Friar Bellows

From my balcony during most of the year I get an excellent view of the Southern Cross at night. Adjacent to this popular symbol is the Alpha Centauri star system, visible to the naked eye as a single point of light, but actually consisting of two main sequence stars closely orbiting each other and a smaller companion (Proxima Centauri, the ugly sister?) further away from the main two. Just a few degrees adjacent to that system is the globular cluster, Omega Centauri.

Globular clusters are vast, spherical concentrations of up to a million stars. They are distributed around their host galaxies in a roughly spherical manner. Our own Milky Way has about 150 of them (and probably a few we don't know about) and many of them are visible in small telescopes and binoculars. Omega Centauri is the biggest and brightest of the lot, and is one of the few globular clusters visible to the naked eye (on a dark night). Indeed, it's so bright that it was initially classified as a star, hence its name.

To the naked eye, Omega Centauri appears as a faint and fuzzy star. Through my 8" telescope, it is resolved into many points of light, representing the brightest of its stars, probably giants. But among the stars not visible with my telescope are white dwarfs, which make up about 10% of the stars in a typical globular cluster. White dwarfs are hot dense carbon-oxygen remnants of stars which have exhausted their nuclear fuel. They shine (relatively feebly) because they're hot, and take billions of years to cool down. They cool down in such a predictable manner that they can be used as clocks to "date" the globular cluster itself.

Recently, astronomers using the Hubble Space Telescope (HST) applied such "dating" techniques to the globular cluster, M4, which is a few degrees away from Antares, a red supergiant. M4 is 7,000 light years away from the Earth, and so its faintest and oldest white dwarfs require the full power of the HST to be visible. The astronomers found that these white dwarfs are 12 to 13 billion years old, and so must have formed only a billion or so years after the Big Bang.

And that's how we go from my balcony to the age of the universe.

Some links:

<a href="http://oposite.stsci.edu/pubinfo/pr/2002/10/index.html" target="_blank">Hubble Uncovers Oldest "Clocks" in Space to Read Age of Universe</a>

(The press release kit from the Space Telescope Science Institute. Click on the links on the left of that page to learn more about it and see some pictures.)

<a href="http://oposite.stsci.edu/pubinfo/pr/2002/10/rel/0210richer_b.pdf" target="_blank">The White Dwarf Cooling Sequence Of The Globular Cluster Messier 4</a>

(A direct link to the scientific paper on the subject, in PDF format)

SmashingIdols

First off, your balcony sounds like a happening place.. that's not an 8" refractor, is it?

I guess I have a lot of reading to do (in my spare time) to catch up. Are all galaxies the same age?

Friar Bellows

Yeah, if I move the semi-trailer over a bit, then there's room for the refractor.

But, seriously, my 8" is a second-hand Celestron C8 I bought over a decade ago. I keep it at my parents place, because they have a nice backyard and less light pollution.

Quite possibly, within a couple of billion years, that is, but we don't know for sure. There could be ongoing galaxy formation, but we don't really know. I also don't know much about the current status of the subject, so don't take my word for it! Keywords to use in Google and arxiv.org are "galaxy formation" and "young galaxies" and "protogalaxies".

Friar Bellows

A better link to the scientific paper on this subject:

<a href="http://arxiv.org/abs/astro-ph/0205087" target="_blank">The White Dwarf Cooling Sequence of the Globular Cluster Messier 4</a>

It's not too hard to understand this paper assuming you have a basic knowledge of astronomy. Of course, some terms and concepts may go over your head, like they did over mine.

And a related paper:

<a href="http://arxiv.org/abs/astro-ph/0205086" target="_blank">The Lower Main Sequence and Mass Function of the Globular Cluster Messier 4</a>

I usually view these papers in PDF format. Sometimes there are papers I can actually understand at arxiv.org. Occasionally, scientists will put their course notes or popular-level lecture transcripts on this site. So it's a nice source of interesting reading. And it's free!

case

arXiv.org is an excellent site. I've heard rumors that it's moving though. Anyone know for sure?