# Why do planets orbit stars?

Apr 15, 2018

There are two ways of explaining this phenomena :-

#### Explanation:

1)  Newtonian Gravitational theory :-

A Planet revolve around a Star because of the mutual gravitational interaction between them and this force is given by $F$

$\left\{F = \frac{G M m}{r} ^ 2\right\}$

where $M$ is the mass of the star

$m$ is the mass of the planet

$r$ is the distance between their centres

$G$ is the Universal Gravitational constant

2) Einstein's General theory of Relativity :-

This theory tells us that the Space-Time is like a piece of Fabric and the mass of an object causes to bend the curvature of Space-Time around it. And more massive the object is , the more space it bends around it.

So, in case of Star and a planet , since the star is more massive ; so it bends the space around it much more than the planet does ; which causes the planet to be in a state of falling towards the star ( just like gravitational interaction) which causes it to orbit the star.