Happening of Aurora

You may be very delighted to see the wonderful scenes of northern lights from Earth, but have you ever thought how it happens, lets see.
Sun have huge magnetic field around it, which clashes with other magnetic fields in space, this led to throwing of heavy rocks and dust away from it. This is called Solar winds. Solar winds are very dangerous. But on earth we don't need to worry because of earth's own magnetic field arose due to spinning of molten iron over core. This magnetic field repels the dust particles making us safer. But when heavier rocks hit earth's magnetic field with great speed, the atmosphere shakes a little causing disturbance in surrounding a refraction of light causind auroras.

The mystery of Black Holes!

Black Holes have been 

Let us consider an example how a black hole is formed. On the stars nuclear fusion of four hydrogen atom to form a helium atom goes on continuously. Slowly in the later time when the gases i.e. fuel goes on decreasing on a star the star approaches its death. A stage comes when the fuel over it completely depletes. This is the time when gravitational force wins and the star shrinks to a high density ball. Ratio of the radius is just like earth compared to a football. According to the formula of escape velocity

V_esc = square root of (GM/R)

Where;

 G stands for gravitational constant

M stands for mass of star

R for radius of star

Now refer the table and see the effect on escape velocity.

Class	Mass	Size
Supermassive black hole	~105–109 times MSun	~0.001-10 AU
Intermediate-mass black hole	~103 times MSun	~103 km = radius of earth
Stellar black hole	~10 times MSun	~30 km
Micro black hole	up to ~MMoon	Up to ~0.1 mm

See this, the escape velocity becomes greater than even the highest speed limit i.e. velocity of light. This means even  light cannot escape a black hole.