Astronomers have found the first evidence of the remains of a Kuiper Belt object analog scattered around a white dwarf star. The research was published this week in the Astrophysical Journal Letters.
This artist’s impression shows a massive, comet-like object falling towards a white dwarf. Image credit: NASA / ESA / Z. Levy, STScI.
Lead author Siyi Xu, an astronomer at the European Southern Observatory, and his colleagues from the University of California, Los Angeles, and the University of Montreal observed the white dwarf WD 1425+540, about 170 light-years from Earth in the constellation Boötes.
This star was first spotted in 1974 and is part of a wide binary system, with a K dwarf companion (G200-40) separated by 2,000 times the distance that the Earth is from the Sun.
WD 1425+540 has a helium-dominated atmosphere but also contains a large amount of hydrogen.
While studying its atmosphere using both the NASA/ESA Hubble Space Telescope and the W. M. Keck Observatory Dr. Xu and co-authors found evidence that a massive, comet-like object was falling onto the star, getting tidally disrupted while doing so.
The astronomers determined that the object had a chemical composition similar to the famous Halley’s Comet, but it was 100,000 times more massive and had twice the proportion of water as its local counterpart.
Spectral analysis showed that the object was rich in the elements essential for life, including carbon, oxygen, sulfur and even nitrogen.
This makes it the first detection of nitrogen in the debris falling onto a white dwarf.
“Nitrogen is a very important element for life as we know it,” Dr. Xu said.
“This particular object is quite rich in nitrogen, more so than any object observed in our Solar System.”
There are already more than a dozen white dwarfs known to be polluted with infalling debris from rocky, asteroid-like objects, but this is the first time a body made of icy, comet-like material has been seen polluting a white dwarf’s atmosphere.
These findings are evidence for a belt of comet-like bodies, similar to our Solar System’s Kuiper Belt, orbiting the white dwarf. These icy bodies apparently survived the star’s evolution from a main sequence star — similar to our Sun — to a red giant and its final collapse to a small, dense white dwarf.
“If there is water in Kuiper belt-like objects around other stars, as there now appears to be, then when rocky planets form they need not contain life’s ingredients,” Dr. Xu said.
“Now we’re seeing in a planetary system outside our Solar System that there are minor planets where water, nitrogen and carbon are present in abundance, as in our Solar System’s Kuiper Belt.”
“If Earth obtained its water, nitrogen and carbon from the impact of such objects, then rocky planets in other planetary systems could also obtain their water, nitrogen and carbon this way.”
The astronomers also considered how this massive object got from its original, distant orbit onto a collision course with its parent star.
“The object that has been accreted by WD 1425+540 likely was orbiting the white dwarf out beyond 300 AU before it began its fateful journey toward oblivion,” they said.
The change in the orbit could have been caused by the gravitational distribution by so far undetected, surviving planets which have perturbed the belt of comets.
Another explanation could be that G200-40 disturbed the belt and caused objects from the belt to travel toward the white dwarf.
The change in orbit could also have been caused by a combination of these two scenarios.
The Kuiper Belt in our Solar System is home to many dwarf planets, comets, and other small bodies left over from the formation of the Solar System.
The new findings now provide observational evidence to support the idea that icy bodies are also present in other planetary systems and have survived throughout the history of the star’s evolution.
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S. Xu et al. 2017. The Chemical Composition of an Extrasolar Kuiper-Belt-Object. ApJL 836, L7; doi: 10.3847/2041-8213/836/1/L7
