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7.2
Galaxies
(p.268-274)
PRESENTATION - NOTE
Galaxies
What is a galaxy? The word “galaxy” derives
from the ancient Greek galaktos, which means
milk.
-some galaxies (such as the Milky Way) have a
whitish colour, and often seem like a swirl or
droplet of milk.
Let’s Take a Look
The Black Eye Galaxy
Spiral Galaxy M74
Cartwheel Galaxy
Properties of Galaxies
A galaxy is an immense grouping of stars,
planets and dust. The matter in a galaxy is held
together by gravitational attraction (i.e. it
doesn’t just fall apart and separate)
Within galaxies, there are many long cycles of
star formation (from dust and gas) and
supernovae; more dust and gases.
BLACK HOLES
My picture of the epicentre of a black hole
A simulated view of a black hole
BLACK HOLES
-So what is a black hole?
A black hole is a region of space where gravity is so strong
that nothing, not even light, can escape.
-Why?
Black holes have extremely strong gravitational pulls. They
can pull in stars and accumulate the mass of the stars.
-Where are black holes located?
Astronomers believe that each galaxy contains at least one
supermassive black hole at its centre.
Dark Matter
Astronomers speculate that about 25% of the
universe is filled with dark matter.
DARK MATTER is invisible matter which does
not interact with light or any other type of
radiation (waves).
Because of this, we cannot directly see dark
matter by telescope observation.
GALAXY SHAPES
Okay, so what exactly do galaxies look like?
There are 4 main galaxy shapes by which we
classify:
-SPIRAL
- ELLIPTICAL
-BARRED SPIRAL
- IRREGULAR
Spiral and Barred Spiral Galaxies
Spiral galaxies are named for their spiral shape,
and their spiral arm-like shapes which radiate
from the galaxies centre.
Barred spiral galaxies have what seems to be a
bar across them. The Milky Way is a barred
spiral galaxy.
Spiral and Barred Spiral Galaxies
Spiral Galaxy
Barred Spiral Galaxy
Elliptical Galaxies
Elliptical galaxies are, simply:
-galaxies with an elliptical shape
Their shapes range from almost spherical to footballshaped, to long and cylindrical (like a pencil)
-The largest galaxies in the universe are elliptical
-Contain very little dust-they have fewer young stars than
spiral galaxies. Elliptical galaxies have extremely old stars.
Elliptical Galaxies
Giant elliptical galaxy NGC 1316
Irregular Galaxies
-Irregular galaxies are neither spiral nor
elliptical.
-Because they have NO regular shape, they are
called irregular galaxies.
-Irregular galaxies may be shaped in such
obscure ways because of a collision between
two galaxies or the gravitational pull of one
galaxy which drew stars away.
Irregular Galaxies
Irregular Galaxy NGC 1427A