Failed Stars Could Reveal New Clues About How Planets Form

Artist’s impression of a low-mass stellar object surrounded by a planetary disk. Robin Dienel

The current picture of planetary formation is quite simple. When a star forms from a large cloud of gas, it is surrounded by a material that flattens out into a disk where planets eventually form. Disks are more likely to be found around larger stars, so it came as quite a surprise to find four low-mass stars with disks.

“Finding disks in low-mass systems is really interesting to us, because objects that exist at the lower limit of what defines a star and that still have disks that indicate planet formation can tell us a lot about both stellar and planetary evolution,” said first author Anne Boucher, from the University of Montreal, in a statement.

Three of the four objects are brown dwarfs, failed stars that weren’t heavy enough to start nuclear fusion at their core. They are between 13 and 18 times the mass of Jupiter. The fourth one is a lot heavier, with a mass about 120 times that of Jupiter. While that’s impressive, it is still a small fraction of the Sun’s mass, which is more than 1,000 times the mass of Jupiter.

The systems are all in the wider solar neighborhood, between 110 and 250 light-years from Earth, and they are also very young. Two of the brown dwarfs are just 10 million years old, and the other two objects are between 42 and 45 million years.

As reported in a paper, to be published by the Astrophysical Journal, the planetary disks seen around these four objects seem to be in the active stage of accretion and they are potentially forming planets, making two of them the oldest objects with an active planet-forming disk.

“There is still so much to learn about disks around low-mass objects such as these four,” added co-author Jonathan Gagné of the Carnegie Institute of Science. “Hopefully, we can conduct further research on them and be able to narrow down what kind of activity is happening in them and whether or not they would be good targets for future planet hunters.”

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