Coldest Place in the Universe

Chris Gondek writes "The Sydney Morning Herald has an article on how NASA has released a high-quality image of the coldest place found in the universe. Five thousand light years from Earth in the constellation of Centaurus, the nebula, a gas cloud formed from a dying star, has a temperature of minus 272 degrees. It is only one degree warmer than absolute zero, the coldest possible temperature, when atoms cease to vibrate and radiate no heat whatsoever. This radiation is the remnant of the Big Bang, the explosion which forged the universe in trillion-degree temperatures. More than 11 billion years later, this heat has cooled to minus 270 degrees, but is still detectable."

Comments

Grumble, grumble - absolute zero

[altairmaine]

As it turns out, absolute zero is not the "coldest possible temperature". It is impossible to attain absolute zero, as a little basic quantum mechanics tells us. Particles will ALWAYS retain some amount of energy, the "Zero Point Energy", which cannot be removed. More accurately, we can say that absolute zero is the lower bound on the range of possible temperatures - but is not included.

Re:Grumble, grumble - absolute zero

[JohnFluxx]

I just thought... one way to perhaps show that you can't reach zero is that to cool something you either need:

*) Something colder, to cool it - but you can't get colder than 0.

*) A bigger space to put the nonzero heat it - but trivally if you expand something with non-zero temperature into an finite space, then the result is still going to be above zero.

*) If it radiates/conducts/etc heat away, then it must be into an area that has a non-zero heat, so that will (instinctively) also radiate an equal or greater amount of heat back again. Hmm, thinking about it this means you can't have a one-way heat shield, or something that absorbes without emitting. (Unless a material stops radiating/conducting below a certain temperature.)

There's probably some other cases I missed - I don't know anything about this field. :) Is there any other way to cool something other than these cases?

Re:Grumble, grumble - absolute zero

[Tim C]

Energy is not quantised. The energy states of a bound particle, eg an electron orbiting a nucleus, are quantised.

The energy of a free particle is not, and can take on pretty-much any value.

Re:Grumble, grumble - absolute zero

[Anonymous Coward]

yes. the zero point energy is correct... but not to be a pest, atoms cannot vibrate as is suggested in the original post. only molecules may vibrate. the zero point energy comes into play for molecules because the energy, E, of a simple harmonic oscillator (simplest approximation) will be:

E = nu ( v + 1/2)

where v is the vibrational quantum number and nu is related to the force contant. nu is positive, and v is always a non-negative integer, so even when v is zero the energy is nu/2. freshman chemistry students are told that this is to accomodate the heisenberg uncertainty principle in that a particle that is not vibrating would have a definite position and momentum.

another poster hinted on what has been stated eloquenty for hundreds of years and restated by homer: in this house, we obey the laws of thermodynamics! the third law states:

"if the entropy of every element in its most stable state at T=0 is taken as zero, then every substance has a positive entropy which at T=0 may become zero, and which does become zero for all perfect crystalline substances, including compounts"

WTF? an alternate statement has more meaning in our context:

"it is impossible to reach T=0 in a finite number of steps".

thus, as altairmaine suggests, it is impossible to reach absolute zero. other posters suggested that it is only possible to cool things by contact with a colder substance. for those people i would suggest doing a google search on the term "adiabatic demagnetization". research into bose-einstein condensates work with clusters of atoms at fractions of a kelvin, and it is not because they have a super-secret stash of a zero-kelvin heat sink. :)

reference: "Physical Chemistry" by Peter Atkins. 5th ed.

Re:Grumble, grumble - absolute zero

[jovlinger]

ah. You have taken the "hell is endothermic" physics test (google that for a laugh: any test whose answers include "take into account the fact that I still have not succeeded in having sexual relations with her" has got to be good).

On a more serious note, look into laser evaporation. It turns out that if you have a laser and an atom, you can tune laser so that only in the presence (sp?) of positive dopler shift (ie, atom moving towards the laser source) will the atom be able to absorb a photon. If you gradually tune the laser to a smaller and smaller band, and you have such a laser pointing from every which way, you have effectively used a laser to cool the atom.

Think of it as shooting ball bearings to stop a bowling ball.

Re:cold radiation??

[dpp]

temperature is defined by the movement of atoms, right? how can microwave radiation have temperature?

It's because the cosmic microwave background has the spectrum of a blackbody with the given temperature (2.7K).

Vibration

[4lex]

The lowest level of energy ("fundamental" energy level of a quantum system), which we can equate to absolute zero, because there is no allowed state with less energy *does* have energy, including vibrational energy. Atoms *cannot* "cease" to vibrate, because by doing so they would violate Heisenberg's indetermination principle (they would have an exactly determinate position _and_ moment).

I hope someone corrects me if I am wrong :)

Re:Someone please explain

[dpp]

and what iluminates it? It's bright enough to see with a telescope, but it's -272?

From the article:

"One can say the Boomerang acts as a refrigerator," said astronomer Lars-Ake Nyman, who measured its temperature using the European Southern Observatory radio telescope in Chile. He did this by comparing signals received from carbon monoxide in the nebula with signals from the background radiation.

So it was done with a radio telescope, possibly SEST, by looking at molecular lines from CO. It sounds like they found that the CO was absorbing some of the background radiation. So it wasn't "seen" with a telescope in the way that you're thinking.

Re:Houston we have a problem here

[Xilman]

Conclusion - unless there is some sort of active cooling, nothing can cool down to less than temperature of the background radiation (3K).

Correct.

There is active cooling in this case, and it works the same as a domestic refrigorator. Both systems cool down because gases are expanded, thereby doing work. That energy has to come from somewhere and it comes from the heat content of the gas: it cools in other words.

At the center of nebulae like these is a star which is driving off the remnants of what was previously its outer layers. That is, its atmosphere is expanding. If the heat loss through expansion is greater than the heat input from the rest of the universe, the gas will cool.

Paul