Sign up ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

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.

share|cite|improve this question
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

1 Answer 1

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.

To answer your specific questions:

  1. You're getting mixed up with liquid helium. The interstellar helium is a gas so by definition it can't be a superfluid. In principle it could form a Bose Einstein condensate, but I'd guess that it's temperature is too high for this. You mention superconductivity, but again, it's a gas so it can't be a superconductor.

  2. As I mentioned above, the lowest energy state for helium is a neutral atom, but space is awash with UV light from stars and this ionises the helium atoms. Where it's dark, or on Earth where UV is screened out by the atmosphere, helium will recombine with electrons to form the neutral atom.

  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.

share|cite|improve this answer
Thanks John. What I am really looking for, is a theoretical, like for like, of the 2 states. The lowest temp. found in the Universe is <1K well below He's Lambada point. If the 2 types of He, were together at this temp, would the plasma be a superfluid & supercondutive. As you say, He is easy to ionized here on Earth and the non plasma type is regularly taken to <1K in Labs. I cannot find any records, of similar Lab tests on plasma.- An aside - I also started programming on a Commodore Pet - Purchased on their release date, 1st Oct, 1983. Regards – Clive Ballard Mar 30 '12 at 11:41
A plasma can only form at high temperatures, because at low temperatures the ions and electrons recombine to form neutral atoms again. So you can't study the properties of a helium plasma at 1K. You might argue that space is cold, but actually the helium ions are not cold because they are being heated by UV radiation. If you turn off the starlight the helium ions will cool and form neutral helium again. – John Rennie Mar 30 '12 at 13:15
You are right. Certainly explains why I could not find anything WITH regards to Lab tests on Helium plasma. I certainly got my wires crossed. Actually, there seems very little info out there, relating to the properties of Helium plasma, though there is plenty, relating to the use of Helium plasma in industry, which is not what I was looking for. – Clive Ballard Mar 30 '12 at 22:37

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.