Colision of Comets at the Helix Nebula

[Image:NASA/JPL-Caltech/Univ. Arizona]

Kate Su (University of Arizona, U.S.A.) and collaborators, find evidence for a high number of collisions between comets at the Helix Nebula, using the
Spitzer Space Telescope (NASA).
The Helix Nebula is at about 700 light-years of distance from the Earth and it is the final phase of a star similar to the Sun: a white dwarf surrounded by a distant cloud of gas and dust.
The Spitzer Telescope operates in the infra-red, hence it does not get images in the visible like the Hubble Telescope does. However, it is capable to detect the thermal radiation from tiny close objects or from very distant objects. The different intensities of the detected radiation are transformed into false colors to create an image.
Kate Su's team detected an excess of "thermal brightness" between 35 and 150 Astronomical Units (1 AU = Earth-Sun Distance = 150 000 000 km) of distance from the white dwarf at the center of the Helix Nebula. Most probably due to a dust disk. One did not expect to find dust at such distances around this type of star. However, in our Solar System, at the same distance from the Sun, we have the Kuiper Belt. And, in reality, it is a large reservoir of comets which, simplifying, are no more than "dirty ice balls". It is then most likely that that the detected dust was released by a large number of collisions between comets that gravitate, or gravitated, around the nebula's central star.

The Spitzer press-release is available on-line.

The article's abstract: Su et al., 2007, Debris Disk around the Central Star of the Helix Nebula?, Astrophysical Journal Letters, Vol. 657, L41-L46, is also available.