Milky Way – Introduction
The milky way is a galaxy which contains our Solar System. It contains a dim glowing band arching across the night sky, so it’s name is ‘milky’. It is a barred spiral galaxy. It’s diameter is approximately 1,00,000 – 1,20,000 light years long.
Until 1920, most astronomers think that it contains all stars of our universe but in 1920, some astronomers show that it is the one of many galaxy. It is just a part of universe.
In the observable universe, there are approximately 200 billion galaxy. Milky way have approximately 100-400 billion stars. It have approximately 100 billion planets.
Our solar system located within disk which is 27,000 light years away from Galactic center, on the inner edge of the spiral shaped concentrations of gas and dust called the Orion Arm. Galactic center is a rotational center of the milky way which is evidence of Supermassive Black Hole (SMBH). Scientists say that there are a SMBH in the center of the every galaxy. In milky way, there are a SMBH which name is Sagittarius-A. The mass of the SMBH is 4.1-4.5 million times of the mass of the sun.
Orion Arm is a minor spiral arm of he milky way which is (Orion Arm) 3,500 light years across and 10,000 light years in length. Our solar system lies in the Orion Arm. Other name of the Orion Arm is Local Arm, Orion Spur, Local Spur, Orion Bridge. The full name of Orion Arm is Orion cygnus Arm. Most of the brightest stars are located in the Orion Arm.
All stars and gases which are far away from Galactic center orbit at 200 km/sec. and their rotational period is 240 million years. So we can say that our sun orbit at 200 km/sec.(0.073%of the speed of light) around the milky way and it complete its orbit in 240 million years. The sun orbit around the milky way approximately 18-20 times in lifetime.
The oldest star in our milky way was made when universe began. Milky way has many satellite galaxies. Milky way is a part of Local group (Local group is a group of galaxy. There are 54 galaxy in our Local group.) of galaxies which is component of Virgo Supercluster. All observable stars by naked eye at night is a part of the milky way.
Milky way has a relatively low surface brightness. It looks very brightest from Sagittarius-A. Milky way is a second largest galaxy in local group. Mass of the Milky Way is 5.8 times of 10^11 solar masses which is less than mass of the Andromeda galaxy. Most of the mass of the Milky way appears in the Dark matter. The space between stars is called Interstellar Medium which is a disk of gas and dust.