The stars are different colors because they have different masses or are at different stages of their lives, which affect their temperature and brilliance. In a sense, this image of the Omega Centauri cluster is a chart of star life. Until the late 1800s, scientists doubted that Earth had been around for billions of years because they couldn't see how the sun could be on fire for such a long time. But it's not on fire. A star is a fusion reactor. Life on Earth can evolve for a long time because stars are fairly efficient at transforming matter into sunshine.
Size matters. If a star has more than about eight times the mass of our sun, at some point, gravity will overwhelm the dying force of its fusion reaction, and the core will collapse to a point of unfathomable density. When that happens, a shock wave forms, and all the outer layers of the star are exploded into space at 10,000 miles per second. That's your supernova.
When the red supergiant star Betelgeuse blows -- and it will someday, erupting on Orion's shoulder, 640 light-years from Earth -- it'll be so bright, we'll be able to see it in the daytime. All that will be left will be a tiny neutron star. A teaspoon of a neutron star would weigh about a billion tons. Very, very large stars, bigger than Betelgeuse, collapse into something even denser than a neutron star: a black hole. The matter is so dense that nothing, not even light, can escape its gravity.
The Omega Centauri cluster is hardly representative of the universe as a whole. Much of the universe consists of great gulfs of intergalactic void. We don't see images of the holes, the gaps, the great realms of nothing much. Moreover, if you want to get really technical about it, most of the matter in the universe isn't lighted up in the form of stars. It's dark. We're not sure what it is, exactly, but we can tell it's there from its gravitational effect on galaxies. And even ordinary matter is mostly dispersed in "empty" space. So stars are special features of space. It's a shame that "stars" is already taken as a metaphor, because otherwise we could say that stars are the stars of the universe.
It's hard to look at the Omega Centauri image without thinking, We are not alone. How could we be?
This is a common sentiment among scientists. But there's a counterargument: There are a lot more ways to be dead than to be alive in this universe. In fact, when you look at all those stars in this globular cluster, you're looking at a patch of sky where life may never have taken hold. The stars are so close together that they would create a gravitational maelstrom that would prevent planet formation. Moreover, exploding stars would sterilize everything nearby.
"When you've gone to a globular cluster, you've gone to a not terribly good neighborhood," says Mario Livio, an astrophysicist with the Space Telescope Science Institute.
Earths aren't exactly a dime a dozen. Space all but screams at us: Take care of your planet, because you aren't likely to have a second chance.
Schopf's recitation of the Copernican Principle -- the realization that the universe doesn't revolve around Earth, that we're not in a special position -- can be extended even further: Not only is the universe not about us, the universe isn't necessarily about the thing we love most, which is life. Sure, the universe is filled with "vital dust" -- complex molecules that prime the pump for the possible emergence of living things. But the universe is also saturated with lethal radiation. Space is a harsh environment, in general. It would be wrong to see the place as preferentially biased toward habitability. There's lots of ice out there. Amazing rocks. It may be that God is a geologist
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