Friday, April 13, 2012

Dusty Disc Found Around Nearby Star thought to smashed comets

Fomalhaut is a star twice as massivea as our Sun and 25 light years away. The IRAS infrared satellite had found evidence of that the star was surrounded by large amounts of dust about 30 years ago. Now ESA's Herschel Space Observatory now has produced a higher resolution image of the star and its dust disk. It shows the star to be surrounded by hot dust and gas, but also that it has has a dusty belt of material at the outer fringes of the star system. This belt is lacated over 100 times AU's from the star making it very cold, with a temperature of about -200 Celsius. Consisting of about water ice the Fomalhaut icy dust belt forms a narrow off-centre ring with respect to Fomalhaut suggesting the presence of planets orbiting close to it or as suggested by the 2004-2006 Hubble imaging of a planet orbiting on the edge of the ring.

Based the disk's affect on starlight the grains have been found to be as small grains a few thousandths of a millimeter across. Along with the Hubble image suggesting larger particles indicates fluffy dust grains consisting of small particles stuck loosely together forming the larger ones. However these fluffy grains should have been blown away by the light pressure from Fomalhaut. The explanation proposed by astronomers is that continuous collisions and disintegration of larger asteroid-sized comets re-supplies the small particles. The dificulty is that re-supplying the large amount of dust observed requires the destruction of 2,000 1km across comets every day. Maintaining that many collisions per day requires trillions of comets to be orbiting inside the ring.

The flaw in this conclusion is that there seems to be no indication of these trillions of comets in the data. The claim that this dust is the result of thousands of dally comet collisions is based on two assumptions.The first is the age if the star. If Fomalhaut is actually considerably younger then generally thought then this dust would not require re-supplying.The second assumption is that this dust is a result of the stars formation from a larger dust cloud. If this dust came from a planet breaking up or evaporating from internal heat; a model supported by the 2004-2006 Hubble image of Fomalhaut showing a planet on the edge of the ring..

Astronomers analysing this data started with these two assumptions and there fore did not consider the other options. The result is a need for a minimum of a thousand of dally collisions of unobserved comets. That come to about 42 collisions an hour or about one collision every 87 second. This is an amazingly high collision rate. Even if this theory is true is presents a problem for planet formation theory since it shows that larger peaces material in these dust clouds tend to get broken up as opposed to forming new planet.
Dusty Disc Found Around Nearby Star

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