3. What is Galaxy ?
A galaxy is a gravitationally bound system of stars,
interstellar gas, dust, and dark matter.
4. Types of Galaxy
There are three main types of galaxies:
Elliptical
Spiral and
Irregular
5. Elliptical Galaxy
Elliptical galaxies are shaped like a
spheriod, or elongated sphere. In the sky,
where we can only see two of their three
dimensions, these galaxies look like
elliptical, or oval, shaped disks
Elliptical galaxies have no particular axis
of rotation
6. Spiral Galaxy
Spiral galaxies have three main
components: a bulge, disk, and halo.
The bulge is a spherical structure found
in the center of the galaxy. This feature
mostly contains older stars.
The disk is made up of dust, gas, and
younger stars.
The halo contains old clusters of stars,
known as globular clusters.
7. Irregular Galaxy
Irregular galaxies have no regular or
symmetrical structure.
Having a lot of gas and dust means
that these galaxies have a lot of star
formation going on within them. This
can make them very bright.
The Large Magellanic Clouds are
examples of irregular galaxies.
8. Milky Way Galaxy
The Milky Way is a barred spiral galaxy.
Milky Way is the galaxy that contains our Solar
System
The Milky Way is estimated to contain 100–400
billion stars. There are probably at least 100
billion planets in the Milky Way .
The Milky Way consists of a bar-shaped core
region surrounded by a disk of gas, dust and
stars.
9. Whirlpool Galaxy
The Whirlpool Galaxy, also known
as Messier 51a, M51a, and NGC 5194.
It was the first galaxy to be classified
as a spiral galaxy.
Its mass is estimated to be 160 billion
solar masses.
Overall the galaxy is about 35% the
size of the Milky Way.
11. What is Star ?
A star is a luminous ball of gas, mostly hydrogen and helium, held together by
its own gravity.
The nearest star to Earth is the Sun.
12. Different Types 0f Stars ?
Protostar
T Tauri Star
Main Sequence Star
Red Giant Star
White Dwarf Star
Red Dwarf Star
Neutron Star
Supergiant Star
13. Protostar
A protostar is a very young star.
Protostar is a collection of gas that has
collapsed down from a giant molecular
cloud.
14. T Tauri Star
A very young, lightweight star, less than
10 million years old.
T Tauri stars don’t have enough pressure
and temperature at their cores to
generate nuclear fusion.
15. Main Sequence Star
The majority of all stars in our galaxy,
and even the Universe, are main
sequence stars.
Our Sun is a main sequence star.
Main sequence stars can vary in size,
mass and brightness.
16. Red Giant Star
A red giant is a luminous giant star of low or
intermediate mass in a late phase of stellar
evolution.
They have radii tens to hundreds of times
larger than that of the Sun.
17. White Dwarf Star
When a star has completely run out of
hydrogen fuel it becomes a white dwarf
star.
A white dwarf shines because it was a hot
star once, but there’s no fusion reactions
happening any more.
18. Red Dwarf Star
A red dwarf is a small and relatively cool
star.
Red dwarfs are very-low-mass stars. As a
result, they have relatively low pressures, a
low fusion rate, and hence, a low
temperature.
Red dwarf stars are able to keep the
hydrogen fuel mixing into their core.
19. Neutron Star
Neutron stars are the smallest and densest stars
known to exist.
Neutron stars are created when giant stars die
in supernovas and their cores collapse.
At present, there are about 2000 known
neutron stars in the Milky Way and the
Magellanic clouds.
20. Supergiant Star
The largest stars in the Universe are
supergiant stars.
They can be thousands of times bigger
than our Sun and have a mass up to 100
times greater.
Direct image of the star “ UY Scuti ” , a red
supergiant which is one of the largest known
stars.
