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Birth of Stars
October 17th, 2016
Nicole Arulanantham
Image Credit: NASA/JPL-Caltech/STScI
Energy from stars is essential to life!
Colliding atoms (green
circles) undergo
nuclear fusion in the
stellar core, which
releases energy
Stars come in a wide range of
temperatures!
Our Sun
Spectral Type: G2
What would happen to the liquid
water on Earth if…
• We moved it to an O-type star (T = 30,000 K) and
placed it at the same distance that it currently is
from our Sun (T = 5800 K)
• We moved it to an M-type star (T = 3000 K) and
placed it at the same distance that it currently is
from our Sun
• In each of these cases, where should we place
the Earth to prevent these effects?
Stellar Nurseries
• Stars are born in large interstellar clouds of
gas: Giant Molecular Clouds
• Each cloud can make thousands of stars
• Make-up: ¾ Hydrogen, ¼ Helium, 1-2%
heavier elements, called ‘metals’
• Life is made from the metals!
Stellar Nurseries
Image Credit: NASA/JPL-Caltech/STScI
Stars form in
spiral arms of
galaxies, e.g.
the Southern
Whirlpool
Protostars in
Aquila
Protostars erupt
Lives of Stars
• Metals are crucial to life, they are made in
stars
• When a star dies, it returns these to the
spaces between stars, the ‘interstellar
medium’
• New stars incorporate the metals, also into
their surrounding disks, where planets form
• Thus, life depends on the life cycle of stars!
• ‘We are stardust’ (Joni Mitchell)
Figure 8.1
Star’s
Life
Cycle
© 2014 Pearson Education, Inc.
Larger (hotter) stars return material to the interstellar
medium through supernova explosions (like the Crab
Nebula)
Image Credit: NASA, ESA, J. Hester, A.Loll (ASU)
Smaller (cooler) stars eject their outer layers as
planetary nebulae (like the Ring Nebula)
Image Credit: NASA/ESA, and the Hubble
Heritage/Hubble Collaboration
Table 8.1
Contents of the
Solar Nebula
© 2014 Pearson Education, Inc.
Most of the “stuff” in stars is hydrogen
and helium!
Figure 8.4a
Stars form in the
center of broad,
spinning disks
Arms
out,
slower
spin
Arms
in,
faster
spin
© The Worlds of David Darling
© 2014 Pearson Education, Inc.
Figure 8.4b
© 2014 Pearson Education, Inc.
Summary: Birth of Stars
• Originally only gas and dust, no stars
• First stars form from Giant Molecular Clouds
• Later stars include metals essential to life from
earlier stars: solid planets possible
• Stars form in the spiral arms
• Star forms from disk, then planets too