FORMATION OF HUGE GASEOUS MASS: STAR
- By Rahul Kumar
- Batch(2k18), Deptt. of chemical Engg.
- BIT Sindri, Dhanbad
What comes to your mind when you hear
the word star! I guess, the famous rhyme of our early childhood-Twinkle twinkle
little star, how I wonder what you are? But the question is why do stars twinkle?
In this blog we will focus on the gaseous component of stars, their types, and some
unfamiliar facts regarding their ages.
Stars are huge celestial bodies made
up mostly of gaseous components along with dust layers. They are luminous
(light emitting) components made up of plasma. It contains gaseous composition
of hydrogen and helium, which make the whole body luminous along with heat. The
process of releasing energy pushes the weight of layers outside the star making
it stable.
Stars are the main components of our
galaxies, or to be precise, the building block of the universe although there
are billions more present. According to
the data collected by astronomers, there are 300 billion stars in our Milky Way
galaxy. So, it becomes impossible to predict the actual figure. The closest
star to our Earth is the Sun.
HOW DO STARS FORM?
Stars get formed due to the gaseous
composition and the dust clouds called “nebulae”. “Nebulae”, which is the most
famous and closest cloud to Earth, lies about 1500 light years away and is
visible to observers from November through April each year. The composition is
mainly molecular hydrogen that gets converted into helium and radiating x-rays.
It also emits an enormous amount of energy, keeping the star hot and shining
brightly. The life cycle of a star spans billions of years. In general, more
massive the star, shorter it’s life span.
Over a span of thousand years,
gravity cause clouds of dense matter inside the nebula to collapse under their
own weight due to the spinning motion of the huge cloud. Clumps (bunch of
stars) begin to form, and they start becoming hotter and hotter as they gain more
mass. When the temperature inside such a “young interstellar” (matter and a radiation exist in a space between
the star systems in a galaxy) reaches 10 million degrees Celsius, a process
called “nuclear fusion” ignites, and a star is born. It takes millions of years
to create families of stars.
Below illustration shows several
steps during the formation of sun like stars.
(A) – Dust and gas in the space
between stars, also called the interstellar medium, ISM collapse into a dense
ball of gas called prestellar core.
(B) - The prestellar core eventually
becomes the sun, a very huge structure.
(C) - During the collapse, a disk
like structure forms around the core, while at the poles two jets are emitted.
(D) - The star stops growing at a
certain point, but the gas continues falling into the disk. After a few million
years this process also halts.
(E) - The star is now born, while
the planets are being formed from the left-over material, which will eventually
become a solar system.
(F) - A solar system typically lives
for 10 billion years after the formation process.
HOW DO STARS DIE?
Stars take millions of years to die unlike
humans but eventually they too meet their ends. Star's death depends upon its
mass after they finish their formation. Stars with masses similar to the sun
die much differently from stars that have more solar masses. But the process of
star death turns out the same for all stars: as they run out of fuel. Firstly,
star fuses its gases present in the nuclei i.e. hydrogen to make helium. When
that runs out, the stars fuses helium which is turned into carbon. Each level
of fusion releases more energy, which heats up the star.
In sun-like stars, the increased
heating causes them to swell up to become giant stars. Any nearby planets get
enveloped by this expanding star. Eventually the outer stellar atmosphere blows
away, creating an expanding cloud of gas around the star. This is called a
“planetary nebula”. What’s left out, slowly shrinks and cools. Eventually they become
a white dwarf.
The fusion process takes place until
they reach a point where the core collapses as these stars are much more
massive than the Sun. The outer layers also collapse onto the core and then
rebound out to space in a catastrophic explosion called a supernova (powerful
and luminous stellar explosion).
When stars die, all the elements
created in their cores are scattered in space, to become part of interstellar
clouds of gas and dust. These chemical elements serve as seed materials for new
generations of stars, planets, and life.
TYPES OF STARS -
CLASSIFICATION
Although there are several ways to classify the
types of stars. The easiest system for understanding the classification of
stars is Morgan – Keenan system. Stars are classified in this system using
letters O, B, A, F, G, K, and M. They are classified based on their
temperature. The hottest is O and the coolest is M. Further, the temperature of
each class of spectral letter is then sub divided by the addition of a number
where 0 stands for the hottest and 9 for the coolest.
FACTS ABOUT STARS
• Approximately, there are 9,096 stars visible to
our naked eye in the entire sky. For more, one must take a telescope in their
use to reveal stars.
• You can only see about 2,000 stars on a very
dark night with the naked eye from any given place on Earth. To do this, you
need to observe them on a moonless night and be far away from sources of light
pollution.
• Astronomers estimate suggest there are trillions
of stars in the Milky Way Galaxy.
• Most stars travel the galaxy with companions or
in clusters. But not all stars do that; our Sun, for example, moves throughout
the galaxy without a stellar companion.
• The more massive a star, the shorter its
lifespan. A very massive star may live only tens of millions of years, while a
cool dwarf will shine on for billions of years. At an age of about 4.5 billion
years, our Sun is considered middle-aged.
• The oldest accurately dated star chart appeared
in ancient Egyptian astronomy in 1534 BC.
• In 185 AD Chinese astronomers were the first to
record a supernova (powerful and luminous stellar explosion) which is now
classified as SN 185.
• The distance of an individual star has been
observed. It is about 100 million light years from the Earth in the M100 galaxy
of the Virgo Cluster.
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