|
|
|
|
|
Dwarfs gave way to giants HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS NEWS RELEASE Posted: May 17, 2006 The first galaxies were small - about 10,000 times less massive than the Milky Way. Billions of years ago, those mini-furnaces forged a multitude of hot, massive stars. In the process, they sowed the seeds for their own destruction by bathing the universe in ultraviolet radiation. According to theory, that radiation shut off further dwarf galaxy formation by both ionizing and heating surrounding hydrogen gas. Now, astronomers Stuart Wyithe (University of Melbourne) and Avi Loeb (Harvard-Smithsonian Center for Astrophysics) are presenting direct evidence in support of this theory.
"The first dwarf galaxies sabotaged their own growth and that of their siblings," says Loeb. "This was theoretically expected, but we identified the first observational evidence for the self-destructive behavior of early galaxies." Their research is being reported in the May 18, 2006 issue of Nature. Nearly 14 billion years ago, the Big Bang filled the universe with hot matter in the form of electrons and hydrogen and helium ions. As space expanded and cooled, electrons and ions combined to form neutral atoms. Those atoms efficiently absorbed light, yielding a pervasive dark fog throughout space. Astronomers have dubbed this era the "Dark Ages." The first generation of stars began clearing that fog by bathing the universe in ultraviolet radiation. UV radiation splits atoms into negatively charged electrons and positively charged ions in a process called ionization. Since the Big Bang created an ionized universe that later became neutral, this second phase of ionization by stars is known as the "epoch of reionization." It took place in the first few hundred million years of existence. "We want to study this time period because that's when the primordial soup evolved into the rich zoo of objects we now see," said Loeb. During this key epoch in the history of the universe, gas was not only ionized, but also heated. While cool gas easily clumps together to form stars and galaxies, hot gas refuses to be constrained. The hotter the gas, the more massive a galactic "seed" must be to attract enough matter to become a galaxy. Before the epoch of reionization, galaxies containing only 100 million solar masses of material could form easily. After the epoch of reionization, galaxies required more than 10 billion solar masses of material to be assembled. To determine typical galaxy masses, Wyithe and Loeb looked at light from quasars - powerful light sources visible across vast distances. The light from the farthest known quasars left them nearly 13 billion years ago, when the universe was a fraction of its present age. Quasar light is absorbed by intervening clouds of hydrogen associated with early galaxies, leaving telltale bumps and wiggles in the quasar's spectrum. By comparing the spectra of different quasars along different lines of sight, Wyithe and Loeb determined typical galaxy sizes in the infant universe. The presence of fewer, larger galaxies leads to more variation in the absorption seen along various lines of sight. Statistically, large variation is exactly what Wyithe and Loeb found. "As an analogy, suppose you are in a room where everybody is talking," explains Wyithe. "If this room is sparsely populated, then the background noise is louder in some parts of the room than others. However if the room is crowded, then the background noise is the same everywhere. The fact that we see fluctuations in the light from quasars implies that the early universe was more like the sparse room than the crowded room." Astronomers hope to confirm the suppression of dwarf galaxy formation using the next generation of telescopes - both radio telescopes that can detect distant hydrogen and infrared telescopes that can directly image young galaxies. Within the next decade, researchers using these new instruments will illuminate the "Dark Ages" of the universe. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe. |
|
|
|
 |
|||||||||||||||||||||
Eight astronauts, the largest crew in history, spent a week in space during the fall of 1985 aboard shuttle Challenger for mission STS-61A, the first flight dedicated to the German Spacelab. The crew worked in the Spacelab D-1 laboratory conducting a range of experiments, including a quick-moving sled that traveled along tracks in the module. A small satellite was ejected from a canister in the payload bay as well. The astronauts narrate the highlights of the mission in this post-flight film.
Perched atop a trailer-like transporter, space shuttle Discovery was moved May 12 from its hangar to the 52-story Vehicle Assembly Building for mating to its external fuel tank and twin solid rocket boosters in preparation for the STS-121 mission.
The U.S. Astronaut Hall of Fame inducted its 2006 class of shuttle commanders Henry Hartsfield, Brewster Shaw and Charles Bolden. The ceremony was held inside the Saturn 5 museum at Kennedy Space Center.
NASA's twin Solar Terrestrial Relations Observatory satellites (STEREO) arrive via truck at the Astrotech processing facility outside Kennedy Space Center for final pre-launch testing and preparations. They will be launched this summer aboard a Boeing Delta 2 rocket to provide the first 3-D "stereo" views of the sun and solar wind. 
Space shuttle Challenger was transformed into an orbiting observatory to study the sun, stars and space environment during the Spacelab 2 mission in the summer of 1985. But getting into space wasn't easy. The shuttle suffered an engine shutdown on the launch pad, then during ascent two weeks later lost one of its three main engines. It marked the first Abort To Orbit in shuttle history. In this post-flight film, the crew of STS-51F narrates highlights of the mission that includes tests using a small plasma-monitoring satellite was launched from Challenger's robot arm.
A seven-person crew featuring payload specialists from France and Saudi Arabia flew aboard the June 1985 mission of space shuttle Discovery. They narrate the highlights of STS-51G in this post-flight film. Three communications satellites -- for Mexico, the Arab countries and the U.S. -- were launched from the payload bay. And the SPARTAN 1 astrophysics spacecraft was deployed from the shuttle's robot arm for a two-day freeflight to make its science observations before being retrieved and returned to Earth.