Radiation Leaks In Local Galaxy Used To Study Reionization Of The Universe

Chuck Bednar for redOrbit.com – Your Universe Online
By measuring the radiation leaks in a large, densely-packed star-forming galaxy, astronomers have been able to learn more about how the universe evolved as the first stars were formed, according to research published online Thursday in the journal Science.
Lead author Sanchayeeta Borthakur, an assistant research scientist at Johns Hopkins University, and her colleagues reported how they used a method of analyzing star-forming galaxies that leak radiation to help them locate one that contained holes in its cold gas cover, with the hopes that they could pinpoint a galaxy with the right characteristics so they could learn how the radiation produced by stars is used during the ionization process.
The cold gas cover of these star-forming galaxies are comprised of thick, dense cold gas that stretches across the galaxy like a blanket, the researchers explained, and while this is an effective tool for the creation of stars, it has been a challenge for astrophysicists hoping to learn more about its role in the ionization process. Some experts have been searching for decades to find a galaxy with just the right traits, they added.
“It’s like the ozone layer, but in reverse. The ozone layer protects us from the sun’s radiation but we want the gas cover the other way around,” Borthakur said in a statement. “The star forming regions in galaxies are covered with cold gases so the radiation cannot come out. If we can find out how the radiation gets out of the galaxy, we can learn what mechanisms ionized the universe.”
According to Space.com contributor Nola Taylor Redd, Borthakur and her fellow investigators focused their analysis on a nearby compact galaxy known as J0921+4509, which is located roughly three billion light years from the Milky Way and has been rapidly producing stars. The star-forming regions of the galaxy are surrounded closely by dense gas clouds, she added, but holes in those clouds allow radiation to leak out, mimicking events that would have occurred during the early universe.
Redd explained that J0921+4509 produces approximately 50 solar-masses’ worth of stars each year, or over 33 times the number created annually by the Milky Way. While the majority of stars found elsewhere remain trapped in the gas that helps form them, the high density of stars located in one compact region of the galaxy creates holes that allow the radiation to escape, Borthakur explained to Space.com via email.
“For star-gazers, reionization is core to the history of the cosmos as it marks the birth of the very first stars and galaxies,” the university said. Shortly after the Big Bang, the newly created universe began to expand and cool rapidly. Several thousands of years later, free proton and electron particles in the universe began to come together to form neutral hydrogen atoms, which then started collapsing into the first stars and galaxies, the authors noted.
“Events from the dark ages of the universe, including its reionization, cannot be directly studied. Instead, astronomers must search for similar processes in objects they can examine today, such as those found in the starburst galaxy J0921,” Redd added. Since the stars in J0921+4509 are so close together, “that radiation and rapid heating from the winds flowing from the stars out of the galaxy widen existing small holes, allowing the ionizing radiation to escape.”
Borthakur and co-authors Timothy Heckman, director of the Center for Astrophysical Sciences at Johns Hopkins, Claus Leitherer from the Space Telescope Science Institute and Roderik Overzier from the Observatorio Nacional in Rio de Janeiro, were able to capture those leaks using the Hubble Space Telescope’s Cosmic Origin Spectrograph.
They credit a combination of unusually strong winds, intense radiation and a massive, highly star-forming galaxy for helping them prove that the galaxy was a valid study target. The method they used was first developed by Heckman in 2001, and by using it, the study authors can determine which gas is present and accurately measure the percentage of holes in the gas cover. The research was funded by a NASA grant.
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