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Astronomy/Supermassive Black Holes

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Question
Is it possible that supermassive black hole at the galactic core would eventually swallow all matter of milky way; if yes what is the approximate time it'll take; if not why?
do this galactic center wanders around? i also read that black holes wanders into the space...if it is true what is possibility to come in close encounters with solar system or is there any evidence so far in our galaxy for such an event?

Answer
I just noticed this question in the Question Pool (that is, the list of questions that were not directed to me, but were not answered by anyone else).

The black hole at the center of the galaxy can only swallow up matter that naturally happens to wander its way. Objects that happen to have paths that take them close to the center of the galaxy could be affected by the black hole, but objects like our Sun that are moving in orbits around the galaxy, instead of through the middle, can never pass close to the black hole, and therefore cannot be swallowed up by it. For this reason, black holes are unlikely to ever grow to be more than a very small percentage of the mass of a typical galaxy.

Black holes near galaxy centers could move around a little, but most of them are very near the center of mass, and have very little net motion relative to that. So not only are we not likely to get anywhere near them, they are not likely to get anywhere near us.

There are black holes that are the result of individual stellar deaths that are moving around the galaxy, more or less in the same way that the stars that turned into those black holes were doing prior to their deaths. Those could pass "close" to us, but the solar system is so small compared to the distance between stars (being tens of thousands of times smaller than typical interstellar distances in our part of the Galaxy) that near-misses close enough to actually affect the orbits of any of the objects in the Solar System are very unlikely, in any short period of time (such as the current age of the Universe). Odds are that there has never been any near passage of any black hole to our Solar System close enough to affect the motions of objects in our Solar System to any great extent during the entire 4+ billion years that the Solar System has existed.

Of course if you greatly increase the length of time involved, then even very unlikely things become more likely. I forget exactly how long the timescale is for truly close encounters with black holes, but seem to recall reading something a decade or so ago that put the average time between such events at something like 40 or 80 zeroes longer than the current age of the Universe. In other words, in the 10+ billion years the Universe has existed so far, which involves only 10 zeroes to express its age, there is essentially zero chance of anything having come close enough to us to have any significant effect. But come back when the age of the Universe has 50 or 100 zeroes, and we might have had one such encounter.

I hope this helps, and welcome you to contact me if you have any other questions.  

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Courtney Seligman

Expertise

I can answer almost any question about astronomy and related sciences, such as physics and geology. I will not answer questions about astrology and similar pseudo-scientific rubbish.

Experience

I have been a professor of astronomy for over 40 years, and am working on an online text/encyclopedia of astronomy, and an online catalog of NGC/IC objects.

Publications
Astronomical Journal, Publications of the Astronomical Society of the Pacific (too long ago to be really relevant, but you could search for Courtney Seligman on Google Scholar)

Education/Credentials
I received a BA in astronomy and physics and a MA in astronomy, both from UCLA. I was working on my doctoral dissertation when I started teaching, and discovered that I preferred teaching to research.

Awards and Honors
(too long ago to be relevant, but Phi Beta Kappa and Sigma Xi still keep trying to get me to become a paying member)

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