Star Nurseries

This has to do with how a star forms.

Astronomers have known for some time that stars form in interstellar clouds, basically nebula, but not much was known about the process.

What they do know is that a cloud of gas and dust will remain in hydrostatic equilibrium until something changes. In other words the kinetic energy of the gas is balanced with the potential energy of the gravitational force. What has to happen is some sort of kick in the cloud, so to speak, in which supernova explosion or cloud collision sends out a wave of energy that compresses the gas cloud so that it causes a gravitational collapse. As the gas spirals around, a core forms that begins to increase the pressure on the gas in the core. As the pressure increases in the core it heats up to millions of degrees. Eventually, over a few hundred thousand years, the core is dense enough and hot enough to begin fusing hydrogen into helium. When this happens a new star is born.

The heat is needed because hydrogen atoms don't want to fuse and just repel one another. They have to be moving fast enough to overcome this repelling force.

The birth of stars was previously not observable because of the opacity of the gas cloud they form in. Using infrared, observing the birth event becomes possible. X-rays are also useful for observing the formation and development of new stars.

Keep in mind that this is how our sun formed. The process is common and is happening all over the universe, but observing the process in distant galaxies is not easy. Most of the observations of new stars have been made in our galaxy. Even then, stars that we see today were born thousands of years ago, and the photons from the star take thousands of years to get out of the star's core to its surface before it can get to us.

The reality is that what we see when we look up at the sky is a diverse history of star formation, life on the main sequence, and death. Stars like ours have a finite lifespan, and these phases of their lives are visible in space.

Thanks for reading.