HUDF-JD2 (UDF 033238.7 -274839.8 or BBG 3179) is a distant, massive, post-

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 formatio ...

that was discovered with the

Hubble Ultra Deep Field The Hubble Ultra-Deep Field (HUDF) is a deep-field image of a small region of space in the constellation Fornax, containing an estimated 10,000 galaxies. The original data for the image was collected by the Hubble Space Telescope from Septemb ...

(HUDF) image. It was the most distant galaxy identified in the HUDF, in 2005. It is located at in the constellation of

Fornax Fornax () is a constellation in the southern celestial hemisphere, partly ringed by the celestial river Eridanus. Its name is Latin for furnace. It was named by French astronomer Nicolas Louis de Lacaille in 1756. Fornax is one of the 88 modern ...

. In a 2005 search for very red galaxies in the HUDF that were not detected at wavelengths shorter than the near-infrared J band, two objects were detected. The second, initially designated UDF033238.7-274839.8, displayed a high

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...

and showed characteristics of a post-starburst galaxy. The derived photometric redshift yielded ''z'' approximately equal to 6.5, which indicates it is most likely being viewed from a time when the Universe was only 830 million years old. The estimated bolometric luminosity of this galaxy is a trillion (10¹²) times the

solar luminosity The solar luminosity (), is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

(the luminosity of the Sun) and it has a mass of approximately . The

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of this object indicates that most of its energy is being emitted by stars with three solar masses or less. Hence, as larger stars will exist for shorter periods, this galaxy has an age of more than 300 million years. The period of initial active star formation in this galaxy may have lasted less than 100 million years, during which the galaxy likely participated in the

reionization In the fields of Big Bang theory and cosmology, reionization is the process that caused matter in the universe to reionize after the lapse of the " dark ages". Reionization is the second of two major phase transitions of gas in the universe (t ...

event. The unusually high mass estimate for this object may be explained by other factors. If it has an

active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not pr ...

, this may reduce the mass estimate to half the current value. The estimate could also be effected by

gravitational lensing A gravitational lens is a distribution of matter (such as a galaxy cluster, cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This ...

, although it is too far away from the nearest visible object that could produce that effect: a foreground

spiral galaxy Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''List of the most distant astronomical objects This article documents the most distant astronomical objects discovered and verified so far, and the time periods in which they were so classified. For comparisons with the light travel distance of the astronomical objects listed below, the age of ...

References

External links

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Hubblesite HUDF.JD2
{{DEFAULTSORT:HUDF-JD2 Starburst galaxies Fornax (constellation) Hubble Ultra-Deep Field Hubble Space Telescope