GALEX Sees First Light
June 4, 2003 | NASA's Galaxy Evolution Explorer launched on April 28, 2003. Less than a month later, on May 21 and May 22, the satellite, also known as GALEX, made its first-ever observations, imaging a region of space in Hercules with its near- and far-ultraviolet cameras. The piece of sky itself was significant, as it was the same spot of sky as seen from Mission Control in Houston, Texas, where the late Space Shuttle Columbia made its final audio contact with NASA.
GALEX will be the first space telescope to make a complete ultraviolet map of the sky. For the next 28 months, it will survey 10 billion years of galactic evolution in UV light. The first-light images are available for download from the NASA Planetary Photojournal. For more information about GALEX, visit the mission website: http://www.galex.caltech.edu/.
Hubble "Finderscope" Gauges Explosive Stellar Duos
June 4, 2003| The Hubble Space Telescope's digital cameras take such glorious astrophotos that their awkward acronyms (ACS, WFPC2, and STIS) have become household words among astronomy aficionados. But essential advances continue to come from Hubble's little-known "finderscope," the Fine Guidance Sensor (FGS) system. The three FGS interferometers are constantly used to keep Hubble steadily pointed at its targets. But they also can do double duty as scientific instruments in their own right: their ability to measure star positions and brightnesses with great precision has enabled dozens of studies on everything from extrasolar planets to the pulsating Cephid variable stars undergirding the cosmic distance scale.
At their Nashville, Tennessee, meeting last week, members of the American Astronomical Society learned of yet another FGS-enabled study: trigonometric parallaxes (and hence solid distances) for six well-known dwarf novae, cataclysmic variable stars that erupt every few weeks or months. Led by Joni Johnson (New Mexico State University), the study dramatized a previously suspected but incompletely documented relationship between the orbital periods of these binary-star systems and the brightnesses of their outbursts, which occur when a relatively cool main-sequence star dumps matter onto its partner, a superdense white dwarf. Not only does the tight relationship between these systems' orbital periods and their outburst energies support the consensus view, in which material swirls around in a disk before spiraling down toward the white dwarf; the finding also raises hopes of using cataclysmic variables as a new kind of "standard candle" with which to gauge distances within the Milky Way.
"Rural" Galaxies Are Prolific, New Study Shows
June 3, 2003 | The reigning cold-dark-matter theory predicts that galaxies form earliest, and evolve most rapidly, where matter is most concentrated: in the "urban environments" of dense galaxy clusters and filaments. And the evidence seems to bear these theories out: densely populated clusters are dominated by gas-poor elliptical galaxies whose star-forming days are mostly over. (The requisite raw materials have either been converted into stars during collision-driven bursts of activity or stripped out of the galaxies altogether.) At the other end of the spectrum, galaxies in underpopulated, rural voids — the 100-million-light-year-wide holes in the universe's Swiss-cheese-shaped large-scale structure — are expected to remain in the throes of star formation, converting still-pristine gas into stars. Such expectations were bolstered three years ago by a pioneering galaxy census based at the Harvard-Smithsonian Center for Astrophysics. But that groundbreaking study sampled the universe's rural hinterlands rather sparsely. That's why a new sample of more than 1,000 void galaxies from the Sloan Digital Sky Survey should excite devotees of cosmology and galaxy evolution. At last week's meeting of the American Astronomical Society, a Drexel University trio led by graduate student Randall R. Rojas announced that void galaxies are bluer and flatter than their counterparts in surrounding suburban "walls" and that their spectra bear the fingerprints of elevated star-forming activity.
Jupiter's Moon Count Hits 61
June 3, 2003| On May 29th, a team of astronomers led by Brett Gladman (University of British Columbia) uncovered yet another Jovian satellite. As its temporary designation of S/2003 J 21 indicates, it's the 21st moon discovered in 2003 around the gas giant. Like its newly found brethren, the object is only a few kilometers across. The team made the discovery with the 3.6-meter Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii.
For a tabulation of all known moons see SkyandTelescope.com's Guide to Planetary Satellites