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WHEN ATOMS COLLIDE
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.