The Johns Hopkins Gazette: July 21, 2003
July 21, 2003
VOL. 32, NO. 40


New NASA probe to study origins of galaxies

By Michael Purdy

Johns Hopkins Gazette Online Edition

For astronomers hoping to launch observatories and probes into orbit or beyond, the path to space always leads across a fearful threshold: launch time, when all the sensitive, delicate equipment that researchers have worked on so hard and so long is put atop a huge container of explosive materials and fired into the sky.

For nail-biting launches, though, it's hard to beat the sendoff for the Galaxy Evolution Explorer, an orbital probe of early galaxy evolution also known as GALEX.

Luciana Bianchi, principal research scientist at the Center for Astrophysical Sciences at Johns Hopkins, had worked on this project for 10 years when GALEX's moment of truth finally came late in April. NASA had chosen to send the probe off not via the conventional ground-based rocket but on a Pegasus missile carried into the sky and dropped over the ocean by an L-1011 airplane.

"It saves dollars and energy, but it also has some risk of failure," Bianchi said, noting her own anxiousness over the unusual liftoff. "The pilot flies about 100 miles out over the ocean, and then he drops the rocket and has about five seconds to veer out of the way before the missile fires."

NASA's decision paid off, though: Everything went well on launch day and has done so ever since. The missile boosted GALEX into a 700 kilometers -- high orbit, and after a period of rest dedicated to allowing contaminants and gases to escape from the spacecraft, controllers on the ground opened up the telescope and took their first images with it on May 21 and 22.

"Everything is going very well," Bianchi said with clear delight, "and now the excitement can finally begin."

The "excitement" GALEX will supply is a first look at the entire sky in near ultraviolet light, a range of radiation just above the shortest wavelengths visible to the human eye.

"It's hard to believe, but there have been surveys of the whole sky at every other wavelength," Bianchi said. "The ultraviolet is the only small window through which we have never explored the entire universe yet. And that's the most exciting part for me. That's why I got started with GALEX."

Bianchi teamed up in 1992 with Chris Martin, now a professor at CalTech, to propose a mission for the first ultraviolet sky-survey, which went into development a decade ago as a joint NASA-Italian Space Agency research project. Budget issues led to the project's cancellation at one point, but it was resurrected in 1997, with a slightly updated design and the name GALEX, as a NASA mission. Partners in the project, in addition to NASA and NASA's Jet Propulsion Laboratory, now include Johns Hopkins, the University of California-Berkeley, Yonsei University of South Korea and the Space Astronomy Laboratory of France.

Martin continues to be GALEX's principal investigator. Bianchi, who came to Johns Hopkins in 1996, recruited Johns Hopkins professors Alex Szalay and Timothy Heckman to join the project. Postdoctoral associates David Thilker, Charles Hoopes and Tamas Budavari joined recently and will participate in the analysis of the GALEX data.

One of GALEX's main goals, according to Bianchi, will be to analyze ultraviolet light from 10 million distant galaxies.

"At the same time we're measuring the light from these galaxies, we'll get their distance," Bianchi said. "This will provide the entire history of star formation over 10 billion years, which is 80 percent of the life of the universe."

Rather than focusing on star formation in one galaxy or a cluster of galaxies, Bianchi and other GALEX investigators are hoping to amass enough information to gain a statistical sense for rates and patterns of star formation over the course of the history of the universe.

"We want to have a view of the cosmic history of star formation -- to take a census of all star-forming galaxies, which represent different types and epochs, and then we can reconstruct the entire picture," Bianchi said.

She compared the process to studying the growth of flowers in a garden: Looking at any one flower in a garden at any one point during the year can yield useful information on the flowers, but a more thorough understanding can be had by taking pictures of various regions of the garden at different times during the year.

The range of ultraviolet radiation analyzed by GALEX will be ideal for these purposes because it lets astronomers home in on hot, massive, short-lived stars.

"These stars last only a few million years, which is nothing in terms of cosmic history," Bianchi said. "But if you're looking for the most important peaks in star formation, say 5 billion years ago, that can be totally smeared out by light from longer-lived stars unless you're measuring the star formation of large UV-emitting stars, which is not confused by all the emissions from prior star formation."

Massive short-lived stars are also important because they created the heavier elements that made life on Earth possible.

"Everything that was formed in the Big Bang was this boring light element, hydrogen, and really, you can do nothing with that!" Bianchi joked. "Only when the stars started processing hydrogen into heavier elements did you have carbon, nitrogen, oxygen and other elements which can react and are active and can sustain life."

These elements are dispersed from the massive stars in their explosive deaths, a process GALEX investigators hope to learn more about.

What has Bianchi most excited about GALEX, though, are the unpredictable discoveries it will likely make.

"In human history, whenever we have explored uncharted territory, the most exciting part has always turned out to be the unexpected discoveries," Bianchi said. "The unusual objects we discover will -- I promise -- call for further observation with GALEX and with other telescopes."

One of the main instruments to be used for follow-up study probably will be the orbiting Far Ultraviolet Spectroscopic Explorer, or FUSE, a NASA observatory operated and managed from the Johns Hopkins Homewood campus that observes higher frequencies of ultraviolet radiation than GALEX.

"For most types of physical phenomena, it's very useful to have both UV ranges," Bianchi noted. "The complete picture of the sky in ultraviolet provided by GALEX will be the perfect sky survey for picking out UV-bright objects and interesting targets for FUSE and the Hubble Space Telescope, which also observes some of these regions of ultraviolet light."

Over the course of its 29-month mission, GALEX will acquire huge quantities of data, and Bianchi and others are working to make sure that data can be made quickly accessible to the astronomical community at large.

"It will be an avalanche," she said of the data GALEX will soon start producing, "and for this reason we want to try to make it available to the entire worldwide scientific community in the best and most accessible form to exploit."