A Guest post by Atul Kumar Sinha from physics in my view

Star to Blackhole

Well, whatever is born; must die at some point. Its nature’s one and only
inevitable rule that everyone has to follow. I mean, whether it is you, or me,
or anyone; one day everyone has to die. Therefore, so is the fate of a star.
The death of a star is its eventual fate. In this article, I will give you a
stellar glimpse related to the death of a star. In other words, I will tell you
how do stars die? Or what happens when a star dies?

Death Of A Star

Well, nothing lasts forever. Frankly speaking, I hate this catchphrase.
Because it’s a painful and saddest truth you will ever listen to. Coming back
to the topic of discussion. You would be amused to know that star’s life and
death are somehow related to each other. I mean both of them occurs due to the
same astronomical phenomena. The gravitational collapse is responsible for both
the formation of a star as well as the death of a star.

What Causes The Gravitational Collapse Of A Star

A star is nothing but a ball of hydrogen gases. Though, there are other
gases too that constitute the mass of a star. But these additional gases are
almost negligible as compared to the available mass of hydrogen gas in stars.
So, when a star runs out its nuclear fuel (i.e hydrogen and other gases), it
gravitationally collapses under its own gravity. Meaning, the thermal energy
will no longer be able to prevent the star from collapsing.

Well, thermal energy or thermal pressure is the energy generated inside the
stellar core due to the nuclear fusion reaction. So, when there is no nuclear
fuel left, meaning there is no thermal energy generated. Therefore, there is no
energy or pressure (thermal energy) to counterbalance the effect of gravity. As
a result, a star will collapse causing a supernova. Hence a star collapses i.e
the stellar death of a star.

 

How Do Stars Die?

Well, the death of a star doesn’t mean that it has met its eventual fate. In
fact, after its stellar death, the story of a star becomes more interesting.
The questions like what happens when a star dies can only be answered after the
stellar death of a star. I mean, after the death of a star, it can either
become a white dwarf or a neutron star. A star can even become a black hole.
Well, all these possibilities that whether a star will become a white dwarf or
a neutron star or it will become a black hole simply depends on the stellar
mass of a star.

For A Star To Become A White Dwarf

As I said, the stellar mass of a star plays a prominent role. For a star to become a white dwarf, its stellar mass should
be in the range of 0.07 to 10.0 solar masses. For a star, whose mass is between
the mentioned mass, it will continue to collapse until an equilibrium position
is reached.

In the case of white dwarfs, the electron degeneracy pressure will
counterbalance the effect of gravity to protect the star from further
collapsing. The remnant of a star ( in this case is a white dwarf) can have
mass up to 1.4 solar masses. This mass limiting formula is known as Chandrashekar Limit.

For A Star To Become A Neutron Star

Well, for a star to become a neutron star, its stellar mass
should be in the range of 10.0 to 29 solar masses. In the case of neutron
stars, the neutron degeneracy pressure will counterbalance the effect of
gravity to protect the star from further collapsing. (At 10. 0 solar mass,
there can be overlapping between neutron stars and white dwarf); that is still
a riddle to be solved.

The remnant of a star ( in this case is a neutron star) can have a mass of
up to 2.14 solar masses. This mass limiting formula is known as
Tolman-Oppenheimer-Volkoff Limit i.e TOV limit. Unlike, Chandrashekar limit,
the TOM limit is still debatable. Meaning the TOM limit has no certain
mathematical value. It changes as per the latest discovery of a neutron star.

For A Star To Become A Black Hole

Similarly, for a star to become a black hole, its stellar mass should
be more than 29.0 solar masses. Well, there is no upper mass limit for a black
hole. I mean, to date, we don’t have it. But maybe in the near coming future, we
could have it. Or maybe won’t. I mean black holes are the
eventual fate a star can have. Therefore, there is no need for any upper mass
limit for a black hole.

 

Fate Of Our Sun

How is it possible that I would conclude this article without discussing the
eventual fate of our sun. I mean the sun is also a star. Therefore, in the
future, it will too run out of its fuel and eventually collapse under its own
gravity. Now you would be wondering what could be the fate of our sun. I mean, what will happen when the sun dies? Will the sun become a
black hole? Will the sun become a neutron star? OR, Will the sun become a white
dwarf?

The sun, also known as G-type main-sequence star will die after almost 5
billion years. And when it will die, it will eventually become a white dwarf.
Simply because of its stellar mass. The sun is not big enough to become a
neutron star or a black hole. But I can assure you that it will eventually
become a white dwarf. But for that to happen, it will take more than 5 billion
years. Therefore, if you want to see the eventual fate of our sun, you have to
wait for 5 billion years. Can you?

 This article was originally written by Atul Kumar Sinha. He holds a webpage physics in my view. Thanks Atul for the Guest posting in our blog. Hope more articles colloboration help us preach science to all.