MAGNIFICENT DETAILS
IN A DUSTY SPIRAL GALAXY
In 1995, the majestic spiral galaxy
NGC 4414 was imaged by the Hubble Space Telescope
as part of the HST Key Project on the Extragalactic
Distance Scale. An international team of astronomers,
led by Dr. Wendy Freedman of the Observatories of
the Carnegie Institution of Washington, observed
this galaxy on 13 different occasions over the course
of two months.
Images were obtained with Hubble's
Wide Field Planetary Camera 2 through three different
color filters. Based on their discovery and careful
brightness measurements of variable stars in NGC
4414, the Key Project astronomers were able to make
an accurate determination of the distance to the
galaxy.
The resulting distance to NGC 4414,
19.1 Megaparsecs or about 60 million light-years,
along with similarly determined distances to other
nearby galaxies, contributes to astronomers' overall
knowledge of the rate of expansion of the universe.
The Hubble Constant (H0) is the ratio of how fast
galaxies are moving away from us to their distance
from us. This astronomical value is used to determine
distances, sizes, and the intrinsic luminosities
for many objects in our universe, and the age of
the universe itself.
Due to the large size of the galaxy
compared to the WFPC2 detectors, only half of the
galaxy observed was visible in the datasets collected
by the Key Project astronomers in 1995. In 1999,
the Hubble Heritage Team revisited NGC 4414 and
completed its portrait by observing the other half
with the same filters as were used in 1995. The
end result is a stunning full-color look at the
entire dusty spiral galaxy. The new Hubble picture
shows that the central regions of this galaxy, as
is typical of most spirals, contain primarily older,
yellow and red stars. The outer spiral arms are
considerably bluer due to ongoing formation of young,
blue stars, the brightest of which can be seen individually
at the high resolution provided by the Hubble camera.
The arms are also very rich in clouds of interstellar
dust, seen as dark patches and streaks silhouetted
against the starlight.
Credit: NASA, ESA, and the Hubble
Heritage Team (STScI/AURA)
Acknowledgment: W.L. Freedman (Observatories of
the Carnegie Institution of Washington) |
