April 12, 2012
Comets Collide To Create Dust Belt
The ESA´s Herschel Space Observatory has been studying the dust near the star Fomalhaut and has found the surrounding dust appears to have come from the dust of destroyed comets.
A young star, Fomalhaut is estimated to be just a few million years old and twice as large as the sun. The dust belt near the star was discovered in the 1980s by the Infrared Astronomical Satellite (IRAS). Herschel's imaging technology and capabilities are able to capture a clearer picture of this dust belt, however, presenting scientists with a better understanding of what makes up this dust belt.
Bram Acke works with the University of Leuven in Belgium. He and his colleagues studied the data from the Herschel observatory and found temperatures of the dust to be between –230 and –170 degrees Celsius. They also noted the southern side of the belt is the warmer and brighter side, as Fomalhaut is slightly off-center and closer to the southern side.
Earlier Hubble images suggested the reason for the belt´s asymmetrical and narrow shape was due to gravity and a possible planet in orbit around the star. Herschel´s newest images confirm these suspicions, as well as reveal the dust in the belt to have the thermal properties of small solid particles. These particles only measure a few millionths of a meter across, according to the ESA.
This created some confusion, as the Hubble telescope had previously shown these particles to be up to 10 times larger.
Dr. Acke and his colleagues suggested the dust particles could be made up of “large, fluffy aggregates” in order to resolve some of the confusion. According to Dr. Acke and his team, these aggregates could be seen as both smaller and larger as they group together.
This solution also lead to more confusion, however, as Fomalhaut has been thought to dispel dust particles from the belt rather quickly. The particles and aggregates found suggest these particles are sticking around rather than being blown out.
One suggestion as to why these dust particles are seen as small and yet large and are sticking around is continuous comet collision. The resulting dust from these collisions continually supplies the belt with newer particles that are seen as both small and large in aggregate form. Dr. Acke and his team say these collisions must be quite impressive to provide the belt with the amount of dust it holds. For example, to produce this kind of dust, 2 comets measuring 6 km or 2000 comets measuring 1 km must be crushed completely.
“I was really surprised,” said Dr Acke, “to me this was an extremely large number.”
If these kinds of collisions are occurring to supply this dust belt with the particles it needs. It is suggested there must be between 260 billion and 83 trillion comets inside the belt. This number is similar to the Milky Way´s Oort Cloud, which was formed when the Sun was young, around the same age as Fomalhaut.
“These beautiful Herschel images have provided the crucial information needed to model the nature of the dust belt around Fomalhaut,” says GÃ¶ran Pilbratt, ESA Herschel Project Scientist.
Image Caption: This image shows the infrared emission from the young star Fomalhaut and the dust disc surrounding it, as recorded with ESA's Herschel Space Observatory at a wavelength of 70 micron. To explain the emission from Fomalhaut's debris disc, astronomers invoke a steady production of dust particles via comet collisions, with an average rate of 2000 daily collisions between comets of one kilometre across or, alternatively, of 2 daily collisions between 10-kilometre-diameter comets. Credits: ESA/Herschel/PACS/Bram Acke, KU Leuven, Belgium