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Re:Astronomers uncover largest group of rogue planets yet by akiselev on Saturday January 01, 2022 @03:14PM (#29762200)
I'm kind of burned out on exoplanet discoveries since they're a dime a dozen nowadays but this title caught my eye because I've been rewatching Star Trek DS9 recently. The antagonist in the latter half of the series is the Dominion empire which is unilaterally controlled by a race of hivemind-y shapeshifters called the Changelings. The only time we get to see most of their species is on their home world, a rogue planet somewhere in the gamma quadrant.

I've been fascinated by the idea of detecting rogue planets ever since and it's incredible they found so many. Unfortunately, it looks like their detection method might not be useful for older (billion+) or rocky planets (from the footnote):

> The exact number of rogue planets found by the team is hard to pin down because the observations don't allow the researchers to measure the masses of the probed objects. Objects with masses higher than about 13 times the mass of Jupiter are most likely not planets, so they cannot be included in the count. However, since the team didn't have values for the mass, they had to rely on studying the planets' brightness to provide an upper limit to the number of rogue planets observed. The brightness is, in turn, related to the age of the planets themselves, as the older the planet, the longer it has been cooling down and reducing in brightness. If the studied region is old, then the brightest objects in the sample are likely above 13 Jupiter masses, and below if the region is on the younger side. Given the uncertainty in the age of the study region, this method gives a rogue planet count of between 70 and 170.

That said, this is exciting news!

> The study suggests there could be many more of these elusive, starless planets that we have yet to discover. "There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star," Bouy explains.

Re:Astronomers uncover largest group of rogue planets yet by Jeff_Brown on Saturday January 01, 2022 @04:13PM (#29762870)
Above 13 Jupiter masses would it have to be a burned out star?
Re:Astronomers uncover largest group of rogue planets yet by TheOtherHobbes on Saturday January 01, 2022 @04:59PM (#29763286)
Brown dwarf? Some sputtering early attempts at fusion, but not enough to become self-sustaining.

13 Mj is on the low side of the definition. It's not a definitive number and goes as high as 80 Mj, depending who you ask.

Re:Astronomers uncover largest group of rogue planets yet by wumpus on Saturday January 01, 2022 @06:57PM (#29764197)
13 Mj is the current mass at which people think deuterium fusion can start. Above 80 Mj, hydrogen fusion will start.

These numbers depend on a lot of details of stellar atmospheres.

I took a graduate-level Stellar Atmospheres class from S. Kumar, who first theorized about this class of not-quite-star.