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Newborn stars emerging
from "eggs" — not the
barnyard variety — but
rather, dense, compact
pockets of interstellar
gas called evaporating
gaseous globules
(EGGs). Hubble found
the "EGGs,"
appropriately enough, in
the Eagle nebula, a
nearby star-forming
region

7,000 light-years

from Earth in the
constellation Serpents

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One of the
nearest globular
star clusters,
called NGC 6397,
resembles a
treasure chest of
glittering jewels.
The cluster is
located

8,200

light-years

away

in the
constellation Ara.

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Stellar swarm, M80
(NGC 6093), one of
the densest of the
147 known globular
star clusters in the
Milky Way Galaxy.
Located about

28,000 light-years

from Earth, M80
contains hundreds
of thousands of
stars, all held
together by their
mutual gravitational
attraction.

The Sagittarius Dwarf Tidal Stream
Drawing Credit & Copyright: David Martinez-Delgado (MPIA) & Gabriel
Perez (IAC)
2003 September 30

Explanation: Recent wide field images and analyses now indicate that
our home galaxy is actually still in the process of devouring its closest
satellite neighbor. This unfortunate neighbor, the Sagittarius Dwarf
galaxy, is now seen to be part of a larger Sagittarius Tidal Stream, a
loose filament of stars, gas, and possibly dark matter that entangles
the

Milky Way

. An artist's depiction of the stream is shown above.

Speculation also holds that the

Sagittarius Dwarf

was once pulled

through the

Milky Way disk

very close to our

Sun's current location

. An

important resulting realization is that galaxies contain a jumble of
clumps and filaments of both dim and dark matter.

NGC 1313, (

13.5 M light years

) a bright but rather isolated galaxy

classified
as a barred spiral galaxy (although with very short and irregular spiral
arms). This galaxy has recently (within the past billion years) collided
with a satellite galaxy, and the material at the bottom-right of this
picture are the remains of the satellite galaxy.

Our galaxy is just one of thousands that lie within 100
million light years. Galaxies tend to cluster into groups,
the largest nearby cluster is the Virgo cluster a
concentration of several hundred galaxies which
dominates the galaxy groups around it. Collectively, all
of these groups of galaxies are known as the Virgo
Super-cluster. The second richest cluster in this volume
of space is the Fornax Cluster, but it is not nearly as
rich as the Virgo cluster.

Number of galaxy groups within 100 million light years

= 200

Number of large galaxies within 100 million light years

= 2500

Number of dwarf galaxies within 100 million light years

= 25000

Number of stars within 100 million light years = 200

trillion

The Virgo Cluster

The Virgo cluster is a massive cluster of galaxies which dominates
the Virgo super-cluster. There are roughly

2000 galaxies

in this

cluster (although ninety percent of them are dwarf galaxies). This
cluster has a diameter of approximately

15 million light years

which is not much larger than our Local Group but it contains fifty
times the number of galaxies.

It is not possible to get a good photograph of the entire Virgo cluster because
the galaxies are rather faint and small objects scattered across 15 degrees of
the sky. Below is photograph of the centre of the cluster showing the inner 4°x4°
region. Most of the brightest objects in this picture are galaxies. The elliptical
galaxy in the centre is M87. On the right can be seen two other large elliptical
galaxies - M86 and M84. To the left of M87 is another large elliptical galaxy
M89 and above M89 is the large spiral galaxy M90.

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Hubble telescope was used to observe 19 galaxies out to

108 million light-

years

. Almost 800 Cepheid variable stars, a special class of pulsating star

used for accurate distance measurements were discovered. Here is a picture
of one of those galaxies. It is the spiral galaxy NGC 4603, the most distant
galaxy in which Cepheid variables have been found. It is associated with the
Centaurus cluster, one of the most massive assemblages of galaxies in the
nearby universe.

A rare and spectacular head-on collision between two galaxies appears in this Hubble telescope

picture of the Cartwheel Galaxy, located

500 million light-years

from Earth in the constellation

Sculptor.
The striking ring-like feature is a direct result of a smaller intruder galaxy — possibly one of two
objects to the right of the ring — that careened through the core [close-up image at lower left]
of the host galaxy. Like a rock tossed into a lake, the collision sent a ripple of energy into space,
plowing gas and dust in front of it. Expanding at 200,000 mph, this cosmic tsunami leaves in its
wake a firestorm of new star creation. Hubble resolves bright blue knots that are gigantic
clusters of newborn stars [close-up image at upper left] and immense loops and bubbles blown
into space by exploding stars (called supernovae) going off like a string of firecrackers

Number of super-clusters in the visible universe = 10 million

Number of galaxy groups in the visible universe = 25 billion

Number of large galaxies in the visible universe = 100 billion

Number of dwarf galaxies in the visible universe = 10 trillion

Number of stars in the visible universe = 20 billion trillion

It is probable that our universe is infinite and has been
filled with matter everywhere since the Big Bang There is
also good evidence that in the early universe, the
universe may have expanded much faster than the speed
of light. It is possible to inflate space so that although
particles are not traveling fast, the space between
particles increases enormously.

The Hubble Deep Field

Almost every object in this image is a galaxy typically lying

5 to 10 billion light years

away.

The galaxies revealed here are all shapes and colors, some are young and blue,
whereas others are old, red and dusty.

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