RX J1856.5-3754

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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]
Mass 0.9 M
Radius 1.9–4.1 km
Age 1 million years
Other designations
RX J185635-3754, 1ES 1853-37.9, 1RXS J185635.1-375433
Database references

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 believed to have been created by 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 appeared to confirm that it was a neutron star, the closest neutron star to Earth yet discovered. It was originally thought to be about 150–200 light-years away, but further observations using the Chandra X-ray Observatory in 2002 appear to show that its distance is greater—about 400 light-years. It was once proposed that RX J1856.5-3754 was too small to be a neutron star and may therefore in fact be a quark star (see also 3C 58). However, this theory is not currently considered to have much supporting evidence.[2]

By combining Chandra X-ray Observatory and Hubble Space Telescope data, astronomers previously found that RX J1856 radiates like a solid body with a temperature of 700,000 degrees Celsius and has a diameter of about 4–8 km. This estimated size was too small to reconcile with the standard models of neutron stars, therefore it was suggested that it might be a quark star.[3] However, later refined analysis of improved Chandra and Hubble observations revealed that the surface temperature of the star is lower, only 434,000 degrees, and respectively the radius is larger, about 14 km (with account of the effects of general relativity the observed radius appears about 17 km).[4] Thus, RX J1856.5-3754 is now excluded from the list of quark star candidates.

RX J1856 is one of the Magnificent Seven, a group of young neutron stars at distances between 200 and 500 parsecs (652 and 1630 light years) of Earth.


  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. ^ 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. 
  3. ^ 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. 
  4. ^ 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. 

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