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Hubble observes celestial composition SPACE TELESCOPE SCIENCE INSTITUTE NEWS RELEASE Posted: September 4, 2003
In November 1994, the light of a supernova in nearby NGC 3370 reached Earth. This stellar outburst briefly outshone all of the tens of billions of other stars in its galaxy. Although supernovae are common, with one exploding every few seconds somewhere in the universe, this one was special. Designated SN 1994ae, this supernova was one of the nearest and best observed supernovae since the advent of modern, digital detectors. It resides 98 million light-years (30 megaparsecs) from Earth. The supernova was also a member of a special subclass of supernovae, the type Ia, the best tool astronomers have to chart the growth rate of the expanding universe. Recently, astronomers have compared nearby type Ia supernovae to more distant ones, determining that the universe is now accelerating in its expansion and is filled with mysterious "dark energy." Such measurements are akin to measuring the size of your room by stepping it off with your feet. However, a careful measurement of the length of your foot (to convert your measurements into inches or centimeters) is still needed to know the true size of your room. Similarly, astronomers must calibrate the true brightness of type Ia supernovae to measure the true size and expansion rate of the universe.
Adam Riess, an astronomer at Space Telescope Science Institute in Baltimore, Md., observed NGC 3370 a dozen times over the course of a month and has seen many Cepheid variables. Already he and his colleagues can see that these Cepheids are the most distant yet observed with Hubble. Because of their need to observe this galaxy with great frequency to record the variation of the Cepheids, the total exposure time for this galaxy is extremely long (about one full day), and the combined image provides one of the deepest views taken by Hubble. As a result, thousands of distant galaxies in the background are easily discernable.
The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). |
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