# Some black holes may actually be Quark Stars

Gold Member
Some black holes may actually be "Quark Stars"

http://www.usatoday.com/tech/scienc...ies+(Tech+-+Science+and+Space+-+Top+Stories)": excerpts below:
"Stellar" black holes, ones only a few times heavier than the sun, may actually be something even weirder called a quark star, or "strange" star.

A physics team led by Zoltan Kovacs of the University of Hong Kong sizes up the issue in the current Monthly Notices of the Royal Astronomical Society. Quark stars are only theoretical right now, but "the observational identification of quarks stars would represent a major scientific achievement," Kovacs says.

First suggested in 1970, a strange star is a collapsed star that doesn't quite crumple enough to turn into a full-fledged black hole and yet is too heavy to become a so-called neutron star (at least 1.4 times heavier than the sun.)\

In a quark star, gravity would be so strong that it squeezes the subatomic particles called quarks right out of the protons and neutron building blocks of the original star's atoms. That would leave behind a solid mass of quark stuff called strange matter, hence the name "strange star."

Earlier in the decade, astronomers suggested that a neutron star called RX J1856, about 400 light-years away (one light-year is about 5.9 trillion miles) was about one-third too small and might be a quark star. But a 2004 Nuclear Physics B journal report showed the star's intense magnetic field explained its size, so it really was a neutron star.
So how is a "quark star" detected ?
So, if size alone won't reveal a quark star, what will? In the new study, Kovacs and his colleagues, Cheng Kwong-sang and Tiberiu Harko, analyze the disks of dust and gas circling supposed black holes. Whipped to high speeds by the intense gravity of a black hole, these disks are thought to heat to high temperatures and emit powerful radiation. For a quark star, the radiation would be about 10% less than predicted around a black hole, they find. And a quark star would give off a dim light (called bremsstrahlung emission), unlike a black hole, emitted by a thin layer of electrons on its surface.

http://en.wikipedia.org/wiki/Bremsstrahlung" [Broken] means braking radiation, produced by the acceleration of a charged particle when deflected by another charged particle. It was discovered over 100 years ago by Nikola Tesla.

So far, no "quark stars" have been confirmed, but:
The find would confirm a "strange-matter hypothesis," suggesting that normal matter will decay into strange matter if it comes into contact with some of the stuff. "It would be a great surprise to most physicists, and most people I think, to discover that matter as we know it is not stable, and it all really 'wants' to turn in to strange matter," Alford adds. So, in theory, like "Ice-9" in Kurt Vonnegut's novel Cat's Cradle, strange matter could eat up the universe.

But Manjari Bagchi of India's Inter University Centre for Astronomy and Astrophysics in Pune says studying pulsar pairs will reveal whether quark stars exist sooner, based purely on their orbits, not on the brightness or dimness of the stars. Or finding a neutron star that weighs less than the sun would mean that it has to be a quark star, he says, because neutron stars wouldn't have enough gravity to hold their neutrons together at that size.

If strange matter exists, though, Alford suggests it might be the culprit for the dark matter observed only by its gravitational effects. Although dark matter can't be seen (it's literally dark to telescopes), it outweighs normal matter by about six times, judged by its gravitational effects throughout the universe. Some dark matter might just be "strangelets" roaming the cosmos, blasted free from quark stars.

Finally:
But Manjari Bagchi of India's Inter University Centre for Astronomy and Astrophysics in Pune says studying pulsar pairs will reveal whether quark stars exist sooner, based purely on their orbits, not on the brightness or dimness of the stars. Or finding a neutron star that weighs less than the sun would mean that it has to be a quark star, he says, because neutron stars wouldn't have enough gravity to hold their neutrons together at that size.

If strange matter exists, though, Alford suggests it might be the culprit for the dark matter observed only by its gravitational effects. Although dark matter can't be seen (it's literally dark to telescopes), it outweighs normal matter by about six times, judged by its gravitational effects throughout the universe. Some dark matter might just be "strangelets" roaming the cosmos, blasted free from quark stars.

To summarize: Dark Stars should:

Have mass more than 1.4 times our sun​
Have 10% less mass than predicted around a (minimal?) black hole​
If dark stars are in fact, dark matter, they should weigh about 6 times that of normal matter​

PFer's are a pretty tough crowd, is there anything the article missed ?

Could quark stars cores contain the elusive: quark-gluon plasma created/detected at RHIC ?

Rhody...

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Chronos
Gold Member

Quark stars could fill the gap between the mass of neutron stars and stellar black holes - it is a pretty big gap. They would be very dim and difficult to detect.

Interesting, thanks for the post.

I'd have more to say,maybe, but Chronos quote always distracts me (heh,heh)

In the beginning the Universe was created. This has made a lot of people very angry and has been widely regarded as a bad move.

Ok, I have regained what little composure I possess:

In a quark star, gravity would be so strong that it squeezes the subatomic particles called quarks right out of the protons and neutron building blocks of the original star's atoms

I don't know enough about quarks to comment...do they have a degeneracy pressure, like say electrons...
they are spin 1/2 particles so Pauli exclusion applies, right??? Electron degeneracy pressure is computed here,
http://en.wikipedia.org/wiki/Electron_degeneracy_pressure

so I guess somebody knows what it is for quarks and whether that fits the described "strange star" at all....??

Gold Member

Thanks for the responses:

I have a question, does current thinking/theory predict that deconfined quarks in the form of quark-gluon plasma exist in the core of Quark Stars ?

Rhody...

Thanks for the responses:

I have a question, does current thinking/theory predict that deconfined quarks in the form of quark-gluon plasma exist in the core of Quark Stars ?

Rhody...

We unfortunately have no way of knowing this. Our current theory does, in fact, allow such states to exist. Whether they represent reality, though, is another question.

Our current theory which rules in the high density matter inside a neutron star is quantum chromodynamics (QCD). As one ventures deeper into a neutron star, the pressure will change, as will the density and temperature. The way pressure behaves as density and temperature changes is called the equation of state. Different types of matter have different equations of state, and there have been a large number of proposed equations of state to predict how matter behaves at the extreme conditions of a neutron star.

Because a neutron star is held up by the nucleon-nucleon interaction pressure, this equation of state really affects the size of the neutron star. The mass, and the pressure behavior, also depend on the mass of the star.

Currently, our observations of the masses and radii of neutron stars have significant errors associated with the measurements. In fact, every proposed realistic equation of state cannot be ruled out with our observations, whether it be the equation of state that predicts quark stars, strange stars, less exotic neutron stars, or something different.

stevebd1
Gold Member

Thanks for the responses:

I have a question, does current thinking/theory predict that deconfined quarks in the form of quark-gluon plasma exist in the core of Quark Stars ?

Rhody...

It's a bit old but this is an interesting article regarding phase transitions in neutron stars-

http://www.lbl.gov/Science-Articles/Archive/sb/Nov-2004/03-neutron-stars.html" [Broken]

and a couple of papers that look at quark deconfinement in neutron/strange stars-

http://arxiv.org/abs/0705.2708v2
Neutron Star Interiors and the Equation of State of Superdense Matter

http://arxiv.org/abs/astro-ph/0407155
Strange Quark Matter and Compact Stars

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Gold Member

It's a bit old but this is an interesting article regarding phase transitions in neutron stars-

http://www.lbl.gov/Science-Articles/Archive/sb/Nov-2004/03-neutron-stars.html" [Broken]

and a couple of papers that look at quark deconfinement in neutron/strange stars-

http://arxiv.org/abs/0705.2708v2
Neutron Star Interiors and the Equation of State of Superdense Matter

http://arxiv.org/abs/astro-ph/0407155
Strange Quark Matter and Compact Stars

Thanks stevebd1,

Those links led me to this:http://www.lbl.gov/Science-Articles/Research-Review/Highlights/1998/PHYS_neutron.html#"

which suggests that from the article:

"First at the center and then in an expanding region, the relatively incompressible nuclear matter will be converted to the highly compressible quark matter phase," says Glendenning. "This conversion to quark matter (which has been likened to the consistency of soup) allows the pulsar to rapidly shrink."

The pulsar's sudden reduction in size results in a "spin-up," much like rotating ice skaters spin faster when they tuck their arms in close to their bodies. For example, a pulsar spinning at 200 rotations per second might, for a time, spin at 202 rotations per second.

meaning if a spinning pulsar can be detected that for a short period increases its rotational frequency, that this may be a signature that in fact, quark-gluon plasma has been created in the interior of the neutron star.

BTW...

Do you happen to know if Dr Norman Glendenning is still alive or not ? I tried searching for an obituary for him and could find none (for free that is).

He had some predictions of the quark-gluon plasma that may be of interest to the BNL folks who are analyzing the RHIC data, and may be of interest to members of the LHC who are about to start colliding those 3.5TEV beams in a week or so.

Its funny, but whenever you are looking into something deeply, it always pays to conduct an extensive search for those who blazed a trail before you did. History repeats this over and over.

From the little I have read so far about Dr Glendenning, it appears he was ahead of his peers, only time and new discoveries will confirm that for sure, though.

Rhody...

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Gold Member

http://arxiv.org/abs/0705.2708v2
Neutron Star Interiors and the Equation of State of Superdense Matter

stevebd1,

This is a good paper, thanks. Glendenning is sited 4 times in the references (192 of them!), it appears that there are about 7 models (see page 4), and that the core appears to be made up of up, down, and strange quarks, and exist in what is known as color superconducting state (see page 12, 3.5). On page 24, the author(s) pose a series of 25 conclusions/questions. It is obvious to me that a great deal of work needs to be done in order to come to grips with the conclusions/questions presented below:

I will address some of the most important open
questions regarding the composition of neutron star matter and its associated
equation of state, and will mention new tools, telescopes, observations, and
calculations that are needed to answer these questions:
• There is no clear picture yet as to what kind of matter exists in the cores of
neutron stars. They may contain significant hyperon populations, boson
condensates, a mixed phase of quarks and hadrons, and/or pure quark
matter made of unconfined up, down, and strange quarks.
• Pure neutron matter constitutes an excited state relative to many-baryon
matter and, therefore, will quickly transform via weak reactions to such
matter.
• Neutron stars made up of pure, interacting neutron matter cannot rotate
as rapidly as the very recently discovered pulsars PSR J1748-2446ad,which
spins at 716 Hz. The equation of state of such matter, therfore, imposes
an upper bound on the equation of state of neutron star matter that is
tighter than the usual P = ǫ constraint (see Fig. 2).
• Charm quarks do not play a role for neutron star physics, since they become
populated at densities which are around 100 times greater than the
densities encountered in the cores of neutron stars. While hydrostatically
stable, “charm” stars are unstable against radial oscillations and, thus,
cannot exist stably in the universe [131].
• Multi-quark states like the H-particle appear to make neutron stars unstable.
• Significant populations of ’s are predicted by relativistic Brueckner-
Hartree-Fock calculations, but not by standard mean-field calculations
which do not account for dynamical correlations among baryons computed
from the relativistic T-matrix equation.
• The finite temperatures of proto neutron stars favors the population of
’s already at the mean-field level.
Rosenfield
• The r-modes are of key interest for several reasons: 1. they may explain
why young neutron stars spin slowly, 2. why rapidly accreting neutron
stars (LMXB) spin slowly and within a narrow band, and 3. they may
produce gravitational waves detectable by LIGO. Knowing the bulk viscosity
originating from processes like n+n− > p++Σ− and the superfluid
critical temperature of Σ−, both are poorly understood at present, will be
key.
• The loss of pressure resulting from the appearance of additional hadronic
degrees of freedom at high densities reduces the (maximum) mass of neutron
stars. This feature may serve as a key criteria to distinguish between,
and eliminate certain, classes of equations of state [6, 7, 185].
• Heavy neutron stars, with masses of around two solar masses, do not automatically
rule out the presence of hyperons or quarks in the cores of
neutron stars [186].
• Depending on the densities reached in the cores of neutron stars, both
Schroedinger-based models as well as relativistic field-theoretical models
may be applicable to neutron star studies.
• The density dependence of the coupling constants of particles in ultradense
neutron star matter needs be taken into account in stellar structure
calculations. Density dependent relativistic field theories are being developed
which account for this feature..
• The models used to study the quark-hadron phase transition in the cores
of neutron stars are extremely phenomenological and require considerable
improvements.
• If quark matter exists in the cores of neutron stars, it will be a color
superconductor whose complex condensation pattern is likely to change
with density inside the star. The exploration of the numerous astrophysical
facets of (color superconducting) quark matter is therefore of uppermost
importance. What are the signatures of color superconducting quark matter
in neutron stars? So far it has mostly been demonstrated that color
superconductivity is compatible with observed neutron star properties.
• A two-step quark-hadron phase transition (1. from nuclear matter to regular
quark matter, 2. from regular quark matter to color superconducting
quark matter) may explain long quiescent gamma-ray bursts due to the
two phase transitions involved.
• Are there isolated pulsar that are spinning up? Such a (backbending) phenomenon
could be caused by a strong first-order-like quark-hadron phase
transitions in the core of a neutron star [105, 187, 188].
• Was the mass of the neutron star created in SN 1987A around 1.5M⊙?
And did SN 1987A go into a black hole or not? If the answer to both questions
were yes, a serious conflict with the observation of heavy neutron
stars would arise. On the other hand, it could also indicate the existence
generically different classes of “neutron” stars with very different maximum
masses.
• Sources known to increase the masses of neutron stars are differential rotation,
magnetic fields, and electric fields. Some of these sources are more
effective (and plausible) than others though.
• Nuclear processes in non-equilibrium nuclear crusts (e.g. pycnonuclear reactions)
and/or cores (heating caused by changes in the composition) of
neutron stars can alter the thermal evolution of such stars significantly.
We are just beginning to study these processes in greater detail.
• What is the shell structure for very neutron rich nuclei in the crusts of
neutron stars?
• Do N=50 and N=82 remain magic numbers? Such questions will be addressed
• Are there pulsars that rotate below one millisecond? Such objects may be
composed of absolutely stable strange quark matter instead of purely gravitationally
bound hadronic matter. Experimental physicists have searched
unsuccessfully for stable or quasistable strange matter systems over the
past two decades. These searches fall in three main categories: (a) searches
for strange matter (strange nuggets or strangelets) in cosmic rays, (b)
searches for strange matter in samples of ordinary matter, and (c) attempts
to produce strange matter at accelerators. An overview of these
search experiments is given in table 1.
• Strange stars may be enveloped in a crust. There is a critical surface
tension below which the quark star surfaces will fragment into a crystalline
crust made of charged strangelets immersed in an electron gas [128, 132]
• If bare, the quark star surface will have peculiar properties which distinguishes
a quark star from a neutron star [137, 138, 189, 190].
• A very high-luminosity flare took place in the Large Magellanic Cloud
(LMC), some 55 kpc away, on 5 March 1979. Another giant flare was
observed on 27 August 1998 from SGR 1900+14. The inferred peak luminosities
for both events is ∼ 107 times the Eddington limit for a solar mass
object, and the rise time is very much smaller than the time needed to drop
∼ 1025 g (about 10−8M⊙) of normal material onto a neutron star. Alcock et
al. [18] suggested a detailed model for the 5 March 1979 event burst which
The model assumes that a lump of strange matter of ∼ 10−8M⊙ fell onto
a rotating strange star. Since the lump is entirely made up of self-bound
high-density matter, there would be only little tidal distortion of the lump,
and so the duration of the impact can be very short, around ∼ 10−6 s,
which would explain the observed rapid onset of the gamma ray flash.
The light curves expected for such giant bursts [137, 138, 139, 140] should
posses characteristic features that are well within the capabilities of ESA’s
INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL [192])
launched by the European Space Agency in October of 2002.

Rhody...

interior charge function...

Can anyone here demonstrate how to graph the interior charge function of a charged neutron star?

Neutron star interior charge function: (ref.1 - pg. 20 - eq. 24)
$$Q(r) = 4 \pi \int_0^r j^0 e^{\frac{(\nu(r) + \lambda(r))}{2}} dr$$

I specifically do not know what the solution is for the electric current $$I$$ for the relativistic current density $$j^0$$.

Relativistic current density ???: (ref.1 - pg. 21 - eq. 34)
$$j^0 = \frac{I}{A_s} = \frac{dQ(r)}{dt} \frac{e^{\frac{(\nu(r) + \lambda(r))}{2}}}{4 \pi r^2}$$

$$I$$ - electric current
$$A_s$$ - sphere surface area

Reference:
http://arxiv.org/abs/0705.2708v2" [Broken]
http://en.wikipedia.org/wiki/Electric_current#Current_density"
http://en.wikipedia.org/wiki/Sphere#Surface_area_of_a_sphere"

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