Ben-Gurion University of the NegevAstrophysics and Cosmology GroupAstrophysics, Relativity, Cosmology, and Space Physics |
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Speaker: Vladimir Usov (WIS) April 17, 2013 Strange stars and their observational appearance
Strange
stars made almost entirely of deconfined quarks have long been proposed
as a possible alternative to neutron stars. The possible existance of
strange stars is a direct consequence of the conjecture that strange
quark matter (SQM) composed of roughly equal number of up, down, and
strange quarks may be the absolute ground state of the strong
interaction, i.e., absolutely stable with respect to
56Fe. We review briefly the main properties of SQM and its
surface. SQM with the density of ∼ 5 10^14 g/cm^3
might exist up to the surface of strange stars. Such bare strange
stars (BSSs) differ qualitatively from neutron stars which have the
density at the surface (more exactly at the photosphere) of about 0.1-1
g/cm^3. This opens observational possibilities to distinguish BSSs from
neutrons stars. We discuss the thermal emission of photons and
electron-positron pairs from the surface of hot SQM. Since SQM at the
surface of a BSS is bound via strong interaction rather than gravity,
such a star is not subject to the Eddington limit in contrast to a
neutron star, and its thermal luminosity in photons and pairs may be up
to ∼ 10^52 ergs/s or even more. Using the thermal emission
from BSSs as a boundary condition at the stellar surface, we consider
numerically the structure of pair winds from such stars. Thermal
equilibrium of outflowing pairs and photons is not assumed. We find
that for the total luminosity L > 2 10^35 ergs/s, photons
dominate the emerging emission. As L increases from ∼ 10^34
to 10^42 ergs/s, the mean energy of emergent photons decreases from ∼
400 − 500 keV to ∼ 40 keV, as the spectrum changes in shape from that
of a wide annihilation line to nearly a blackbody spectrum with a high
energy (> 100 keV) tail. This differs substantially from the thermal
spectrum expected from a neutron star with the same luminosity and
might help distinguishthe putative BSSs from neutron stars.
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Last updated
by Uri Keshet,
2013 |