The Rogue Star
on Thursday January 5th, 2017, By Pavan Maru

​Those of you have watched Interstellar and are now familiar with the concepts of blackholes and wormholes, while, some of you might still be banging their heads over it. Well, that’s where we come in and help you understand the concept of black holes.

All the stars, including our sun, burn because of nuclear fusion reactions taking place on their surface and their core. Eventually, they will run out of fuel required for these reactions and when this happens, they can no longer sustain themselves.
So, what happens to them when they cannot sustain themselves? 

Stars like the Sun

When the core runs out of hydrogen fuel, it will contract under the weight of gravity. However, some hydrogen fusion will occur in the upper layers. As the core contracts, it heats up. The core will become hot enough to cause the helium to fuse into carbon. When the helium fuel runs out, the core will expand and cool. The upper layers will expand and eject material that will collect around the dying star to form a planetary nebula. Finally, the core will cool into a white dwarf and then eventually into a black dwarf. This entire process will take a few billion years.

Stars More Massive Than the Sun

When the core runs out of hydrogen, these stars fuse helium into carbon just like the Sun. However, after the helium is gone, their mass is enough to fuse carbon into heavier elements such as oxygen, neon, silicon, magnesium, sulfur and iron. Once the core has turned to iron, it can burn no longer. The star collapses by its own gravity and the iron core heats up. The core becomes so tightly packed that protons and electrons merge to form neutrons. In less than a second, the iron core, which is about the size of the Earth, shrinks to a neutron core with a radius of about 6 miles (10 kilometers).

The outer layers of the star fall inward on the neutron core, thereby crushing it further. The core heats to billions of degrees and explodes (supernova), thereby releasing large amounts of energy and material into space. The shock wave from the supernova can initiate star formation in other interstellar clouds. The remains of the core can form a neutron star or a black hole depending upon the mass of the original star.

When the core forms a black hole , it’s density increases and a large amount of mass is concentrated in a core of a small volume. The gravitational field increases several times and to such a level that not even light can escape it and thus we cannot see them as there is no light coming out of them. They can however be located due to the distortions they cause in space and time.

It is largely believed that black holes slow down the time around them due to the massive gravitational energy, and this property is known as time dialation. Let’s not forget that time is relative quantity!
Let us now talk about some common terms related to black holes:

1) Event Horizon
   : It is the defining feature of any black hole, a boundary beyond which events cannot affect an outside viewer . If matter and energy cross this boundary, they cannot return. They  can only travel in one direction, i.e. towards the black hole due to the massive gravitational pull. Light emitted from inside the event horizon can never reach the outside observer. Likewise, any object approaching the horizon from the observer’s side appears to slow down and never quite pass through the horizon, with its image becoming more and more red-shifted as time elapses. The traveling object, however, experiences no strange effects and does, in fact, pass through the horizon in a finite amount of proper time. From here to the central singularity will take 0.0001 seconds in proper time, in free fall, for a 30 solar mass(1 solar mass=1.389*10^30 kg, the mass of our sun) black hole. This infall time is proportional to the mass of the black hole. It is the point of no return. This is one of the reasons why the mass of black holes always increases.

2)Singularity      : It is the point inside the black hole where all its mass is concentrated. A region where the space time curvature becomes infinte and the volume reduces to zero. Therefore , its density is infinite. This gravitational singularity is a point for non-rotating black holes and is smeared out in the form of a ring , lying in the plane of rotation, for rotating black holes. Observers falling into a ‘Schwarszchild’ black hole( non-rotating and uncharged) cannot avoid being pulled into the singularity , once they cross the event horizon.

To conclude this topic:

Will  you  survive the journey?

The answer is NO! Before you reach the singularity , you will be pulled by the tidal forces and be torn apart. This process is called ‘Sphagettification’ or the ‘Noodle Efffect’. If by some miracle you survive this and reach the singularity , you will be crushed to zero volume there and your mass will be added to the total mass of the black hole!

Black holes are very important.They are the life force of each and every galaxy, and are present at the centres , and all the galaxies revolve around them.

 

Pavan Maru

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