What is a Galaxy?
A Galaxy is a large system of stars, gas, dust.
Galaxies are held together by gravity.
Galaxies come in different shapes spiral,elliptical, and irregular.
Galaxies are constantly moving and can collide with each other.
How do the galaxy form?
After 100 million years after the Big Bang, hot and dense gas
allowed first stars to form, with new stars being born 10 times
faster than today's Universe.
Galactic Composition
Galaxies are collections of stars, dust, gas, and dark matter,
which are bound together by the gravitational attraction that
results from their own mass.
A small dwarf galaxy contains a few million stars, whilst the
biggest known galaxies can contain up to a hundred trillion
stars.
Types of Galaxy
Elliptical galaxies-These galaxies are round or oval in shape,
with stars spread fairly evenly throughout.
Spiral galaxies-These galaxies have a distinctive shape with
spiral arms, a central bulge, and a faint halo of stars.
Irregular galaxies -These galaxies have no identifiable shape
or structure, and often appear chaotic.
Milky Way Galaxy
The Milky Way, which includes the Solar System, is our galaxy.
It is a spiral galaxy with a black hole and a bulge in the middle.
You can see a band that looks as though milk is spilt through
the night sky from a really dark place. This is the milky way
Galaxies around us
The Local Group is a group of galaxies that includes Milky Way
and around 80 other galaxies
Some of the galaxies include Andromeda galaxy, large
Magellanic Cloud and Canis Major dwarf galaxy
Collisions
Galaxy collisions play an important role in the evolution of
galaxies.
When two galaxies collide, their gravitational fields interact,
causing the galaxies to deform the stars and other bodies
within them to rearrange.
Though galaxies contain a lot of empty space, collisions can
compress gas clouds, spurring new bouts of star formation,
creating a starburst galaxy.
This is a violent process, but the galaxies don't smash into
each other. Instead, the galaxies' stars follow new
trajectories.
Mergers
If colliding galaxies don’t have enough momentum to move past
each other, they can merge to form a single larger galaxy.
A merged galaxy can look very different from the two that
created it. For example, if a spiral and elliptical merge, the
result could be an irregular galaxy.
The Milky Way and Andromeda galaxies are also expected to
collide and merge in a few billion years.
Galactic Cannibalism
Galactic cannibalism is a type of merger that occurs when one
galaxy is much larger than the other.
The larger galaxy often absorbs most of the smaller galaxy's
gas and stars, with little other significant effect on the larger
galaxy.
Gravitational ripples can disturb both, throwing gas, dust, and
stars outward. The result can be a ring of material at the edge
of the new galaxy that is full of the material needed to form
new stars – a ring galaxy.
While some material is thrown outward, other material can
stream toward the core and fuel the galaxy’s central black
hole, resulting in an active galactic nucleus.
The Milky Way is thought to be currently engaging in galactic
cannibalism, absorbing smaller galaxies like the Canis Major
Dwarf Galaxy and the Magellanic Clouds
Zombie Galaxy
A zombie galaxy is a galaxy that's considered "dead" but they
still collide and produces stars at a diminished rate
Usually in Zombie galaxies, old massive stars run out of fuel
that produces energy and they explode creating a Supernova.
The Supernova releases a lot of cosmic dust which can help to
create new planets and new life.
Sometimes the supernova develops into a black hole giving more
strength to the galaxy.
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