* Astronomy

Title: Strange Quarks Nuggets in Space: Charges in Seven Settings
Authors: E. S. Abers (UCLA), A. K. Bhatia (NASA/Goddard), D. A. Dicus (UT), W. W. Repko (MSU), D. C. Rosenbaum (SMU), V. L. Teplitz (NASA/Goddard)

We have computed the charge that develops on an SQN in space as a result of balance between the rates of ionisation by ambient gammas and capture of ambient electrons. We have also computed the times for achieving that equilibrium and binding energy of the least bound SQN electrons. We have done this for seven different settings. We sketch the calculations here and give their results in the Figure and Table II; details are in the Physical Review D.79.023513 (2009).

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Title: Do Black Holes End up as Quark Stars ?
Authors: R.K.Thakur

The possibility of the existence of quark stars has been discussed by several authors since 1970. Recently, it has been pointed out that two putative neutron stars, RXJ 1856.5 - 3754 in Corona Australis and 3C58 in Cassiopeia are too small and too dense to be neutron stars; they show evidence of being quark stars. Apart from these two objects, there are several other compact objects which fit neither in the category of neutron stars nor in that of black holes. It has been suggested that they may be quark stars. In this paper it is shown that a black hole cannot collapse to a singularity, instead it may end up as a quark star. In this context it is shown that a gravitationally collapsing black hole acts as an ultrahigh energy particle accelerator, hitherto inconceivable in any terrestrial laboratory, that continually accelerates particles comprising the matter in the black hole. When the energy E of the particles in the black hole is \geq 10^{2}GeV, or equivalently the temperature T of the matter in the black holes is \geq 10^{15}K, the entire matter in the black hole will be converted into quark-gluon plasma permeated by leptons. Since quarks and leptons are spin 1/2 particles, they are governed by Pauli's exclusion principle. Consequently, one of the two possibilities will occur; either Pauli's exclusion principle would be violated and the black hole would collapse to a singularity, or the collapse of the black hole to a singularity would be inhibited by Pauli's exclusion principle, and the black hole would eventually explode with a mini bang of a sort. After explosion, the remnant core would stabilize as a quark star.

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According to the "Strange Matter Hypothesis," which gained popularity in the paranormal 1980's, nuclear matter, too, can be strange. The hypothesis suggests that small conglomerations of quarks, the infinitesimally tiny particles that attract by a strong nuclear force to form neutrons and protons in atoms, are the true ground state of matter. The theory has captivated particle physicists worldwide, including Washington University’s Mark Alford, who, with colleagues, has discovered some strange properties.
Mark Alford, Ph.D., Washington University in St. Louis assistant professor of physics in Arts & Sciences, and collaborators from MIT and the Lawrence Berkeley National Laboratory and Los Alamos National Laboratory, have used mathematical modelling to discover some properties of theoretical "strange stars," composed entirely of quark matter. Alford and his colleagues have found that under the right conditions the surface of a strange star could fragment into blobs of quark material called "strangelets," forming a rigid halo that contradicts traditional strange star models. This means that collapsed stars' nuclear leftovers, like the famously resplendent crab nebula, could be stranger than physicists think.
Alford and his colleagues published their results in a recent issue of Physical Review D 73, 114016 (2006).

The standard account of the dramatic death of a heavy star is that, after exploding in a supernova that rivals a whole galaxy in brightness, what is left is a "neutron star," a profoundly dense remnant, made mostly of neutrons, with a mass one and a half times that of our sun, crammed into an area with the radius of Saint Louis.
A strange star is an alternate ending of this story. If the Strange Matter Hypothesis is correct, then what is left behind is not a neutron star but an even denser strange star, made of quark matter rather than neutrons. And until recently, physicists thought that the two presented very different faces to the world.
A neutron star has a complicated multilayered surface. According to a description by M. Coleman Miller, Ph.D., of the University of Maryland, the deeper portions of the crust has voids that can be likened to Swiss cheese, overlaid by regions with sheets like lasagna, rods like spaghetti, and finally blobs like sprinklings of meatballs on the outside.
A strange star, on the other hand, was generally assumed to have a much simpler surface, consisting of a sharp interface between strange matter and the vacuum of surrounding space.

"A sharp interface between quark matter and the vacuum would have very different properties from the surface of a neutron star. But couldn't strange stars also have complicated surfaces And if they did, could we even tell neutron stars and strange stars apart" - Mark Alford.

Earlier this year, Alford's colleagues concocted a radical proposal. If blobs of quark matter (strangelets) have the right properties, maybe the strange star crust is something more like a kaleidoscopic aura of matter than a melon rind.

"The idea was that the surface of a quark star might be as complicated as that of a neutron star, with a sort of crystalline halo or crust of strangelets. If strangelets exist in reality, they will have a preferred size. If small strangelets are preferable, then big ones will split up into smaller ones. Conversely, if big strangelets are more stable, then small ones could fuse with other small ones--if they happened to bump in to each other--to make big ones" - Mark Alford.

If strangelets prefer to be big, then the strange star's surface will be the conventional simple sharp interface, with particles fused into the main body of the star. But if strangelets prefer to be small, then the surface will evaporate small strangelets to form a crystalline aura of strangelets floating in a sea of electrons.
His colleagues found that if surface tension along the interface and electrical forces within the charge distribution were neglected, then strangelets prefer to be small, and the strange star's surface indeed fragments into strangelets.
To follow, Alford joined the researchers in a more definitive investigation, addressing key parameters like surface tension and electrical forces that were neglected in the original study. Their results show that as long as the surface tension is below a low critical value, the large strangelets are indeed unstable to fragmentation and strange stars naturally come with complex strangelet crusts, analogous to those of neutron stars. Their results will fuel the ongoing debate among astrophysicists about the nature and existence of strange stars.

"A strange star believer would say: See, they showed that if the quark matter surface tension was low, then a strange star would have this strangelet crust, so perhaps some of the objects we think are neutron stars could actually be strange stars. A strange star skeptic would say: Oh well, but the surface tension would have to be absurdly low for that to happen. These results basically show that for any reasonable value of the surface tension there is no crust, and strange stars are completely different" - Mark Alford.

The strange star theory has its staunch defenders, but most physicists think it's merely an interesting, though improbable idea. But Alford and his colleagues are keeping its possibility afloat.

"There is still enough doubt about our understanding of these things, to leave room for speculation that there may be strange stars out there" - Mark Alford.

Source Washington University in St. Louis

Scientists from around the world, including the UK, participating in the CDF collaboration at the Fermi National Accelerator Laboratory, Fermilab, announced today (23rd October) the discovery of two rare types of particles, exotic relatives of the much more common proton and neutron.

"CDF has discovered two new particles which though predicted by our theories, have never been observed before. These are variants on the familiar proton and neutrons found in atoms, but in each case, one of the quarks inside them has been replaced with a much heavier bottom quark" - Dr Todd Huffman of the University of Oxford, one of the UK scientists in CDF.

Like protons and neutrons, the new particles are made of three quarks, the building blocks of matter. There are six different types of quarks: up, down, strange, charm, bottom and top (u,d,s,c,b,t). Protons contain two up quarks and one down quark (u-u-d), while neutrons have two down and one up (d-d-u).
The CDF collaboration has discovered two new three-quark particles involving the bottom quark, featuring u-u-b and d-d-b quark combinations. Quark theory predicts six different types of baryons with one bottom quark. Only one had been observed in the past, and the CDF experiment now accounts for two additional ones.

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