Astronomers keen to observe the formation of planets are in a race to find the youngest planetary disks, or the most newly formed planets. The reverse can be interesting too, however, including the discovery of the oldest disk circling a star that, despite its slow evolution, will probably eventually coalesce into planets.
At the website DiskDetective.org anyone with an Internet connection and some spare time can identify candidates for disks that will someday become planets around other stars. Humans are still better than computers at distinguishing these disks from other sorts of astronomical objects, using 10-second videos from NASA surveys.
Among the 2 million objects classified by some 30,000 volunteers is AWI0005x3s, an apparently undistinguished red dwarf. Around AWI0005x3s, these citizen scientists recognized a protoplanetary disk, a swirling cloud of gas and dust that will eventually coalesce into planets.
This discovery was rare enough, since, for unknown reasons, red dwarfs are much less likely to host such disks than larger stars. When University of Oklahoma graduate student Steven Silverberg examined AWI0005x3s in more detail he found something more unusual still.
"Most disks of this kind fade away in less than 30 million years," Silverberg said in a statement. Yet AWI0005x3s is thought to be a member of the Carina stellar association, a group of stars that formed together 45 million years ago and are now drifting apart. If its membership of the group is confirmed, it sets a record for the longest maintenance of such a disk.
Silverberg published the discovery in The Astrophysical Journal Letters, where he reports that, based on AWI0005x3s' path through the galaxy, there is a 93.9 percent chance it is a member of the Carina association. At a distance of 150 to 300 light-years, it is also a suitable subject for study with many different sorts of telescopes.
AWI0005x3s holds extra interest because its spectral classification of 5.5 is close to that of Proxima Centauri (6.0). Besides being the closest star to the Sun, Proxima was recently found to host a planet. The inner edge of this disk has a radius around 10 million kilometers (6 million miles), which is one and a half times the distance between Proxima Centauri and its planet.
Earlier this year the same team of authors announced disks discovered with the assistance of citizen scientists using DiskDetective, including the first around a star with a white dwarf companion.
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