FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

The Perfect Galaxy? The Milky Way

If you could give away one galaxy in our universe to as many people as you could, how many people would receive one before you ran out? Thousands of people? Hundreds of thousands?

It turns out that everybody on this entire planet could have his or her own galaxy. Wait! Make that many galaxies. Amazingly, there are enough galaxies out there that every man, woman, and child on planet Earth could call more than 20 galaxies their own. There are at least 100 billion of them out there, each with tens to hundreds of billions of stars.

Needless to say, the universe is big and chock-full of galaxies.

We have an idea of how big the visible universe is and approximately how many galaxies are out there, but no one can really comprehend the enormity of it all.

So at the risk of drowning you - and myself - in the vastness of space, let's just talk today about how galaxies are arranged and why the location of our own galaxy, the Milky Way, is so critical to life on Earth.

At the very beginning, over 13 billion years ago, just after the creation of the universe, what "stuff" there was in those early days began to clump under the influence of its own gravity.

Now back then there was nothing much more than hydrogen and helium, as far as the "normal" stuff goes. The other stuff would include dark matter, but that's for another day.

This hydrogen and helium could clump together to form the first stars. Those first fields of stars would be like wannabe galaxies, things we might describe as misshapen starry blotches in the cosmos.

Through mechanisms still not well understood, these first mini-collections of stars could attract each other into enormous collections of stars - the first recognizable galaxies.

All this clumping and coming together meant that a lot of the universe became uninhabited, that is, vast voids opened up between those clumps. The universe would start to look like a map of our country – far-reaching stretches of emptiness lined through with roads of small burgs and large metropolises.

Some of those monstrous galaxy factories could churn out 1000's of galaxies in a particular area of the universe, a collection we humans would later call galaxy “clusters.”

We ourselves belong to a huge cluster of clusters called - to no one's surprise - the Local Supercluster.

Now this would be nothing much more than some interesting space trivia, except for the fact that our place in this supercluster is supercritical to life on this planet. Why?

We do not want to be in the middle of those clusters, believe me. Those seemingly innocent galaxies are not just sitting around doing nothing. They are close. They are interacting. They are gravitationally attracted to each other. They are tearing each other apart.

But aren’t they really far, far away from each other? Not really.

The average distance between the stars within those galaxies is enormous, to be sure. If an average star were the size of a grapefruit, the next nearest grapefruit star would be on the other side of our country. There is puh-lenty of space between them.
But if the average galaxy were grapefruit-sized, the next nearest grapefruit galaxy would just be tens of feet away. That’s very close and leads to a lot of intergalactic harassment.

We should be thankful that the Milky Way galaxy, our home, is sitting out here in the distant suburbs of our cluster. Here we are practically alone. Here we can retain our incredibly critical spiral shape. There are no other nearby biggies that will rip us up into galactic shreds. And life on this little planet can flourish.

Again, even when we aren’t looking for it, we inevitably find another way our planet is perfect for life. Earth is placed perfectly in a perfect type of galaxy in a perfect location on the outskirts of a perfect cluster. What a wonderful world!

Until next time, clear skies!
Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me