A galaxy is a large collection of stars, gas, and dust held together by gravity. The Milky Way galaxy is the one that contains our solar system. There are different types of galaxies including spiral, elliptical, and irregular galaxies. Estimates suggest there are between 100 billion and 200 billion galaxies in the observable universe. The smallest known galaxy is the dwarf galaxy Sextans, while the largest galaxy discovered is over 16 million light years long.

1. The Galaxies
PHYSICS PRESENTATION

2. What is a Galaxy?

3. Supermassive Black Hole

4. The begginig of galaxies: Quasars

5. The Milky Way
 The Milky way is the galaxy in
which we live, it covers the
entire solar system and of
course our planet, it is located
in the center of the local group
together with the Andromeda
galaxy and the triangle galaxy.

6. Types of Galaxies: Spiral Galaxies
 This ones can be recognized by their wide, flat disks of rotating gas and dust,
some spirals have wide flung arms, while others have spirals that are more tightly
bound.

7. Elliptical galaxies
 Elliptic galaxies: contain mostly older stars, this means that they are often not as
bright as spiral galaxy

8. Irregulars galaxies
 Irregulars galaxies: There are unidentified shapes
whose stars, gas and dust are scattered randomly

9. How many galaxies are there in the
observable universe?
 An acceptable range is between 100 billion and 200 billion

10. The smallest Galaxy
 This is the dwarf galaxy Sextans which, with a mass 100,000 times less than the
Milky Way, has devoured an even smaller companion

11. The biggest Galaxy
 The galaxy, called Alcyoneus, is 16.3
million light-years long, about 80 bigger
than the Milky Way.

12. What are the closest galaxies to ours?
The closest to the Milky Way is the Canis Major dwarf satellite galaxy.
Then in order we have:
Canis Major dwarf galaxy: 28,000 light years away.
Sagittarius Elliptical Dwarf Galaxy: 70,000 light years away.
Large Magellanic Cloud: 165,000 light years away.
Boötes dwarf galaxy: 197,000 light years away.

13. Philosophical thinking
 We are not alone in space but
we do not have the resources
and technology to discover
whats inside every planet,
black holes, galaxies or
universes