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 at far
left, 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.
The middle 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.
The picture at right 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.
STScI-PRC01-04
January 11, 2001
|
