The cosmic twist: Galaxies

The cosmic twist: Galaxies

The Earth has places that are so breathtaking that they’re definitely in the “must visit before I die” lists of everyone. But what if I say that the most beautiful things in the universe are things you will never be able to visit? Isn’t that a bit sad? That’s the way Universe is teasing us, and its winning, like it always does!

Galaxies are an enormous group of stars and dust swirling together in space. Just like a human chain of a million people refusing to let go of their hands is unbreakable, these stars are also kept from floating away by the gravity of their neighbors. Nobody will ever drift away. At least until something bigger having more gravity knocks them apart.

Unfortunately, we don’t know much about how galaxies are born. You see, galaxies formed billions of years ago, and we can’t really observe the formation of galaxies. The general idea is that when multiple stars evolve nearby, they make a scattered group called a cluster. This cluster then consolidates slowly into a galaxy. Something like how heating milk slowly creates a fat layer at the top. Of course, there are many other theories and the debate is ongoing.

Galactic Types

Galaxies come in many shapes and sizes (an amazing marketing strategy of the Universe). Based on their appearance and behaviour, scientists classify them into different types. Let’s have a look at them!

Elliptical Galaxies

NGC 3923, an elliptical galaxy 90 million light-years away

Elliptical galaxies look like a big glowing ball. They’re mostly made up of old, mature stars that are circling around a common gravitational center. They have a very reduced star formation rate. Elliptical galaxies are the largest galaxies that we’ve observed so far. They are believed to form when two galaxies collide, much more about that later.

Spiral Galaxies

A spiral galaxy

Spiral galaxies resemble spiraling pinwheels with a central bright bulge out of which massive arms made up of stars and dust extend out. The central bulge contains old stars and a supermassive black hole around which the entire galaxy orbits.

A barred spiral galaxy. Notice how two “bars” extend out of the center and eventually become its arms.

A subtype of a spiral galaxy is a barred spiral galaxy. Barred Spirals make up most of the spiral galaxies. Our Milky Way is also a barred spiral galaxy. They have two bars extending out from the core, which eventually merge into arms. Confused? These image should help you compare between these two types of galaxies.

Irregular Galaxies

Irregular galaxies don’t have a defined spiral or elliptical shape. It is estimated that 25% of all galaxies are irregular galaxies. It is also thought that some irregular galaxies were once spiral or elliptical galaxies that were deformed by an external gravitational force.

Lenticular Galaxies

NGC 6861 – a lenticular galaxy

Lenticular galaxies fall somewhere between elliptical and spiral galaxies. Like elliptical galaxies, they look like glowing balls of stars, although they also contain a disc structure without any arms. They consist of mainly aging stars, just like elliptical galaxies.

Ring Galaxies

Hoag’s Ring – a ring galaxy

A rare sight is a ring galaxy, which appears as a ring of stars around a luminous ball at the center. Ring galaxies contain mostly young stars and are believed to form when a galaxy passes through the center of another but doesn’t merge. The resulting gravitational forces sometimes align stars into a ring shape. Obviously, this is just a hypothesis, but an amazing sight regardless!

Collision Course

IRAS 06076-2139, a pair of galaxies colliding with each other.

Sometimes, galaxies collide as they wander around in empty space. When this happens, the galaxies usually merge into one large elliptical galaxy.

In fact, the Milky Way galaxy (our home) and the Andromeda Galaxy (the nearest major galaxy) are on a collision course. Andromeda Galaxy is moving towards us at a speed of 110 km/s (that’s slow in a cosmic scale), and at this rate it will take about 4 billion years for the collision to occur. We would have been long gone by then.

The collision will merge the two galaxies into one elliptical galaxy. It is also hypothesized that a third galaxy, the Triangulum Galaxy will also participate in the collision. Even though the collision will be an incredible event, galaxies have plenty of empty space, and it’s improbable that any two stars will actually collide. They’ll just reposition themselves, and rest assured – our solar system will survive.

I guess its moving day in 4 billion years?

Until next time!

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