[X] My Assistant

[Stu]

http://www.spaceref.com/news/viewpr.html?pid=26414

See also: http://blogs.discovermagazine.com/badastro...-a-sunlike-star

[ngunn]

Greg, your thinking parallels mine on this topic more or less exactly. I see no compelling reason why stars cannot have sub-stellar companions over the full range of distances and dynamical arrangements that we find among stellar binaries and multiple systems. Theories of star formation may suggest otherwise, and hence we get a sharp distinction made between objects that had their own accretion discs and objects that formed within the accretion disc of a larger primary. I'm pretty sure that nature will confound this neat categorisation as we find ways of observing smaller and smaller objects over stellar distances.

[Greg Hullender]

. . . hence we get a sharp distinction made between objects that had their own accretion discs and objects that formed within the accretion disc of a larger primary. I'm pretty sure that nature will confound this neat categorisation as we find ways of observing smaller and smaller objects over stellar distances.

Grin. Yep, that's where a lot of the fun in science comes from, isn't it? The unexpected result that gives someone a chance to create a better explanation.

Naively, I'd expect a brown dwarf to be mostly hydrogen and helium, with no icy or rocky core to speak of, but a planet -- even a giant planet -- formed in an accretion disk would be more like Jupiter or Saturn. My reasoning is that the heat of the star ought to push some of the hydrogen and helium out of the disk, making planets rather different from brown dwarves, even if they had the same mass.

Obviously we'd have to observe a few for real to know much for sure, but since we have the privilege of talking to some real experts in here, I'm hoping to learn whether there's some a priori reason either not to expect brown dwarves at all, or else not to expect them to differ much from gas giants.

--Greg

[Del Palmer]

Naively, I'd expect a brown dwarf to be mostly hydrogen and helium, with no icy or rocky core to speak of, but a planet -- even a giant planet -- formed in an accretion disk would be more like Jupiter or Saturn. My reasoning is that the heat of the star ought to push some of the hydrogen and helium out of the disk, making planets rather different from brown dwarves, even if they had the same mass.

Spectrally, brown dwarfs appear to have similar composition to Jupiter (and even similar weather activity!) Bear in mind that the early solar nebula disk was 99% H and He compared to the heavy elements -- if the Sun had driven-off the H and He, you would not be able to build a Jupiter, which also shares the same H/He ratio as the Sun.

If this is a binary system, it would be remarkable, as star-formation simulations are unable to produce systems with such extreme mass ratios.