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Supermassive Blackholes

  1. Mar 24, 2010 #1

    I was watching a show on one of DirectTV's Science channels last night about supermassive blackholes. They stated the these supermassive blackholes exist in two phases : 1. When they are sucking in everything around them (stars, planets, moons, etc). 2. When they aren't sucking in everything around them.

    Question: When the supermassive blackhole is in Phase 2 (not sucking in stars), how to the stars stay in orbit around the hole? The planets in our solar system orbit the sun in a slightly elliptical manner, rather than perfectly circular. This is due to our sun's gravity accelerating our planets', then pulling it back in, no? I was thinking with a supermassive blackhole, wouldn't the stars around that blackhole orbit in an extremely obvious elongated elliptical shape?

    *Note: I wasn't sure what forum to post this in but figured blackholes = gravity = einstein = GR...
    Last edited: Mar 24, 2010
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  3. Mar 24, 2010 #2


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  4. Mar 24, 2010 #3


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    From a more theoretical perspective, when you are far enough away from a black hole, you cannot tell the difference between it and a normal star. So for all intents and purposes, large orbits around black holes are the same as orbits around any other body. You can have circular, or elliptical orbits just as with any other body. Things get strange as you get closer to the hole though, with things like unstable circular orbits and zones where you cannot orbit at all. But I think the vast majority of stellar objects in orbit around SMBHs do not fall into these categories.
  5. Mar 25, 2010 #4
    As Nabeshin mentioned when far enough away from the SMBH event horizon things will go unnoticed due to the amount of mass the star once had isn't changing, it is just getting condensed according to the Schwarzschild radius. In fact our orbital velocity would not change if the Sun became a black hole. Now as an object gets closer and closer to the event horizon their orbit will change dramatically, turning quite chaotic. The only difference between a quiet SMBH (within our own Milky Way) and an active SMBH (like the one in M87) is that all of the stars which were close enough or inside the event horizon have been sucked in, leaving stars that were far enough away, untouched. Other than that they are pretty much the same.
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