RX J1856.5−3754

RX J1856.5−3754 (also called RX J185635−3754, RX J185635−375, and various other designations) is a nearby neutron star in the constellation Corona Australis. It is the closest neutron star to Earth yet discovered.

RX J1856.5-3754

X-ray image of RX J1856.5−3754
Observation data
Epoch 1996.7      Equinox J2000.0[1]
Constellation Corona Australis
Right ascension  18h 56m 35s [1]
Declination −37° 54′ 36″[1]
Apparent magnitude (V) ~25.6[1]
Details
Mass0.9 M☉
Radius19–41 km
Age1 million years
Other designations
RX J185635−3754, 1ES 1853−37.9, 1RXS J185635.1−375433
Database references
SIMBADdata

Discovery and location

RX J1856.5−3754 is thought to have formed in a supernova explosion of its companion star about one million years ago and is moving at 108 km/s across the sky. It was discovered in 1992, and observations in 1996 confirmed that it is a neutron star, the closest to Earth discovered to date.[2]

It was originally thought to be about 150–200 light-years away,[3] but further observations using the Chandra X-ray Observatory in 2002 indicate that its distance is greater—about 400 light-years.[4][5]

RX J1856 is one of the Magnificent Seven, a group of young neutron stars at distances between 130 and 500 parsecs (400 and 1600 light-years) of Earth.

Quark star hypothesis

By combining Chandra X-ray Observatory and Hubble Space Telescope data, astronomers previously estimated that RX J1856 radiates like a solid body with a temperature of 700,000 °C and has a diameter of about 4–8 km. This estimated size was too small to reconcile with the standard models of neutron stars, and it was therefore suggested that it might be a quark star.[4]

However, later refined analysis[5][6] of improved Chandra and Hubble observations revealed that the surface temperature of the star is lower, only 434,000 °C, and respectively the diameter is larger, about 14 km (with account of the effects of general relativity, the observed radius appears about 17 km).[5] Thus, RX J1856.5-3754 is now excluded from the list of quark star candidates.[6]

See also
  • 3C 58, a possible quark star.

References
  1. RX J185635-3754 - an Isolated Neutron Star, F. M. Walter, web page at the Department of Physics and Astronomy, State University of New York at Stony Brook. Accessed on line June 29, 2007.
  2. Rees, Martin (2012). Universe. Dorling Kindersley. p. 528. ISBN 978-1-4093-7650-7.
  3. "The Mystery of the Lonely Neutron Star". European Southern Observatory press release, September 11, 2000. Accessed online at spaceref.com May 20, 2007.
  4. Drake J. J.; et al. (2002). "Is RX J1856.5-3754 a Quark Star?". Astrophys. J. 572 (2): 996–1001. arXiv:astro-ph/0204159. Bibcode:2002ApJ...572..996D. doi:10.1086/340368.
  5. Ho W. C. G.; et al. (2007). "Magnetic hydrogen atmosphere models and the neutron star RX J1856.5–3754". Monthly Notices of the Royal Astronomical Society. 375 (2): 821–830. arXiv:astro-ph/0612145v1. Bibcode:2007MNRAS.375..821H. doi:10.1111/j.1365-2966.2006.11376.x.
  6. Truemper, J. E.; Burwitz, V.; Haberl, F.; Zavlin, V. E. (June 2004). "The puzzles of RX J1856.5-3754: neutron star or quark star?". Nuclear Physics B: Proceedings Supplements. 132: 560–565. arXiv:astro-ph/0312600. Bibcode:2004NuPhS.132..560T. doi:10.1016/j.nuclphysbps.2004.04.094.
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