• Foggy, Foggy BangFog is the bane of Astronomy, but one type of fog inspires fascination rather than frustration: the universe-spanning haze that formed soon after the Big Bang. It burned away as the first stars lit up, so figuring out when and where that happened will clarify how the universe began its astonishing transition from darkness to light. In August, researchers filled in a big piece of the puzzle, spotting two galaxies at the very edge of the cosmic fog bank.
When the early universe grew cool enough for atoms to form, subatomic particles combined into extensive clouds of neutral hydrogen and helium, which efficiently absorbed ultraviolet light from the earliest stars. "It's like looking at them through sunglasses," says astronomer George Djorgovski of the California Institute of Technology. Over time, however, energetic rays from the stars stripped electrons from the atoms, transforming them into transparent charged ions. In this way, radiation carved out hollows in the haze—like holes in Swiss cheese—that grew ever larger until the clear regions merged. "The clouds are never entirely destroyed," says astronomer David Tytler of the University of California at San Diego. "The last wisps survive to this day."
Attempts to glimpse the earliest birthing stages of stars and galaxies have been thwarted in part by the light-snuffing clouds. Undaunted, two teams (one of them led by Djorgovski, another by Robert Becker of the University of California at Davis) went to work using the giant Keck telescope. The effort paid off: Each team obtained good data on a quasar, a type of active galaxy, that was shining when the universe was about a billion years old, just as the fog was beginning to clear. The findings give the best indication yet of when the process happened. Djorgovski's quasar, which is 100 million years older than the one studied by Becker, appears to be largely in the clear. The younger galaxy is still partly socked in, which suggests that the lifting of the veil occurred in between the formation of the quasars. The timing of that transition confirms cosmologists' models of the early universe.
Probing the edge of the fog bank should help explain how quasars and galaxies managed to form soon after the tumult of the Big Bang. "Right now, it's a bit of a challenge to explain how to make things so quickly," Djorgovski says. "We'll be able to learn some things by looking at how lumpy the edge of the cloud is." In the coming decade, NASA's Next Generation Space Telescope should be able to pierce the fog entirely and reveal, to an eager audience, the first galaxies lighting up one by one. — Jeffrey Winters
• King of the Small FryPluto is the last planet in the pecking order—distant, dim, and so small at 1,400 miles across that some scientists are trying to demote it to an asteroid. Pluto's status grew even more uncertain in May, when astronomers discovered an object roughly half as large in the same region of the solar system. Some regarded it as a challenge to Pluto's planethood; others noted Pluto's larger size still makes it stand out. "You can use this object as ammunition for either side of the debate," says Robert Millis of the Lowell Observatory in Flagstaff, Arizona, who led the team that spotted it.
