Active Galaxies Demystified

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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 😉

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A Full Story of Galactic Evolution

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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?

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Why Galactic Nuclei Erupt

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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?

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How Supermassive Black Holes Work

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We first took a peek at supermassive black holes back in our discussion of galaxies. But now that we’ve covered a few types of active galaxies, it’s time to take a deeper dive.

Okay, I guess we won’t really be diving into a black hole…sorry to disappoint!

(Honestly, though, you really wouldn’t want to. It would be very uncomfortable, to say the least…and, of course, it’s a one-way trip.)

Supermassive holes are thought to lie at the hearts of most galaxies, including our own. They seem to be key to galactic structure. Most of them–including our own–are quiet. But a few percent of the galaxies in the universe emit titanic amounts of energy from their nuclei, and supermassive black holes are the ultimate culprit.

But how?

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How to Safely View a Total Solar Eclipse

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Did you know that a total solar eclipse is coming up on April 8, 2024?

This one is primarily visible from North America; you can find more information about where to see it (and if it’ll be visible from your location) over here on TimeAndDate.com.

I was planning to travel to “totality” myself, but those plans fell through because I couldn’t get the time off work. Nevertheless, I’ll be helping out at a viewing event up north of Joshua Tree National Park!

In this post, I’ll take you through what you’ll see during a total solar eclipse–and, at each phase, I’ll let you know exactly how to safely view the sun!

(Later this week, we’ll be back to our regularly scheduled programming on active galaxies.)

Important: Always use solar glasses and solar filters that conform to the safety standard ISO 12312-2. Be careful! There are bad actors on the market that print this standard on unsafe equipment. Use this list of trustworthy suppliers from the American Astronomical Society.

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What is a Solar Eclipse?

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solar eclipse.jpg

This post has been updated and republished from Sept 2017.

A solar eclipse is the most amazing astronomical sight you’ll ever see.

Not only is it the only time you’ll ever be able to clearly see the “new moon” phase of the moon, it’s the only time you’ll ever see the sun’s corona. And it’s the only time that, under very specific circumstances, you can actually look directly at the sun for a few moments.

But it’s not just an astronomical event. It’s an experience. You can see the moon’s shadow rushing toward you. Nature falls silent. It’s night during the day.

And there’s one coming up on April 8, 2024.

So, let me tell you a bit about what’s happening in the sky—and give you a few important safety warnings!

(If you’re wondering what happened to our unit on active galaxies, not to worry–I’m still publishing the next post this week!)

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What the Heck is a Quasar?

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I’ll give you a hint: this is not an image of a quasar.

This image is from a first-season Star Trek: The Original Series episode, “The Galileo Seven”–the original footage, before it was remastered (and before astronomers had clear images of actual quasars).

According to the story, the crew of the USS Enterprise had standing orders to investigate any quasar they came across. A landing party spent the episode struggling to survive after they crashed on a primitive planetary body within a strange nebulosity that they called a “quasar.”

At times like these, Star Trek provides a fun glimpse into the past. TOS aired in the 1960s, just as very strange “quasi-stellar objects” were being discovered. Dubbed “quasars” for short, they were a new frontier of research and discovery.

The remastered footage uses an actual (if substantially edited) image of a quasar. But the “quasar” portrayed in the story…well…yeah, not even close.

So…what are quasars, really?

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Exploring Radio Lobes

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Meet galaxy NGC 5128, also known as Centaurus A.

Anyone notice something weird going on here?

If you’ve been following my recent posts on galaxies, you might notice that this does not look like a typical galaxy. It has a clear dust band, so it can’t be an elliptical; elliptical galaxies have no obvious dust or gas. But it doesn’t look much like a spiral, either: it has a bright, spherical cloud of stars you’d more expect from an elliptical!

And it’s definitely not an irregular galaxy. It definitely has a disk shape, and irregulars are not disk galaxies.

So what the heck is going on with this galaxy?

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What are Seyfert Galaxies?

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Meet NGC 1566, an intermediate spiral galaxy in the constellation Fornax.

To the human eye, this galaxy looks almost like any other spiral: It has a central nucleus and spiral arms, and it’s full of gas and dust. As an “intermediate” spiral, its nucleus has a bit of a barred structure, but not a strong one. All that’s pretty normal, as galaxies go.

But if we look a little closer, we see that this galaxy’s nucleus is unusually bright, especially for its small size.

As it turns out, NGC 1566 isn’t so normal after all…

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Galaxies Demystified

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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… 😉)

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