RX J1856.5-3754

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**RX J1856.5-3754**
Observation data Epoch 1996.7 (equinox J2000.0)^[1]
X-ray image of RX J1856.5-3754
Constellation (pronunciation)	Corona Australis
Right ascension	18^h 56^m 35^s^[1]
Declination	-37° 54′ 36″^[1]
Apparent magnitude (V)	~25.6^[1]
Details
Mass	0.9 M_☉
Radius	1.9 - 4.1 km R_☉
Luminosity	? L_☉
Temperature	? K
Metallicity	?
Rotation	?
Age	1 million years
Other designations
RX J185635-3754, 1ES 1853-37.9, 1RXS J185635.1-375433
Database references
SIMBAD	data

RX J1856.5-3754 (also called RX J185635-3754, RX J185635-375, and various other designations) is a nearby neutron star. It is believed to have been created by a supernova explosion of its companion star about one million years ago and is moving 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 450 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 3C58). However, this theory is not currently considered to have much supporting evidence.^{[citation needed]}