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Author Topic: What is the correct age for a quasar?  (Read 2687 times)

Offline Alan McDougall

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What is the correct age for a quasar?
« on: 22/06/2008 05:25:46 »
Greetings people,

I am new, My question is how are these distant objects some estimated at 14 billion light years came to get so remote from the earth, given that the universe is supposed to be only 14 billion years old.

I am aware of the red shift, and some quasars receding at a red shift of almost 6 or about 160 000 miles a second near the speed of light.

Regards

Alan
« Last Edit: 22/06/2008 10:18:34 by chris »


 

Offline Soul Surfer

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Re: What is the correct age for a quasar?
« Reply #1 on: 22/06/2008 09:52:20 »
I think that you have a problem with approximations there because the quasars were around mostly a few billion years after the big bang but are not so common now.  It is generally considered that they are largish black holes in a feeding frenzy with plenty of food in the form of the ordinary stuff of the universe around.

Let me explain a bit.  Black holes can have angular momentum and rotate but not all that much because they are very small compared with other bodies of a similar mass.  A billion solar mass black hole is only about as big as the orbit of Jupiter (a few light hours across) instead of being the size of a small galaxy say several tens of thousands of light years across  (a factor of about 100 million on size.  OK the black hole can gather a lot of stuff near it with its strong gravity but it has to loose lots of angular momentum energy before it can get inside it and this means everything gets very hot and violent die to collisions betwee the atoms in the gas and they are very bright.  That's why we can see them so far away.  A galaxy would be very faint and difficult to see but they can just be detected at that distance.  There are just as many if not more big black holes around now in the middle of galaxies and globular clusters but most of the material close to them has settled down to become stars and is not loose gas.  stars are so small that they just about never collide compared with the collision rate in even quite a tenuous gas and so do not lose energy very quickly and so the black holes are mostly quiet and there are no quasars.  Some galaxies have got active centres though(Seyfert galaxies).

 

Offline Alan McDougall

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Quasars please explain
« Reply #2 on: 22/06/2008 10:19:23 »
SoulSurfer,

Some believe that because these remote quasars that are 13 to 14 billion years distant from earth they must have also receded by that amount. E.g. 14 billion light year quasar, now 28 billion years further from earth.

This is erroneous thinking what we get is a snap shop of an extremely bright object as it was when it was still young. In fact, it has aged considerably since the light left it some 13/14 billion years ago. It might indeed be (as you said) by now exists as a very old black hole or some burned out cinder we cannot see. We are seeing a very very old object as it was when it was young not as it is at present.

Assuming the red shift is an accurate measure of how far an object is from us, it must be the 13/14 light year distance that the photons impacting on our telescope suggest according to the red shift.

Say we had a huge ruler or protractor observed an object 14 billion light years away according to the red shift and at the exact instance its light impacted on our telescope, and measured the exact distance by our magical protactor.

We would find it at approximately the distance the red shift indicated. Not receding out by another 26/28 light years as some suggest.

You might be surprised by how many informed persons remain confused by this the quasar earth distant gap.

What is your take on my explanation

Regards

Alan
 
« Last Edit: 22/06/2008 10:33:10 by Alan McDougall »
 

Offline Soul Surfer

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What is the correct age for a quasar?
« Reply #3 on: 22/06/2008 10:41:12 »
The red shift is a very convenient fact that allows us to understand a lot more about the universe.  Without it it is very difficult (but not impossible) to get a good grip on the true cosmic distance scale.  The finite velocity of light also means that as we are looking further away we are also looking back in time and see the universe as it was in the past.  AS to where the objects that we are looking at now at a great distance are now in real time this is questionable and not possible to measure it mainly depends on whether you thing the rate of expansion of the universe has decreased stayed the same or increased.  Some observations suggest that this expansion rate has in fact increased with time and so these distant objects may be even further away now.

These measurements depend on finding other yardstics than the red shift that allow the size of the universe to be measured.  even then this expansion rate may not be completely uniform it may be that space expands faster in some places than others.  so there are still a lot of unknowns around.
« Last Edit: 22/06/2008 10:44:55 by Soul Surfer »
 

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What is the correct age for a quasar?
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