page_title: Starburst galaxy
section_title: Definition
hierarchical_section_title: Starburst galaxy / Definition
caption_attribution_description: English: Visible as a small, sparkling hook in the dark sky, this beautiful object is known as J082354.96+280621.6, or J082354.96 for short. It is a starburst galaxy, so named because of the incredibly (and unusually) high rate of star formation occurring within it. One way in which astronomers probe the nature and structure of galaxies like this is by observing the behaviour of their dust and gas components; in particular, the Lyman-alpha emission. This occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so. This emission is interesting because this light leaves its host galaxy only after extensive scattering in the nearby gas — meaning that this light can be used as a pretty direct probe of what a galaxy is made up of. The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) [1] is investigating the same effect in galaxies that are closer by. Astronomers chose fourteen galaxies, including this one, and used spectroscopy and imaging to see what was happening within them. They found that these Lyman-alpha photons can travel much further if a galaxy has less dust — meaning that we can use this emission to infer how dusty the source galaxy is. The LARS study relies heavily on the high resolving power of Hubble. When Hubble is decommissioned, no telescope will be able to make observations like this in the far ultraviolet part of the spectrum — meaning that small, glittering galaxies imaged and probed by studies like LARS may give us some of the most detailed data we have to work with for some time to come.
context_page_description: A starburst galaxy is a galaxy 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, however, starburst galaxies can experience star formation rates that are more than a factor of 33 times greater. 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, and IC 10.
context_section_description: 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, normalised by the past-averaged SFR, is much greater than unity. This ratio is referred to as the "birthrate parameter".
caption: Light and dust in a nearby starburst galaxy[2]
exif: {"Image ImageDescription": "Visible  as a small, sparkling hook in the dark sky, this beautiful object is  known as J082354.96+280621.6, or J082354.96 for short. It is a starburst  galaxy, so named because of the incredibly (and unusually) high rate of  star formation occurring within it. One  way in which astronomers probe the nature and structure of galaxies  like this is by observing the behaviour of their dust and gas  components; in particular, the Lyman-alpha emission.  This occurs when electrons within a hydrogen atom fall from a higher  energy level to a lower one, emitting light as they do so. This emission  is interesting because this light leaves its host galaxy only after  extensive scattering in the nearby gas \u2014 meaning that this light can be  used as a pretty direct probe of what a galaxy is made up of. The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) [1] is investigating the same effect in galaxies that are closer by.  Astronomers chose fourteen galaxies, including this one, and used  spectroscopy and imaging to see what was happening within them. They  found that these Lyman-alpha photons can travel much further if a galaxy  has less dust \u2014 meaning that we can use this emission to infer how dusty the source galaxy is. The  LARS study relies heavily on the high resolving power of Hubble. When  Hubble is decommissioned, no telescope will be able to make observations  like this in the far ultraviolet part of the spectrum \u2014 meaning that  small, glittering galaxies imaged and probed by studies like LARS may  give us some of the most detailed data we have to work with for some  time to come. Credit: ESA/Hubble & NASA, M. Hayes Notes [1] Hayes, \u00d6stlin et al., The Lyman Alpha Reference Sample: extended Lyman alpha halos produced at low dust content, The Astrophysical Journal, 2013."}