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Quark Stars
BigGar' writes "Astronomers seem to have discovered a new type of star. It would lie between a neutron star and and a black hole in the hierarchy of stars and consist of quark matter. Further observations with the Chandra X-ray telescope will be needed to confirm the results."
Quark stars are a new and interesting idea, but quark matter in general is not a new idea. "Quark matter", more usually "quark plasma" or "quark-gluon plasma", is believed to be the dominant form of matter in the universe just following the big bang. There is also early evidence that it's been witnessed in some of the largest particle accelerators.
In normal matter quarks group together in sets of 3 to form protons and nuetrons. Rare particles, like pions, can be formed from pairs of quarks, but quarks never appear in isolation, for them it's always in groups of 2 or 3. In quark plasmas though there aren't any distinct groups of twos and threes. All the quarks are smushed into a single substance with arbitrarily large numbers of quarks.
One analogy is if atoms are built out of "solid" quarks (in the from of protons and nuetrons), then the quark plasma is like melting them so they all run together. Prior to this announcement the only time that quark plasmas were expected to appear was in the presence of extraordinarily high energies and temperatures.
We could predict that nuetrons stars should exist because the "nuetron degeneracy pressure" which makes them possible was well understood theoretically. The theory that governs quark interaction is known as quantum chromodynamics and is far more complicated. I'm not sure whether anyone knows how to apply it to massive collapsing stars, and it doesn't surprise me if no one ever tried. It will be interesting to see if the existing theory can be made to justify quark stars. If not, well that's when things really start to get exciting.
Does anyone know if all up quarks are the same as all other up quarks...
Well the up quark, like any quark, is not as cleanly defined as the word "particle" might indicate. The up quark and the properties associated are not just a measure of how much "mass" or "spin" has been shoved into a sphere called the quark. The properties of quarks actually come from an extremely complex cloud of virtual particles that pop into and out of existence in close proximity to the area we call the quark. There seem to only be a few stable configurations of energy, spin, and charge that can result in a quark. The properties of the quarks seem to result from some intrinsic properties defining the way these virtual particles can interact, so you can't just put a little more of something into a quark, because that would require changing the rules of the interactions. Unfortunately, the precise details of all of the above is still a subject of some speculation, since no one quite knows for sure all the virtual particles that can pop in and out and all of their properties.
Well, there is no revealed truth in science, so we don't ever know absolutely that something is real. It has happened before that a theory turns out to be based on a house of cards. Most of that time, in retrospect, it can be seen that the theory got way out in front of experiment and so was improperly constrained. That is, the less we've studied an area, the more likely the theoriest are wrong. As facts come in, theories get revised or strengthened.
On the other hand, remember that in physics, most "revolutions" change our understanding of how things work but do not invalidate existing theories in their realm of applicability. For example, relativity didn't kill Newtonian theory. Indeed, that's still where we start today in physics education. Why didn't it? Because at human-scale speeds, with human-scale masses, objects obey Newton's Law pretty well... that's the region in which the theory was derived and it fits the experiments there. At the very fast, it breaks down, and then relativity is needed.
Now, we insist the Universe is "really" relativistic at all speeds, so in that sense the new theory wiped out the old. But we also insist that for slow objects relativity must reduce to Newton's Law (and it does). So the earlier theory reamins a useful, if admittedly inadequate, tool.
The Mongrel Dogs Who Teach
I am one of the authors of a competing paper on RX J1856 that was published yesterday, as well as a co-discoverer of the pulsar in 3C58. In my opinion these results, while definitely a possibility are certainly very preliminary. And in fact, there are other possibilities that make quite a bit more sense.
In the case of RX J1856, there is a ~15% chance that the lack of pulsations (one of the biggest reasons for suspecting a quark star) is simply the result of an unfortunate emitting geometry or viewing alignment. Given that there are ~7 objects known that are similar to RX J1856, having at least one of them in this 15% seems quite likely to me -- and avoids having to invoke a new form of "star stuff".
As for 3C58, the neutron star cooling problem can be mitigated (but not completely removed) by assuming a larger age for the supernova remnant (and therefore the neutron star) -- which expansion measurements and pulsar timing measurements also suggest.
In other words, there are simpler explanations for the facts. Although those explanations certainly wouldn't get as much press...