Halley-like comet destroyed by white dwarf

The discovery of a comet-like icy body being ripped apart in the atmosphere of a white dwarf star suggests a belt of such objects exists in another planetary system, and has survived stellar evolution.

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An artist’s impression of a comet-like object falling towards a white dwarf
Credit: NASA, ESA, and Z. Levy (STScI)

An comet of similar composition to the famous Halley’s Comet has been ripped apart in the atmosphere of a white dwarf star, and astronomers have been using the Hubble Space Telescope and W.M. Keck Observatory to observe the aftermath.

The discovery suggests that a belt of comet-like objects like the Kuiper Belt in our own Solar System could be orbiting the white dwarf.

White dwarves are the compact, dense remnants of stars, and astronomers have been looking at WD 1425+540, which lies about 170 lightyears from Earth in the Boötes constellation. While studying the white dwarf’s atmosphere, the team found evidence that an object was falling into it.

Studies revealed it to have a similar chemical composition to Halley’s Comet in our Solar System, yet 100,000 times more massive and with twice the proportion of water. It also contains elements essential for life to exist, including carbon, oxygen, sulphur and nitrogen.

“Nitrogen is a very important element for life as we know it,” says lead author Siyi Xu of the European Southern Observatory. “This particular object is quite rich in nitrogen, more so than any object observed in our Solar System.”

The discovery is the first time a large body of icy material like a comet has been seen falling into a white dwarf’s atmosphere. It could mean that numerous comets are orbiting the white dwarf, like the Kuiper Belt in our own Solar System. Also, it suggests that the comets survived the process by which stars expand into a red giant and then collapse to a dense white dwarf.

However, it is still unclear how the comet would have moved from its orbit circling the white dwarf to falling into it. Perhaps the gravitational pull of undiscovered planets caused the orbit to change dramatically. Regardless, it provides evidence for the theory that icy bodies exist in planetary systems outside our own, and that they could survive the extremes of stellar evolution.


 
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