Our sun and other stars similar to it, do not stay exactly
as they look now. Stellar lifetimes are much longer than ours, but like us they
progress through the different stages of their life. The progression of these
stages is connected to the formation of planets, their fate and events to come
billions of years from now. In this article we will try to learn about the life
cycle of our sun and other stars like it.
The sun
was born in a dense cold cloud of gas similar to nearby cloud in Perseus
Constellation. Within these clouds gravity causes pockets of gas to collapse
into individual stars. Collapse lasts about half a million years. Small amounts
of gas collapse and there remains a disk around the star. Over several million
years the disk may form planets like those in our solar system.
Eventually
the center of the star becomes dense enough to fuse hydrogen atoms into helium
atoms and star takes its place on the main sequence, where it will spend much
of its life. On a main sequence, a star’s luminosity determines its size, mass
and future evolution. After hydrogen burning ends the star starts to leave main
sequence properties and moves on. At 4.5 billion years old our sun is middle
aged star and it is still in the main sequence. Over the next few billion years
the rate of hydrogen fusion will gradually increase causing the sun’s
temperature to increase and its radius to swell. This will cause earth’s ocean
to evaporate and the earth will take an appearance similar to Venus whose
surface is molten. 5 billion years from now the supply of the sun’s hydrogen
for fusion reaction will run out. The Sun once the hydrogen in its core is gone
will leave the main sequence and will become a red giant star. During this
stage the outer layers of the sun will expand until it reaches the 200 times
larger than its current size. This new sun will be larger than the orbits of
Mercury and Venus. They will be swallowed by this expanding star and maybe it
will also swallow earth too.
The Red
Giant phase will last few million years until all the helium in its core also
runs out like hydrogen. Then the sun will go under a cataclysmic process,
blasting out its outer layers and will become a white dwarf. The discarded
layers will be visible as a planetary nebula. As a white dwarf the sun will be
the size of earth and nuclear fusion reaction will no longer occur, but it will
still be luminous because its temperature will remain thousands of degrees. Over
tens of billions of years, this white dwarf will become much cooler and will
become dim and cold as a black dwarf. The time required for a white dwarf to
become a black dwarf is more than the current age of the universe. This means
that there are no black dwarfs now in the universe for us to observe. So we
don’t know what will happen to our sun after trillions of years. So for now we
are save and sun in not a bigger threat to us.
(If you find any error or
miscalculation in this article then please feel free to share in comment and if
you want to expand this article then comment below)
Very well thought out and written. If I may ask a question? When are the heavier elements formed and how?
ReplyDeletehigher elements are formed in stars not in main sequence.... i am preparing another article for this topic... keep visiting... :-)
DeleteVery well. I'm understanding.
Delete