Stars form within dense clouds of cold gas and dust. As the gas
collapses under its own gravitational attraction, the core heats up
until nuclear fusion begins - a star is born. All this occurs deep
within clouds so dense that visible light cannot escape. But, radio
waves can escape and we can use those radio waves
to figure out what happens when a star is born. Once a star or a
cluster of stars "turns on", the heat from the star can ionize
parts of the cloud around it producing regions of ionized gas (HII
regions) which emit radio waves. The new star(s) also heat dust in
the cloud which then emits radio waves which we can detect. This
"warm" dust (at a temperature of only 10 to 100 degrees above
absolute zero) may be located in a circumstellar disk around the new
star - a disk that astronomers believe may be the birth place of
planets like our own solar system.
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