The Naked Scientists

The Naked Scientists Forum

Author Topic: About Black Holes?  (Read 5381 times)

Offline Karen W.

  • Moderator
  • Naked Science Forum GOD!
  • *****
  • Posts: 31653
  • Thanked: 5 times
  • "come fly with me"
    • View Profile
About Black Holes?
« on: 02/01/2008 15:22:11 »
In the center of the milkyway I understand we have a

black hole which to me seems very very big!

I understand it is small in comparison to others, Yes?

Well if so, what is the largest black hole we know about

and where is it located?


 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
About Black Holes?
« Reply #1 on: 02/01/2008 16:57:17 »
The largest one that we can measure directly is in the middle of the giant elliptical galaxy M87 in Virgo at the centre of our local supercluster of galaxies  about 60 million light yrars away  There are probably much larger ones at the centres of more remote superclusters but they are too far away to measure easily.  These big black holes have a mass of 3 billion times that of the sun and are about as big as the solar system.

If you fell into it you would hardly notice because the gravity gradient is so small
 

Offline Dick1038

  • Full Member
  • ***
  • Posts: 56
    • View Profile
About Black Holes?
« Reply #2 on: 02/01/2008 18:09:32 »
An object falling toward a black hole will appear to come to a stop at the event horizon because time stand still there.  It would appear to us to take an eternity to get past the EH, yet to the object falling in, time would appear to pass normally.  I don't know how to reconcile the two phenomenons. Got an answer Soul Surfer?
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
About Black Holes?
« Reply #3 on: 02/01/2008 19:32:25 »
The largest one that we can measure directly is in the middle of the giant elliptical galaxy M87 in Virgo at the centre of our local supercluster of galaxies  about 60 million light yrars away  There are probably much larger ones at the centres of more remote superclusters but they are too far away to measure easily.  These big black holes have a mass of 3 billion times that of the sun and are about as big as the solar system.

Are you sure? It seems strange to me that the largest black hole is in the "Virgo"   ;D
(I'm joking of course).
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
About Black Holes?
« Reply #4 on: 02/01/2008 23:17:24 »
Both statements are quite true.
 
The problem is one of scale. Most people's mental images are very wrong. The bit about an object falling into a black hole appearing to stop and slowly fade out assumes that the observer is a long way from the event horizon and the oject was falling straight into the black hole.  A solar mass black hole is about a mile across and a safe distance to observe it from is about the distance of the earth from the sun where you would only need to be orbiting it at about the same speed as the earth goes round the sun that is around 18 miles per second however any object much bigger than a grain of sand would be ripped to shreds by the differential gravity forces as they approached it at a velocity close to that of light.  So you need to watch an object the size of a grain of sand from the distance of the sun.

For the 3 billion solar mass hole the hole is approximately the size of the solar system and a suitable observation distance is several light years and the object the size of a space ship although you might get a small star into the very biggest ones without distrupting it.

 

Offline Karen W.

  • Moderator
  • Naked Science Forum GOD!
  • *****
  • Posts: 31653
  • Thanked: 5 times
  • "come fly with me"
    • View Profile
About Black Holes?
« Reply #5 on: 03/01/2008 00:47:14 »
The largest one that we can measure directly is in the middle of the giant elliptical galaxy M87 in Virgo at the centre of our local supercluster of galaxies  about 60 million light yrars away  There are probably much larger ones at the centres of more remote superclusters but they are too far away to measure easily.  These big black holes have a mass of 3 billion times that of the sun and are about as big as the solar system.

If you fell into it you would hardly notice because the gravity gradient is so small

That is huge.. I can't even fathom the small ones let alone ones that could be so massive...

Thanks Ian
 

Offline Dick1038

  • Full Member
  • ***
  • Posts: 56
    • View Profile
About Black Holes?
« Reply #6 on: 03/01/2008 17:50:09 »
Another problem I have with black holes is that any object that fall in disappears from our universe. The mass of the object is another form of energy.  So, the conservation of energy law seems to be violated. How do the physicists reconcile this?

A non-physicist's opinion: Perhaps that's why we see "jets" of material/energy beaming out while the BH is "eating."  The universe is reclaiming the energy.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
About Black Holes?
« Reply #7 on: 03/01/2008 23:52:16 »
No problem with the conservation of energy because the mass of the object just adds to the mass of the black hole and makes it a bit bigger.

The jets from the vicinity of the black hole are a way that material obiting the black hole looses angular momentum by throwing some out so that part of it can fall into the hole.  It is in fact rather difficult for material to fall into the hole because it probably has far too much angular momentum because of the hole's very small size.  You might expect material to fly off tangentially from the equator like a spin dryer but it does not work like that it comes out of the poles
« Last Edit: 03/01/2008 23:55:08 by Soul Surfer »
 

Offline Dick1038

  • Full Member
  • ***
  • Posts: 56
    • View Profile
About Black Holes?
« Reply #8 on: 04/01/2008 22:15:15 »
I bet the stuff orbiting close to the EH is really moving fast, perhaps, close to the speed of light?

Also, has any of the string theorist conjectured that the BH center is a collapsed ball of strings? That would make it extremely small and close to the theoretical singularity size.
 

Offline ukmicky

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 3011
    • View Profile
    • http://www.space-talk.com/
About Black Holes?
« Reply #9 on: 14/01/2008 23:41:32 »
test
 

The Naked Scientists Forum

About Black Holes?
« Reply #9 on: 14/01/2008 23:41:32 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums