The Life Cycle From birth to death
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The Life Cycle
From birth to death
What is a star?
The objects that heat and light the planets in a system
A star is a ball of plasma held together by its own gravity
Nuclear reactions occur in stars
(H He)
Energy from the nuclear reactions is released as electromagnetic radiation
Characteristics of Stars
1) DISTANCE
Measured in light-years
The distance which a ray of light would travel in one year
About 6,000,000,000,000 (6 trillion) miles
186,000 miles per second
2) Magnitude (brightness)
A measure of brightness of celestial objects
Smaller values represent brighter objects than larger values
Apparent magnitude
How bright a star appears to be from Earth
Absolute magnitude (luminosity)
How bright a star actually is
3 & 4) Temperature & Color
The color of a star indicates the Temperature of the star
Stars are classified by Temperature
Decreasing Temp. (bright to dim)
http://www.seasky.org/cosmic/sky7a01.html
Hertzsprung-Russell Diagram
Birth of All Stars
In the nebula
Gases swirl and get hot - nuclear
fusion starts = a star is born!!!
Protostar - “earliest” star
Here is a nebula.
……and a protostar is born.
Life SpanDepends on its mass
Less mass = longer life
Small stars can live to 200 billion years
Medium (like our sun) live about 10
billion
Large (15x bigger than the sun) can live 10
million years
Death of Stars
Occurs when they run out of fuel
No more nuclear fusion
Beginning of the end
All main sequence (average) stars
become red giants
This is the beginning of the death
of a star
The inside shrinks and the
outside expands
The core heats up and releases energy.
The star heats, expands, reddens and
becomes a ……
Red Giant
The helium core continues to heat.
The last of the hydrogen gases drift
away.
These drifting gases form a nebula ring around
the star.
The star is dying. It grows fainter and
fainter.
Gravity causes its matter to collapse
inward.
The star is squeezed into a……
White Dwarf
Blue/white core is left behind
Size of Earth - very dense
Glow faintly
A chunk of the white dwarf the size of a sugar cube
They are so packed together…..
When the white dwarf’s energy is
gone,
it becomes a dead star/black dwarf
Would equal the mass of a CAR!
This is a white dwarf with a nebula cloud around it.
Massive Stars
……begin with about 6 times as much mass as our sun.
Like medium sized stars:
They burn hydrogen at first.
They redden as their helium core forms.
But, instead of becoming red giants ….
they become supergiants.
They expand into supergiants.
What happens next?
When the fuel runs out, gravity collapses the core
even more.
The iron core absorbs energy instead of releasing it….
The star breaks apart in a terrific
The entire sky is lit up for weeks.
The temperature can be more than 100 billion degrees.
The iron atoms fuse into uranium.
The uranium and gases explode into space.
A gigantic cloud of gas and dust is left and
may become a new nebula.
New stars can come from the nebula
remains.
A Supernova
This supernova is
surrounded by a nebula ring.
Neutron StarAfter the supernova explosion of a star 6-30 times
the mass of the sun, a neutron star remains.
How big is it?
a chunk the size of a sugar cube
It’s only about 16Km in diameter,
but it has so much mass packed into it,
has the mass of ~ 100
MILLION CARS!!!
Black Hole
Caused by the most massive stars - 40x
more massive than the Sun
Mass is left - gravity is so strong it
compacts
Packing 5 Suns into 15 miles!
The gravity from this black hole
is pulling this matter into itself.
Black holes are like invisible cosmic vacuum cleaners.
They swallow both matter and energy.
How can we find them if we can’t see them?
Matter falling into a black hole
releases large bursts of X-rays.
We can’t, for sure.
We can detect these.
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