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Author Topic: What happens to our solor system galactic orbit if we remove all stars but...  (Read 1953 times)

Offline RAJ1

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Just another hypothetical question.

Lets assume that the center of the milky way does contain a massive black hole.

1. What would happen to our suns orbit if we removed all the stars but the sun and the milky way center (black hole)? 

2. If you were say superman and could withstand any force what would you find if you flew into a black hole?   Would there me a solid object (size of a house)of insanely dense material?
Or would it be nothing at all?   



 

Offline imatfaal

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Raj

1. Nothing for a very long time - gravitational changes will propagates at the same speed as light and most of the stars are many light years away.  What would happen would depend on the arrangement of stars now - and that's beyond me. i would think that the sun would head off on its own into inter-galatic space; but I am really now sure.  As i guess you are aware this is intimately tied to your question about the gravity within a hollow sphere - cosmologists use Newton's Shell theorem all the time, but I am no clued up enough to help you here.  Lets hope Soulsurfer or Syhprum swings by

2.  No one knows.  All our present ideas of physics break down at the singularity.  Lots of people would dodge the question by saying that any material that could withstand the tidal forces within the centre of black hole is impossible and therefore the question cannot be sensibly considered.  It is generally agreed that if the black hole is big enough (big black holes mean smaller tidal forces) then it would be possible to cross the event horizon - but even then you could not measure anything, even light would would never go towards the centre and bounce back with information for you.  I will reiterate - no one knows. 
 

Offline CliffordK

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The most likely thing is that the sun would just go about its way orbiting the black hole, although if the mass at the galactic center decreased substantially, then the sun would probably take up a more distant orbit.
 

Offline imatfaal

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Cliff - would depend on whether the velocity of the solar system was greater than the escape velocity.

I suppose you could do a rough sum with ve = sqrt(2GM/r) 
ok so here is my guesstimate at suns speed around the galactic centre at present
(pi*2*26,000*9.46*10^15)/(225000000*365*24*60*60)  - its around 220,000 m/s
2 pi radius of orbit / orbit time

and my guestimate of the escape velocity  - it's around 2000 m/s
((2*(6.67*10^-11) * (2*10^30)*(4.1*10^6))/((9.46*10^15)*26000))^.5
sqrt of (2 * Newtons Constant * 4.1 million * one solar mass) / radius of orbit

I hereby nominate those for the two silliest sums ever posted.   But I make the suns velocity much larger than the escape velocity.  that makes sense to me because the supermassive black hole at centre of milky way (in sagitarius) is thought to be pretty small (at 4.1 million solar masses) - so whilst much bigger than anything else - it is drawfed by the addition of all the stars in the galactic centre

And i bet I have made a silly mistake in the maths or the physics or both!!!  the sums are clickable to wolfram alpha if you need to correct
 

Offline syhprum

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I agree the mass of the black hole is pretty trivial compared with the mass of the surrounding stars so the sun would be moving well above its escape velocity and off it would go.
 

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