September 24, 1997: Astronomers using the Hubble telescope have taken their first direct look in visible light at a lone neutron star. This view offers a unique opportunity to pinpoint the star's size and to narrow theories about the composition and structure of this bizarre class of gravitationally collapsed, burned out stars.
The Hubble results show that the star [marked by white arrow] is very hot and can be no larger than 16.8 miles (28 kilometers) across. These findings prove that the object must be a neutron star, for no other known type of object can be this hot, small, and dim.See the rest:
Credit: Fred Walter (State University of New York at Stony Brook) and NASA