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A telescope points to the night sky.
Photo Credit: Keith Vanderlinde/Antarctic Photo Library
Auroras shimmer above the South Pole Telescope during the winter. New data from the experiment indicate that the birth of the first massive galaxies that lit up the early universe was an explosive event, happening faster and ending sooner than suspected.

Explosive event

South Pole Telescope eyes birth of first massive galaxies

New data from the South Pole Telescope (SPT) External Non-U.S. government site indicate that the birth of the first massive galaxies that lit up the early universe was an explosive event, happening faster and ending sooner than suspected.

Extremely bright, active galaxies formed and fully illuminated the universe by the time it was 750 million years old, or about 13 billion years ago, according to a new report published in the Sept. 1 print edition of The Astrophysical Journal.

The latest results are based on a new analysis that combines measurements taken by the National Science Foundation External U.S. government site-funded SPT, which operates at millimeter wavelengths to make high-resolution images of the cosmic microwave background (CMB), the light left over from the Big Bang.

The data provide new constraints on the universe’s first era of galaxy formation, called the Epoch of Reionization. Most astronomers think that early stars came to life in massive gas clouds, generating the first galaxies. The energetic light pumped out by these stars is thought to have ionized the hydrogen gas in and around the galaxies, creating “ionization bubbles” millions of light years across that left a lasting, telltale signature in the CMB.

“We find that the Epoch of Reionization lasted less than 500 million years and began when the universe was at least 250 million years old,” said lead author Oliver Zahn External Non-U.S. government site, a postdoctoral fellow at the Berkeley Center for Cosmological Physics (BCCP) at the University of California, Berkeley External Non-U.S. government site. “Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began.”

The first epoch of ionization occurred after the universe was born in the Big Bang External U.S. government site. Everything was so hot that all the gas, mostly hydrogen, was ionized. The universe only cooled enough for electrons to latch onto protons to form neutral hydrogen atoms when the universe was about 400,000 years old.

Photo Credit: John Mallon III/Antarctic Photo Library
South Pole Telescope

“Studying the Epoch of Reionization is important because it represents one of the few ways by which we can study the first stars and galaxies,” said study co-author John Carlstrom External Non-U.S. government site of the University of Chicago External Non-U.S. government site who is the principal investigator for the SPT experiment.

The epoch’s short duration suggests that reionization was more explosive than scientists had previously thought. It suggests that massive galaxies played a key role in reionization, because smaller galaxies would have formed much earlier. Rapid reionization also argues against many proposed astrophysical phenomena that would slow the process.

This is only the beginning of what astronomers expect to learn about reionization from the SPT. The current results are based on only the first third of the telescope’s full survey.

“We expect to measure the duration of reionization to within 50 million years with the current survey,” said study co-author Christian Reichardt External Non-U.S. government site, a Berkeley astrophysicist. “With planned upgrades to the instrument, we hope to improve this even further in the next five years.”

The finding follows a report in the journal Nature last month that the SPT discovered a massive galaxy cluster where stars are forming at the highest rate ever observed. [See previous article — Cluster of discoveries: South Pole Telescope finds fastest star-making region in the universe.]

The 280-ton telescope stands more than 60 meters tall and is the largest astronomical telescope ever built in Antarctica’s clear, dry air. It sits at an elevation of more than 2,800 meters on the polar plateau. Because of its location at the Earth’s axis, it can conduct long-term observations of a single patch of sky.

The University of Chicago leads the SPT collaboration, which includes research groups from Argonne National Laboratory External U.S. government site, Cardiff University External Non-U.S. government site, Case Western Reserve University, Harvard University External Non-U.S. government site, Ludwig-Maximilians-Universitat External Non-U.S. government site, Smithsonian Astrophysical Observatory External Non-U.S. government site, McGill University External Non-U.S. government site, University of California at Berkeley, University of California at Davis External Non-U.S. government site, University of Colorado at Boulder External Non-U.S. government site, University of Michigan External Non-U.S. government site and individual scientists at several other institutions.

NSF-funded research in this article: John Carlstrom, John Ruhl, Joseph Mohr, William Holzapfel and Nils Halverson, University of Chicago, Award No. 0638937 External U.S. government site. Partial support also is provided by the NSF-funded Physics Frontier Center External U.S. government site of UChicago’s Kavli Institute for Cosmological Physics External Non-U.S. government site, the Kavli Foundation External Non-U.S. government site, and the Gordon and Betty Moore Foundation External Non-U.S. government site.

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