How milky way and other galaxies are divided?

How milky way and other galaxies are divided?

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1 Answers

Shobhit Varshney IIT Roorkee
askIITians Faculty 33 Points
8 years ago

The galaxy we live in, called the Milky Way Galaxy, is abarred spiral galaxycomposed of at least 100 billion stars. It is approximately 100,000 light years across and about 1000 light years thick. It has a central bulge that is about 10,000 light years in diameter.Our solar system is about a third of the way towards the edge of the Galaxy from the central bulge. If the Solar System were inside the bulge, at night we would be able to see a million stars as bright as Sirius (the brightest star in our night sky). The night sky would be so bright, that it would not seem much different than day. The Sun and Solar System are within the 1,000 light year thick disk, and we are only about 95 light years from the central plane.
The disk of our galaxy appears blue because it has a large proportion of young, hot O and B main sequence stars. The disk contains gas and dust from which stars can form. The central bulge of our galaxy appears yellow or reddish because it contains many red giants and red super giants, but not the short lived blue O and B stars. This shows that the central bulge does not have active star formation going on. The stars in the disk of the Galaxy are generally younger, population I stars, which orbit the central bulge along paths within the disk. The stars and globular clusters in the halo of our galaxy are very old population II stars. They orbit the Galaxy along paths tilted at random angles to the disk. Many of the single stars in the halo orbit the galaxy at very high speeds, relative to the sun and are called high-velocity stars.

At the center of the Milky Way Galaxy is a supermassive black hole. The region where the black hole is located is called Sagittarius A* (prounounced "A star"). The black hole itself cannot be observed partly because it emits no light, and partly because there is too much gas and dust between us and that region for us to be able to observe it. The stars around Sagittarius A* move at such great speeds, that astronomers know that it must be incredibly massive. Estimates show that it must be at least 3.7 million times more massive than our sun. However, it is very compact and at most 45 AU (6.7 billion km) across.

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