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View Full Version : Is Star Formation Declining?



Plat
2004-Sep-01, 05:51 PM
I thought the universe is fairly young?

Brady Yoon
2004-Sep-01, 06:04 PM
I thought the universe is fairly young?

If the universe is an accelerating universe that will continue to expand at increasing rates, as evidence is pointing toward, yes. The universe is so young that its current age of 13-14 billion years is like a millisecond compared to how old the universe will be. 10^100 years may pass by, but the universe will still exist.

And yes, star formation has passed its peak. The peak happened around 5 billion years ago, when the sun formed. It's a little disappointing to me, because the peak happens practically right when the universe is born, and its nothing but dark matter and black holes after that. :(

Grand Vizier
2004-Sep-01, 06:41 PM
And yes, star formation has passed its peak. The peak happened around 5 billion years ago, when the sun formed. It's a little disappointing to me, because the peak happens practically right when the universe is born, and its nothing but dark matter and black holes after that. :(

Nah, it's turtles all the way down...

But cheer up, they weren't very well-designed stars in them days by all accounts. Far too big and uneconomical. Kept exploding after a few Megayears and messing up the neighbourhood. We've got the advantage of fuel economy and stability with the modern designs. Production rate's probably only lower because of the improved quality control process. :)

Plat
2004-Sep-01, 10:31 PM
is it declining fast or normally? some even say that its not declining at all because there are star formation where it shouldnt form

Grand Vizier
2004-Sep-02, 02:07 PM
is it declining fast or normally?


How would we define 'normal'?



some even say that its not declining at all because there are star formation where it shouldnt form

Well, there are huge local bursts of star formation we can see triggered by galactic collisions. We should be going through one round here in a billion years or so, when the Andromeda Galaxy collides with the Milky Way. But I guess we're really only talking about the 'background' rate of star formation - I imagine that it's quite hard to pin down exactly for the whole Universe. But locally we can easily determine the age of star clusters. Statistically, if there's a fall off in young clusters, that would say something about the past few hundred million years or so...

Spacewriter
2004-Sep-02, 02:33 PM
Yeah, I wouldn't say it's declining so much as it is moving into a new stage. All those first-generation stars were just for practice. Now that the universe has got its act together it's making more complex stars (more metallic, many smaller ones, some brown dwarfs,) and some planets. It's all part of the giant recycling plan...

Brady Yoon
2004-Sep-02, 04:40 PM
As far as I know, star formation's going to be around for a very long time until it finally ends, but it will go on a decline all the way. Trillions of years later, the only way stars will form is when two brown dwarfs smash into each other-which is extremely rare.

Cougar
2004-Sep-02, 08:29 PM
is it declining fast or normally? some even say that its not declining at all because there are star formation where it shouldnt form

This is a pretty old graph (1996) from the Hubble Site (http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/37/image/b), but as you can see, the star formation rate has already dropped off considerably from its peak. (More recent studies have placed the peak at about 8 billion years after the big bang.)
http://www.xmission.com/~dcc/sfr.jpg
It also appears to be leveling off, so the rate of decline is not nearly as steep as it was several billion years ago.
Of course, this graph and its conclusions are based on the idea that spectral redshift is caused by the expansion of space. (Gravitation and proper motion can add only minor contributions to spectral shift.) This view will likely continue to be held by a vast majority of the scientific community unless large spectral shifting can be attributed to another cause.

Plat
2004-Sep-02, 11:12 PM
i get it, so the quantity of stars is declining just alittle bit but the quality is increasing, i get it, i agree with Spacewriter, its like a recycling plan