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Published online: 30 September 2009 | doi:10.1038/nchina.2009.191

Stellar astronomy: Pulsar model on the blink

Felix Cheung

Introduction

© (2009) NASA

Pulsars are the 'cosmic lighthouses' of the Universe. Like rotating beacons, they emit electromagnetic radiation that can be seen on Earth as an intermittent blinking. In 2007¹, scientists reported evidence of a pulsar that rotates at 1,122 Hz, corresponding to one rotation about once every millisecond. The swift rotational speed of this pulsar challenged the conventional view that pulsars are rotating neutron stars.

Yuanjie Du at the Chinese Academy of Sciences in Beijing and co-workers² have now proposed a model for the formation of sub-millisecond pulsars. As the basis for their model, they assumed that sub-millisecond pulsars are in fact rotating quark stars formed by the accretion-induced collapse (AIC) of white dwarfs.

Based on this assumption, the researchers found that newborn quark stars can have initial rotational periods of as short as 0.1 ms. The energy loss from the AIC event is also theoretically high enough to produce electromagnetic radiation equivalent to that of normal pulsars, even for quark stars with low masses. Furthermore, the lifetimes of sub-millisecond pulsars should in most cases be long enough that they are likely to be detected in our scans of the cosmos.

The researchers compared their AIC model with the conventional 'accretion spin-up' model. They found that quark stars formed through AIC have rotational periods shorter than 0.5 ms, whereas neutron stars spun up through accretion have rotational periods longer than 0.5 ms. The findings suggest that if a sub-millisecond pulsar is ever to be found, it is likely to be a quark star.

The authors of this work are from:
National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China; Department of Astronomy, Peking University, Beijing, China.

References

1. Kaaret, P. et al. Evidence of 1122 Hz x-ray burst oscillations from the neutron star x-ray transient XTE J1739-285. Astrophys. J. 657, L97–L100 (2009).
    | Article | ADS | OpenURL
2. Du, Y. J., Xu, R. X., Qiao, G. J. & Han, J. L. The formation of submillisecond pulsars and the possibility of detection. Mon. Not. R. Astron. Soc. doi:10.1111/j.1365-2966.2009.15373.x (2009). | Article | OpenURL