Thursday, September 8, 2011

The Milky Way Galaxy: A Memoir

Galaxies like me live for hundreds of billions of years, which seems like a long time, but a lot has happened in the mere 13 billion years of my existence so far. My life has been anything but boring.

Galaxy Birth

The memories of my very first years remain fuzzy and diffuse, but I know I came into existence soon after the Big Bang. The first stars that formed in the Universe were BIG! So big that they lived very brief and powerful lives and quickly exploded, causing a series of events that resulted in my formation!

The energy from the explosions of the first stars initiated the gravitational collapse of huge halos of material. I am the result of one of these gravitationally bound systems. When I was born I contained lots of dark matter and gas, which quickly churned into thousands of millions of stars.

Star Formation and Supernovae Explosions

Hydrogen gas was the fuel inside me that I turned into a range of stars, big and small. The stars were either born as twins, gravitationally bound to each other as they slowly moved around my center every 200 million years or so, or they formed their own planets, or both!

I contain about 400 billion stars today and continue to form new stars at a steady rate of a few each year. I probably harbour more planets than stars, but the planets are very hard for me to sense since they are so tiny and do not produce their own light.

A recently discovered supernova in the Pinwheel Galaxy.  Image Credit:  LCOGT

My biggest stars shine very brightly from nuclear fusion in their cores, turning hydrogen into helium and eventually into oxygen and carbon. During my adolescent years of formative star formation, which lasted several billion years, once every hundred years or so one of the most massive stars in my spiral arms would explode as a supernova, sending surrounding gas flying forcefully out in all directions.

When I was young, the gas near the supernova left me for good and was lost in space, because I wasnt yet big enough to gravitationally keep hold of it after the explosion. Eventually I gained enough mass, by collecting more loose gas and forming new stars, that I was able to hold onto almost anything that passed nearby, including other very small galaxies!

My life progressed in much the same way for a few thousand million years, and I grew massive enough that supernova explosions no longer blew away my loose gas.

Supermassive Black Hole

One year I realized something was growing deep inside my core. It felt like indegestion, but it was actually a supermassive black hole! No one seems to know exactly how the supermassive black hole initially formed at my center, but almost every massive galaxy that has been thoroughly examined has been found to bear one as well. Strange, huh?

I first noticed my supermassive black hole because the material near my center was swirling in closer and closer and heating up. During my supermassive black hole's most active phase, the gas in my core reached temperatures of millions of degrees and started emitting X-ray radiation into space.

This active phase only lasted a few million years before the supermassive black hole exhausted nearly all the energy around my core and quietly faded away, to the point where I sometimes forget it's still there.

One species of tiny lifeforms on a planet named Earth, 26,000 light years from my center, calls the region around my supermassive black hole Sagittarius A* (pronounced "Sagittarius A star"). The mass of the black hole at my centre is four million times the mass of that planetary system's sun.

Merging with Neighboring Galaxies

I live in a small neighborhood of galaxies unimaginitely called the Local Group. There are about 50 of us living here, gravitationally bound to each other despite the expanding universe around us. I'm the most massive galaxy in the group, and there is one other big spiral galaxy nearby called Andromeda.

Arp 271 - a hint of what the Milky Way and Andromeda might do one day.

Since my gravity is the strongest in the neighborhood, I recently devoured a few dwarf galaxies living nearby. They remain visible though, as streams of stars orbiting around my central core.

My biggest gravitational attraction is to the Andromeda galaxy, which lives a mere three million light years away. The two of us are slowly spiraling toward each other in a fateful gravitational dance that will guide us to become one massive, egg-shaped galaxy in a few billion years.

The space between our individual stars is so huge that probably no two stars will collide during our eventual merger, but their orbits will change completely and my beautiful spiral arm disk will be destroyed as a result.

Despite losing my shape and gaining so much more mass, I'm looking forward to merging with Andromeda. Its spiral shape will look incredibly beautiful in the sky as we gradually approach each other, and our merger is sure to form a whole new generation of stars.

I've always been referred to as the Milky Way Galaxy by the inhabitants of Earth, but I wonder if I will acquire a new name for the next phase of my life. Something to look forward to!


Jad said...

So the "arms" of the spiral galaxy are the remnants of smaller galaxies that have been drawn in to the larger?

heroineworshipper said...

You should make videos of yourself reading. Think of it as continuing 60 symbols on your own.

Unknown said...

jad - no, the spiral arms are solid components of the galaxy and usually way more substantial and massive than what a digested dwarf galaxy would produce.

when one of these smaller galaxies gets caught by a bigger one, it forms "tidal arms" around the big galaxy, usually in a different plane than the main disk of spiral arms.

today's APOD has a great view of such a system.... the faint, whispy bits surrounding the spiral galaxy are likely tidal remnants of a dwarf galaxy that fell in...