Tag Archives: Hydrogen

Stellar Evolution Part 2: Main Sequence Stars

When a protostar’s core reaches 15,000,000 degrees Celsius, nuclear fusion begins in its core. This ignition marks the star’s birth as it becomes a main sequence star.

Stars part 2

Main sequence stars have a ton of variety. They range from cooler red stars to hotly burning blue ones, and their size can range from a fraction of our sun’s mass up to several hundred times as large. The only thing that matters for the main sequence is the presence of hydrogen fusion in the core. Hydrogen fusion takes hydrogen ions and turns them into helium, creating massive amounts of energy in the process. The outwards radiation pressure resists the force of gravity, preventing the star from collapsing any further.

Stars Hydrogen Fusion

But once the core runs out of hydrogen, the star starts to contract again briefly, until a shell of hydrogen around the core becomes hot enough to fuse into helium. When this happens, the radiation pushes the outer layers of the star far out into space, turning the star into a red giant. The core continues to collapse, however, continuing to heat up until it reaches 200,000,000 degrees Celsius. At this point, the helium that now makes up the core begins to fuse into carbon. Eventually, the helium will also run out. When this happens, the outer layers of the star continues to expand and cool down until finally all that is left is a planetary nebula with the remnant of the core at the center. We call this remnant a white dwarf.

Stars Planetary Nebula

You may be surprised to not hear the word “supernova” being thrown around. This is because supernovae only occur in incredibly large stars. For most of the main sequence stars, their deaths will be relatively calm and quiet, going out not with a bang, but with a sigh.

Written By: Scott Yarbrough


Explore Hydrogen: WARNING DANGER!

Hydrogen: it’s the most common element in our universe, the main ingredient in stellar fusion, and the lightest element of them all. We love to play with hydrogen in the classroom because it’s highly combustible, which means it’s great for explosions! In this experiment — which is not one we recommend for home DIY — we’ll fill soap bubbles with hydrogen and light them on fire.


Warning: Don’t try this at home!

Hydrogen and oxygen react to form water molecules. So, how do they create such violent explosions? The water molecules have less potential energy than the sum of their hydrogen & oxygen parts, and that extra energy has to go somewhere. It’s released as light and heat! This kind of reaction is called exothermic.


Warning: Don’t try this at home!

In this experiment we trap hydrogen inside of soap bubbles until we’re ready to trigger an explosion. Any container will do the trick, though, as long as it doesn’t block the activation energy. A balloon full of hydrogen creates a bigger fireball than the bubbles you see here. A single spark transforms a blimp filled with hydrogen into a massive firestorm– exactly what happened in the Hindenburg tragedy of 1937. Once the explosion is set in motion, it continues until all available fuel is consumed, for better or for worse.


Photo credit: NBC News


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