RX J1856.5-3754
 X-ray image of RX J1856.5-3754 |
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| Observation data Epoch 1996.7 Equinox J2000.0 |
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|---|---|
| Constellation | Corona Australis |
| Right ascension | 18h 56m 35s |
| Declination | −37° 54′ 36″ |
| Apparent magnitude (V) | ~25.6 |
| Details | |
| Mass | 0.9 M☉ |
| Radius | 1.9–4.1 km |
| Age | 1 million years |
| Other designations | |
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RX J185635-3754, 1ES 1853-37.9, 1RXS J185635.1-375433
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| 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 in the constellation Corona Australis.
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.
It was originally thought to be about 150–200 light-years away, but further observations using the Chandra X-ray Observatory in 2002 indicate that its distance is greater—about 400 light-years.
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.
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, therefore it was suggested that it might be a quark star.
However, later refined analysis 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). Thus, RX J1856.5-3754 is now excluded from the list of quark star candidates.
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