, black hole have the same mass as the collapsing star (before starting slowly to dissipate). Thus the same gravity as the as the star would be felt at the same distance. There is albeit a difference, within the schwarschild radius, the gravity pull is enough to pull everything without possible escape even light. Normally this radius smaller than the radius of the star itself before collapsing, if the mass would be at a point. In other word if the sun was to suddenly transform in black hole, the earth would happily go wander on the same orbit.
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If you lived on a planet of the star closest to the black hole, would the passing of your time be measurably different from ours?
Measurably but imperceptibly different from ours. But for the planet, no different than before. The gravity along a planet's orbit would be unchanged by the star's collapse. If it survives the red giant phase or the explosion, a planet's orbit won't be expected to change. By me, anyway.
The interesting spacetime effects that we associate with black holes take plase close to the singularity at the center, in regions of space that were formerly buried under the original star's surface. It would be hard to explain how you could find a planet bound in a stable orbit in there now. In the absence of gravity from a third body, things will either strike the singularity or take a mostly hyperbolic trajectory past it.
And be careful what you mean when you say "would the passing of your time be measurably different from ours" because some people take that to mean that you'll look down at your watch and see the hands moving faster or slower than usual. You'll always experience proper time for your reference frame, which basically means you'll never see that. The difference is with clocks far away from the black hole, which tick more quickly than clocks closer to it.
"Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk." - http://en.wikipedia.org/wiki/Globular_cluster What this makes me wonder is how the Globular Cluster, being much older than other galactic structures neither spins, nor contracts into itself. I would think that a Black Hole at the center would gobble the stars closest to it, increasing its gravitational attraction so that all of the surrounding stars would free fall straight "down" into it. The spin of other galaxies makes it so that stars do not just fall straight down into their own central black holes, but instead fall in a spiral toward it so that it takes a very long time for them to fall into it. But the Globular Cluster, with stars just hanging there in a spherical shape around it... I must ask - how come the stars have not fallen into the center long, long ago? Anyone have a theory on that?