Transcript Codes of Life

The Life Cycle of Stars
The Life of Stars
• Stars have a life cycle that goes from Birth
to Death and undergo various changes
during their life cycle.
The Birth of Stars
• Stars are formed by the collapse of large clouds of
interstellar matter – which is mostly hydrogen gas.
• The raw ingredients of a star are produced in nebulae.
Forming a Protostar
• The nebula’s gas and dust come closer together,
forming a protostar.
• As more material is packed into the protostar, the
centre gets hotter and hotter until a nuclear fusion
reaction begins.
The main Sequence Star
• Once the fusion reactions start a
main sequence star, like our
Sun, is formed.
• In these reactions atoms of
hydrogen are fused together to
form helium with vast amounts
of heat and light given out.
Death of a star
• Stars have a limited amount of hydrogen fuel
which eventually runs out. Those stars, like our
Sun will last for about 10 billion years before this
happens.
• Eventually when all of the hydrogen has been
consumed the star expands massively in diameter
to become either a red giant or red supergiant –
depending upon the size of the original star.
Stars the size of our Sun
• A star the size of our Sun will
start to use helium as a fuel
producing carbon. It also begins
burning hydrogen in its
atmosphere and will expand 100
times to become the red giant
• When this happens to our Sun (in
about 4 billion years) all inner
planets and the Earth will be
incinerated.
Stars the size of our Sun
• Outer layers of the star and the
carbon within them are blown
away to form clouds in space
which form new stars and planets
(planetery nebula).
• Without the pressure produced by
the nuclear reactions the
remaining centre collapses to
form a very dense core called a
white dwarf.
Stars with a mass ten times the Sun
• Stars with a mass 10 x the
Sun use up the hydrogen fuel
much more rapidly (about 30
million years) and become a
red supergiant.
• The inner core collapses in
less than a second causing a
huge explosion called a
supernova.
Stars with a mass ten times the Sun
• The supernova explosion blasts
matter into space and shines for
about a month.
• The remains of the star form a
neutron star having a mass three
times the Sun but with a diameter of
only 20 kilometres!
• A teaspoon of matter from a neutron
star would have a mass of a billion
tonnes!
Pulsars
• A pulsar is a rapidly rotating neutron star with a strong
magnetic field.
• A pulsar emits radio waves that sweep across space as it
rotates.
Black Holes
• If a star is massive enough, it collapses even more than
a neutron star to form a black hole – an object so dense
that anything close by will be drawn into it by its
overpowering gravity.
The following remaining slides
contain some images of nebulas
taken by the Hubble space telescope
• THE TRIFID NEBULA. A 'STELLAR NURSERY', 9,000
LIGHT YEARS FROM HERE, IT IS WHERE NEW
STARS ARE BEING BORN.
• THE PERFECT STORM, A SMALL REGION IN THE
SWAN NEBULA, 5,500 LIGHT YEARS AWAY,
DESCRIBED AS 'A BUBBLY OCEAN OF HYDROGEN
AND SMALL AMOUNTS OF OXYGEN, SULPHUR
AND OTHER ELEMENTS'.
• THE ANT NEBULA, A CLOUD OF DUST AND GAS WHOSE
TECHNICAL NAME IS MZ3, RESEMBLES AN ANT WHEN
OBSERVED USING GROUND-BASED TELESCOPES. THE
NEBULA LIES WITHIN OUR GALAXY BETWEEN 3,000 AND
6,000 LIGHT YEARS FROM EARTH.
• NEBULA NGC 2392, CALLED ESKIMO BECAUSE IT
LOOKS LIKE A FACE SURROUNDED BY A FURRY
HOOD. THE HOOD IS, IN FACT, A RING OF COMETSHAPED OBJECTS FLYING AWAY FROM A DYING
STAR. ESKIMO IS 5,000 LIGHT YEARS FROM
EARTH.