Young star HR 4796A enveloped by dusty material, Hubble says


A young star HR 4796A is surrounded by a vast, complex dust structure, spanning 150 billion miles across according to data collected by the Hubble space telescope.

Previous studies have already shown presence of a bright, narrow, inner ring of dust which may have been corralled by the gravitational pull of an unseen giant planet. The latest discovery of the huge complex structure around the system may have implications for what this yet-unseen planetary system looks like around the 8-million-year-old star, which is in its formative years of planet construction.

According to scientists involved with the find, the debris field of very fine dust was likely created from collisions among developing infant planets near the star, evidenced by a bright ring of dusty debris seen 7 billion miles from the star. The pressure of starlight from the star, which is 23 times more luminous than the Sun, then expelled the dust far into space.

Observations reveal that the puffy outer dust structure around the star is like a donut-shaped inner tube that got hit by a truck. It is much more extended in one direction than in the other and so looks squashed on one side even after accounting for its inclined projection on the sky. This may be due to the motion of the host star plowing through the interstellar medium, like the bow wave from a boat crossing a lake. Or it may be influenced by a tidal tug from the star's red dwarf binary companion (HR 4796B), located at least 54 billion miles from the primary star.

Though long hypothesized, the first evidence for a debris disk around any star was uncovered in 1983 with NASA's Infrared Astronomical Satellite. Later photographs revealed an edge-on debris disk around the southern star Beta Pictoris. In the late 1990s, Hubble's second-generation instruments, which had the capability of blocking out the glare of a central star, allowed many more disks to be photographed. Now, such debris rings are thought to be common around stars. About 40 such systems have been imaged to date, largely by Hubble.