Magnetic ‘bubbles’ may be key force in galaxy clusters

WASHINGTON, D.C. – Astronomers have suspected that magnetic fields in space play a key role in the makeup of galaxy clusters – the basic building blocks of the universe. Now, an Ohio University-led research team has uncovered what may be the origin of those fields, a finding that has eluded scientists for more than a decade.

The scientists analyzed data collected from NASA’s Chandra X-ray Observatory and discovered a series of enormous cosmic “bubbles,” formed more than 100 million years ago, that may contain and transport magnetic fields. These bubbles also may play a role in the creation of new stars in today’s galaxies, and may have been critical in the early stages of the universe.

“We think magnetism, in some locations of the universe, could have been as important as gravity in shaping the overall structure,” said Brian McNamara, an Ohio University astronomer who presented the findings today at the annual meeting of the American Astronomical Society in Washington, D.C.

Using the Chandra observatory, an orbiting spacecraft that houses the most powerful X-ray telescope in existence, McNamara and his collaborators have been examining the forces at work in several galaxy clusters. Galaxy clusters are made of individual galaxies, hot gases and dark matter.

The researchers initially discovered that the X-ray emissions from several galaxy clusters were full of holes, or cavities, that contained bright radio emissions. These cavities probably were created by an explosion of high-energy particles, which left the radio emissions in its wake.

However, the Chandra data on another galaxy cluster known as Abell 2597, located more than 1 billion light years away from Earth, showed a surprising difference. The cluster’s cavities – which the researchers dubbed “ghost cavities” – contained only faint radio emissions. They seemed to float out of the centers of galaxy clusters like bubbles in a glass of soda pop, McNamara said. But these bubbles are 60,000 light years across in size, almost as big as the Milky Way galaxy.

The data suggest that the ghost cavities are filled with magnetic fields, which are released into the cosmos when the cavities burst apart. This could explain the strong magnetic forces that make up the structure of galaxy clusters, according to the astronomers.

“We’ve known for the past 15 to 20 years that magnetic fields exist, but we didn’t understand how they got there,” said McNamara, an associate professor of physics and astronomy in the College of Arts and Sciences whose research is funded by NASA. “This could be a viable mechanism.”

The ghost cavities also may play an indirect role in star formation, according to the scientists. As the cavities move out of the center of the galaxy cluster, the surrounding gases cool and matter becomes dense, falling into a supermassive black hole in the cluster center. That triggers an explosion of radio emission, which sprays matter through the galaxy cluster. Under certain conditions, the matter may form new stars.

This process may happen from a dozen to hundreds of times during the life of the galaxy cluster, McNamara said, and most likely occurs in other galaxy clusters.

The key role of magnetic forces in galaxy clusters suggests that they also may have been an important mechanism in creating cosmic structure in the distant past, when the universe was smaller and the radio emission was more powerful, McNamara added.

Next the scientists will conduct a more detailed analysis of the properties of ghost cavities and their role in galaxy clusters.

“We have a sketch of what’s going on, but the details are foggy at this point,” McNamara said.

Collaborators on the project are Michael Wise of the Massachusetts Institute of Technology, Paul Nulsen of the University of Wollongong in Australia, Larry David of the Harvard-Smithsonian Center for Astrophysics, Chris Carilli of the National Radio Astronomy Observatory, Craig Sarazin of the University of Virginia, and a group of astronomers from the Space Telescope Science Institute and the University of Virginia.

Written by Andrea Gibson.

Attention Reporters, Editors: Images and video of the ghost cavities are available. Contact Andrea Gibson at (740) 597-2166 or gibsona@ohio.edu.

Contacts: Before Jan. 10, Andrea Gibson, (740) 597-2166, gibsona@ohio.edu; after Jan. 10, Brian McNamara, (740) 593-0063, or mcnamara@helios.phy.ohiou.edu.