Insight into a white dwarf’s menu: Astronomers have discovered the signatures of debris in the atmosphere of a burned-out stellar remnant, apparently from both the inner and outer regions of the former system. The white dwarf has engulfed material formed by metal and rock, as well as substances typical of icy celestial bodies. The results clarify the chaotic processes at the end of the stellar development history and provide information on the composition of celestial bodies in planetary systems that are still intact, the scientists explain.
Birth, evolution and death also characterize the history of the stars and their planetary systems. As for the category of our sun, astronomers predict that it will expand into a red giant at the end of its active life. The dying stars then shed their outer layers. In the end, all that remains is a compact, faintly glowing remnant of stars in which nuclear fusion no longer takes place – a white dwarf. It is assumed that in the course of this process many celestial bodies of the former planetary system will be thrown off course and destroyed. The remnants then orbit white dwarfs and gradually fall to their surface.
Signatures of cannibalistic meals
That story is now reflected in observational data of the white dwarf dubbed G238-44, astronomers report on the 240th Earth Day. Congress of the American Astronomical Society in Pasadena. The results are based on spectroscopic analysis of archival footage from NASA’s Hubble Space Telescope and other NASA observatories. Certain signatures of the light reaching us from the white dwarf can infer elements in its atmosphere from material it has recently ingested.
In this way, the trail of “stellar cannibalism” could already be shown in other white dwarfs. But the new data now significantly expand the spectrum: The scientists have discovered the signatures of elements that indicate that G238-44 has incorporated metallic and rocky materials typical of celestial bodies in the inner system, but also of matter, such as they feature frozen bodies found in the Kuiper Belt of our outer solar system. “We have never seen these two types of objects accrete simultaneously on a white dwarf,” says co-author Ted Johnson of the University of California at Los Angeles. His colleague Benjamin Zuckerman adds: “The abundances of the elements we see on this white dwarf suggest that they came partly from a rocky parent body and partly from one shaped by frozen volatiles.”
Food from near and far
As the researchers explain, the detection of high amounts of iron in particular is an indication of fragments of metallic cores from terrestrial planets such as Earth, Venus, Mars and Mercury. The unexpectedly high nitrogen abundance, however, led the researchers to conclude that icy bodies were present. “The best match for our data was an almost two-to-one mix of Mercury-like matter and comet-like material, which is made up of ice and dust,” says Johnson. “Ferrous metal and nitrogen ice point to completely different conditions during formation. There is no known object in our solar system that contains so much of both,” explains the astronomer.
The study thus illustrates how intensely a planetary system can be disrupted and thrown into disarray by the chaotic processes at the end of a star’s existence. As a result, material from its former vicinity as well as from the Kuiper belt-like regions can be on the white dwarf’s menu. As the scientists point out, studies of the accretion material can also provide clues to earlier phases of development: “They can lead to a better understanding of planetary systems that are still intact,” says Johnson.
The current results are particularly interesting against the background that small icy objects are said to play an important role in the “irrigation” of rocky planets. In the case of our solar system, comets and asteroids are thought to have brought water to Earth billions of years ago, creating the conditions for life as we know it. In this context, the putative composition of the celestial bodies raining down on the white dwarf G238-44 now suggests that corresponding reservoirs could be widespread in planetary systems in space, says Johnson.
Source: NASA