Star-Formation

Read: Chapter 17

Key Concepts:

Stars form by the gravitational 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 protostellar disk turns into a system of planets orbiting the star.

Schematic of Star-formation Process:

Fragmentation of protostars in a molecular cloud.

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:

Pictures of Star-forming Regions

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 main-sequence phase?

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 DEGENERACY PRESSURE

Electrons cannot be smushed so hard that two electrons occupy the same place at the same time.

(Pauli Exclusion Principle)

ANIMATIONS:

Triggered Star Formation Animation (from IPAC website)

This 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)

Formation of a Star Cluster: Computer simulations show that a collapsing gas cloud fragments into individual stars with disks, jets, etc.

Movie 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.

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