Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Do strange stars exist in the Universe?   Definitely, an affirmative answer to this question would have implications of
fundamental importance for astrophysics (a new class of compact stars), and for
the physics of strong interactions (deconfined phase of quark matter, and
strange matter hypothesis). In the present work, we use observational data for
the newly discovered millisecond X-ray pulsar SAX J1808.4-3658 and for the
atoll source 4U 1728-34 to constrain the radius of the underlying compact
stars. Comparing the mass-radius relation of these two compact stars with
theoretical models for both neutron stars and strange stars, we argue that a
strange star model is more consistent with SAX J1808.4-3658 and 4U 1728-34, and
suggest that they are likely strange star candidates.

13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph