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Finding the Elderly Universe
The Universe >
You can look up in the sky tonight, dear reader, and with nothing more than a pair of binoculars see some of the oldest creatures in the universe, some over 12 billion years old! Are they ancient planets? Dying stars? The Golden Girls? No, these ancient sky mariners are globular clusters.
Globular clusters, a.k.a. globs, are easily spotted. You may not believe this, but globular clusters are actually clusters of stars moving about together in a globular shape. Go figure.
So, when searching for a glob, look for a circularly symmetrical fuzzy sort of celestial object. I have pictures and easy-to-use maps for finding some easy targets near Sagittarius and Hercules at http://firstlightastro.com.
But don't let the cute fuzzy appearance fool you.
These globs are dense. They are only tens to a couple hundred of light
years in diameter --- compared to the 100,000-plus-light-year diameter
our galaxy lays claim to --- but contain literally millions of stars in
that relatively tiny space.
Living
on an imaginary Earth near the middle of a glob would present us with
a spectacular night sky. Being a million times denser in stars than our
local neighborhood, we would enjoy a star spangled banner above us that
would fill the heavens with so many bright points of light you couldn't
pick out the Milky Way.
But what are these creatures anyway? They are the firstborn among the stars in our galaxy. Although the details of how our galaxy formed are still fuzzy, the big picture starts billions of years ago with a supermassive cloud of hydrogen and helium gas. Stars begin to form in small bunches as the cloud collapses under its own gravity eventually forming the monstrous Milky Way disk we live in today.
But those little bunches of firstborn stars --- over 150 of them --- survive intact, not getting swept apart in the collapse. They take up touring about the Milky Way, traversing together high above and deep below the disk, and everywhere in between.
About 12 billion years of years have gone by since their birth. They are now just assemblies of old stars living out the ends of their days. But even an old bag of stars can tell us something about ourselves.
Get a map of all their positions and you'll notice that there are a lot of our busy little bees buzzing in the southern summer skies. In 1917, astronomer Harlow Shapley noticed this, worked out all their positions, and figured out the globs were hovering around a place in the Galaxy way over there in Sagittarius, tens of thousands of light years away.
The big deal --- and it was a great big deal back then --- was that it was generally believed the sun was at the center of the Galaxy. Shapley correctly concluded that globular clusters were trying to tell us we were actually off-center --- by a lot.
Some
of the more cynical astronomers immediately concluded that our place in
the universe was therefore no special place after all, that we were in
some random place with no bearing on our existence or importance.
Others today find reasons to rejoice in our so-called inconsequential eccentric real estate. It turns out now that if our little insignificant system were anywhere nearer to the center of the galaxy (high radiation, many supernovae) or farther from it (little to no planet building material), we would be one insignificant lifeless system.
Our present view of the globular clusters is the perfect view, and a constant reminder of the very special place we inhabit in this grand scheme of things.
Questions or comments? Mark Ritter can be reached here.
Posted by Administrator at 2002.08.31 02:34 PM | Comments (0)
