Starburst Galaxy - Starburst Definitions

Starburst Definitions

Several definitions of the term starburst galaxy exist and there is no strict definition on which all astronomers agree. However, many generally agree that the definition must in some way be related to these three factors:

1. the rate at which the galaxy is currently converting gas into stars (the star-formation rate, or SFR)
2. the available quantity of gas from which stars can be formed
3. comparison of the timescale of star formation with the age or rotation period of the galaxy.

Commonly used definitions include:

• Continued star-formation with the current SFR would exhaust the available gas reservoir in much less than the age of the Universe (the Hubble Time). This is sometimes referred to as a "true" starburst.
• Continued star-formation with 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, normalised by the past-averaged SFR is much greater than unity. This ratio is referred to as the birthrate parameter.