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ToSeek
2005-Jun-30, 08:39 PM
New Method Pinpoints the Age of the Milky Way (http://www.universetoday.com/am/publish/pinpoint_age_milky_way.html)


University of Chicago researcher Nicolas Dauphas has developed a new method to calculate the age of the Milky Way by measuring two long-lived radioactive elements in meteorites. By calculating the amount of uranium-238 and thorium-232, Dauphas determined that the Milky Way is approximately 14.5 billion years old, give or take 2 billion. This is a close match for the age of the Universe, calculated to be 13.7 billion years by NASA's WMAP spacecraft. This means that it probably didn't take much time after the Big Bang for large structures, such as the Milky Way, to form.

novaderrik
2005-Jul-01, 02:18 AM
so, the milky way was here 800 million years before the universe that surrounds it.
man, this astronomy math is confusing...

Champion_Munch
2005-Jul-01, 04:41 AM
It said, give or take 2 billion. So if we take away 2 billion from 14.5, we end up within the existance of the universe, but only recently after it's 'appearance'.

Really it's just showing that the different ways of calculating the age of the universe/old structures (ie. Milky Way) all appear to coincide nicely. :)

with regards

Jens
2005-Jul-01, 04:57 AM
It says in the article that we know that globular clusters are old because they have a high content of hydrogen, helium and whatever that other one was, lithium? Is this true? I thought globular clusters were just big groupings of stars, and the stars have presumably aged, so why don't the stars have compositions similar to other stellar populations?

Or then again, maybe I misunderstood the article.

gopher65
2005-Jul-01, 01:00 PM
Stars in some globular clusters don't have much in the way of heavy elements. Only three elements were formed in large quanties by the Big Bang: Hydrogen (lots), Helium (quite a bit), and Lithium (a small amount). If you could find stars made up ONLY of these elements you would be looking at the first generation of stars that formed after the big bang. If you find stars with heavier elements in them (Carbon, Oxygen, or even iron) you know that they were formed from the rotting corpses of other stars ;), because only Fusion and Supernovae make those heavy elements.

Because stars in globular clusters (some of them) have low quanties of heavy(ier) elements, we assume they were formed shortly after the first generation of stars. They may even be second generation stars. AFAIK we have never seen a first generation star. Likely most of them were ginormas and supernovaed shortly after their birth.

wackywizjr
2005-Jul-01, 01:13 PM
So how many generations would it take to get the elements listed in the quote above?

Eroica
2005-Jul-01, 02:48 PM
So how many generations would it take to get the elements listed in the quote above?
One! A single large first-generation star going supernova could create all the "metallic" elements.

ngc3314
2005-Jul-01, 03:36 PM
It says in the article that we know that globular clusters are old because they have a high content of hydrogen, helium and whatever that other one was, lithium? Is this true? I thought globular clusters were just big groupings of stars, and the stars have presumably aged, so why don't the stars have compositions similar to other stellar populations?

Or then again, maybe I misunderstood the article.

That's not the only (and not the original) way to tell globulars are old. Looking at the stellar populations via the Hertzsprung-Russell diagram, we see that they contain no main-sequence stars more massive than, say, 0.8 solar mass [caveat: except for a few blue stragglers in those parts of the clusters in which you'd expect direct stellar collisions over the cluster lifetime], and only fairly low-mass red giants. The whole pattern is a good fit for old populations of stars (10-14 Gyr). The relation between age and metal abundance came out later (once there were age indicators to compare to). Our galaxy just about forgot how to make globulars a long time ago (well, just maybe NGC 3603 and Westerlund 1 might someday look like that), but other galaxies have made them much mpore recently and at higher metal abundance. (Oh, yeah, there's Terzan 1 down near the galactic center with almost solar metallicity; but things could happen a lot faster down there than out here in the boonies). Galaxy interactions and mergers, along with some bar perturbations, can form luminous star clusters that look a lot like young globular clusters - the buzzphrase is "super star clusters". 30 Doradus in the LMC is the nearest example that's easy to see (our galaxy may have one or two, but they are so heavily dust-obscured that the comparison is still not as exact as one would like).

That said, globulars have compositions overall similar to individual stars of similar age and location in the galaxy (although it takes a lot more work to tell that, what with needing individual distances to stars). The more exact description might be that globulars are the oldest easily recognizable systems in the Galaxy (and some of them may have originated in dwarf satellite galaxies that have been tidally disrupted, although the detailed chemistry sometimes suggests otherwise).

Jens
2005-Jul-02, 06:35 AM
Stars in some globular clusters don't have much in the way of heavy elements.

Admittedly, I don't know all that much about stellar evolution, but doesn't it make sense from a sort of statistical distribution way of thinking that there would have been some bigger stars among them, which would have supernovaed, sending heavier elements into their neighborhoods. Isn't it strange that a group of stars would have formed with almost identical properties, in such a small space?

Also, I asked this on another thread, but I didn't get a response there, and perhaps someone has an idea on this. Why don't globular clusters have their own angular momentum? Is it because they are orbiting the galaxies, and are somehow tidally locked in?

uniqueuponhim
2005-Jul-02, 10:02 AM
Great, I can hear the anti-scientists already. They'll be saying things like "Science says the galaxy is older than the universe so it contradicts itself so that means the earth has to be 6000 years old"
*sigh*

01101001
2005-Jul-02, 02:01 PM
Also, I asked this on another thread, but I didn't get a response there, and perhaps someone has an idea on this. Why don't globular clusters have their own angular momentum? Is it because they are orbiting the galaxies, and are somehow tidally locked in?

If the theory (http://www.universetoday.com/am/publish/star_clusters_galaxy_remnants.html?1382004) about their being remnants of swallowed irregular dwarf galaxies is right, maybe they never had much angular momentum to begin with.

Also, I don't see how an amorphous collection of stars, all chaotically orbiting each other to maintain their group formation, could be tidally locked to anything.