By far the most common question I get while working at the observatory is, “What is a Nebula?” The answer is complex, because there are many different kinds of nebulae. One of the things many nebulae have in common is that they are related to the lives of stars in very interesting ways. Nebulae can serve as both the graveyard and the birthing ground of stars.

One type of nebula, called a molecular cloud, is basically just a sparse cloud of atoms and molecules. The action begins when the cloud is in some way compressed, either by its own gravity or by some kind of shock, like a nearby supernova. This creates unusually dense regions, which collapse and trigger star formation. The first stars to form will be the big hot blue ones, which simultaneously illuminate the surrounding gas while stripping it away, carving out luminous, colorful bubbles in the interstellar medium.

Now we’ll skip ahead to when a star dies. During the latter stages of their lives, stars expel large amounts of material into space. If a star is around the mass of the Sun, when it dies it will collapse into a white dwarf, a highly dense and hot object which excites and ionizes the gas around it. The gas then emits its own radiation in beautiful spectral lines. I love to study planetary nebulae, because while they often have similar structures, they are all so unique and beautiful.

In the case that a star is several times more massive than the Sun, when it dies, it will go out in the form of a supernova. Supernovae are evidence that God likes explosions too.  You can quote me on that. The star’s outer layers will explode outwards while its core will collapse into either a neutron star or a black hole. Once the unimaginably intense light from the supernova fades, the light signatures from the various elements in the gas can be seen in dazzling array. The supernova’s shock wave is propelled outwards at speeds up to 30,000 km/s (10 percent the speed of light), compressing the interstellar medium and enriching it.  This leads to the birth of new stars with more heavy elements, which also means a greater chance of forming a terrestrial planet like Earth.

This has been only a brief overview of the different kinds of nebulae out there.  Hopefully you have gained a new appreciation for these incredible objects. For high resolution zoomable images of awesome nebulae, go to hubblesite.org, or check out Calvin’s own observatory website for images that we’ve taken. If you want to see nebulae for yourself, I invite you to come visit the observatory. Calvin’s observatory is open Monday through Thursday from 7:30 p.m. to 11 p.m. if it’s clear.