Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How to tell a gravastar from a black hole   Gravastars have been recently proposed as potential alternatives to explain
the astrophysical phenomenology traditionally associated to black holes,
raising the question of whether the two objects can be distinguished at all.
Leaving aside the debate about the processes that would lead to the formation
of a gravastar and the astronomical evidence in their support, we here address
two basic questions: Is a gravastar stable against generic perturbations? If
stable, can an observer distinguish it from a black hole of the same mass? To
answer these questions we construct a general class of gravastars and determine
the conditions they must satisfy in order to exist as equilibrium solutions of
the Einstein equations. For such models we perform a systematic stability
analysis against axial-perturbations, computing the real and imaginary parts of
the eigenfrequencies. Overall, we find that gravastars are stable to axial
perturbations, but also that their quasi-normal modes differ from those of a
black hole of the same mass and thus can be used to discern, beyond dispute, a
gravastar from a black hole.

11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio