Black holes may be well known for their gluttonous tendencies, but they're not the only dead stars capable of slurping down passing objects. For years, evidence has been mounting that white dwarf stars also have a penchant for snacking – and on the
"These are numerical models that calculate how quickly an element sinks out of the atmosphere into the star, and that tells you how much is falling into the atmosphere as an accretion rate. You can then work backwards and work out how much of an element was in the parent body, whether a planet, moon, orThis new work is different.
When a compact object such as a white dwarf or a black hole accretes another object, it's not a clean event. First, the orbiting body is tidally disrupted – that is, the gravitational stresses as it grows too close to the dead star tear the object apart. Then, this orbiting stream of material spools into the star from a disk for an extended accretion event.
Cunningham and his team used the Chandra X-Ray Observatory, which is used to detect X-rays from accreting black holes and neutron stars, to study a polluted white dwarf named G 29-38, located 57 light-years away. It's thought to be relatively young, having collapsed just 600 million years ago; previous studies also suggest the white dwarf is surrounded by a debris disk, and has heavy elements in its atmosphere.
With Chandra, the researchers were able to isolate G 29-38 from other X-ray sources in the sky; sure enough, they found the X-ray signal generated by accretion. The result finally confirms that white dwarfs are indeed quite violent objects, and gives astronomers a new tool for probing these fascinating interactions.
"What's really exciting about this result is that we're working at a different wavelength, X-rays, and that allows us to probe a completely different type of physics,""This detection provides the first direct evidence that white dwarfs are currently accreting the remnants of old planetary systems.