Apparent radii of neutron stars and equation of state of dense matter
N. Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland
Received:
20
July
2001
Accepted:
20
September
2001
Apparent (radiation) radius of neutron star,
, depends on the star gravitational mass
in quite a different way than the standard coordinate
radius in the Schwarzschild metric, R.
We show that, for a broad set of equations
of state of dense matter,
for the configurations with maximum allowable masses
is very close to
the absolute lower bound on at fixed
M,
resulting from the very definition of
.
Also, the value of at given M,
corresponding to the
maximum compactness (minimum R) of neutron star consistent with
general relativity and condition 
,
is only 0.6% higher than this absolute
lower bound.
Theoretical predictions for are compared with
existing observational estimates of the apparent radii of
neutron stars.
Key words: dense matter / equation of state / stars: neutron / stars: general
© ESO, 2001