The star Fomalhaut and its debris disc

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This image shows the thermal emission from the young star Fomalhaut and the debris disc surrounding it, as recorded with ESA's Herschel Space Observatory at a wavelength of 70 micron. Together with other data, this image suggests that the dust in Fomalhaut's debris disc consists of 'fluffy' aggregates: large conglomerates of small dust grains with lots of empty space in the structure.

This new images reveal the glow from dust in the debris disc - a structure resembling the Kuiper Belt in the primordial Solar System - around the young star Fomalhaut. Detailed studies suggest that the dust in this debris disc consists of 'fluffy' aggregates of grains, which are produced by the frequent collisions taking place between comets within the disc.

When a planetary system, like our Solar System, takes shape around a star, not all the material present in the early proto-planetary disc aggregates to form big planets. Eventually, there might be regions in the system that are populated only by smaller bodies like comets and asteroids. Two examples of such regions are found in our Solar System: the asteroid belt, located between the orbits of Mars and Jupiter, and the Kuiper Belt, a rich reservoir of icy objects located beyond the orbit of Neptune and thought to be the source of short-period comets.

Collisions among these small bodies may be both frequent and violent, especially in the early formation phase of a planetary system. These collisions produce large amounts of dust grains, giving rise to circumstellar structures known as 'debris discs'. Astronomers can detect debris discs around stars other than the Sun both in visible light, as dust particles in the disc scatter the radiation emitted by the central star, or at longer wavelengths, via the thermal glow of dust itself. By studying these extrasolar debris discs, astronomers are collecting valuable insight into the nature of exoplanetary systems.

The nearby, young star Fomalhaut harbours one of the most prominent debris discs yet observed. This star has a mass twice that of the Sun and is only a couple of hundred million years old. About 20 times younger than the Sun, Fomalhaut is surrounded by a structure that might bear some resemblance to the Kuiper Belt in the Solar System's early days. Due to this star's proximity to us – only 25 light years away – its debris disc subtends a relatively large angular size on the sky, comparable to that subtended by Jupiter. In addition, this disc has a relatively large inclination with respect to our line of sight, allowing astronomers to study its full extent in great detail.

"Herschel has allowed us to see the emission from Fomalhaut's debris disc in all its glory," comments Acke. Both the star and a smooth ring-like structure – the debris disc – are distinctly visible in the data from Herschel's shortest wavelength channel at 70 micron, where highest resolution can be achieved. Emission from the disc is clearly detected also in four other channels – 160, 250, 350 and 500 micron, respectively. "Observations at all five wavelengths are crucial to learn more about the properties of dust in the disc," notes Acke.

"The spectacular Herschel images of Fomalhaut's debris disc gives us an unprecedented view of this extrasolar Kuiper Belt," comments Göran Pilbratt, Herschel Project Scientist at ESA. "The study of the disc's dust content, based on both Herschel and Hubble data, demonstrates once more the fruitful synergy of probing the sky at very different wavelengths," he concludes.

Related publications

Acke, B., et al., "Herschel Images of Fomalhaut – An extrasolar Kuiper Belt at the height of its dynamical activity", 2012, Astronomy & Astrophysics, 540, A125. DOI:10.1051/0004-6361/201118581

Copyright: ESA/Herschel/PACS/Bram Acke, KU Leuven, Belgium

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