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Understanding the Fate of Planetary Systems Beyond Main Sequence Stars
Once a star evolves beyond the main sequence, the fate of any planetary system it may have had is an enigma. Astronomers generally don’t know what happens to planets beyond this point, or whether they can even survive. However, a recent study sheds some light on the fate of these planetary remains.
Studying the Helix Nebula
In a paper published in The Astronomical Journal, researchers used new data from the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Atacama Large Millimeter/submillimeter Array (ALMA), as well as archival data from the Spitzer Space Telescope and the Herschel Space Observatory, to study the Helix Nebula. These observations provide one potential explanation for the fate of these planetary remains.
A Process of Elimination, and a Disruptive Origin
The Helix Nebula is an old planetary nebula – expanding, glowing gas ejected from its host star after its main-sequence life ended. The nebula has a very young white dwarf at its center, but this central white dwarf is peculiar. It emits more infrared radiation than expected. The astronomers first determined where the excess emission couldn’t have come from.
Collisions between planetesimals – small, solid objects formed out of cosmic dust left over from the creation of a planetary system around a star – can produce this type of excess emission, but SOFIA and ALMA failed to see the large dust grains required for such objects to exist, ruling out one option. The astronomers also didn’t find any of the carbon monoxide or silicon monoxide molecules characteristic of the gas disks that can surround evolving post-main-sequence stellar systems that precede objects like the Helix Nebula, excluding another potential explanation.
Disrupted Planetary System the Likely Answer
Different strands of evidence place strict constraints on the size, structure, and orbit of the source of the emission. Eventually, they come together to identify the same culprit: dust – from full-fledged planets destroyed during the nebula’s formation – returning toward its inner regions. Once they realized the remnants of a former planetary system are at the origin of the infrared emission, they calculated how many grains need to be returning to the Helix Nebula’s center to account for the emission: about 500 million over the 100,000-year lifetime of the planetary nebula, conservatively.
SOFIA’s Role
SOFIA’s capabilities fell right into a gap between the previous Spitzer and Herschel observations, allowing the group to understand the shape and brightness of the dust, and improving the resolution of how far it spreads out.
Studying Other Late-Stage Stars
Though the researchers are not planning any follow-up observations of the Helix Nebula in particular, this study is a piece in a larger effort to use observations to understand what happens to planetary systems once their star evolves past the main sequence. The group hopes to study other late-stage stars using similar techniques.
FAQs
Q: What is the Helix Nebula?
A: The Helix Nebula is an old planetary nebula – expanding, glowing gas ejected from its host star after its main-sequence life ended.
Q: Why is the central white dwarf of the Helix Nebula peculiar?
A: The central white dwarf of the Helix Nebula emits more infrared radiation than expected.
Q: What can SOFIA and ALMA rule out from explanations for the excess infrared radiation?
A: SOFIA and ALMA ruled out two possibilities: collisions between planetesimals and gas disks that can surround evolving post-main-sequence stellar systems.
Q: What is the likely explanation for the excess infrared radiation coming from the Helix Nebula?
A: Evidence suggests that dust from full-fledged planets destroyed during the nebula’s formation is returning toward its inner regions.
Q: How many grains need to be returning to the Helix Nebula’s center to account for the excess infrared radiation?
A: About 500 million grains need to be returning over the 100,000-year lifetime of the planetary nebula, conservatively.
Q: What is the goal of this study?
A: This study is a piece in a larger effort to use observations to understand what happens to planetary systems once their star evolves past the main sequence.
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