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The Wow Factor: Joel Achenbach gives us an even briefer history of time and space
Maybe life could, in theory, be based on exotic, harder-to-get elements. But life throughout the universe probably uses the stuff we use -- because any other strategy would mean going at things the hard way.
Next up, the stellar jet in the Carina Nebula. This is a double image that tells us that there's no single way that the universe "looks." The top image shows a star-forming gas and dust cloud as seen in visible light (the pillar glows from being irradiated by the golden light of out-of-frame stars). The bottom image shows the same structure as seen in infrared light. Visible light is, obviously, the wavelengths we pick up with our eyeballs. Infrared is what you'd see with night-vision goggles; infrared light is given off by any hot object, and it passes through intervening dust. In the infrared photo, the dusty cloud all but vanishes, and we see stars that had been hidden in the upper image. One star is firing jets of material in opposite directions. If Earth were directly in the path of a relatively nearby stellar jet, it would be lights out for all of us. Ditto if we were close to a supernova or to two super-dense neutron stars colliding and emitting a burst of gamma rays. The universe is violent. Almost every galaxy has a black hole at its core. At the center of our galaxy, which we call the Milky Way, there's a black hole with the mass of millions of stars. Fortunately, that's about 26,000 light-years away. We're in Sleepyville.
"We're in a very lucky, quiescent place in the universe," says Matt Mountain, the director of the Space Telescope Science Institute in Baltimore.
A light-year is about 6 trillion miles. The cloud we're looking at in the Carina Nebula is about three light-years from top to bottom. Earth has a diameter of about 8,000 miles, so if Earth were in this picture, it would be imperceptibly tiny. Other than some dust here and there, the universe is fundamentally transparent. This is why astronomy is possible. You can see stuff far away. But it was not always so.
"The early universe was very foggy," says physicist Brian Greene, author of "The Elegant Universe," among other best-sellers. For thousands of years after the origin of our universe in what is known as the big bang, the elementary particles such as protons and electrons sloshed around in a hot, chaotic soup. Light couldn't penetrate the stuff. It was only when the particles finally organized themselves in the form of atoms that light could suddenly zip through space freely. That transition toward transparency -- the cosmic Let There Be Light Moment -- happened about 400,000 years after the big bang. Cosmology, the study of the largest thing we know (the universe), is intimately connected to particle physics, the study of things that are vanishingly small.
Now we come to the globular star cluster Omega Centauri. And gosh, that's a lot of stars. This single image shows a region containing about 100,000 stars, out of roughly 10 million in the globular cluster.
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.