Early Galaxies UDFy-38135539
and UDFj-39546284

In an article published in the journal Nature on January 26, 2011, astronomers using the Hubble Space Telescope from 2009 to 2010 revealed the detection of old known galaxy at at a cosmological redshift of Z~10, around 13.2 billion years away. Designated UDFj-39546284, the compact proto-galaxy of young and massive, blue stars is imaged at around 480 million years after the Big Bang (four percent of the universe's current age). The astronomers believe that their observations provide supporting evidence that the universe was forming stars at a very fast rate grew during a 200-million-year time span, when "the rate of star birth increased by about a factor of ten going from 480 million years to 650 million years after the Big Bang," possibly "from gas trapped in a pocket of "dark matter." Located in Constellation Fornax like proto-galaxy UDFy-38135539 (the previous record holder), UDFj-39546284 is visible only at the farthest infrared wavelengths detectable by Hubble, and so even farther objects are thought by the astronomers to require the James Webb space telescope, which is optimized for infrared light observation and planned for deployment later this decade (Hubble new release with more images and videos; and Bouwens et al, 2011).

Bouwens et al, 2011; HUDF09 Team,
ESA, NASA


Larger and jumbo composite images.


Located around 13.2 billion light-years away,
UDFj-39546284 may be the earliest galaxy identified
as such, as of January 26, 2011 (more).

Djorgovski et al, 2006;
Digital Media Center, CalTech





Larger and jumbo illustrationa.





The Epoch of Reionization
began during the Cosmic
Dark Ages, when neutral
hydrogen clouds made the
cosmos opaque to light.

In August and September 2009, astronomers using the new Wide Field Camera 3 on the Hubble Space Telescope discovered several objects in near-infrared light, which appeared to be part of a primordial population of compact, ultra-blue galaxies that had never been detected before, shining through the fog of reionisation (NASA news release). The apparent galaxies were so blue that they appeared to be extremely deficient in elements heavier than hydrogen and helium ("metals"). Confirming the distances to those faint, remote objects required reliable spectroscopy from very large ground-based telescopes and measurement of the redshift of each galaxy’s light. After the announcement of its discovery, UDFy-38135539 was observed with the enormous collecting power of an 8.2-meter telescope in the European Southern Observatory's Very Large Telescope (VLT) array and the extreme sensitivity of the infrared spectroscopic instrument, SINFONI, which allowed a team of astronomers to more precisely estimate UDFy-38135539's distance.

Marcelo Alvarez, Ralf Kaehler, and
Tom Abel; and Alvarez et al, 2009



Larger and jumbo composite images.



UDFy-38135539 was found in the
Reionization Epoch, just around
a few hundred million years after
the Big Bang during the Cosmic
Dark Ages (more).

The astronomers evaluating UDFy-38135539 concluded that its UV radiation was not powerful enough on its own to clear out the hydrogen fog within its local region. They believe that there must have been other galaxies, probably fainter and less massive nearby companions of UDFy-38135539, which were helping make the space around the galaxy transparent. Without the the additional UV radiation, the light from UDFy-38135539 would not have been able to penetrate the surrounding hydrogen fog and arrive at Earth some 13.1 billion years later.

WMAP, GSFC, NASA -- more animation images.

While small, UDFy-38135539 may have had a greater
proportionate population of massive stars that brighter,
hotter, and more massive than even today's luminous
blue variable stars, such as Eta Carinae and the
Pistol Star, that were born with as much as 200 Solar-
masses, or even R136a1 with 265 Solar-masses.

UDFy-38135539 is quite small compared to a modern spiral galaxy. As observed 13.1 billion years ago, it probably only had only a tenth to a hundredth of the stars in the Milky Way today. On the other hand, it probably burned relatively bright for its size with a greater proportionate population of very massive, hot blue stars possible when gas metallicity is low.