Starburst galaxy
A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formation rate of the Milky Way galaxy is approximately 3 M☉/yr, while starburst galaxies can experience star formation rates of 100 M☉/yr or more. In a starburst galaxy, the rate of star formation is so large that the galaxy will consume all of its gas reservoir, from which the stars are forming, on a timescale much shorter than the age of the galaxy. As such, the starburst nature of a galaxy is a phase, and one that typically occupies a brief period of a galaxy's evolution. The majority of starburst galaxies are in the midst of a merger or close encounter with another galaxy. Starburst galaxies include M82, NGC 4038/NGC 4039 (the Antennae Galaxies), and IC 10. Starburst galaxies are defined by these three interrelated factors: The rate at which the galaxy is currently converting gas into stars (the star-formation rate, or SFR). The available quantity of gas from which stars can be formed. A comparison of the timescale on which star formation will consume the available gas with the age or rotation period of the galaxy. Commonly used definitions include: Continued star-formation where the current SFR would exhaust the available gas reservoir in much less than the age of the Universe (the Hubble Time). Continued star-formation where the current SFR would exhaust the available gas reservoir in much less than the dynamical timescale of the galaxy (perhaps one rotation period in a disk type galaxy). The current SFR, normalized by the past-averaged SFR, is much greater than unity. This ratio is referred to as the "birthrate parameter". Mergers and tidal interactions between gas-rich galaxies play a large role in driving starbursts. Galaxies in the midst of a starburst frequently show tidal tails, an indication of a close encounter with another galaxy, or are in the midst of a merger.
