Last week, I was fortunate enough to interview Professor Mike Shull at the University of Colorado about his recent publication. Although I've reviewed this research before, I thought some revisions were necessary. For more in-depth info about the project, you can check out the transcript of our chat here.
Imagine our universe - but smaller, hotter, brighter, and more dense. What you are picturing is the cosmos when it was a mere 2 billion years old. A team of astronomers from the University of Colorado at Boulder has devoted years to studying this epoch in an effort to understand a phenomenon that has recently been christened "universal warming." This period of reheating stalled the formation of dwarf galaxies in the early universe and tore tightly-bound electrons from the helium atoms that had been cooked up during the big bang. How does such dramatic warming happen? Professor J. Michael Shull and his team of observers believe they may have the answer.
As it turns out, the epoch of reheating coincides with a time in the past when extremely powerful, outrageously luminous balls of ultraviolet radiation called quasars ruled the universe. "A quasar, or a quasi-stellar object, is a generic active galactic nucleus,” explains Shull. "Something in the center of a galaxy goes haywire." Quasars emit a huge amount of energy, and his team believes this energy is responsible for the 500 million-year period of aggressive warming that halted the growth of small, low-mass galaxies nearly 12 billion years ago.
The team's work centers on a piece of equipment on the Hubble Space Telescope called the Cosmic Origins Spectrograph, or COS. Astronomers use COS to learn about very distant, very energetic objects by analyzing the way their light is absorbed by electrons in the intervening gas. Shull's team used COS to observe incoming light from a quasar as it passed through distant helium gas, and found that there was no absorption of light between 11.7 billion and 11.2 billion lightyears away. "When the absorption goes away, we’re assuming that it’s because now, helium is fully ionized," said Shull. "Once it’s a bare helium nucleus with no electrons, there’s no absorption." Thanks to the blistering energy of quasars, helium was reionized and star-forming gas heated to escape velocity, preventing the growth of dwarf galaxies.
This isn't a new project for the group at Boulder. Students and faculty in the Department of Astrophysical and Planetary Sciences have been working on this research since 1994, and they hope to continue their investigation for many years to come. In the coming months, Shull and his team plan to repeat their observations using a few different sightlines in order to determine whether reheating occurred at the same time in other regions of the universe. The team's research was published in the October 20 issue of The Astrophysical Journal.