The Birthplace of Stars The space between the stars is not completely empty. Thin clouds of hydrogen and helium, seeded with the “dust” from dying stars, form in interstellar space.

Dark Clouds gather

Molecular Clouds Sometimes (especially in spiral arms), the gas is compressed enough that the dust is thick and gravity can collapse knots in these “molecular” clouds to make new stars.

The Initial Collapse The center of the cloud is densest, so it collapses first. Pressure is removed in an wave moving out at the speed of sound. Material free-falls inside this wave and crashes into a growing (and glowing) central object. We see only the infrared light emerging from the large dust core.

Galactic shear and turbulence give every core a little spin (once round in 10 million years). But they get a lot smaller, and the spin goes up – to orbital! It is for this reason that we believe there are many planetary systems – it is part and parcel of the star formation process to make a disk. Typical Galactic spin makes disks about the size of our Solar System… A little bit of spin goes a long way…

The Sword of Orion The nearest great stellar nursery to us is the great Orion molecular cloud which is about 1000 light years away, and manufacturing thousands of stars. This is probably how the typical star is made.

The glowing tip of a molecular “cigar” The Orion nebula is powered by 4 high mass luminous stars, which have cleared out their birthplace and are eating at a long cloud pointed at us. The Trapezium

Nearby, lower mass stars are forming Hubble Space Telescope

They look like little windsocks The blast from the luminous stars is eating away at the little guys

The heart of them contains a potential new solar system “Proplyds” are new star-disk systems

With powerful bipolar jets

The Star-Disk System Forms while infall continues

Jets remove excess angular momentum

In the center - T Tauri Stars The new young star is exposed, while the accretion disk is still in place. The spectrum of all is seen together (so we don’t have to image disks in order to know they are there).

Half the time, two (or more) stars form

Most stars form in clusters The typical cluster doesn’t stay bound once the stars form. The remaining 80-90% of the gas dissipates and the stars drift apart.

Star Formation is Beautiful, but ephemeral Within about 10 million years, the birth-cloud is shredded, and the disks are dissipated. The process of starbirth has ended.

The stage is set for planet formation