April 1, 2008

Astronomers Find New Jets From Newborn Brown Dwarfs

Scientists working at the Dublin Institute for Advanced Studies have found a clutch of jets from newborn brown dwarfs. In her talk on Tuesday 1 April at the RAS National Astronomy Meeting in Belfast, postdoctoral researcher Dr Emma Whelan will announce the discovery of more jets from these intriguing objects, bringing the total to 4.

New stars form in cold clouds of gas and dust. These so-called stellar nurseries are not only home to forming stars (protostars) but also harbor forming brown dwarfs. These are objects with masses between 13 and 75 times the mass of the gas giant planet Jupiter and bridge the gap between stars and planets.

Brown dwarfs are often described as ''failed stars'', simply because they never become massive enough for nuclear fusion reactions to take place in their cores (in normal stars like the Sun energy is released as hydrogen is fused to make helium).

Young brown dwarfs are more ''star-like'' than their status as ''failed stars'' suggests. In particular, the Dublin scientists have found that they drive outflows like those from protostars and the pace of discovery implies that these are common.

Astronomers have long asked whether brown dwarfs form like stars or like planets. A star like the Sun originates through the gravitational collapse of a "Ëœclump' of material. As the collapse proceeds, a protostar forms at the center of a disk of dust and gas with the star-disk system surrounded by a halo of infalling matter. Because the central star and disk are rotating, some of the infalling material is thrown out of the system as an outflow or jet.

Dr Whelan comments, "The new discoveries mean that jets are confirmed to flow from a huge range of objects, from tiny brown dwarfs to the largest black holes with masses of billions of Suns found at the heart of some galaxies. This leads us to the tantalizing prospect that even large planets may drive outflows and jets as they form."


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