![]() With Chandra's improved angular resolution over other telescopes they could isolate the target star from other X-ray sources and viewed, for the first time, X-rays from an isolated white dwarf. So the astronomers took advantage of the Chandra X-ray Observatory, normally used to detect X-rays from black holes and neutron stars that are accreting, to analyse the nearby white dwarf G29–38. Commonly known for their use in medicine, in astronomy X-rays are the key fingerprint of material raining down on exotic objects such as black holes and neutron stars.ĭetecting these X-rays is very challenging as the small amount that reaches Earth can be lost amongst other bright X-ray sources in the sky. They are created by very fast-moving electrons (the outer shells of atoms, which make up all the matter around us). X-rays are similar to the light our eyes can see, but have much more energy. This plasma, with a temperature between 100,000 to a million degrees kelvin, then settles on the surface, and as it cools it emits X-rays that can be detected. ![]() ![]() As material from those bodies is pulled into the star at a high enough rate it slams into the surface of the star, forming a shock-heated plasma. You can then work backwards and work out how much of an element was in the parent body, whether a planet, moon or asteroid."Ī white dwarf is a star that has burnt up all its fuel and shed its outer layers, potentially destroying or unsettling any orbital bodies in the process. 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. "Previously, measurements of accretion rates have used spectroscopy and have been dependent on white dwarf models. What's quite remarkable is that it agrees extremely well with what's been done before. It is the first time we've been able to derive an accretion rate that doesn't depend on detailed models of the white dwarf atmosphere. Tim Cunningham of the University of Warwick Department of Physics said: "We have finally seen material actually entering the star's atmosphere. Until now though, astronomers had not seen the material as it was pulled into the star.ĭr. ![]() Astronomers have indirect evidence that these objects are actively accreting from spectroscopic observations, which show 25–50% of white dwarfs with heavy elements such as iron, calcium, magnesium polluting their atmospheres. Over 300,000 white dwarf stars have been discovered in our galaxy, and many are believed to be accreting the debris from planets and other objects that once orbited them.įor several decades, astronomers have used spectroscopy at optical and ultraviolet wavelengths to measure the abundances of elements on the surface of the star and work out from that the composition of the object it came from. The fate of most stars, including those like our Sun, is to become a white dwarf. The observed event occurred billions of years after the formation of the planetary system. Published today (9 February) in the journal Nature, the results are the first direct measurement of the accretion of rocky material onto a white dwarf, and confirm decades of indirect evidence of accretion in over a thousand stars so far. They have used X-rays to detect the rocky and gaseous material left behind by a planetary system after its host star dies as it collides and is consumed within the surface of the star.
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