Giant Molecular Clouds

This image shows a filament of cosmic dust over ten light years long! It’s part of a giant cloud of cold gas and dust that’s starting to collapse under its own gravity to form stars. Newborn stars are hidden inside. The cosmic dust grains here are so cold that observations at millimeter wavelengths were needed to detect their faint glow, shown as orange in this false-color image.

Giant molecular clouds like this range from 15 to 600 light-years across. And they’re very dense… for outer space, that is. While space in the Solar System has about one atom per cubic centimeter, a giant molecular cloud has between 10 or 1000, and this shoots up in regions that are collapsing. The total mass of a giant molecular cloud can thus be huge: over 10,000 times that of the Sun.

As a giant molecular cloud collapses, it forms filaments and clumps. The dense parts of these filaments and clumps are called ‘molecular cores’. These can easily have 1000 to 1,000,000 particles per cubic centimeter. Of course this rises much higher in regions where stars are formed.

Somewhere like this is where our Solar System was born. The dust grains became our Earth. Some of the complex organic compounds floating around became you and me.

But this one is in the constellation of Taurus. It’s called the Taurus molecular cloud, and hundreds of new stars are being born here:

• Wikipedia, Taurus molecular cloud.

Most of the gas in a giant molecular cloud is molecular hydrogen, helium, and carbon monoxide. They also contain methanol, ethanol, benzene, ammonia and other things. The dust is mainly silicates, iron and organic compounds along with some ices. Next time I’ll tell you about polycyclic aromatic hydrocarbons, which get pretty complicated and interesting: