Read: Chapter 17
- Stars form by
collapse of dense clumps of interstellar gas, molecules and dust.
- The collapsing
protostar forms a
disk and jet.
- The collapse
stops when nuclear
fusion begins in the protostar core.
- When a giant
molecular cloud of
interstellar gas forms stars it fragments into several protostars, and
eventually a cluster of stars forms.
- If the clump is
too massive it
splits into a binary star system.
- Eventually the
turns into a system of planets orbiting the star.
Schematic of Star-formation
Fragmentation of protostars in a
Protostellar disks and jets:
A real protostellar disk and jet,
with dark dust lane running through the disk:
A jet from a protostar (at left)
ramming into surrounding gas:
Protostars in the H-R diagram:
How long does it take a protostar
to "reach" the main-sequence, i.e. start nuclear fusion? It
depends on its mass:
What do stars look like inside
when they just finish the proto-star stage and start their
Failed stars: If mass <
0.08 solar masses, nuclear fusion never starts, and we call the object
a "brown dwarf".
Gravitational contraction in brown
dwarfs is halted by Electron
Electrons cannot be smushed so
hard that two electrons occupy the same place at the same time.
(Pauli Exclusion Principle)
animation illustrates the process of triggered star formation.
First, a massive star in its final death throes explodes or "goes
supernova," shooting a shock wave through surrounding clouds of gas and
dust. Next, the shock wave compresses the gas and dust, gravity kicks
in, and finally, a new wave of stars is born. The whole progression,
from the death of one star to the birth of others, takes millions of
years to complete. (14.3 Mb)
of a Star Cluster: Computer simulations show that a
collapsing gas cloud fragments into individual stars with disks, jets,
showing the full evolution of a star cluster, twice. The annotations give the
time (yrs), size (AU), and column density scale (g/cm2)
during the animation.