Download Stars and Galaxies

Stars & Galaxies
A star is born…

A star is made up of a large amount of
gas, in a relatively small volume.

A stellar nebula, on the other hand, is a
large amount of gas and dust,
spread out in an immense
volume.

All stars begin their lives as parts of
stellar nebulas.
A star is born…

Gravity can pull some of the gas and
dust in a nebula together.

The contracting cloud is
then called a protostar.

A star is born when the contracting
gas and dust become so hot that
nuclear fusion begins.
Lifetimes of Stars…

Before they can tell how old a star is,
astronomers must determine its mass.

Medium - Mass stars, such as the Sun,
exist for about 10 billion years.
Lifetimes of Stars…

Stars with more mass have shorter
lives than those with less mass.

Small stars use up their fuel more
slowly than large stars, so they have
much longer lives, about 200 billion
years.
Lifetimes of Stars…
Stars form in a stellar
nebula, from collapsing
clouds of interstellar gas
and dust.
The rest of the life
cycle depends on the
mass of the star
When a star runs out of fuel, it
will become a white dwarf, a
neutron star, or a black hole.
Main Sequence Stars…

Small and medium stars first
become red giants.

Their outer layers expand to become red
supergiants.

Eventually, the outer parts grow bigger
still and drift out into space.
Main Sequence Stars...

The blue, white, hot core is left
behind causing a white dwarf.

When there is no more energy, it
becomes a black dwarf. It is the
remaining burnt-out cinder left, as the
star goes out.
Supernova…

A dying giant, or supergiant star, can
suddenly explode. Within hours, the star
blazes millions of times brighter.

The explosion is called a supernova.
Neutron Stars…

After a star explodes, some material
from the star is left behind. This
material may become part of a
planetary nebula.

The core will compress
and form a neutron star.

Neutron stars are even
smaller and more dense
than white dwarfs.
Black Holes…

The most massive stars may have more
than 40 times the mass of the Sun. One
might have more than 5 times the mass
of the Sun left, after it becomes a
supernova.

The gravity of this mass is so strong
that the gas is pulled inward, packing it
into a smaller and smaller space. These
massive stars become black holes when
they die.
Types of Galaxies – Quasars…

A quasar is a distant
galaxy with a black
hole at its center.

As enormous
amounts of gas
revolve around a
black hole, the gas
heats up and shines
brightly.
Types of Galaxies – Elliptical...

Elliptical galaxies look like
flattened balls.

These galaxies contain billions
of stars, but have little gas and
dust between the stars.

Because of the lack of gas and dust,
new stars cannot form in most
elliptical galaxies, and so they
contain only old stars.
Types of Galaxies – Irregular…

Some galaxies
do not have
definable,
regular shapes
and are known
as irregular
galaxies.
Types of Galaxies – Spiral

Our Milky Way galaxy has
recently (in the 1990s) been
confirmed to be a type of
spiral galaxy known as a
barred spiral galaxy.

Spiral galaxies consist of a
flat, rotating disk with stars,
gas, and dust and a central
concentration of stars,
known as the bulge. The
bulge is surrounded by a
much fainter halo of stars.
The Universe…

Universe is space and everything in it.