January 11, 2001
Photo No: H2001-04a
Hubble's Ultraviolet Views of Nearby Galaxies Yield Clues to Early Universe
Astronomers are using three NASA Hubble Space Telescope images to
help tackle the question of why distant galaxies have such odd shapes,
appearing markedly different from the typical elliptical and spiral
galaxies seen in the nearby universe.
Do faraway galaxies look weird because they are truly weird? Or, are
they actually normal galaxies that look like oddballs, because
astronomers are getting an incomplete picture of them, seeing only the
brightest pieces? Light from these galaxies travels great distances
(billions of light-years) to reach Earth. During its journey, the light
is "stretched" due to the expansion of space. As a result, the light
is no longer visible, but has been shifted to the infrared where present
instruments are less sensitive. About the only light astronomers can see
comes from regions where hot, young stars reside. These stars emit
mostly ultraviolet light. But this light is stretched, appearing as
visible light by the time it reaches Earth. Studying these distant
galaxies is like trying to put together a puzzle with some of the
What, then, do distant galaxies really look like? Astronomers studied 37
nearby galaxies to find out. By viewing these galaxies in ultraviolet
light, astronomers can compare their shapes with those of their distant
relatives. These three Hubble telescope pictures, taken with the Wide
Field and Planetary Camera 2, represent a sampling from that survey.
Astronomers observed the galaxies in ultraviolet and visible light to
study all the stars that make up these "cities of stars." The results of
their survey support the idea that astronomers are detecting the "tip of
the iceberg" of very distant galaxies. Based on these Hubble ultraviolet
images, not all the faraway galaxies necessarily possess intrinsically
odd shapes. The results are being presented today at the 197th meeting
of the American Astronomical Society in San Diego, CA.
The central region of this "star-burst" spiral galaxy, NGC
3310, shows young and old stars evenly distributed. If this were the
case with most galaxies, astronomers would be able to recognize faraway
galaxies fairly easily. In most galaxies, however, the stars are
segregated by age, making classifying the distant ones more difficult.
NGC 3310 is 46 million light-years from Earth in the constellation Ursa
Major. The image was taken Sept. 12-13, 2000.
Photo credits: NASA, Rogier Windhorst (Arizona State University, Tempe,
AZ), and the Hubble mid-UV team.