galaxy merger

Active Galaxies Demystified

/ Emma / 4 Comments

Active galaxies are, without a doubt, absolutely spectacular.

Though rare, they tell a critical part of the story of galaxies–and of the universe as a whole. And we’ve spent the last few posts exploring them in depth.

But I know they can also be a bit perplexing. These are some of the most powerful and violent objects in the universe; it comes with the territory!

So, let’s boil this down to the basics and tie it all together. And let’s try not to get caught in a supermassive black hole in the process 😉

Continue reading →

A Full Story of Galactic Evolution

/ Emma / Leave a comment

Over the course of the last few posts, we’ve explored different types of active galactic nuclei: Seyfert galaxies, double-lobed radio sources, and quasars.

At the heart of each of these galaxies lies a supermassive black hole, feeding off an energy feast of infalling material and producing titanic eruptions of energy.

Most galaxies, though, are not active. The majority of supermassive black holes–like the one sleeping at the heart of our own galaxy–are on “starvation diets,” living off minuscule streams of dust from cannibalized satellite galaxies.

We know what causes these supermassive black holes to erupt. But why are they so rare? What part do they play in galactic evolution?

Continue reading →

Why Galactic Nuclei Erupt

/ Emma / Leave a comment

Astronomers know that when galaxies’ nuclei become active–releasing tremendous floods of energy–supermassive black holes are the ultimate culprit.

We also know that supermassive black holes lurk at the hearts of most large galaxies.

But most galaxies are not active; only a small percentage are. Our home galaxy is host to a supermassive black hole, but it’s not active. Neither is the black hole within the nucleus of our nearest galactic neighbor, Andromeda.

So, what makes a supermassive black hole erupt?

Continue reading →

Galaxies Demystified

/ Emma / 3 Comments

From the smallest of irregular and dwarf galaxies, to the most spectacular of spirals, to the most massive of ellipticals, there’s no denying that galaxies are incredible objects.

On this blog, we’ve covered a great deal of information about galaxies. We’ve followed their stories from the dawn of time in the universe to the present day, and we’ve explored all their different shapes and sizes, their masses, and the forces that shape their evolution.

If it seems like a lot, I understand.

So, let’s round up what we know and boil it down to a summary. Hopefully I can make galaxies more easily digestible!

(Though I do hope none of you actually try to eat one… 😉)

Continue reading →

How Galaxies Evolve

/ Emma / Leave a comment

Ever since astronomers realized that the mysterious, fuzzy objects known as “spiral nebulae” were, in fact, separate galaxies beyond our own, we’ve sought to understand the stories of galaxies.

We’ve since discovered that most galaxies are found in galaxy clusters. There are two types: rich clusters, which are home to thousands of galaxies, and poor clusters like our own “Local Group,” which are home to only a few dozen to a few hundred galaxies.

We’ve also discovered that collisions between galaxies are quite common, and can drastically alter their shapes.

And we’ve observed something even more curious. Spiral galaxies, like our own Milky Way, are most often found in poor clusters. Rich clusters are dominated by elliptical galaxies.

It would seem that spiral galaxies thrive best in uncrowded galactic environments.

But what can that tell us about galactic evolution?

Continue reading →

When Galaxies Collide

/ Emma / Leave a comment

Meet the Whirlpool Galaxy, a spiral galaxy in the constellation Canes Venatici. This was actually the first galaxy to be classified as a spiral.

Specifically, the Whirlpool Galaxy is what we call a grand-design spiral: a galaxy with a very distinct pattern of two spiral arms. It was discovered by Charles Messier way back in 1773 and added to the Messier catalog as a “spiral nebula,” way back before astronomers knew what galaxies were.

But…hold on just a second.

Anybody notice there isn’t just one galaxy here?

The Whirlpool’s companion is known as NGC 5195–or, if you prefer, M51b. Together, the two galaxies are designated in the Messier catalog as M51.

We are, in fact, viewing them in the aftermath of a collision that drastically altered the shape of both galaxies. Both of these were likely once uniform disk galaxies with no spiral arms.

So, what happens when galaxies collide? And does this happen often?

Continue reading →