New Object Found Closest Brown Dwarf

[renormalised (Carl)]

Just recently, they've found a new brown dwarf, UGPS 0722-05, which appears to be only 9.6 light years from Earth. It's also the coolest brown dwarf ever found, at 400-500K (130-230 degrees Celcius). Considering its dimness and the small patch of sky it was found in, there is a strong possibility of even more (and closer) objects will be found. Given its temperature, they believe it maybe the first example of a T9.9 brown dwarf or might be the first member of a new spectral class.

New Scientist Article

Discovery of a very cool brown dwarf amongst the ten nearest stars to the Solar System

[Robh (Rob)]

It will be interesting to see just how frequent these brown dwarfs turn out to be. It seems reasonable to expect a full range of masses from the smallest of planets through to giant stars depending on the availability of local resources. I wonder at what point a giant planet is distinguished from a brown dwarf? Should a precondition for a brown dwarf be that it has at some stage carried out fusion reactions?

Regards, Rob.

[renormalised (Carl)]

The cutoff point between BD's and giant planets is a real hazy one. There is a size definition of anything including and over 13 Jupiter masses. At this size, a body can begin to fuse deuterium in its core. It can also fuse lithium if the core temp is higher than 7 million K. However, then you also have to take into account how the object forms, and this is where things really get blurry. Reason being that it's quite possible for very large planets to form in the same manner as stars do, i.e. gravitational collapse of a pre-existing mass of gas (the "top down" approach), as well as from both methods of the "bottom up" approach (core accretion via planetesimals and slow gas accumulation, or core accretion via large, low density cores and rapid gas accumulation). It depends on time and the characteristics of the accretion disk they form out of. Accretion disks around most stars don't last for very long...for a star like the Sun, around 10-15 million years. So it doesn't give the planets much time to build up. A Jupiter sized world really only has about 2-5 million years to reach its full size before a substantial amount of gaseous material is lost during the star's T Tauri phase. For terrestrial planets, which take longer to grow (especially for Earth size planets and larger) than the giants, they can carry on longer due to the presence of larger sized dust grain material and bigger objects (such as asteroids etc) which are still hanging around after the T Tauri phase.

I think the best cutoff point for distinguishing a planet from a brown dwarf would be this...1. Top down development via gravitational collapse, and 2. Fusion of low temperature elements such as deuterium and lithium. That would probably put the cutoff point in a range between 13-18 Jupiter masses. If the object still formed much like a star but is below the mass cutoff/no fusion, then it's a planet. If it's heavier than the cutoff and is fusing deuterium, and apparently formed like a normal gas giant planet (bottom up approach), then it should be classed as a "superplanet". There are a few examples of objects like this, e.g CoRoT 3b, XO-3b. Both these objects are very dense and probably have substantial rocky cores, or a lot of rocky material in their cores, and they're both substantially larger than Jupiter.

So, this is where we have to be careful about how we define what a planet is and how it forms. It can get rather murky!!.

[OneOfOne (Trevor)]

Originally Posted by renormalised

[snip]
1. Top down development via gravitational collapse, and 2. Fusion of low temperature elements such as deuterium and lithium. That would probably put the cutoff point in a range between 13-18 Jupiter masses. If the object still formed much like a star but is below the mass cutoff/no fusion, then it's a planet. If it's heavier than the cutoff and is fusing deuterium, and apparently formed like a normal gas giant planet (bottom up approach), then it should be classed as a "superplanet".
[snip]

It could get even murkier, what if the object forms according to the above and is defined as a "planet", but subsequently we find it does not orbit anything else but has objects orbiting it, ie it is the centre of a "system". This would make these objects "moons". So we would have a planetary system that orbits no star, a rogue planet I guess. And what if these "moons" were to have objects orbiting them, do we continue to define a moon as anything that orbits something that is not a star or planet? Fortunately, we may never have the technology to find this amount of detail....my head hurts thinking about it.

[renormalised (Carl)]

Originally Posted by OneOfOne

It could get even murkier, what if the object forms according to the above and is defined as a "planet", but subsequently we find it does not orbit anything else but has objects orbiting it, ie it is the centre of a "system". This would make these objects "moons". So we would have a planetary system that orbits no star, a rogue planet I guess. And what if these "moons" were to have objects orbiting them, do we continue to define a moon as anything that orbits something that is not a star or planet? Fortunately, we may never have the technology to find this amount of detail....my head hurts thinking about it.

Platonic epicycles gone mad!!!

Best way to solve this crisis is to liberally apply Occam's Razor and a judicious amount of denial...."No, never saw that object at all in the pics...doesn't exist!!"

[michaellxv (Michael)]

If there are enough of these objects, is this where some of the missing matter of the universe is hiding? If so, what would the estimate be for how much?

After the Pluto debate a planet has a very specific definition. An object such as a brown dwarf or similar smaller object would not satisfy that definition. If it does not qualify as a star then a new classification would be required.

How would you distinguish between a 'failed star' and a 'rogue planet'? Would there be a significant difference in their compsition?

[OneOfOne (Trevor)]

Originally Posted by michaellxv

How would you distinguish between a 'failed star' and a 'rogue planet'? Would there be a significant difference in their compsition?

At the moment I think they would say that a "rogue" planet is one that was formed as part of the "normal" process (ie. around a star) and then thrown out of the system as a result of interactions with other large objects. "Fortunately" the likelihood of finding some of these things is soooooo remote that we may not find any and have to deal with the question...famous last words It is probably more likely to be remain a theoretical discussion.

[renormalised (Carl)]

Originally Posted by OneOfOne

At the moment I think they would say that a "rogue" planet is one that was formed as part of the "normal" process (ie. around a star) and then thrown out of the system as a result of interactions with other large objects. "Fortunately" the likelihood of finding some of these things is soooooo remote that we may not find any and have to deal with the question...famous last words It is probably more likely to be remain a theoretical discussion.

Actually, they've found quite a few of them...there are quite a few in Orion and in the Taurus complex...Jupiter mass/sized objects floating about in the ether so to speak.

[renormalised (Carl)]

Originally Posted by michaellxv

If there are enough of these objects, is this where some of the missing matter of the universe is hiding? If so, what would the estimate be for how much?

After the Pluto debate a planet has a very specific definition. An object such as a brown dwarf or similar smaller object would not satisfy that definition. If it does not qualify as a star then a new classification would be required.

How would you distinguish between a 'failed star' and a 'rogue planet'? Would there be a significant difference in their compsition?

Even given the likelihood that BD's are more numerous than all the normal stars, their numbers wouldn't add any more than a few percent more mass to what's missing, so you'd still have the majority of the mass to account for.

The definition that the IAU conference came up with is not a good one. It has too may holes in the definition and is rather wishy washy at best. They need to hone the definition a lot more. BD's, are by definition, not planets but sub stellar objects. We have already discussed their classification here, in previous posts. At present, a BD is any sub stellar object of 13 Jupiter masses and greater, which has at some stage in its evolution been able to sustain a short period of deuterium and/or lithium fusion in its core, and forms in the same manner as a star.

Well...mass, for one. That would be the primary determination as to whether we have a rogue planet or a BD. But for massive planets near the cutoff, and those heavier than the cutoff, it would be difficult to separate between BD's and these planets if they were lone objects. Composition wise, they would as near to indistinguishable as you could make them. The only real way to tell them apart would be to actually go to them and probe their internal structure by mapping their gravitational fields.

The only other way to tell them apart would be temperature. But then again, it would depend on the age of the objects. Young giant planets can be very hot objects and therefore hard to tell from low mass BD's of a similar age. Once they reach a certain age, though, they cool much faster than their BD siblings.

[michaellxv (Michael)]

Originally Posted by renormalised

Even given the likelihood that BD's are more numerous than all the normal stars, their numbers wouldn't add any more than a few percent more mass to what's missing, so you'd still have the majority of the mass to account for.

That's what I was thinking. I guess my crackport theory is that DM is a few % BD, a few % black holes, a few % other normal things yet to be itemised and a significant chunk of new fangled stuff that we don't understand yet.

Originally Posted by renormalised

The only real way to tell them apart would be to actually go to them and probe their internal structure by mapping their gravitational fields.

If giant planets have a rocky core. Stars don't. Why not? BD have a core of what?

[renormalised (Carl)]

If giant planets have a rocky core. Stars don't. Why not? BD have a core of what?

Stars don't have rocky cores because their cores are completely ionised, even though many have a substantial amount of heavy elements present. BD's would normally have cores much like stars, except not ionised to the same extent (if at all). Some though, may have a substantial amount of solids present, depending on how they formed and the conditions in their core regions.

Planets are a weird bunch...you can have planets with weak cores or well developed cores, planets with mostly ice and metallic gases and a smattering of scattered heavy elements, small to medium sized rocky cores surrounded by mantles of ice and liquid/metallic gases, or massive rocky cores with little or no ices/metallic gases...and everything in between. You can find numerous examples of all possible internal structures present in the planets they've found.

[xstream (John)]

I have deleted 5 posts from this thread.

Those of you of you who wish to bicker, take it to PM.

[renormalised (Carl)]

Originally Posted by xstream

I have deleted 5 posts from this thread.

Those of you of you who wish to bicker, take it to PM.

Thanks John....he wasn't contributing to the discussion at all.

[Astro78]

well well wasn't this an intersting find. So few of the hobbyist's wanted to listen that these ARE WAY POSSIBLE NEARBY .

Let's comprehend for one second just how close this is - 9.6 Light years, the 2nd closest 'star' of millions x millions we know of. Smack, right there, dark but warm, in many ways sharing the characteristics of a black hole.

Wont be long unitl we share/'find' the closer one(s)

Just as Uranus' axis of spin is unique to the solar system norm, so is the orbit of an intersting object or two.

In fact that's one of my prime theories i want recorded here first and dated; the axis position and relation of the planets are due to a V heavy mass in parallel orbit causing their spin, the orbit of this object varies and is drawn to one planet each pass, temporarily increasing the planets spin. Uranus' unique spin is due a second brown dwarf (yes 2nd in our solar system) orbiting close by Uranus each pass, almost perpendicular to the others.

[Astro78]

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