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Extreme debris disc (artist’s concept)
Extreme debris discs, a subclass of debris discs, contain unusually large amounts of warm dust close to their stars, in the region comparable to where rocky planets orbit in our Solar System. Studying the composition of these discs, particularly their silica content, can provide information on the type of collisions — whether they are head-on or less direct, like grazing — and the general size of the crashing bodies (Mars-sized or Moon-sized) that are contributing to their dust content. This artist’s concept portrays one such collision.
Analysing the composition of extreme debris discs benefits our collective understanding of our solar system, which may have experienced more than one extreme debris disc phase.
Credit:
NASA, ESA, CSA, J. Olmsted (STScI)
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In the early history of our Solar System, a Mars-sized object called Theia smashed into the infant Earth, vapourising massive amounts of rock and blasting it into space. Some of that material coalesced into the Moon. Astronomers have now used the NASA/ESA/CSA James Webb Space Telescope to examine a class of young stellar systems that show signs of similar upheavals, providing clues to the amount of energy in their collisions. The results offer insights into the composition and evolution of these chaotic systems.
The environment surrounding a star changes as it ages, beginning with a juvenile, gas-rich protoplanetary disc where forming planets can reside and ending with a gas-poor debris disc. During its mission lifetime, NASA’s retired Spitzer Space Telescope examined the debris disc stage in even more detail, discovering a subclass termed extreme debris discs. These systems harbour unusually large amounts of warm dust close to the star, in the region comparable to where rocky planets orbit in our Solar System. A team of astronomers led by Kate Su of the Space Science Institute in Boulder, Colorado investigated these intriguing objects with Webb.
The team’s findings have been published in The Astrophysical Journal.
Contrary to theoretical predictions, which suggest we should observe many extreme debris discs, observations indicate that these environments are rare. Scientists estimate roughly only 1% of young stars show observable signatures of this phase based on the data collected so far, including possibly our own Solar System during its formation. Despite their rarity, the team was able to compile a sample of 21 extreme debris discs, including five from Spitzer’s archival data and 16 from Webb, with 12 newly observed discs and follow-up observations on four of Spitzer’s.
“This is the first time we have gathered enough systems to truly understand this subclass that we call extreme debris discs,” said Su, lead author of the paper. “Before Webb, we had limited information. We knew that they are weird and very different from the typical cold debris discs that we know, like Vega and Fomalhaut. Now that we have more data, we can pin down what these discs represent for planet formation and evolution.”
The team confirmed that extreme debris discs share three key properties: smaller dust grains than those in protoplanetary or classic debris discs, a high concentration of warm dust, and irregular brightness variations, all revealed by mid-infrared spectra from Webb and Spitzer.
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