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 discovered so far.

RX J1856.5-3754
RX J1856.5-3754.jpg
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]
Mass0.9 M
Radius19–41 km
Age1 million years
Other designations
RX J185635−3754, 1ES 1853−37.9, 1RXS J185635.1−375433
Database references

Discovery and locationEdit

Zooming in on the very faint neutron star RX J1856.5-3754

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 hypothesisEdit

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 alsoEdit

  • 3C 58, a possible quark star.


  1. ^ a b c d 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. ^ a b 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. ^ a b c 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. ^ a b 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.

External linksEdit