Across the Universe
Department of Physics and Astronomy
In August, the WVU Board of Governors officially approved the Department of Physics’ name change to the Department of Physics and Astronomy. The new name better reflects all that the prestigious program has to offer, particularly as students and faculty garner national and international attention for their research of stars, radio waves, and galaxies far, far away.
“Achieving international leadership in radio astronomy” is one of WVU’s five “Mountains of Excellence,” or areas of research with a strong potential for growth and a substantial return on investment. WVU has invested $1 million in financial support for the Green Bank Telescope over the next two years. WVU faculty and students will receive 500 additional hours of research time on the telescope
as a result.
The Lorimer Burst
Two WVU postdoctoral research assistants have discovered faint, frequent burst of radio waves coming from intergalactic space, millions of light-years away and have closed the door on a mystery nearly seven years old.
In 2007, David Narkevic, a then-undergraduate physics student at West Virginia University, and his professor Duncan Lorimer discovered a single, short burst of radio waves from another galaxy using the Parkes Radio Telescope in New South Wales, Australia.
The sudden burst of waves came only once, and nothing like it was ever spotted again—until now.
“The implication was that there were many other (bursts) going off that we weren’t seeing,” Lorimer, Woodburn Professor of Physics, said. “They just proved very difficult to find.”
In 2012, two WVU postdoctoral research assistants, Sam Bates and Lina Levin, were working as part of an international research team led by Dan Thornton at the University of Manchester. Using the same telescope with upgraded electronics, the team discovered four more bursts of radio waves. These bursts have become known as Fast Radio Bursts.
“Since (Lorimer’s research) had only been published a year or two before, it was kind of in everyone’s minds that that was something we’d want to look for,” Bates said.
Fast Radio Bursts are more faint and frequent than the original burst in 2007 and appear much more often, roughly once every ten seconds somewhere on the sky. “It’s quite unusual and something entirely new. We don’t currently know what they are,” Lorimer said. “It must be something very compact because it is a short-duration event. There are of course many theories at present, but their origin remains a mystery.” He said if scientists can identify what is causing these waves it would allow them to measure the distance to the sources of the waves.
“When you’re looking at these sources, you’re seeing events that happened when the universe was a lot younger. There might be a galaxy in which the source emitted and went off, and we see the light today. That’s very exciting,” he said. “We’re looking at the universe in earlier times.”
As far as extraterrestrial life is concerned, humanity may have to wait just a bit longer for that discovery. Lorimer, Bates, and Levin all agree that it is nearly impossible an extraterrestrial being emitted these waves.
“With one event, which we had in 2007, you could get away with that theory, but now, if we’ve got these bursts going on all over the sky it’s very unlikely, impossible I would say,” Lorimer said.
A Big Universe with Lots Left to Discover
The Andromeda and Triangulum galaxies, neighbors to the Milky Way, are constructed of an immense number of stars. But a new study, led by WVU graduate student Spencer Wolfe, has revealed a never-before-seen cluster of gas clouds between the galaxies that could potentially fuel the formation of more stars.
The study is in the May 2013 issue of Nature, a weekly journal that highlights original and groundbreaking research in science. Lead author Wolfe, and assistant physics professor Daniel Pisano worked with researchers from Case Western Reserve University, the University of Maryland, and the National Radio Astronomy Observatory.
The astronomers detected the clouds using the National Science Foundation’s Green Bank Telescope (GBT) at the National Radio Astronomy Observatory in Green Bank, West Virginia. Although previous observations of the Local Group, a galaxy group that includes the Milky Way, have indicated the possible presence of diffuse hydrogen gas between its members, this is the first time there has been such a detailed view.
“The question we’re trying to answer is in what way is the Local Group and its members evolving,” Wolfe said. “A lot of people tend to forget that when they see pictures of the Milky Way that we’re embedded in it. If it’s evolving, we’re going to evolve with it so understanding the details of how galaxies like the Milky Way can acquire new gas and keep forming stars is important.”
Observations completed by the group have shown that portions of the gas are clumped together mimicking dwarf galaxies. Dwarf galaxies are relatively small collections of stars bound together by gravity. They can contain anywhere from a few thousand to a few million stars. The telescope also was able to track the motion of these newly discovered clouds.
“The study would not be possible without the unique capabilities of the Green Bank Telescope,” Pisano said. “Its combination of sensitivity, resolution, and its unique optical design were all critical for this study. There are no other telescopes currently operating or planned that will be as capable of doing this type of work as the GBT.”
Through their observations, the astronomers suggested the clouds represent a previously unrecognized source of hydrogen gas that could lead to future generations of star formation.
“It is a remarkable thing that there are still new things to discover in the backyard of our own galactic neighborhood,” said Stacy McGaugh, a professor of astronomy at Case Western Reserve University and coauthor of the study.
“I’m fond of saying it is a big universe with lots left to discover; apparently that’s still true of our own ‘little’ corner of the universe.”
Mapping the Galaxy
Loren Anderson, an assistant professor of physics at WVU, and his colleagues have discovered hundreds of previously unknown sites of massive star formation in the Milky Way, including the most distant such objects yet found in our home galaxy. Ongoing studies of these objects promise to give crucial clues about the structure and history of the Milky Way.
Anderson and his colleagues, Thomas Bania of Boston University and Dana Balser at the National Radio Astronomy Observatory, found regions where massive young stars or clusters of such stars are forming. These regions, which astronomers call HII (H-two) regions, serve as markers of the galaxy structure, including its spiral arms and central bar.
HII regions are ionized zones around very massive stars. The stars powering HII regions are more than 20 times the mass of the Sun. Anderson has created a catalogue of all these regions that allows scientists to better characterize the statistical properties of HII regions, trace galactic structure, determine differences in star formation properties in a variety of environments, compare our galaxy with other galaxies in the universe, and examine the impact of evolved HII regions in triggering the creation of second-generation stars.
“The problem to this point had been that it was very difficult to get a complete sample because we did not have a survey of the whole sky that could find all of the HII regions in the galaxy,” Anderson explained. “NASA launched the WISE (Widefield Infrared Survey Explorer) satellite a few years ago, and the data were released this past March. The WISE all-sky survey at infrared wavelengths, where these HII regions emit a lot of energy, allowed me to compile a complete sample of HII regions in the galaxy for the first time.”
Anderson reports that data from WISE shows about 2,000 new HII-region candidates that the team is studying. The three men presented their work to the American Astronomical Society’s meeting in Long Beach, California. “We’re vastly improving the census of our galaxy, and that’s a key to understanding both its current nature and its past history, including the history of possible mergers with other galaxies,” Bania said.
The astronomers are using the are using the GBT and Arecibo and Arecibo Telescope in Puerto Rico, and data from NASA’s Spitzer and WISE satellites. They plan to expand the effort to include Australian radio telescopes.
The effort began with a survey of the Milky Way using the GBT. Anderson and his colleagues looked for HII regions by seeking faint emission of hydrogen atoms at radio wavelengths that are unobscured by the dust in the galaxy’s disk. By detecting these emissions, dubbed radio recombination lines, or RRLs, the GBT survey more than doubled the number of known HII regions in the Milky Way. They continued that work using the Arecibo Telescope, finding additional objects, including the largest HII region yet known, nearly 300 light-years across.
Data from previous surveys with radio and infrared telescopes, including Spitzer and WISE, helped to guide the new search. Later work analyzed similar emissions of helium and carbon atoms.
“The great sensitivity of the GBT and the Arecibo Telescope, along with advanced electronics, made our new surveys possible,” Balser said. The work so far has helped refine astronomers’ understanding of the galaxy’s structure. They found concentrations of star formation in poorly understood distant spiral arms and at the end of the galaxy’s central bar.
Another major focus of the surveys is to study chemical variations in different regions of the galaxy. Variations in the abundance of elements heavier than hydrogen can trace the history of star formation, and also indicate regions possibly containing material incorporated into the galaxy through mergers with other galaxies throughout its history.
“We’ve already been surprised to learn that the thin, tenuous gas between the stars is not as well mixed as we thought,” Balser said. “Finding areas that are chemically different from their surroundings can point to where gas clouds or smaller galaxies may have fallen into the Milky Way,” he added. “Just as geologists traverse the landscape, mapping different rock types to reconstruct the Earth’s history, we’re working to improve the map of our galaxy to advance our understanding of its structure and its history,” Bania said.
This research was made possible by a grant worth $255,083 from NASA to Loren Anderson.