Nearby galaxies yield clues to early universe
SPACE TELESCOPE SCIENCE INSTITUTE RELEASE
Posted: January 11, 2001
Astronomers are using these 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 pieces missing.
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 the "star-burst" spiral galaxy above, 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.
NGC 3310. Photo: NASA, Rogier Windhorst (Arizona State University, Tempe, AZ), and the Hubble mid-UV team SEE FULL PAGE IMAGE
This second image is an example of a tiny, youthful spiral galaxy. ESO
418-008 is representative of the myriad of dwarf galaxies astronomers
have seen in deep surveys. These galaxies are much smaller than typical
ones like our Milky Way. In this galaxy, the population of stars is more
strongly segregated by age. The older stars [red] reside in the center;
the younger [blue], in the developing spiral arms. These small, young
galaxies may be the building blocks of galaxy formation. ESO 418-008 is
56 million light-years from Earth in the southern constellation Fornax.
The image was taken Oct. 10, 2000.
ESO 418-008. Photo: NASA, Rogier Windhorst (Arizona State University, Tempe, AZ), and the Hubble mid-UV team
The last picture shows a cosmic collision between two galaxies, UGC
06471 and UGC 06472. These collisions occurred frequently in the early
universe, producing galaxies of unusual shapes. The Hubble telescope has
spied many such galaxies in the deep field surveys. The ultraviolet
images of this galaxy merger suggest the presence of large amounts of
dust, which were produced by massive stars that formed before or during
this dramatic collision. This dust reddens the starlight in many places,
just like a dusty atmosphere reddens the sunset. Studying the effects of
this nearby collision could help astronomers explain the peculiar shapes
seen in some of the distant galaxies. UGC 06471 and UGC 06472 are 145
million light-years from Earth in the constellation Ursa Major. The
image was taken July 11, 2000.
UGC 06471 and UGC 06472. Photo: NASA, Rogier Windhorst (Arizona State University, Tempe, AZ), and the Hubble mid-UV team SEE FULL PAGE IMAGE