Life cycle of a star

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Transcript Life cycle of a star

Life Cycle of a Star
A Star Nursery!
– Stars are born in nebulae.
– Nebulae are huge clouds of dust and gas
– Protostars (young stars) are formed when
the dust and gas collapse (come together and
become a dense “ball”) as gravitational
attraction increases
– Main sequence stars form when protostars
further collapse
Dumbbell nebula
Large Ant Nebula
Horsehead nebula
How are different Stars formed?
Nuclear fusion occurs in the center of the
Hydrogen fuses with other Hydrogen to
form Helium
Its size will change how fast the Hydrogen
fuses, determining what type of star it will
Fusion and Gravity
The energy released by fusion causes the
gases to expand while gravity tries to
compact it.
This battle continues throughout the life of
the star.
These two forces determine the stage and
size of the star throughout its life.
Life of a Star
Size of the star determines its life span.
Example: Betelgeuse
– red supergiant
– 20 times more massive than the Sun; 14,000 times
– burns nuclear fuel 14,000 times faster than the Sun.
– The Sun will live about 7,000 times longer than a
massive star like Betelgeuse.
Our Sun - 10 billion year life (5 Billion years have
– Stars less massive than the Sun have even longer life
Main Sequence Stars - Young Stars
Energy comes from nuclear fusion,
– convert Hydrogen to Helium.
– Most stars (about 90%) are Main Sequence Stars.
Hotter = brighter (white, yellow, red).
The hotter they are the quicker they burn
The sun is a typical Main Sequence star.
Red Giant
Relatively old star
Diameter is about 100 times bigger than
when first formed.
Cooler than when formed (the surface
temperature is under 6,500 K).
Red Giant
After a few billion years the center of a star runs
out of hydrogen.
It then begins to cool and contract. The outer
layers of the star fall inwards and heat up the
center. A shell surrounding the central core
becomes hot enough to fuse protons so the star
gains a new source of energy. Because it is
hotter now, the outer parts start to swell.
The star becomes a red giant.
Planetary nebula
When the helium core runs out, and
the outer layers drift of away from the
core as a gaseous shell, this gas that
surrounds the core is called a
Planetary Nebula.
The remaining core (that's 80% of the original
star) is now in its final stages. The core
becomes a White Dwarf the star eventually
cools and dims. When it stops shining, the
now dead star is called a Black Dwarf.
Supernovas occur when a red supergiant
Supernovas are considered to be the most
powerful explosions in the universe, as
they represent the collapse of the most
massive stars.
Smaller supernovas leave the supergiant's
core behind in the form of a neutron star.
Neutron Star
Neutron stars are really dense. They have
between 1.4 and 3 times as much mass as
the Sun, but are compressed into a ball
with a radius of about 10 km.
A thimbleful of a neutron star would weigh
more than 100 million tons on earth
Neutron stars can
sometimes be
detected as pulsars
Pulsars are neutron
stars that rotate and
emit electromagnetic
radiation only along a
single axis. They
seem to “pulse”
Black Holes
Black Holes
• Created when the remaining core of a
giant star continues to collapse on itself,
essentially creating a hole in space.
• Black holes are so dense that nothing
entering its gravitational field ever
escapes, not even light! The edge of a
black hole, the point of no return, is
referred to as the event horizon.