Astronomers peer back to 'dawn of galaxies'

Oct 01, 2004

Detailed analysis of Hubble Space Telescope images has allowed astronomers to determine a major event in the evolution of the universe. The astronomers used the Hubble Space Telescope’s Ultra Deep Field (UDF) to peer 95 percent of the way back to the beginning of time – to 750 million years after the Big Bang – and they found a population of dim young dwarf galaxies whose collective light likely was responsible for "reionizing" hydrogen in the universe, an event that led to major galaxy formation.

Reionization is a critical period in the development of the universe, according to Rogier Windhorst, an ASU professor of astronomy.

“It lifted the veil of cold, primordial hydrogen, which was largely opaque when it cooled after the Big Bang,” says Windhorst, a member of one of four teams of astronomers that analyzed Hubble UDF data. The four teams presented their findings at a Sept. 23 workshop in Baltimore.

“This is the dawn of galaxy formation,” Windhorst says. “Before this, there were probably just star clusters and giant molecular clouds like the Orion nebula in our galaxy. There were big, massive stars but probably nothing like the shape of ordinary or even tiny galaxies.”

NASA’s new 6.5 meter James Webb Space Telescope, planned for launch in 2011, will peer even further back in time to the epoch of first light to see these first stars and star clusters.

In the past couple of decades astronomers have documented evidence that we live in a reionized or “refried” universe. The reionization epoch was a critical watershed for the evolving universe. During that early time, cold hydrogen atoms drifting in space were pumped up with so much energy from ultraviolet starlight from newly formed, hot young stars that they were stripped of their electrons. The universe once again became transparent, like the Sun burning off an early morning fog.

This early period is called reionization because the primeval universe was initially ionized as a “soup” of hydrogen and helium nuclei and free-moving electrons, Windhorst said. As the universe cooled through expansion, these electrons were captured by hydrogen nuclei to make neutral hydrogen. But the electrons were lost again when the first fiercely bright stars fired up.

The reionization epoch is thought to have ended between 500 million and 1 billion years after the Big Bang (the universe is estimated to be 13.7 billion years old). Prior to the period of reionization, the universe was a very different place than today, which now includes billions of stars residing in billions of galaxies.

Using special instruments on the Hubble telescope, astronomers were able to discern the long sought, yet very faint galaxies that probably had enough energy among them to reionize the young universe.

The Hubble Ultra Deep Field images show that at about one billion years after the Big Bang, the early universe was filled with fledgling dwarf galaxies, but no fully formed galaxies like our Milky Way galaxy. After careful analysis, the astronomers were able to sort out between 54 and 108 dim red smudges sprinkled across the Hubble UDF image.

“Instead of some giant, pulling the trigger on a single gun, it turns out that all of these little galaxies produced all of the ultraviolet light and collectively lifted the hydrogen veil,” Windhorst said.

To look at it in a hierarchical way, he added, the universe at that time was filled with “mom and pop” stores, which eventually merged into businesses and later into giant corporations – the majestic galaxies we see today.

Windhorst worked with ASU alumnus Haojing Yan, now a postdoctoral fellow at the California Institute of Technology’s Spitzer Science Center, Pasadena, Calif., on the analysis. They published a paper on their work, “Candidates of z~5.5 – 7 Galaxies in the Hubble Space Telescope Ultra Deep Field,” in the Sept.10 Astrophysical Journal Letters.

Source: ASU

Explore further: NASA craft set to beam home close-ups of Pluto

add to favorites email to friend print save as pdf

Related Stories

Obama recommends extended wilderness zone in Alaska

10 hours ago

US President Barack Obama said Sunday he would recommend a large swath of Alaska be designated as wilderness, the highest level of federal protection, in a move likely to anger oil proponents.

NASA craft set to beam home close-ups of Pluto

10 hours ago

Nine years after leaving Earth, the New Horizons spacecraft is at last drawing close to Pluto and on Sunday was expected to start shooting photographs of the dwarf planet.

Navy wants to increase use of sonar-emitting buoys

12 hours ago

The U.S. Navy is seeking permits to expand sonar and other training exercises off the Pacific Coast, a proposal raising concerns from animal advocates who say that more sonar-emitting buoys would harm whales and other creatures ...

Uganda seizes massive ivory and pangolin haul

12 hours ago

Ugandan wildlife officers have seized a huge haul of elephant ivory and pangolin scales, representing the deaths of hundreds of endangered animals, police said Sunday.

Recommended for you

Cosmic puzzle settled: Comets give us shooting stars

3 hours ago

Suspicions that shooting stars come from comet dust, transformed into fiery streaks as they hit Earth's atmosphere, have been bolstered by Europe's Rosetta space mission, scientists reported Monday.

Swarm of microprobes to head for Jupiter

5 hours ago

A swarm of tiny probes each with a different sensor could be fired into the clouds of Jupiter and grab data as they fall before burning up in the gas giant planet's atmosphere. The probes would last an estimated ...

Mysteries in Nili Fossae

6 hours ago

These new images from the high-resolution stereo camera on ESA's Mars Express show Nili Fossae, one of the most enticing regions on Mars. This 'graben system' lies northeast of the volcanic region of Syrtis ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.