PSR J2144−3933

PSR J2144−3933 is a pulsar about 180 parsecs from Earth. It is the coldest known neutron star with a surface temperature less than 42,000 Kelvin as measured by the Hubble Space Telescope. It was previously thought to have a period of 2.84 seconds but is now known to have a period of 8.5098 seconds, which is among the longest-known radio pulsars.
PSR J2144−3933 is also notable for other reasons: its mean pulse profile is very narrow in comparison to the pulse period, with a half-intensity width of less than one degree of longitude. It also has the lowest spindown luminosity of any pulsar at about.
Writing in Nature, astrophysicists M. D. Young and coworkers consider this object and suggest that its existence throws current theories into doubt. They state:
The fact that PSR J2144−3933 is the coldest observed neutron star has been exploited to constrain the properties of dark matter.