I've always been a sucker for mysterious things in outer space. No, not little green beings or monsters from Cryzalix IV or alien face-things on other planets that turn out to be eroded mesas. I'm talking about the real deal: strange things that really do exist, but when scientists first think about them, or observe them, they kind of scratch their heads and go "huh?" Black holes fit in that category. And, you know what? A LOT of people are really curious about black holes. If you're a planetarium lecturer or a scientist who does outreach, or a teacher who finds time to fit in some astronomy between all those other unfunded educational mandates you have to follow, you already know this. Black holes are just about the first thing anybody asks about as soon as the topic of astronomy comes up.

No, really. It's true. (Well, sometimes they ask about astronaut love triangles, but I don't want to go there and neither do you...)

Anyway, I wish I had US$5 (or 5 Euros, I'm not picky) for every time I've been asked about black holes while standing in a line at the store, or sitting on an airplane talking with somebody, or answering an email from somebody who's read my site. Black holes are just that popular. Yet, I remember a time when they were pretty much flying beneath the public's radar.

Back when I was a kid a few decades ago, black holes were taken seriously more as theoretical constructs—objects that mathematical and scientific models said could exist, but nobody had actually seen in real life. There are a lot of science fiction stories about using wormholes to ride around the universe in; those are based on some theoretical constructs called Einstein-Rosen Bridges.

Pretty speculative, but interesting to think about. And, certainly TV and movie science fiction stories often depend on spectacular special-effects wormholes to keep people moving. But, right now those remain on the dreamers' drawing boards while astronomers study the real-life black holes that are turning up everywhere.

So, black holes hide in a lot of places. Astronomers have known for a while that they exist in the hearts of many galaxies, and they're also the powerful engines under the hoods of quasars. Back when I was a teenager, Quasars were TV sets. Now they're better known as the bright, distant and extremely active core regions of galaxies. Radiation pours out of these things in many wavelengths of light, including x-rays and radio waves.

Last week at the American Astronomical Society, we heard a LOT about black holes. I was especially intrigued with the story out of Vanderbilt University that there could be hundreds of rogue black holes roaming around our own galaxy. They got the galactic heave-ho from the globular clusters where they formed.

But, for my money, the most interesting black holes are the ones that lurk in the hearts of galaxies like our own. You can't see the one making its nest in the core of the Milky Way because it's hidden behind clouds of gas and dust. And, well, you really can't see a black hole anyway. What you DO see is the chaos that is created when a lot of matter swirls into the black hole. In addition to the stars, gas, dust, and other stuff that is getting sucked into the black hole, powerful and twisted magnetic fields are funneling superheated plasmas out to space, in the form of jets.

All this activity gives off those x-rays and radio waves I just mentioned. And, the heat in the region also warms up clouds of gas and dust, which glow in infrared wavelengths. So, looking for black holes is a multi-wavelength (except for visible light) proposition, particularly for the Milky Way's black hole.

If you want to read more about the black hole in the Milky Way's core, I recommend a very cool book called The Black Hole at the Center of our Galaxy by astronomer Fulvio Melia. I reviewed it a while back for Sky & Telescope Magazine, and I still remember what a great read it was. There's a lot we know about black holes, and they're not just for science fiction any more. They play roles in everything from the earliest galaxy formation to stellar evolution.

The latest installment of my little vodcast series about all things astronomical is also about black holes, specifically the one at the heart of the Milky Way. Check it out!

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