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No Slide Title Interior matter estimates of rapidly rotating compact stars Nana Pan1, Xiaoping Zheng2 1.College of Mathematics and Physics, Chongqing University of Posts and Telecommunications 2.The institute of Astrophysics, Huazhong Normal University Introduction their differences could result in diverse behaviors. In Fig 3, the light cyan district refers to our predicted Based on many works that a star may spend much compatible models that could satisfy the genuine more time at the lowest point of r-mode instability rotation constraint together with the mass prediction The interior of neutron stars contains nuclear matter window, we can assume it to be another critical limit analyzed by Leahy et al. (2007) at 99.7% confidence at very high densities, this could provide a high- on the attainable rotation frequency. lever. We find that the ordinary neutron star should pressure condition for numerous subatomic particles be excluded. While hyperon star, hybrid star and to compete with each other. Wherefore, the So the genuine limit rotation of compact stars should strange star are supposed to be the best candidates components and properties of interiors in neutron actually be decided by both Keplerian and r-mode for the millisecond pulsar in SAX J1808.4-3658. stars have attracted much attention since the constraints. Since we have synthesized both the Therefore, the star could contain exotic matter either discovery of the first pulsar and then the equations of state, dynamic properties of matter, this hyperon or strange quark matter at super-nuclear confirmation of it to be a fast rotational neutron star. could exert significantly more stringent constraints to region, but we couldn’t tell them from each other, However, the composition of matter for neutron star estimate the matter composition of compact stars. which must depend on more observational at super-nuclear density is still an indeterminacy information such as the thermal emission data. due to the uncertain nuclear physics. This is also the main central question for the astronomy and XTE J1739-285 : A possible sub-millisecond pulsar astrophysics decadal survey in the future. Since the observational phenomena of pulsars and compact radioactive source with high energy are often relate to the nuclear processes and the composition of dense matter in compact stars, it offers us an effective method to probe the signal of matter composition at super-nuclear density. On one hand, the equation of state (EOS) and dynamic properties would affect the structure and evolution behavior of compact stars, on the other hand, we may estimate the correlative information of nuclear matter according to the observational macroscopic Fig 1. Universal treatment of rotational observation compact star properties such as the structure and constraints on the mass-radius relations of compact stars evolution behavior. Hence, many investigators under various theoretical models. spontaneously expect to probe the super-dense Fig 4. Limit rotation frequencies for various equations of state Sequences of Compact stars’ EOS matter through astrophysical observations. of compact stars. These corresponding thick solid lines are However, up to now, constraints of inferred masses genuine upper frequencies. The wine dash-dot-dot horizontal and radii for pulsars on equations of state cannot Mass & Radius relations line represents the 1122 Hz of burst oscillation in the X-ray uniquely examine and distinguish the compositions transient XTE J1739-285 that is interpreted as due to the inside neutron stars, as they could rule out neither rotation of the central neutron star by Kaaret et al. (2007). Corresponding Compare Corresponding normal neutron stars (Ns) nor hyperon stars (Hps) In Fig 4, we find that only some parts of hybrid star Keplerian limit ν k R-mode limit ν R or quark stars (strange stars (Ss) and hybrid stars sequences could spin above 1122Hz. Therefore, we (Hbs)). Genuine upper frequency could conclude that 1122Hz rotation is an obvious ☞ vC = min(vK ,vR ) evidence for the existence of quark matter inside the Along with the abundance of data about spin neutron star of XTE J1739-285, or this possible sub- Observational data frequency for fast rotating pulsars, researchers millisecond pulsar is a hybrid star. Meanwhile, begin to pay much attention to confirming limit spin compared with situation under SAX J1808.4-3658, of pulsars, which is another way to probe into the Limit or exclude the EOS of compact stars the compatible district here is so small that it vvvv(max)< = min( , ) interior of compact stars. obs C K R probably means that the possibility for the existence of compact stars with sub-millisecond period is small. More stringent constraint Method Fig 2. Schematic diagram of thought about our treatment. Conclusion For a uniform rigid compact star with mass M and radius R, there exist some limits on the attainable rotation frequency. Results The composition of matter in the core of neutron stars has attracted much attention owing to its important significance. In our estimation, we try to The most obvious one is the Keplerian limit We have used our method to discuss two rotating probe the inner components of rapidly rotating (/MM )1/ 2 rapidly compact stars. One with millisecond rotation compact stars such as the millisecond pulsar SAX v =××1.042 103 sun Hz, K (/10)Rkm3/2 period, and the other with possible sub-millisecond. J1808.4-3658 and the possible sub-millisecond pulsar XTE J1739-285 in our own way by comparing Which is also called the mass-shedding limit. It is SAX J1808.4-3658: A millisecond pulsar roughly independent of the equation of state. If we the genuine rotation frequencies under different get the frequency of observed pulsar and assume it theoretical models with the observational data, to be the Keplerian limit, we can obtain a critical which may exert more stringent constraint on matter mass-radius relation in the mass-radius plane to composition of compact stars. According to our constrain various equations of state for compact treatment, the SAX J1808.4-3658 is a star with stars. This is the universal treatments as rotation exotic matter and XTE J1739-285 a hybrid star. limit by many investigators which seems to have no Contact: help in distinguishing the composition of super- nuclear matter just as shown in Fig 1. Email: [email protected] Actually, the emission of gravitational radiation following the excitation of non-radial oscillation Acknowledgements modes may lead to the instability of rotating stars, which can be obtained via This work is supported by the National Natural 11 +=0. Fig 3. Limit rotation frequencies for various compact stars. Science Foundation of China under Grant Nos. These corresponding thick solid lines are genuine upper ττGv 10773004 and 10603002, and the project A2008-58 frequencies. The wine dash-dot-dot horizontal line represents Here τ is the damping timescales due to shear, supported by the Scientific Research Foundation of v the 401Hz rotation frequency of the millisecond pulsar in the bulk viscosities and other rubbings, which relates to transient X-ray burster SAX J1808.4-3658 discovered by Chongqing University of Posts and the viscosities of the matter inside neutron stars and Wijnands and van der Klis (1998). Telecommunications.
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