# Thread: Age of the Universe and Black Holes

1. Member
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Mar 2008
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15

## Age of the Universe and Black Holes

I have a question regarding the age of the universe and black holes. The oldest star is deemed to be about 13.2 billion y old. The universe is estimated at about 13.7.

How can we really know how old the universe is if we can't age a black hole? The black hole is the end result of the life of a massive star.

Can someone fill me in on how we estimate the age of stars and thereby assume an age to the universe?

Thanks!

2. We estimate the age of stars by what type of star they are and where they are sitting on the main sequence. There is no way to age a black hole. It has no properties that will tell you how long it has been around for. So it doesn't factor in when considering the age of the universe. With stars it isn't like we've gone and said "Ok so the oldest one we've found is 13.2 billion years old lets add a few hundred million years and say that is the age. The age of the universe comes more from the analysis of expansion.

3. Originally Posted by cbholmes85
How can we really know how old the universe
We don't. We know the that the observable universe was in a hot dense state (just as in the song ) ca. 13.7 billion years ago.

But like Wayne said above, the timeline back to that point is not dependent on timing stars, much less timing black holes. All of which aren't automatically to be assumed to have formed from collapsed stars BTW - start here:
http://en.wikipedia.org/wiki/Primordial_black_holes

4. Originally Posted by cbholmes85
How can we really know how old the universe is if we can't age a black hole?
That reminds me of that silly creationist argument that the Earth couldn't be billions of years old, because the oldest known tree is less than 5000 years old.

5. Sounds more like an opposite argument to me, actually.

6. Originally Posted by cbholmes85
...How can we really know how old the universe is if we can't age a black hole? The black hole is the end result of the life of a massive star. ...
It sounds like there is an implicit assumption that all stars, not just the most massive, turn into black holes... and that's wrong.

We have observed clusters of stars that seem to be about 13 billion years old (give or take), and the stars we see there are lower mass than the Sun. These are the ones that are still shining after all these years. This is one of the things that WayneFrancis was talking about in terms of main-sequence stars.

7. Member
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Mar 2008
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15
Originally Posted by WayneFrancis
The age of the universe comes more from the analysis of expansion.
Thanks to everyone for the replies.

How do we conclude 13.7 billion years than from this analysis? How did we get to this formula?

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