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 across the sky at 108 km/s.

[5][6] RX J1856 is one of the Magnificent Seven, a group of young neutron stars at distances between 130 and 500 parsecs (420 and 1,630 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.

[2] In 2016 a team of astronomers from Italy, Poland, and the U.K. using the Very Large Telescope reported[9][10] observational indications of vacuum birefringence from RX J1856.5−3754.

A degree of polarization of about 16% was measured from the visible spectrum being large enough to support evidence but not discovery due to the low accuracy of star model and the uncertain direction of the neutron magnetization axis.