Life Cycle of the Stars

Life Cycle of Stars

http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg

Average (sun-like) Stars Massive Stars

Life Cycle of Stars• Begin their lives as clouds of dust and gas called

nebulae

• Gravity causes the nebula to contract

• Matter in the gas cloud will begin to condense into a dense region called a protostar

Here are a few examples of some sweet nebulas…

Horesehead Nebula; 1500 light years distant

http://www.nasa.gov/multimedia/imagegallery/image_feature_73.htmlhttp://www.nasa.gov/mission_pages/spitzer/news/spitzer-20070212.html ____________:

A dense cloud of gas and dust; the birthplace of

stars.

NEBULA

Bubble Nebula

Crab Nebula

Eye (of God) Nebula

Particles in the nebula initially hit each other and stick due to

______________________.

Eventually, ____________ of particles pulls other particles in. The pressure and temperature increase

and a _____________ forms.

GRAVITY

PROTOSTAR

Electrostatic attraction

• Matter in the gas cloud will begin to condense into a dense region called a protostar

• As the protostar continues to condense, it heats up.

• Eventually, the protostar reaches a critical mass and nuclear fusion occurs.

• Thus begins the main sequence phase of the star

• Most of its life is in this phase

When the temperature gets hot enough, _______________ begins and the _______ ____________ stage begins.

FUSIONMAIN SEQUENCE

Nuclear Fusion: The process

of taking atom centers (the nucleus) and fusing them together.

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http://www.cosmosportal.eu/cosmos/tr/node/56058

Life Cycle of StarsLife span of a star depends on its size.

– Very large, massive stars burn their fuel much faster than smaller stars

– Their main sequence may last only a few hundred thousand years

– Smaller stars (average, sun-like stars) will live on for billions of years because they burn their fuel much more slowly

Regardless, eventually the star's fuel will begin to run out...

• After Hydrogen is exhausted in core ...– Energy released from nuclear fusion – Counter-acts inward force of gravity.

• Core collapses, – Kinetic energy of collapse converted into heat.– This heat expands the outer layers.

• Meanwhile, as core collapses, – Increasing temperature and pressure ...

Life Cycle of Stars

Life Cycle of Stars• Average stars will expand into what is

known as a Red Giant

• Massive stars will become Super Red Giants

• In the (Super) Red Giant stage:–After helium is exhausted, the outer layers of the star continue to expand, while the core contracts becoming denser and hot enough to fuse larger atoms:. • 12C + 12C --> 24Mg

or… 12C + 4H 16O

• Through a combination of processes, successively heavier elements are formed and burned.

Life Cycle of Stars

A Red Giant You Know

Betelgeuse (520 light years from Earth)

• After a star completely runs out of fuel, itcollapses instantaneously

creating temps at the core upwards of 100 billion degrees

• What happens next depends on the size of the star….

Life Cycle of Stars

• Most average stars (<1.5x Sun’s mass) will blow away their outer atmospheres to form a planetary nebula(no relation to actual planets)

Life Cycle of Stars

Life Cycle of Stars• Their cores will remain behind and burn as

a white dwarf until they cool down– Size of the Earth with mass of the Sun

• 1 tsp = +100 billion tons– Inward force of gravity balanced by repulsive

force of electrons.

• What will be left is a dark ball of matter knownas a black dwarf

As the fuel runs out in a average sized star, _________ slows down. The star will shrink in size, becoming a _________ _______.

fusionWhite Dwarf

A white dwarf is a small, white-hot remnant. They can reach temperatures of 100,000 Kelvin. They are also very dense.

Review: Small/Medium Stars

1. nebula2. protostar

3. main sequence4. red giant

5. planetary nebula/white dwarf6. black dwarf

What about those MASSIVE stars?

Their path is similar for the first four stages…

1. nebula2. protostar

3. main sequence4. SUPER red giant

Life Cycle of Stars• If the star is

massive enough(>1.5x sun’s mass)

the collapse will trigger a violent explosion known as a supernovaWhat happens next depends on the size of the star…

A ___________________ is an _____________ that marks the end of a very massive star’s life. When it occurs, the exploding star can outshine all of the other stars in the galaxy in total for several days and may leave behind only a crushed core.

SUPERNOVA explosion

1987 SupernovaLarge Magellanic Cloud160,000 light years away

Discovered by 14 year old Catherine Moore, on Nov. 7 2008.

Life Cycle of Stars• If it is a Huge Star (1.5x < sun’s mass < 3x) the core

is unable to support itself and it will collapse further to become a neutron star

• In the time it takes you to blink, a neutron star has rotated three times

After a supernovae the remnant may form a __________________.NEUTRON STAR

http://chandra.harvard.edu/photo/2004/rxj1242/index.html

A neutron star is the core of the star, only now it is made up almost entirely of neutrons. A teaspoon of this material could weigh 10 million tonnes!

http://www2.ph.ed.ac.uk/nuclear/photo/

One scientist explained this is like taking the entire red supergiant and smushing it into a sphere 10 miles in diameter!

Life Cycle of Stars• If it is a Giant (massive) Star (>3x sun’s mass), it

will collapse so completely that it will literally disappear from the universe.

• What is left behind is an intense region of gravity called a black hole

Life Cycle of Stars

• To put it bluntly,black holes willblow your mind.

The most massive stars supernovae and form _________________BLACK

HOLES

A black hole is an extremely massive remnant from which light can

not escape. “Black holes are where God divided by zero” Stephen Wright

Black Holes - Dissected

Jet(not always present)

Accretion Disk Event Horizon

Singularity(deep in center)

Stellar Mass Black Hole

Cygnus X-I (in Milky Way galaxy; 8100 light years from Earth)

Supermassive Black Hole

Andromeda (center of Anrdomeda galaxy; 2.5M light years from Earth)

Review: Massive Stars

1. nebula2. protostar

3. main sequence4. super red giant

5. supernova6. neutron star OR black hole