When we look at a spiral galaxy like the one on the left, we see most of its light coming from the central region. Most of the mass is concentrated at the centre of the galaxy which keeps the stars in circular orbit in the galaxy. Because most of the mass of the galaxy is concentrated in the centre, then we would expect that stars further from the centre would move at a slower velocity than stars closer to the centre. For example, in the solar system, most of the mass of the solar system is concentrated in the Sun.The velocities of planets decreases outwards.
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Have you ever wondered how astronomers know what stars are made up of just from planet earth? Stars like our own sun are million miles away from us, we don't have that advanced technology that we can go there and check what is the basic structure of stars, its mass and its temperature etc. So how astromers study them from earth? Well in this blog I'm going to explain you how just by using simple techinque they study them.
Matter-Antimatter Asymmetry :
Our universe is observed to consist of matter. Today there is no evidence of antimatter in the form of stars, galaxies, galaxy clusters or any form of cosmological antimatter. However, antimatter should have been plentiful when the temperature of the universe was high enough to create matter- antimatter pairs. In order to prevent complete annihilation of matter and antimatter, About four and one half billion years ago our protosun was slowly collapsing under the force of its gravity. As it did this, due to the immense compression caused by gravity it became extremely hot. Millions of degrees centigrade. The more compact it got, the hotter it got.
How do we know dark matter exist?
We know dark matter exist because we can see an effect of dark matter on galaxies and other objects, its gravitational effect on normal matter (the stuff that we are made up of) and we can see the effect through gravitational lensing. |
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