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Дата изменения: Unknown Дата индексирования: Sat Dec 22 01:32:28 2007 Кодировка: Поисковые слова: propulsion |
Astronomy Picture of the Day |
APOD: 2006 March 21 - The Coma Cluster of Galaxies
Explanation:
Almost every object in the above photograph is a galaxy.
The Coma Cluster of Galaxies
pictured above is one of the densest
clusters known - it contains thousands of
galaxies.
Each of these galaxies houses billions of stars -
just as our own Milky Way Galaxy does.
Although nearby when compared to most other
clusters,
light from the Coma Cluster
still takes hundreds of millions of years to reach us.
In fact, the
Coma Cluster is so big it takes light
millions of years just to go from one side to the other!
Most galaxies in Coma and other clusters are
ellipticals,
while most
galaxies outside of clusters are
spirals.
The nature of
Coma's X-ray emission is
still being investigated.
APOD: 2005 November 22 - A Galactic Collision in Cluster Abell 1185
Explanation:
What is a guitar doing in a cluster of galaxies? Colliding.
Clusters of galaxies are sometimes packed so tight that the
galaxies that compose them
collide.
A prominent example occurs on the left of the
above image of the rich
cluster of galaxies Abell 1185.
There at least two galaxies, cataloged as
Arp 105 and dubbed
The Guitar
for their familiar appearance, are pulling each other apart gravitationally.
Most of Abell 1185's hundreds of galaxies are
elliptical galaxies, although
spiral,
lenticular, and
irregular galaxies are all clearly evident.
Many of the spots on the above image are fully galaxies themselves containing
billions of stars, but some spots are foreground stars in our own
Milky Way Galaxy.
Recent observations of
Abell 1185 have found unusual globular clusters of stars that appear to belong
only to the galaxy cluster and not to any individual galaxy.
Abell 1185 spans about one million
light years and lies 400 million light years distant.
APOD: 1999 April 4 - Hot Gas and Dark Matter
Explanation:
Is the
gravity of the galaxies seen in this image
high enough to contain the glowing hot gas? Superposed on
an optical picture of a group of galaxies
is an image taken in X-ray light.
This picture, taken by ROSAT, shows confined hot gas
highlighted in false red color, and provides
clear evidence that the gravity exerted in
groups and
clusters of galaxies
exceeds all the individual component galaxies combined.
The extra gravity is attributed to
dark matter, the nature and abundance of
which is one of the biggest
mysteries in astronomy today.
APOD: 2005 September 26 - Streams of Stars in the Virgo Cluster of Galaxies
Explanation:
How do huge clusters of galaxies evolve?
To help find out, astronomers pointed the wide-angle
Burrell-Schmidt telescope on
Kitt Peak National Observatory in
Arizona,
USA at the nearby
Virgo Cluster of Galaxies.
After hundreds of 15-minute exposures taken over two months in early 2004,
the result is a dramatically deep and wide angle image of
Virgo, the closest
cluster of galaxies to our
Milky Way Galaxy.
Bright foreground stars have been digitally removed from
the image but are still represented by numerous unusual dark spots.
Inspection of the
above image
shows unusually large halos for the brightest galaxies as well as
unusual faint streams of stars connecting
Virgo galaxies
that previously appeared unrelated.
The above image
allows a better reconstruction of the past few billion years
of the gigantic
Virgo cluster and illuminates the dynamics of
clusters of galaxies in general.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings, and
Disclaimers
NASA Official: Jay Norris.
Specific rights apply.
A service of:
EUD at
NASA /
GSFC
& Michigan Tech. U.