APOD: The Coldest Brown Dwarf (2011 Aug 30)

[APOD Robot]

The Coldest Brown Dwarf

Explanation: This cosmic snapshot composed with image data from NASA's Wide-field Infrared Survey Explorer (WISE) satellite captures a multitude of faint stars and distant galaxies toward the constellation Lyra at wavelengths longer than visible light. But the object circled at the center is not quite a star. Cataloged as WISE 1828+2650, it lies within 40 light-years of the Sun and is currently the coldest brown dwarf known. A brown dwarf begins like a star, with the gravitational collapse of a dense cloud of gas and dust, but is not massive enough to achieve the core temperatures and densities that trigger hydrogen fusion, the stable source of a star's energy. Instead the failed star ultimately cools and emits most of its light at infrared wavelengths. Remarkably, brown dwarfs are roughly the size of the planet Jupiter. How cold is WISE 1828+2650? While brown dwarfs have measured surface temperatures of up to 1,400 degrees C (2,600 degress F), this brown dwarf , assigned to spectral class Y, has the estimated temperature of a warm room, less than about 27 degrees C (80 degrees F).

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[blastoff]

if this WISE data starts to indicate that there's way more brown dwarves floating around than previously imagined, could these obscure concentrations of mass begin to account for the perceived missing mass of galaxies (ala "dark matter") ??

[Chris Peterson]

if this WISE data starts to indicate that there's way more brown dwarves floating around than previously imagined, could these obscure concentrations of mass begin to account for the perceived missing mass of galaxies (ala "dark matter") ??

No, for a variety of reasons. Ordinary matter simply does not behave like dark matter- it can't end up in a spherical halo around a galaxy, for instance, but would end up as part of the disc. Observationally, we'd easily detect objects like brown dwarfs as a warm background if there were enough to outmass more luminous matter by a factor of five. And there's no reason to expect intergalactic space to be filled with brown dwarfs, but it is obviously filled with dark matter.

What finding these brown dwarfs does is help to fill in more of the "missing mass"- the 50% or so of ordinary matter that isn't very luminous, and therefore is nearly invisible to our instruments- but not quite. Intergalactic gas and galactic brown dwarfs are probably sufficient to explain this missing mass. Dark matter is still the best explanation for other observed effects, and is a critical component of the strongest cosmological theory.

[bystander]

http://asterisk.apod.com/viewtopic.php?t=24991

[Ann]

Well, we can do better - or cooler - than WISE 1828+2650 in our own solar system! We have a gas dwarf of spectral class, I guess, Z! The temperature of its cloudtops is minus 145 degrees Celsius, which would be 128 degrees Kelvin! Drumroll!!! But the temperature of its core could be as high as 35,500 C. This gas dwarf has never been able to fuse anything whatsoever, but it is still radiating excess heat from its formation about four and a half billion years ago! It contains exactly one Jupiter mass! Its name is... is... is... JUPITER! You may also call it Sol B!

Give it a big hand! A really cool one! And check out the facts here!

Ann

[Dave]

Life?

[Boomer12k]

And is quickly losing what little heat it has left, no doubt...

:-----======

[neufer]

And is quickly losing what little heat it has left, no doubt...

:-----======

Unfortunately, the explanation forgot to mention that:
brown dwarfs are indeed heated by nuclear fusion
...just not by nuclear (light) HYDROGEN-1 fusion.

WISE 1828+2650 will probably be kept nice & toasty by (heavy hydrogen)
deuterium fusion long after the Sun has become a planetary nebula.

<<Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth. Brown dwarfs occupy the mass range between that of large gas giant planets and the lowest-mass stars; this upper limit is between 75 and 80 Jupiter masses (M_J). Currently there is some debate as to what criterion to use to define the separation between a brown dwarf and a giant planet at very low brown dwarf masses (~13 M_J ), and whether brown dwarfs are required to have experienced fusion at some point in their history. In any event, brown dwarfs heavier than 13 M_J do fuse deuterium and those above ~65 M_J also fuse lithium.>>

We have a gas dwarf of spectral class, I guess, Z! The temperature of its cloudtops is only -145 degrees Celsius - that would be 128 degrees Kelvin! Drumroll!!! But the temperature of its core could be as high as 35,500 C. This gas dwarf has never been able to fuse anything whatsoever, but it it still radiating excess heat from its formation about four and a half billion years ago! It contains exactly one Jupiter mass! Its name is... is... is... JUPITER!

Jupiter is kept warm by solar heat & nuclear fission.
Jupiter is NOT a star because there is no fusion taking place.

[Johno]

Would it be correct to assume crushing gravity?

[dankostojnic]

As a physician, I've spent much time watching pulmonary X-rays, so I just have an impression that there is a large "cavity" just left of the brown dwarf which seems to be like expelled from it. This is just an impression

[neufer]

As a physician, I've spent much time watching pulmonary X-rays, so I just have an impression that there is a large "cavity" just left of the brown dwarf which seems to be like expelled from it. This is just an impression

Diffraction spikes
caused by a four-vane spider

There was an old lady who swallowed a spider,
That wriggled and wiggled and tiggled inside her;
She swallowed the spider to catch the fly;
I don't know why she swallowed a fly - Perhaps she'll die!

[John Olson]

While Wikipedia says that “brown dwarves are fully convective,” at 27C and several atmospheres of pressure, there are lots of chemical compounds that would be liquid, solid, or solutes. So there must be clouds and there might be rain on this brown dwarf. And it must get warmer with depth, so the raain would only fall so far before it evaporated and convected up again. Now, I suppose my imagined condensed species may well be advected deeper into the atmosphere by the prevailing hydrogen convection, but nonetheless I don't think it's outrageous to propose that there could be a “wet” layer on such a star, a zone where you could have enough liquid water to be biologically interesting.

I doubt that life could evolve in such a turbulent environment, but if it were seeded from the outside, you might evolve life forms capable of keeping themselves in the wet layer indefinitely. It makes me think of Larry Niven's Integral Trees, though it's a very different environment.

Pure speculation, of course. But fun to think about.

[stephen]

Having lived through an entire Texas summer of triple-digit heat, this place sounds absolutely comfortable!

[Matt]

With those temperatures, is it hypothetical to cruise around in a balloon? Or would the dense atmosphere destroy us?

[Iron Sun 254]

More like the gravity would crush you. With a mass about 10 times that of Jupiter but a radius similar or even smaller than Jupiter, the gravitational pull at the top of the atmosphere would be more than 20 times that of the Earth. An average person would weigh a ton and a half. A balloon could theoretically float carrying instruments (because buoyancy is about balancing out the weight of the surrounding medium so gravity shouldn't be an issue) but no human could survive that.

[Matt]

Sweet, thanks for the info.

[geckzilla]

Is there even a solid surface to be crushed against by gravity? Pretending the atmosphere won't burn a human dropped onto the brown dwarf, what would kill the person - being pulled by the gravity or crushed by the atmospheric pressure? Or perhaps you'd fall towards it so quickly that you'd smash against the atmosphere kind of like dropping off a tall bridge into water.

[Chris Peterson]

Is there even a solid surface to be crushed against by gravity? Pretending the atmosphere won't burn a human dropped onto the brown dwarf, what would kill the person - being pulled by the gravity or crushed by the atmospheric pressure? Or perhaps you'd fall towards it so quickly that you'd smash against the atmosphere kind of like dropping off a tall bridge into water.

There are so many ways to die.

As previously noted, brown dwarfs are about the size of Jupiter, but much more massive. Consequently, by the time you are actually at the top of their atmospheres, the gravitational field is very large. You can beat that by orbiting, but you can't orbit in the atmosphere itself without burning up meteoritically.

Many brown dwarfs are undergoing fusion internally. That means that if you are nearby, there will be all sorts of unpleasant high energy particles to rip apart your DNA and destroy your cells.

You only need to descend a few kilometers into the atmosphere before pressures will exceed those found in the deepest parts of the ocean. I guess the implosion of your spacecraft is quicker than being shredded by radiation of flattened by gravity, though.

A brown dwarf has a convective atmosphere, so I expect that there is some impressive turbulence at the outer edge. Your spacecraft might withstand a few hundred G, but can you?

[orin stepanek]

There are so many ways to die.

http://en.wikipedia.org/wiki/1000_Ways_to_Die

[Mokurai]

Is there even a solid surface to be crushed against by gravity?

That's not how gravity works. You would be crushed against the floor of your balloon, or your chair, or whatever other solid surface you brought with you that was not falling into the star.

[Chris Peterson]

Is there even a solid surface to be crushed against by gravity?

That's not how gravity works. You would be crushed against the floor of your balloon, or your chair, or whatever other solid surface you brought with you that was not falling into the star.

I assume she meant a surface that would crush you when you ultimately hit it. Certainly, the fluid interior of a brown dwarf will reach a density that by human standards we'd call "solid". But you'd never get that far, since in free fall you'd burn up in the atmosphere long before you got that deep, and even if you managed to avoid becoming a meteor, you'd be crushed by the atmospheric pressure before gravity caused you any serious problems.

[geckzilla]

Yeah, I meant that, but I also meant ... like, if you try to stand on water, you sink through it. But if you hit it at sufficient velocity you'd break bones or generally get pulverized. I don't know if the same effect could happen with a gas. Maybe it would depend on how gradual the density of the gas is.

[Chris Peterson]

Yeah, I meant that, but I also meant ... like, if you try to stand on water, you sink through it. But if you hit it at sufficient velocity you'd break bones or generally get pulverized. I don't know if the same effect could happen with a gas. Maybe it would depend on how gradual the density of the gas is.

In essence, that's what happens to a meteor. As a meteoroid drops lower in the atmosphere, it experiences a ram pressure of tens of megapascals, which translates to a deceleration of a few hundred G. That's essentially like hitting a brick wall (and is why large meteoroids typically fragment explosively during their entry). So yes, if you had some sort of ablative heat shield suit that kept you from burning up, you'd certainly experience deceleration forces sufficient to convert you to a mildly viscous liquid in the bottom half of that suit.

[geckzilla]

Well, that would be a unique way to die...

[jackkessler]

While this discussion is interesting it is beside the point. A considerably more interesting question is not whether human being could survive on the surface of a brown dwarf, but whether viruses or even bacteria could. The effects of gravity on creatures at that scale is insignificant on earth. Would they be able to endure on a brown dwarf? Or to evolve there in the first place?

I am not impressed with the radiation argument. We live near a star that produces vastly greater amounts of vastly more energetic radiation and we do just fine with it. The surface would be shielded from thermonuclear processes in the core by the entire radius of the brown dwarf.

If a microbiota could exist there, while it is unlikely that large talking apes such as ourselves would arise, evolution in entirely other directions might well take place.