the latest on the most distant galaxies
selected publications on distant galaxies
meetings on high-z galaxies
The Early Universe
the first galaxies
JWST News & Events
Galaxies at Redshift 10
Astronomer's Area
Hubble Team Breaks Cosmic Distance Record
NASA's Hubble Space Telescope is an amazing time machine; by
looking back through space, astronomers actually look back
through time. Now, by pushing Hubble to its limits, an
international team of astronomers has shattered the cosmic
distance record by viewing the farthest galaxy ever seen.
Named GN-z11, this surprisingly bright, infant galaxy is
seen as it was 13.4 billion years in the past. The
astronomers saw it as it existed just 400 million years
after the big bang, when the universe was only three percent
of its current age. At a spectroscopically confirmed
redshift of 11.1, the galaxy is even farther away than
originally thought. It existed only 200 million to 300
million years after the time when scientists believe the
very first stars started to form. At a billion solar masses,
it is producing stars surprisingly quickly for such an early
time. This new record will most likely stand until the
launch of Hubble's successor, the James Webb Space
Telescope, which will look even deeper into the universe for
early galaxies
NASA Great Observatories Team Up to Discover Ultra-Bright Young Galaxies
NASA's Hubble Space Telescope and Spitzer Space Telescope
joined forces to discover and characterize four unusually
bright galaxies as they appeared more than 13 billion years
ago, just 500 million years after the big bang. Although
Hubble has previously identified galaxies at this early
epoch, astronomers were surprised to find objects that are
about 10 to 20 times more luminous than anything seen
The Beginning of the Universe
A Timeline of the Universe
This diagram shows a short timeline of the universe. At very early times (< 10-32 seconds), it is thought that the universe had this very rapid inflationary phase, where quantum fluctuations were blown up to macroscopic scales. After this brief period of exponential growth, the universe then transitioned into a more gradual phase of expansion and cooling. At a time of 400,000 years after the Big Bang, protons first recombined with the available electrons in an event known as recombination, leaving photons to wander the universe freely. The universe then entered a dark age for a period of several hundred million years, until the first stars and galaxies formed. Subsequent to this time, galaxies have been merging and coalescing to become larger and more mature systems.
It is now widely agreed that the universe started in a hot big bang. The quantum fluctuations which were present shortly after the Planck time were blown up onto macroscopic scales by a short period of highly rapid growth during the first 10-32 seconds of the universe. The early period of rapid growth is called inflation and is thought responsible for the remarkable degree of homogeneity seen in the early universe as well as the small amounts of structure present then.
Then, what followed this early inflationary phase of the universe was a more gradual, normal evolution, where the universe continued to cool and expand. During this cooling phase, the first protons and neutrons condensed out of the mix, and then hydrogen, helium, lithium, and beryllium froze out. Eventually, when the universe was 400,000 years old, the universe had cooled to the point where the ambient photons in the universe were no longer energetic enough to keep hydrogen ionized. This resulted in one of the first truly great phase changes in the state of elemental hydrogen during our universe's history. Hydrogen  -  which up to this point existed in the fully ionized form as free protons  -  recombined with the available electrons to form neutron hydrogen. At the same time, the ambient radiation  -  now too low energy to ionize hydrogen  -  were simply left free to wander the universe. This background radiation is still with us today in a much cooler form and provides us with one of the first and powerful pieces of evidence for existence of the hot Big Bang. The significance of this epoch is such that it has earned the special name "recombination" to highlight this significance.
The Dark Ages/First Light
This timeline of the universe demonstrates how far back the current generation of deep images bring us. For example, galaxies seen in the Hubble Ultra Deep Field (the deepest image ever taken by human kind) date to as early as 700-900 million years after the Big Bang (5-7% of the age of the universe). Since the first galaxies and stars are thought to form just 200-300 million years after the Big Bang, current observations are now bringing us very close to first light.
As time went on, more matter and stars were pulled onto these overdensities, resulting in the formation of the first galaxies. These galaxies then merged with other galaxies to form larger galaxies  -  and the whole process of galaxy buildup had begun.
The formation of the first stars and first galaxies brought about several fundamental changes in the rapidly evolving universe. For one, these stars provided the universe with its first source of elements heavier than beryllium. While conditions early on in the big bang were not appropriate for the generation of the heavier elements, such elements could easily be generated at the cores of massive stars and then later expelled into the surrounding universe when these stars explode as supernovae. The second profound change brought about this first generation of stars was the introduction of high-energy photons into the universe. Previously, the last the universe had seen of such high-energy photons was during the first 400,000 years of the universe when the universe was still very hot and hydrogen still existed in an ionized state.
Here is a cosmological simulation showing the evolution of galaxies from very early times to the present day. Galaxies start out very small in the universe and then progressively merge to form larger and larger systems. Time is demarcated in the simulation as the cosmic redshift "z." Redshift 30 ("z=30") corresponds to a period roughly 100 million years after the Big Bang, while lower redshifts correspond to later times ("z=0" corresponds to the present day).
These high-energy photons started what was likely a rather extended process by which hydrogen in the universe was reionized. This reionization process apparently began several hundred million years after the Big Bang and finished some 600 million years later. Currently, there is great interest in understanding the properties of the first galaxies because they likely played a key role in this process.
The first generation of small galaxies was likely well in place 400 million years after the Big Bang. Following this initial phase of galaxy formation, galaxies then went through an extended phase of merging and coalescence with other galaxies, whereby they built up from masses of several thousand solar masses to billions of solar masses. This buildup process extended until the universe was roughly two billion years old. Then, due to some feedback process -- now predominantly speculated to be AGN feedback -- it is thought that this buildup process halted and gas accretion and star formation in the most massive galaxies halted and galaxies underwent a much different form of evolution. This later evolution continues to the present day.
next: the first galaxies
Current telescopes are just now providing us with a glimpse of galaxy formation at the earliest times. Read More...
UCO/Lick Observatory • University of California Santa Cruz • This work is licensed under a Creative Commons Attribution 3.0 United States License.