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It may take planets around most stars millions of years longer to form than previously believed, which is good news for late bloomers. According to a study published on October 6, planet-making disks around young stars typically last for 5 million to 10 million years. Based on a survey of surrounding young star clusters, that disk lifetime is far longer than the earlier estimate of 1 million to 3 million years. The formation of planets must occur within one to three megayears, according to astrophysicist Susanne Pfalzner of the Forschungszentrum Jülich in Germany. Building planets around young stars is made easier by realizing that we have plenty of time. The disks of gas and dust that swirl around young stars are where planets of all sizes grow (SN: 5/20/20). No new worlds can be created if a disk disappears.
The percentage of young stars of various ages that still have disks has been used in previous research to estimate disk lifetimes; this has been done, in instance, by monitoring star clusters with known ages. However, Pfalzner and her associates made a strange discovery: The estimated disk lifetime of a star cluster decreases with increasing distance from Earth. Why should the lifespan of a protoplanetary disk depend on how far away it is from us, she claims, is beyond reason. It doesn’t, is the short answer. However, most stars are harder to see in farther-off clusters. According to Pfalzner, higher-mass stars are more visible at farther distances because they are brighter and easier to observe. In essence, you can’t see low-mass stars. However, the majority of stars are those with the lowest masses. These cooler, smaller, and fainter than the sun orange and red dwarf stars.
In order to focus on the closest young star clusters, those that are less than 650 light-years from Earth, Pfalzner and her team only looked at them. They discovered that the proportion of stars with planet-making disks was significantly higher than that suggested by earlier research. According to her, this research revealed that low-mass stars have disk lifetimes that are between 5 and 10 megayears longer than what astronomers had previously thought. It is known that disks surrounding greater mass stars scatter more quickly than this, maybe because the stronger light from their suns accelerates the ejection of gas and dust. Lvaro Ribas, an astronomer at the University of Cambridge who was not involved with the investigation, says “I wouldn’t claim that this is solid proof” for such lengthy disk lifetimes around orange and red dwarfs. However, it’s quite convincing.
He hopes to conduct investigations of farther-off star clusters, maybe with the James Webb Space Telescope, to ascertain the proportion of the weakest stars that have maintained their planet-forming disks for between 5 million and 20 million years in order to support the findings (SN: 10/11/22). According to Pfalzner, there may be a distinction between our solar system and that of the majority of red dwarfs if the disks surrounding the lowest mass stars do indeed have extended lifetimes. Gas giants like Jupiter and Saturn, which have diameters roughly equal to that of Earth, are frequently absent from the latter. Instead, such stars usually host a large number of four times the size of Earth ice giants like Uranus and Neptune. Pfalzner hypothesizes that Neptune-sized planets may form in greater quantities when a planet-making disk lasts longer, explaining why these planets frequently orbit smaller stars.