AMAZING WORLD OF STARS By Debkumar Bhadra Shore Point, Bambooflat, S Andaman-744107, Email : debkumar_bhadra@yahoo.com
***** Every one of us had sung the rhyme “twinkle twinkle little star, how I wonder what you are ... “ numerous times during our childhood, isn’t it? Apart from featuring in our nursery rhymes, stars have been
important
to civilizations throughout
the
world.
They
have
been
part
of various
religious practices and used for celestial navigation and orientation. Many ancient astronomers believed stars were permanently affixed to a heavenly sphere, and that they were immutable. By convention, astronomers grouped stars into constellations and used them to track the motions of the planets and inferred the position of the Sun. The motion of the Sun against the background stars (and the horizon) was used to create calendars. The currently used Gregorian calendar is a solar calendar, based on the angle of the Earth's rotational axis relative to its local star, the Sun. Let us explore the amazing world or stars that
night sky. Apart from the Sun, Proxima Centauri,
had mesmerized us with its scintillating
which is 39.9 trillion kilometres or 4.2 light-years
presence. Ask a layman, he would say stars are
away is the next nearest star. Light from the Sun
those heavenly bodies that twinkle in the night
takes about 8 minutes to reach earth but it takes
sky. Those with little scientific know how
about 4.2 years from Proxima Centauri to reach
would describe Stars as heavenly bodies which
Earth. The distance is such large.
has its own light. Some may add Sun is the nearest star. Perhaps all the statements are true.
But terming Stars as mere heavenly bodies is just one side of story. Sun, the star nearest to the Earth is
ball
the ultimate source of energy. You are aware, green
of plasma held together by gravity. There are
plants convert the solar energy into useful organic
countless number of stars spread un-uniformly
compounds,
across
photosynthesis. The process uses carbon dioxide
A star is
a
the
massive,
universe.
luminous
Stars,
along
with
especially sugars
interstellar gas and dust are normally grouped
and releases oxygen essential
into
contains
Green plants draw energy directly from the sun,
hundreds of billions of stars, and there are more
whereas all other life forms depend on green plants
than 100 billion (1011) galaxies in the observable
for their energy requirements. Therefore it could be
universe. The sun is only one among the
said nearly all life depends directly or indirectly on
billions of billions of stars that light up our
the sun for its survival.
galaxies.
A
typical
galaxy
for
through our
survival.
The most interesting aspect relating to a Star is its life cycle similar to that of human beings except that the life cycle of a star lasts for several thousand million years. Stars are formed by accretion of clouds of gases containing Hydrogen, Helium and dust, known as nebulae. These clouds under its own gravity contract setting up a dramatic process which converts this dense gas cloud into a Protostar. As the protostar contract, the atoms in the gas collide frequently raising the inner temperature to about 107 Page 1 of 2
degree Celsius. At this temperature Hydrogen nuclei fuse to form Helium, liberating enormous energy in the form of light radiations of different wavelengths. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective processes. The star at this stage is in a state of dynamic
into a dense ball causing the helium to fuse and
equilibrium under two opposing forces. The
form higher elements like Carbon. At this stage
gravitational force trying to compress and ignite
the star is called a White dwarf.
the fusion reaction and the internal pressure generated by the energy released by fusion reaction. This balance can continue for several thousand million years. Our Sun, formed some 5000 million years ago is presently in this balanced stage of its life. It is estimated our Sun will continue in this stage for another 5000 million years driving different life processes on earth.
On the other hand, if the initial mass of the star is much more than that of the Sun, its end would be quite spectacular. The core of the helium formed during the Red giant stage would continue to contract
building
up
higher
and
higher
temperature. The outer envelop then would explode with a brilliant flash called a Supernova explosion. Such explosion could release in one
As the fusion reaction continues in the interior of
second the same amount of energy that the sun
the star, more and more Hydrogen is converted to
would radiate in about a hundred years time.
Helium and after some time, the matter in its core will mainly consist of Helium. The fusion reaction
After the supernova explosion, only the core
will stop in the core. The internal pressure would
would survive. The vast gravitational forces
drop and it would begin to contract once again
would crush the core to tremendous densities
under its gravity. However in the outer shell, the
forming a Neutron star.
fusion reaction will continue. The outer shell will expand resulting in increase in the surface area and decrease in the intensity of the light radiation. The star at this stage would change colour and appear red hence this stage is called Red giant.
The fate of the neutron star depends on its mass. It has been estimated that a heavy neutron star could continue to contract infinitely. This implies the vast amount of matter in the neutron star would eventually be packed into a small ball of
Once a star reaches the Red giant phase, its future
highly dense matter called a Black hole. The
would depend on its initial mass. It has been
gravitational pull in a black hole is so great even
understood that stars with an initial mass similar
light cannot escape from it. Black holes have been
to that of our Sun would loose its expanding shell.
known to distort the space around them, and can
The core left behind would gradually condense
suck neighbouring matter including stars.
This is how stars pass through different stages of their life as we do. They take birth, grow younger and die after a certain age, lighting up our life during the intervening period of birth and death. So next time when you hear a child singing twinkle twinkle little star, you know there is more to it than the rhyme. Those twinkling stars are in-fact the driver of all life on our planet earth.
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