# Helium plasma in space and its properties

It is said, that, "Most of the Helium in the Universe, is in a plasma state".

Plasma's are now talked of, as the forth state of matter, but this does not seem to be a majority opinion. Plasma's are also normally regarded, to be at a high temperature, I believe because they are formed from elements that would normally be solids at Earth temperatures.

Since the mass of Helium in the Universe is > 20% of the total mass, and the average temperature (CMB), of the Universe, is 2.7K, there must be a lot of Helium Plasma in the Universe at, or below this temperature.

My questions are:

1. 2.7K is very close to the Lambada point of atomic Helium. Does Helium plasma, still have the same Lambada properties as atomic Helium? If so, will Helium plasma, below it Lambada point, be both superfluid and supercondutive?

2. Is there a point, that Helium plasma reverts to atomic Helium and what causes it to revert? I assume there is a point, since some of the small amount of Helium we still have on Earth, trapped in pockets, and which dates from the Earth's birth, would be of the plasma verity, because it origins, are in the Universe.

3. The majority of the Helium in the Universe, is said to be Helium-4. I presume, this is Helium-4 plasma. Apart from the properties mentioned in question 1, are there any other major differences between Helium-4 plasma and atomic Helium-4. If the answer to this question is yes, and the answer to questions 1 & 2 is no, then the differences between the two states, seems so great, that maybe, there is a case for the plasma, to have a different classification, and a different name, even though, their atomic structure, is very similar.

-
You seem to be very confuse about what plasma is. The defining characteristic of a plasma is that it is that a significant portion of the constituent atoms are ionized. –  dmckee Mar 30 '12 at 2:30
Everybody do the lambada! –  user2963 Mar 30 '12 at 2:32
Thank you. Yes I am aware of that, and also that Helium's electrons are no longer bound to its nucleus. There is information about, and comments that suggest, that there is a big difference between these two Helium states. Trouble is' I can find little info, except with regards to Helium plasma's, superconductivity. Is this the only big difference? I know the properties of atomic Helium. What I can't find is the properties of Helium plasma. –  Clive Ballard Mar 30 '12 at 3:38

Most interstellar gas gets ionised by radiation from nearby stars, so the helium will be a mixture of He, He$^+$ and He$^{2+}$. The relative proportions of the neutral and ionised atoms will depend on the local radiation density. In areas well away from stars the ions will eventually recombine with electrons to form neutral He, though this will be slow simply because space is big, so the probablility of the He ion and electron getting close enough will be small.

3. Whether ionised helium is a different state of matter is really down to convention. The plasma is certainly different from neutral helium: for example it conducts electricity. However the transition from neutral to ionised isn't a clear cut phase transition like a gas $\to$ liquid or liquid $\to$ solid phase change, or even the liquid $\to$ superfluid transition.