A black hole is a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. 

• The largest black holes are called “supermassive.” These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center.  
• The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths. 

• Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in.  
• The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now. 
• The sun will never turn into a black hole. The sun is not a big enough star to make a black hole. 

Source: NCERT and The Hindu