The Farthest Galaxy Yet — But Where Are Its Siblings?

Looking back through time to only about 480 million years after the Big Bang, the Hubble Space Telescope has photographed the farthest galaxy ever glimpsed. Its estimated distance from Earth is a mind-boggling 13.2 billion light-years, meaning its light raced at 186,000 miles per second, every second for 13.2 billion years, to reach the telescope.

[NASA released this set of photos Wednesday, zeroing in on the farthest galaxy yet discovered. The view shows a small section of the Fornax constellation]

The galaxy, designated UDFj-3954628, is so small and faint that the orbiting observatory had to collect light from the region for 87 hours. For most of that time, when exposures were made with ordinary light, it didn’t show up at all. It was visible only in the 41 hours of exposures taken with a camera sensitive to far-infrared rays. The images were taken in the summers of 2009 and 2010 and combined into a single view.
NASA experts said the galaxy is a mere 1 percent of the size of our Milky Way. It’s a compact object that would look blue with new stars, if its light hadn’t been red-shifted during the journey to Earth.
Hubble scientists described the findings Wednesday in a news conference that was broadcast live on the Internet.
“This isn’t a blind search,” said Richard Bouwens of Leiden University, Holland, and the University of California, Santa Cruz. “We had a reasonable chance of expecting something in our search.”

Hubble had already photographed the same site in its Ultra Deep Field image, and scientists knew how many galaxies were present as far back as could be seen then, about 650 million years after the Big Bang. They appeared in views taken in ordinary light.

But two years ago a servicing flight to Hubble installed a new camera, the Wide Field Camera 3, that can photograph in the extreme infrared. It can take images of galaxies so distant that their light has been shifted to the red to an extreme degree — shifted entirely out of the range of ordinary light. They are only visible in the deep infrared.

Based on the number of galaxies in the same small field of view that were present 650 million years after the Big Bang and detectable by ordinary light, astronomers had calculated how many of the earlier galaxies should appear that were visible only in infrared. The most startling result of the new study is that the expectations weren’t fully realized.

They had expected to discover 10 galaxies in the same area at 480 million years post Big Bang. Instead, they uncovered just one.

Rachel Somerville of the Space Telescope Science Institute commented, “The most interesting part of this research is the dog that didn’t bark,” the early galaxies that weren’t there.
If the density of galaxies had remained the same as they were about 200 million years later, she added, “they should have found at least 10 times more galaxies.”
Instead, between those periods, galaxies were forming and evolving much more rapidly than had been expected. For some unknown reason, galaxy formation accelerated tremendously.
Through many billions of years galaxies collided and merged, with great periods of starbursts when new stars formed. The peak of starbursts was about 10 billion years ago, with the rate “dropping distinctly and dramatically,” said Garth Illingworth of the University of California at Santa Cruz. Today’s situation is “sort of like the universe is aging and nothing much is happening.”
What was the ultimate fate of those earliest galaxies? We may live on one. The building blocks of the Milky Way might include material from more than 100 of the small, dense galaxies.

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