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xfahctor
2009-Jan-13, 02:17 PM
Ok, I'm sure this thing doesn't exist, but I wanted to confirm with the experts. I was having a discussion in which someone mentioned a "noble gas giant", a suposed invisible gas giant (though I don't see how it could be invisible). Could or does such an object exist? In the same conversation, was mentioned an "inverted black hole", I assume they meant the theoreticl "white hole". Can someone explain that concept to me a bit? and has a "white hole" ever been observed? could it be observed?
thank you.

Swift
2009-Jan-13, 02:25 PM
Well, Jupiter is 25% helium by mass (reference (http://library.thinkquest.org/28327/html/universe/solar_system/planets/jupiter/interior/composition.html)), so I guess it would be possible for a gas giant to have even more. But it would not make it invisible.

I don't know what an inverted black hole is; my guess would be the same as your's. I'll leave it for someone else to explain white holes.

Ara Pacis
2009-Jan-13, 02:31 PM
Is a "noble gas giant" supposed to be a gas giant comprised of noble gasses? Is it supposed to be invisible because the noble gasses are not generally visible in our experience and that opacity and coloration occur due to the particulates and aerosols of other, more reactive elements?

xfahctor
2009-Jan-13, 02:34 PM
Is a "noble gas giant" supposed to be a gas giant comprised of noble gasses? Is it supposed to be invisible because the noble gasses are not generally visible in our experience and that opacity and coloration occur due to the particulates and aerosols of other, more reactive elements?
I am guess ing that is what they were refering to. It was one of those conversations that left me shaking my head. In retrospect, i probably should have put this in the ATM section.

antoniseb
2009-Jan-13, 02:34 PM
A gas giant made of Helium and Neon would not be invisible. At some level in the atmosphere, the gasses would become compressed enough that they would be opaque and reflective.

Swift
2009-Jan-13, 02:37 PM
I am guess ing that is what they were refering to. It was one of those conversations that left me shaking my head. In retrospect, i probably should have put this in the ATM section.
No, its fine. You're not advocating the idea, just asking about it.

Swift
2009-Jan-13, 02:38 PM
A gas giant made of Helium and Neon would not be invisible. At some level in the atmosphere, the gasses would become compressed enough that they would be opaque and reflective.
Not to mention that trace quantities of other gases would probably give it color, just like Jupiter. Hydrogen is just as "invisible" as helium.

Buttercup
2009-Jan-13, 02:40 PM
a "noble gas giant", a suposed invisible gas giant (though I don't see how it could be invisible).

:confused: I've never heard of such a thing (theorized), and I regularly follow astronomy news. Guess it's thought to be (mostly) comprised of one of the "noble gases" which is invisible to regular light (but might show up on infrared)? Beats me.....

xfahctor
2009-Jan-13, 02:50 PM
:confused: I've never heard of such a thing (theorized), and I regularly follow astronomy news. Guess it's thought to be (mostly) comprised of one of the "noble gases" which is invisible to regular light (but might show up on infrared)? Beats me.....

this was put forth by someone with near zero astronomical knowlage. Now, i consider myself to be pretty dumb, but at least I know this, so I ask questions. This person wasn't even willing to go that far, so I decided to pop in here and get the answers myself.

Ara Pacis
2009-Jan-13, 03:05 PM
Even if a large component of the atmosphere was "invisible" above the compression induced opacity, you'd still have refraction effects. More over, you might have some interesting effects from electricity and magnetic fields. I wonder if this would make the planet glow like a neon light or a plasma sphere or just look like an aurora at the poles.

xfahctor
2009-Jan-13, 03:32 PM
once again, you guys have managed to lend sanity to something which I knew was insane but lacked the articulative abilities to prove it. Thanks much.

Spaceman Spiff
2009-Jan-13, 04:06 PM
A gas giant made of Helium and Neon would not be invisible. At some level in the atmosphere, the gasses would become compressed enough that they would be opaque and reflective.

That's opaque and emissive. Stars (or rather their photospheres) do not reflect much light, but absorb nearly all that is incident upon them.

Helium gas has bound-bound transitions, bound-free transitions, and (if partially ionized) free-free emission/absorption -- all of which would modify the thermal radiation spectrum emitted by photosphere, depending on the temperature.

If this is supposed to be a "helium main sequence" star (fusing helium into carbon in its central core), these would be smaller, hotter and more luminous than their (existing) 3/4(hydrogen)--1/4(helium) main sequence star counterparts.

On the other hand, if this is supposed to be some sort of (pure) helium white dwarf star which has cooled to very low temperatures, then its interior and surface properties would differ from that of the above. Nevertheless, they are not invisible -- nothing is. :lol:

My guess is that the person who proposed it has no idea what it is they're proposing, and just blowing a lot of hot air.

eburacum45
2009-Jan-13, 07:30 PM
I think the original post is talking about a non-emissive object, rather than a star, Spiff; it would probably resemble Neptune most of all, coloured by Rayleigh scattering to a nice blue colour, something like a clear Sudarsky class III giant.
http://en.wikipedia.org/wiki/Appearance_of_extrasolar_planets#Class_III:_Clear

A helium-only planet (or one which only contained noble gases, such as neon, argon, krypton and so-on) would not have any clouds so would be clear, unless it was cold enough for one or more of those gases to condense).

However a noble gas giant would be unlikely to occur naturally, as far as I can see; despite the fact that helium and neon are very common elements in the universe, I can't imagine any process that would allow them to form without including a substantial amount of hydrogen in the mix.

Ara Pacis
2009-Jan-14, 02:46 AM
However a noble gas giant would be unlikely to occur naturally, as far as I can see; despite the fact that helium and neon are very common elements in the universe, I can't imagine any process that would allow them to form without including a substantial amount of hydrogen in the mix.

Or we could custom order one from Magrathea. :)

dgavin
2009-Jan-14, 08:24 PM
I think the whole concept of an invisible planet forgets one thing. Take Ozone for instance, it naturaly absorbs and reemits in the UV spectrum. Technically, it's an invisible gas, even if not a noble gas.

However, say a panet started with 100% Ozone atmosphere, UV absorbsion causes some of the Ozone to break down into Oxygen. After only a few million years of this, there would be a enjough O2 in the atmosphere to give the planet a pale blue color.

So it's sort of a logical falicy to say a planet is invisible. As gasses absorb light (unseen as well as seen), some times the molecules are split into other compounds, or merge with other compounds. Eventualy you no long have a pure gas environment.

Ilya
2009-Jan-14, 08:55 PM
My guess is that the person who proposed it has no idea what it is they're proposing, and just blowing a lot of hot air.

He was blowing a commoner gas.

Spaceman Spiff
2009-Jan-15, 03:32 AM
He was blowing a commoner gas.

:lol::lol::lol::lol: