When Atoms Collide

Narrator (April Hobart, CXC): Where can we observe light emitted by atoms? The answer: Here, there, and everywhere.

Atoms are the building blocks of matter. They are also constantly in motion, moving at speeds of thousands of miles per hour at room temperature up to millions of miles per hour behind a supernova shockwave. When an atom collides with another atom at such tremendously high speeds, energy gets transferred. This extra energy has to go somewhere and it is often released in the form of a light wave.

You may not think you have seen this happen, but chances are you have. Most of us have seen the neon lights of a diner or maybe even the strip of Las Vegas. Those bright neon lights glow because of these atomic collisions. Here's how: These signs are made from glass tubes filled with atoms of neon, argon, mercury or other gases. When an electric field is run through the tube, this energizes the atoms inside, making them collide. Each type of atom will release different colors of light, which is how we see these kaleidoscope displays on signs everywhere.

Some of us have also been lucky enough to see the light from colliding atoms on an even bigger scale here on Earth. We're talking about the famous light shows called the "Northern Lights" in the Northern Hemisphere, or "auroras" in other parts of the world. Auroras happen when streams of charged particles from the Sun push on the Earth's magnetic field and energize electrons and protons. These pumped-up particles are then channeled toward the Earth's North and South poles where they collide with atoms in the Earth's atmosphere. There's mostly oxygen and nitrogen in the Earth's atmosphere, and those two atoms are responsible for the red, green, and purple colors we see in these spectacular displays.

The phenomenon of light being produced from the collision of atoms is not confined to events here on Earth. Rather, we see this same process millions and billions of miles away in space. When a massive star explodes, it generates an outgoing shock wave that travels through the gas around the now-dead star. The shock wave heats the atoms and electrons in this gas to several millions of degrees. Collisions between fast-moving electrons and atoms behind the shock wave transfer energy to the atoms in the debris field, such as oxygen, neon, silicon and iron. The excess energy is then radiated as X-rays, which we can see using telescopes like NASA's Chandra X-ray Observatory.

So remember, the next time you see the inviting lights of a diner, it's not just the owner who’s responsible for putting up that neon sign. You are witnessing a process that helps light up objects and places from here on Earth all the way to those far away across the Universe.