1. What is a Quark Star?
A quark star is a hypothetical neutron star with a core of
superdense strange quark matter. The basic principle is that the
matter within a quark star is more densely packed, even than
nuclear matter. This ‘squashed’ area is thought to be composed of
free quarks, or crystallized [material arranged into a lattice] sub-
nuclear particles, rather than neutrons.
To understand a quark star, we must consider a neutron star.
The most compact solid objects in the universe known to exist are
neutron stars; 16 miles across and about 1.5 times as massive as
our Sun. The density is perhaps a thousand million million tons per
cubic metre,1000 million million times that of water.(Moore 0,
p.269) (Spacedaily.com 2008)
A neutron star is the result of an area of space, with extremely high
mass, and small volume. They are usually formed by the
gravitational collapse of a giant star at the end of a supernova.
This collapse is caused when the star can no longer sustain tqhe
processes that counteract the crushing effects of gravity on the
mass of the star. (Odenwald n.d.)
The theory is that within this collapsing star, gravitational pressure
is high enough to overcome the nuclear bonds that repel normal
matter, creating neutron degenerate matter; where electrons fuse
with protons, creating a substance consisting of nothing but
neutrons. This is a ‘typical’ neutron star.
A hypothetical upper limit to this mass is the Tolman-
Oppenheimer-Volkoff limit, and mass more concentrated than
this is thought to degenerate into quark matter, or collapse into a
black hole. Many scientists believe that there would be no neutron
to quark phase change, and that such objects would collapse
immediately into black holes(Seggewiss & de Boer 2009, p.233)
Anyone who has seen ice melt has seen matter change phases,
and when electrons, atoms and other specs of matter change
quantum phases, they behave just as differently as do ice and
water in a glass. “ - (Hulet 2006)
Quark stars are the product of the ‘strange matter’ hypothesis.
The protons and neutrons of normal matter in the everyday world
are made of two types of quark –‘up’ and ‘down’. This baryonic

2. matter is the most predominant form of matter we experience, and
it is matter than includes atoms of any sort.
A quark star can be seen as a single gigantic hadron (a proton or
neutron), but consisting of many quadrillions of quarks rather than
the typical three, which comprise a ‘normal’ hadron. (Annisimov
n.d.)
Strange matter, however, is composed of up, down, and strange
quarks. Its properties are thought to be different from normal
matter. Strange matter is expected to be colour superconducting.
This means that it’s constituent quarks form ‘cooper pairs’. These
pairs only interact with quarks from their flavour (type); so ‘up’ pair
with ‘up’ and so on(Mark Alford et al. 1998). Like the matter in a
neutron star this is a degenerative state, and can only be
overcome by additional gravitational pressure. This pressure
causes a collapse into the next (and hypothesized final) state of
matter, a black hole.
The problem with strange matter is that it has not yet been
accepted hypothetically, let alone physically observed.
"Strange matter may exist or it may not…It's not proven
theoretically - it's an open issue." (Shiga 2007)
How would a Quark Star form?
Certain neutron stars more massive than the Tolman-
Oppenheimer-Volkoff limit break down their neutron degenerate
matter into its constituent parts; up quarks, and down quarks.
Some of these quarks possibly become strange quarks (a
different flavour), and create strange matter.
“Calculations suggest that at sufficiently high temperatures or
pressures.. the baryons and mesons either smash into each other
so hard, or get so severely squashed, that they burst open. The
result should be a soup of free quarks and gluons..(Baez 1998)
This strange matter behaves differently to neutron degenerate
matter;
In a neutron star, it is the degeneracy pressure between neutrons
that keeps the body from collapsing into a black hole - in a quark
star, it is the pressure between quarks.(Annisimov n.d.)

3. How would we detect a quark star?
Quark stars would be hard to distinguish from neutron stars, in part
because the strange quark matter could be enveloped in a shell of
normal matter(Minkel 2002)
But, there are a number of ways that we could detect quark star
candidates.
Over-dense Neutron Stars
Quark stars that appear to be too ‘small’ in size for their mass
imply that some of their matter is packed tighter than nuclear
matter, and although we have no direct observational evidence of
a quark star yet, a number of overly dense neutron stars have
been put forward as candidates.
RX J1856.5-3754(Drake et al. 2002), a neutron star located in
Corona Australis, and 3C 58, a pulsar located in Cassiopeia,
initially appeared too heavy and hot. However later re-
examinations challenged this hypothesis(Slane et al. 2004).
Quark Novae / Super Luminous Supernovae -
Another theory suggests that the conversion from a neutron star to
a quark star creates a release of energy similar to the release in a
supernova event that formed the neutron star.
The transformation.. blasts the neutron star's outer layers into
space at close to light speed. The layers then slam into debris from
the original supernova, creating an intense glow bright enough to
explain the observations of SN 2006gy” - Rachid Ouyed (Shiga
2007)”
This could be an explanation for ‘super luminous supernovae’;
SN 2006gy is a super luminous supernova remnant, two to three
times brighter than the previous record holder for the brightest
supernova, it is now considered a quark star candidate because of
this. (Shiga 2007)
These energetic explosions also could be responsible for the
mysterious ‘Gamma Ray Burst’ phenomena(Bombaci 2006, p.208)
Magentars:
Magnetars are a class of neutron star with an extremely powerful
magnetic field. The effect of this field is a star that generates

4. enormous amounts of radiation, such as x rays and gamma rays.
As of July 2009, 19 such stars are confirmed to exist. (McGill
University 2009)
Another detection theory suggests that the monstrous magnetic
activity of a magnetar could be caused by the properties of the
strange quark matter contained within its core;
“..Colour ferromagnetism in quark matter could be a viable
mechanism for generating immensely powerful magnetic flux as
observed in magnetars” (O'Neill n.d.)
Conclusion:
Currently, Quark stars are purely hypothetical in nature, and until
evidence of strange quark matter is found, other explanations for
magnetars, superluminous supernovae and dense neutron stars
are likely.
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http://www.universetoday.com/2009/01/07/could-quark-stars-explain-magnetars-strong-magnetic-field/
[Accessed December 8, 2009].
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