What has been will be again: newly forming stars and planets bejewel Orion's sword

It might be true that there's nothing new under the Sun, but what about under the suns, the hundred billion other stars throughout the Milky Way? Not only is what's "under" them often new--planets are still accreting out of disks of dust, for instance--but sometimes so are the stars themselves.

Our Sun is a relatively mature star, now midway through its life cycle. It was born some 5 billion years age, following the gravity-induced collapse of a cloud of gas--a process that is even now repeating itself in other pockets of the galaxy, inside hotbeds of creation the astronomers call stellar nurseries.

To see a particularly vivid example, you need look no further than the Orion Nebula. Only 1,500 light-years from Earth (the visible diameter of our galaxy is about 100,000 light-years; for the invisible part, see "Milky Way Mystery," September 2001), it's practically in our galactic backyard, and probably the stellar nursery closest to Earth. Seen by the naked eye in a location far from city lights, the nebula (from the Latin for "mist" or "cloud") is the faintly fuzzy patch on Orion's sword, which hangs from the constellation's familiar three-star-in a-straight-line belt. For observers using binoculars of a telescope, the nebula's greenish white haze provides one of the most attractive targets in the night sky. To professional astronomers, it may reveal insights into our own planet's origins.

The Orion Nebula is an emission nebula, a giant cloud of gas and dust that's lit from within. In this case, atoms of hydrogen, oxygen, and nitrogen are being ionized by ultraviolet radiation from the Trapezium, a quartet of hot young stars at the nebula's heart. These four stars (as well as two fainter companions) are about 100,000 years old--neonates compared with our Sun but the geezers of their neighborhood.

By peering in wavelenghts not visible to the naked eye, through the nebula's gas and dust, astronomers can identify very young stars and even protostars--those that are about to light up, once the gases reach a critical density. Astronomers estimate that the Orion Nebula may comprise 10,000 stars, many of them similar to our Sun and therefore worthy of intense study. Just this past September, for instance, a team of astronomers using the orbiting Chandra X-Ray Observatory found that these newborns are capable of producing flares hundreds of thousands of times more powerful and hundreds of times more frequent than those generated by our middle-aged Sun. This finding, astrophysicists hope, might help explain the origin of certain mysterious isotopes in our solar system.

But over this past decade, much of the interest in the Orion Nebula has shifted from the stars themselves to what's happening around them. In 1992, when astronomers using the Hubble Space Telescope first detected the presence of protoplanetary disks (now called proplyds), they had to wonder if they were seeing early versions of our own planetary system. In 1997 a team of researchers reported that in particularly dense regions of the Orion Nebula, the disk of dust orbiting a star can be scattered as nearby stars bombard it with radiation. This past year, however, another team found that in the less volatile outer reaches of the nebula, the disks might survive long enough to eventually accrete into planets.

And if that turns out to be the case, then we'll finally know where to look--this month, in the southern sky after nightfall--for a reminder of a moment in cosmic history when there was, without a doubt, something new under our Sun.

Richard Panek's new book, The Invisible Century: Einstein, Freud, and Our Search for Hidden Universes, will be published in 2003 by Viking.

COPYRIGHT 2002 Natural History Magazine, Inc.
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