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A Relic galaxy is a dense, compact ($R_{⊙} < 2 kpc$) galaxy made up of ancient stars (in the order of $t >10 Gyr$).

The determination of this suspected class of galaxy is made from the analysis of star formation histories and observed structural properties. The growth of relic galaxies has progressed differently than the average population of galaxies, and they tend to be extreme outliers by this metric. According to previous calculations by astronomers, one in every thousand massive galaxies is a relic of the early universe. It's an almost esoteric term that describes a galaxy whose properties are still largely the same as when it formed billions of years ago.

A-typical formation
When a new galaxy forms, there are typically several structures that appear within the first billion years. A supermassive black hole at the center, globular clusters surrounding the galactic center, and the formation of a central galactic bulge comprising metal-poor stars. The central black hole plays a key role in regulating galactic growth by limiting the amount of additional matter added. Relic galaxies, however, are surmised to have followed a different evolutionary path than the prescribed two-phase growth channel assumed for the overwhelming majority of massive galaxyies observed and studied so far.

Once the Supermassive black hole (SMBH) and the core of the galaxy are formed at $z ~ 2$, the galaxy skips the second phase, remaining structurally untouched and without further mass and size increases. These galaxies then, are relics from the early (z ~ 2) universe. A galaxy of this class will contain a larger SMBH than what is expected according to its velocity dispersion or bulge mass.

The typical relic galaxy comprises an overwhelming quantity of aging stars (born 10+ billion years ago) and few newer stars. There have been little to no successive generations of star formation for billions of years. This lack of further star formation is distinguished by a heavy presence of older (red) stars and the lack of newer (blue) stars. This galactic red cast has led astronomers to nickname these galaxies "red and dead." It is estimated that only one out of every thousand galaxies is a relic galaxy. Another tell-tale sign of relic galaxies lies in the ancient globular clusters that swarm around them. These reddish clusters are highly indicative that new star formation has been minimized.

The massive, local galaxy, NGC 1277 which is part of the [Perseus Cluster]] 240 million light-years from Earth, and comprising only stars born 10+ billion years ago, is a prime candidate for this model. It was identified as such by a team led by Dr. Ignacio Trujillo from the Instituto de Astrofísica de Canarias, Spain. The galaxy has twice as many stars as our Milky Way Galaxy, but physically it is as small as one quarter the size of the Milky Way. Unlike other galaxies in the universe, NGC 1277 is in a state of ‘arrested development’ and has not undergone further star creation since its early formation.

Candidate galaxies

 * [NGC 1271]]