Galaxy’s Rings Help Astronomers Unveil Its Past
October 31, 2013

Galaxy’s Rings Help Astronomers Unveil Its Past

Lee Rannals for – Your Universe Online

Similar to reading tree rings, astronomers are able to read the rings in a galaxy’s disk to help gain a better understanding of its past.

Scientists using NASA's Wide-field Infrared Survey Explorer (WISE) and Galaxy Evolution Explorer (GALEX) have gained evidence supporting the “inside-out” theory of galaxy growth, which says that formation starts with the bursts of star formation.

"Initially, a rapid star-forming period formed the mass at the center of these galaxies, followed later by a star-forming phase in the outer regions. Eventually, the galaxies stop making stars and become quiescent," Sara Petty of Virginia Tech, Blacksburg, VA, lead author of a paper appearing in the Astronomical Journal, said in a press release. "This later star-forming phase could have been caused by minor mergers with gas-rich neighbors, which provide the fuel for new stars."

The galaxies in the study are known as “red and dead” due to their red color and lack of new star births. The study found these galaxies have a surprising amount of ultraviolet light emanating from the outer regions, which is generated by hot, young stars. The confusing part about this for the scientists is how these galaxies were considered too old to host these young stars.

Researchers used a multi-wavelength approach to prove the unexplained ultraviolet light is coming from a late phase in the lives of older stars, during which they blow off their outer layers. They used GALEX to view the ultraviolet light and WISE to see the infrared light that comes from older stars.

"The synergy between GALEX and WISE produces a very sensitive measurement of where the hot, older stars reside in these red-and-dead galaxies," said Don Neill, co-author of the paper from the California Institute of Technology, Pasadena. "This allows us to map the progress of star formation within each galaxy."

Ned Wright of UCLA, a co-author of the study and a principal investigator of WISE, said the multi-wavelength range of the two telescopes is similar to musical notes. He said WISE covers the equivalent of a three-octave range, while both telescopes together can cover a seven-octave range.

WISE had been decommissioned in February 2011, but NASA took the telescope out of retirement to help it hunt for previously unknown near-Earth objects (NEOs). WISE is now using its 16-inch telescope and infrared cameras to discover NEOs and characterize their size, thermal properties and reflection coefficient.

NASA shut down its GALEX telescope in June after more than a decade of service. The telescope was able to discover a massive, comet-like tail behind a speeding star known as Mira, and also observe a black hole as it consumed a star. Although GALEX has been decommissioned, it’s data from previous missions still lives on to help scientists continue to unlock the secrets to the universe.