Monday, Aug 20 2001
Our Universe -- Low On Planets?
- Divya ThakurDivya Thakur is a 16 year old high school senior in Austin, TX who aspires to major in aeronautical engineering. Fierce with dreams and zeal, Divya is still looking for a way to combine her interests in science, writing and the White House (in that order), though still in vain. When asked for the likelihoods of her finidng such a profession she quoted, "It is hard to find a cat in a dark room especially when there is no cat"-Confucious. Whatever her future might hold in store for her, she knows never to lose her main goal in life, that is to invent a new figure of numbers, a quadrillion, herself being the sole proprieter.
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The picture above, is taken by a terrestrial telescope, shows most of the cluster, a tightly packed group of middle-aged stars held together by mutual gravitational attraction. The box near the center represents the Hubble telescope's view. The image at right shows the Hubble telescope's close-up look at a swarm of 35,000 stars near the cluster's central region. The stars are tightly packed together: They're much closer together than our Sun and its closest stars. The picture, taken by the Wide Field and Planetary Camera 2, depicts the stars' natural colors and tells scientists about their composition and age. For example, the red stars denote bright red giants nearing the end of their lives; the more common yellow stars are similar to our middle-aged Sun. Most of the stars in the cluster are believed to have formed about 10 billion years ago. The bright, blue stars -- thought to be remnants of stellar collisions and mergers -- provide a few rejuvenated, energetic stars in an otherwise old system. The Hubble picture was taken in July 1999. Credits for Hubble image: NASA and Ron Gilliland (STScI). Credits for ground-based image: David Malin, © Anglo-Australian Observatory
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Globular clusters
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Globular clusters are compact and dense, consisting of 100,000 to a few million stars in a ball 100 light years across. The night sky from an imaginary planet in a globular cluster would be a spectacular sight, filled with more than 100,000 stars visible to the naked eye. In contrast, only 6,000 stars are visible to the naked eye on Earth.
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The far reaches of the heavens extend beyond the broadest humanly comprehension. Extending over 15 billion light years, our Universe covets stars, black holes, gas clouds, red dwarfs, asteroids, and anomalies that fail to comply with the understanding of our tiny minds. And yet in our Universe indefinitely expanding ad infinitum, our planet might still be a very unique one.
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These Hubble Space Telescope images show the entire Orion Nebula (left), a central region of the nebula (center) and the bright stars of the Trapezium (right). Credits NASA / HST
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Using the Hubble Space Telescope, the researchers were able to probe the Orion Nebula, an active stellar nursery which has given birth to nearly 20,000 low-mass, sun-like stars in the past 10 million years. The odds of finding an earth like planet in this sea of fire? Odder than you might think. This region also contains super-bright, massive stars that emit so much radiation they scorch the pre-planetary disks that often swirl around their more junior, sun-like neighbors. Even after much detailed study and tedious observation no signatures of extrasolar planets were discovered, disputing the possible existence of an estimated 17 solar systems.
There are a variety of reasons the globular cluster environment may inhibit planet formation. Massive stars that surround younger sun-like stars add a threat to extrasolar system formation: The stars are so tightly compacted in the core of the cluster -- being separated by 1/100th the distance between our Sun and the next nearest star that their powerful gravitational pull can literally strip potential planet-nurturing stars of essential gases - such as hydrogen and helium - necessary for the development of large, gaseous planets.
Another possibility is that a torrent of ultraviolet light from the earliest and biggest stars, which formed in the cluster billions of years ago may have boiled away fragile embryonic dust disks out of which planets would have formed.
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Four of these protoplanetary disks have elongated tails caused by the bombardment of radiation from bright stars in the Orion Nebula. The #5 and #6 proplyds, however, have been unaltered by radiation. (#5 is seen edge-on while #6 is face-on.) Proplyd #5 was found to have large dust grains, suggesting the formation of planets has begun there. Credits John Bally / NASA / STScI
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Based on local star surveys, the current best estimates suggest that only about 6 percent of stars host planets, according to Mark Sykes, a planetary scientist at the University of Arizona. And planet hunters estimate that only 5 percent of these planet-harboring stars have massive, Jupiter-like planets.
These tantalizing findings imply that our solar system may have formed far away from massive stars. Much contrary to popular belief, most stars do not harbor planetary systems, and the misconception that solar systems abound in the universe is certainly far from reality. Our solar system is a relatively rare occurrence, life on Earth, yet another rare phenomenon. Therefore, our existence though not singular, might very well be rare.
Source
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"Globular Clusters", by Ivan R. King, Scientific American, June
1985
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