@article{e64e129e2fc044c494719d49e6929cac,
title = "Approximate universal relations for neutron stars and quark stars",
abstract = "Neutron stars and quark stars are ideal laboratories to study fundamental physics at supra nuclear densities and strong gravitational fields. Astrophysical observables, however, depend strongly on the star's internal structure, which is currently unknown due to uncertainties in the equation of state. Universal relations, however, exist among certain stellar observables that do not depend sensitively on the star's internal structure. One such set of relations is between the star's moment of inertia (I), its tidal Love number (Love) and its quadrupole moment (Q), the so-called I–Love–Q relations. Similar relations hold among the star's multipole moments, which resemble the well-known black hole no-hair theorems. Universal relations break degeneracies among astrophysical observables, leading to a variety of applications: (i) X-ray measurements of the nuclear matter equation of state, (ii) gravitational wave measurements of the intrinsic spin of inspiraling compact objects, and (iii) gravitational and astrophysical tests of General Relativity that are independent of the equation of state. We here review how the universal relations come about and all the applications that have been devised to date.",
keywords = "Gravitational wave, Neutron stars, No-hair theorem, Universal relations, X-ray",
author = "Kent Yagi and Nicol{\'a}s Yunes",
note = "We would like to thank Haris Apostolatos, Joe Bretz, Katerina Chatziioannou, Koutarou Kyutoku, Barun Majumder, George Pappas and Leo Stein for wonderful and insightful collaborations on the universality of neutron stars. We would also like to thank Neil Cornish, Scott Hughes, Jim Lattimer, Luis Lehner, Ben Owen, Paolo Pani, Madappa Prakash, Frans Pretorius, Luciano Rezzolla and Sanjay Reddy and for many discussions and comments on various manuscripts on universality. We would like to thank Fabrizio Canfora, Vladimir Manko and Kentaro Takami for pointing out important references. We further would like to thank Paolo Pani for sharing with us draft of an erratum to one of his papers. We would also like to conclude by thanking Emanuele Berti, Daniela Doneva, Burkhard Kleihaus, Lap-Ming Lin, Barun Majumder, and Paolo Pani for sharing their data with us, which we used to create some of the figures in this review paper. K.Y. acknowledges support from JSPS Postdoctoral Fellowships for Research Abroad and NSF grant PHY-1305682. N.Y. acknowledges support from NSF CAREER Grant PHY-1250636. We would like to thank Haris Apostolatos, Joe Bretz, Katerina Chatziioannou, Koutarou Kyutoku, Barun Majumder, George Pappas and Leo Stein for wonderful and insightful collaborations on the universality of neutron stars. We would also like to thank Neil Cornish, Scott Hughes, Jim Lattimer, Luis Lehner, Ben Owen, Paolo Pani, Madappa Prakash, Frans Pretorius, Luciano Rezzolla and Sanjay Reddy and for many discussions and comments on various manuscripts on universality. We would like to thank Fabrizio Canfora, Vladimir Manko and Kentaro Takami for pointing out important references. We further would like to thank Paolo Pani for sharing with us draft of an erratum to one of his papers. We would also like to conclude by thanking Emanuele Berti, Daniela Doneva, Burkhard Kleihaus, Lap-Ming Lin, Barun Majumder, and Paolo Pani for sharing their data with us, which we used to create some of the figures in this review paper. K.Y. acknowledges support from JSPS Postdoctoral Fellowships for Research Abroad and NSF grant PHY-1305682 . N.Y. acknowledges support from NSF CAREER Grant PHY-1250636 .",
year = "2017",
month = apr,
day = "7",
doi = "10.1016/j.physrep.2017.03.002",
language = "English (US)",
volume = "681",
pages = "1--72",
journal = "Physics Reports",
issn = "0370-1573",
publisher = "Elsevier B.V.",
}