Tycho G has been proposed as the surviving binary companion star of the SN 1572 supernova event. The star is located about 6,400±1,500 light-years away in the constellation Cassiopeia. It is a subgiant, similar to the Sun in temperature, but more evolved and luminous.
Tycho G as seen by Hubble Credit: NASA, ESA, CXO and P. Ruiz-Lapuente (University of Barcelona)
SN 1572, or B Cassiopeiae, was a supernova of Type Ia in the constellation Cassiopeia, one of eight supernovae visible to the naked eye in historical records. It appeared in early November 1572 and was independently discovered by many individuals.
Remnant of SN 1572 as seen in X-ray light from the Chandra X-ray Observatory
The red circle visible in the upper left part of this WISE infrared image is the remnant of SN 1572.