Ultima Thule

In ancient times the northernmost region of the habitable world - hence, any distant, unknown or mysterious land.

Wednesday, September 20, 2006

Subaru Finds the Most Distant Galaxy

By Aussiegirl

I find this photograph, of hundreds upon hundreds of galaxies so many billions of light-years away, truly awe-inspiring. It seems impossible that they could pick out that tiny red dot from all those other dots and determine that it's the most distant galaxy, but the full article explains the procedure very fully.

Universe Today » Archive » Subaru Finds the Most Distant Galaxy

Subaru Finds the Most Distant Galaxy
September 15th, 2006

The powerful Subaru telescope in Hawai’i has found the most distant galaxy ever seen, located 12.88 billion light-years away - this is only 780 million years after the Big Bang. Observing objects this distant is extremely difficult, not only because of the great distances involved, but because much of the Universe was obscured behind neutral hydrogen. Stars only then began clearing out this neutral hydrogen, making the Universe transparent. [....]

This discovery, based on observations made by Masanori Iye of the National Astronomical Observatory of Japan (NAOJ), Kazuaki Ota of the University of Tokyo, Nobunari Kashikawa of NAOJ, and others indicates that galaxies existed only 780 million years after the universe came into existence about 13.66 billion years ago as a hot soup of elementary particles. [....]

The discovery challenges astronomers to determine exactly what happened between 780 and 840 million years after the Big Bang. IOK-1 is one of only two galaxies in the new study that could belong to this distant epoch. Given the number of galaxies that have been discovered from 840 million years after the Big Bang, the research team had expected to find as many as six galaxies at this distance. The comparative rarity of objects like IOK-1 means that the universe must have changed over the 60 million years that separate the two epochs.

The most exciting interpretation of what happened is that we are seeing an event known to astronomers as the reionization of the universe. In this case, 780 million years after the Big Bang, the universe still had enough neutral hydrogen to block our view of young galaxies by absorbing the light produced by their hot young stars. Sixty million years later, there were enough hot young stars to ionize the remaining neutral hydrogen, making the universe transparent and allowing us to see their stars.

Another interpretation of the results says that there were fewer big and bright young galaxies 780 million years after the Big Bang than 60 million years later. In this case, most of the reionization would have taken place earlier than 12.88 billion years ago.

No matter which interpretation finally prevails, the discovery signals that astronomers are now excavating light from the “Dark Ages” of the universe. This is the epoch when the first generations of stars and galaxies came into existence, and an epoch which astronomers have not been able to observe until now. [....]

To put this Subaru accomplishment into context, it is important to review what we know about the history of the early universe. The universe began with the Big Bang, which occurred about 13.66 billion years ago in a fiery chaos of extreme temperature and pressure. Within its first three minutes, the infant universe rapidly expanded and cooled, producing the nuclei of light elements such as hydrogen and helium but very few nuclei of heavier elements. In 380,000 years, things had cooled to a temperature of around 3,000 degrees. At that point, electrons and protons could combine to form neutral hydrogen.

With electrons now bound to atomic nuclei, light could travel through space without being scattered by electrons. We can actually detect the light that permeated the universe back then. However, due to time and distance, it has been stretched by a factor of 1,000, filling the universe with radiation we detect as microwaves (called the Cosmic Microwave Background). The Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft studied this radiation and its data allowed astronomers to calculate the age of the universe at about 13.66 billion years. In addition, these data imply the existence of such things as dark matter and the even more enigmatic dark energy.

Astronomers think that over the first few hundred million years after the Big Bang, the universe continued to cool and that the first generation of stars and galaxies formed in the densest regions of matter and dark matter. This period is known as the “Dark Ages” of the universe. There are no direct observations of these events yet, so astronomers are using computer simulations to tie together theoretical predictions and existing observational evidence to understand the formation of the first stars and galaxies.

Once bright stars are born, their ultraviolet radiation can ionize nearby hydrogen atoms by splitting them back into separate electrons and protons. At some point, there were enough bright stars to ionize almost all the neutral hydrogen in the universe. This process is called the reionization of the universe. The epoch of reionization signals the end of the Dark Ages of the universe. Today most of the hydrogen in the space between galaxies is ionized.

Astronomers have estimated that reionization occurred sometime between 290 to 910 million years after the birth of the universe. Pinpointing the beginning and end of the epoch of reionization is one of the important stepping stones to understanding how the universe evolves, and is an area of intense study in cosmology and astrophysics. [....]


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