The Life Cycle of Stars

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The Life Cycle of Stars
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The Life of Stars

• Stars have a life cycle that goes from Birth to
  Death and undergo various changes during their
  life cycle.

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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.

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Forming a Protostar

• The nebulas 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.

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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.

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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.

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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.

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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.

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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.

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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!

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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.

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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.

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The following remaining slides contain some
images of nebulas taken by the Hubble space
telescope
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• THE TRIFID NEBULA. A 'STELLAR NURSERY', 9,000
  LIGHT YEARS FROM HERE, IT IS WHERE NEW STARS ARE
  BEING BORN.

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• 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'.

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• 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.

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• NEBULA NGC 2392, CALLED ESKIMO BECAUSE IT LOOKS
  LIKE A FACE SURROUNDED BY A FURRY HOOD. THE HOOD
  IS, IN FACT, A RING OF COMET-SHAPED OBJECTS
  FLYING AWAY FROM A DYING STAR. ESKIMO IS 5,000
  LIGHT YEARS FROM EARTH.