Gacrux (Gamma Crucis)

The constellation Crux

Gacrux (Gamma Crucis) is the third brightest star in the constellation Crux, contrasting with its three bright, blue-white constellation neighbors by being a red giant M star. In fact, Gacrux (Gamma Crucis) is the nearest red giant to the Earth. If put in place of the Sun, it would extend over halfway to Earth.


At first, Gacrux looks double, with a faint, nearly seventh magnitude A-type companion about 2' away, but this is just a line-of-sight coincidence. Though usually taken to be single, the fact that Gacrux is a mild barium star hints that its surface may have been contaminated by the stellar wind from a companion that evolved first and is now a dim white dwarf. Certainly, Gacrux is variable, by a few tenths of a magnitude. Though little is known of the nature of the variability, it has been classified as a semi-regular variable. It is also blowing a fairly strong, and noticeably variable wind. Its evolutionary status is uncertain. It may already be fusing helium in its core; if so it is in the process of becoming a second-ascent giant, brightening into the realm of the giant stars for the second time – a speculation reinforced by its variability.


visual magnitude 1.59
absolute magnitude -0.56
spectral type M3.5III
surface temperature 3,400 K
luminosity 1,500 Lsun
radius 113 Rsun
mass 3 Msun
distance 88 light-years
position RA 12h 31m 09.9s;
Dec -57° 06' 48"