Invisible Fascination

Black Holes

Artist's conception of a black hole being fed by surrounding material and shedding excess energy via near-light-speed jets that stream away from the black hole. Courtesy Chandra X-Ray Satellite.

Black holes fascinate people. How do I know this? It’s one of those topics that people bring up when they find out I’m “into” astronomy. I’ve been asked about black holes in supermarket checkout lines, at book signings (back when I used to do those when I had a book to hawk), at public lectures, on planes, and online. I even had a medical professional ask me about them as I was being wheeled on a gurney into a procedure last year. Fortunately they hadn’t given me any anesthetic yet. I can just imagine what my answers to their questions would have sounded like if they had already started giving me the famous “I don’t care” cocktail!

Now, the funny thing about my perception of black holes is that I’m still amazed that they exist. Back when I was a kid and I first heard about this theoretical mathematical construct called a singularity (the high-falutin’ name for a black hole), few people thought we’d actually find any of these things. That was back a few decades ago, and in the years since then, not only have we found black holes, we’ve found them with such regularity that the American Astronomical Society has regular black hole briefings at their twice-a-year meetings. Hubble Space Telescope is getting so good at spotting the effects of black holes on surrounding matter that when a press release comes out describing the latest find, some of us joke about HST finding another “damned black hole.”

What is it about the black holes that fascinate people? Just judging by what they tell me, I’d say it’s the concept of the singularity itself. What it represents. At the very least, it’s a place where space and time act very differently from what we know out here in the non-black hole universe. A black hole is a place where gravity is so strong that light can’t escape it. And, since light carries information that could tell us what is happening inside the singularity, we’ll never be able to see “pictures” of the interior of the black hole.

Black holes are the ultimate “black boxes” of the universe; we can see the effect they have on surrounding space and matter, but we can’t exactly see the black holes themselves. They’re all over the universe, it turns out—from the stellar black holes that form when supermassive stars explode as supernovae, to the centers of galaxies, where black holes that have the mass of millions or billions of stars wallow in the galactic cores, having effects on galaxy evolution that we are only just now beginning to understand.

And, that’s the current story of black holes: not just that we’re discovering them, but that we’re finding out the roles they play in the cosmos are interesting, and possibly even necessary for the ongoing evolution of the universe.

Fascinating!

Space Music Release

More Celebration

From time to time I mention Mr. SpaceMusic. While he does a LOT more than space music (show production and bookkeeping, to name a few other tasks he’s good at), he’s been a space music composer for lo these many years. In fact, he’s been doing it since we were both in college back in the Dark Ages. And so it seems that every few years he produces a new album of music of the genre that I’m referring to as “space” but used to be better known as “that stuff you play in the planetarium” and then morphed into “ambient” and “new age” and “spa music” and who knows what it’ll be called next. Whatever it is, it’s really, really nice.
Well, today Mr. SpaceMusic and I are celebrating the release of his 8th Geodesium album of music, called A Gentle Rain of Starlight. You can hop on over to his website and listen to samples, plus a full version of the title cut.

Album cover for Mr. Space Music's latest album

These albums usually come together after Mr. SpaceMusic has done a soundtrack for a project. This one is no different. It is the music from our just-released set of shows called Seasonal Stargazing. After he finished the soundtrack mixes, we started work on the “listening mixes,” which allow him to bring some of the lovelier bits and pieces “front and center” for the listener. These may or may not be obvious in the actual soundtracks, since (in theory) you’re supposed to be paying a wee bit more attention to the actual narrations, along with the music. But, for the purist, the music can stand on its own, too.

It was my job to listen critically and make suggestions about what tracks should be brought up louder, or quieted down, or whatever they needed. We went through a few versions of what we jokingly call “peer review” (it’s a pun) before the final mix emerged. It’s a nice break from writing (I also wrote the liner notes and a lot of the online material about the album), and I think the whole project turned out really well. I hope other folks enjoy it, too. If you’re a fan of the genre (whatever it’s called these days), go check it out!

Celebratory Motions

Here in the northern hemisphere (planet Earth) we just celebrated the summer solstice yesterday. In the southern hemisphere people celebrated winter solstice. Summer solstice is the occasion to celebrate if you like long, warm, sunny days and short nights; winter solstice usually means colder weather, shorter days, longer nights.

“Solstice” is another of those words that comes down from an ancient tongue (Latin, in this case). It’s two words jammed together: sol for “Sun” and sistere “to stand still.”

Does the Sun really stand still on this day? Well, that’s an interesting question. It depends on the frame of reference you’re using. The Sun is moving through space as part of the Milky Way Galaxy, which is, itself, moving through space as part of the Local Group of Galaxies, which is itself moving through space as part of a supercluster of galaxies, which is itself moving with the expansion of the universe, but possibly also affected by the gravitational pull of dark matter and the effect of dark energy.

Okay, that can get confusing really fast. So, let’s narrow it down a little, to just the motion of the Sun and Earth with respect to each other. The truth is, Earth rotates around the Sun and it also spins on its axis. We have day and night because Earth turns on its axis. We’re sitting on the surface of the planet, riding along as it turns on its axis. So, as the planet turns, things in the sky look like they’re moving across the sky. In reality, they’re more or less sitting still while our point of view is changing. It’s exactly like being on a merry-go-round as it spins around. Everything NOT on the merry-go-round isn’t moving, but it looks like it is.

So, Earth is spinning on its axis, which is tilted. That tilt, plus the apparent motion of the Sun across our sky each day, holds the key to understanding “solstice.” In northern hemisphere summer, the northern hemisphere is tilted toward the Sun. This lets a LOT more warmth and light from the Sun reach the northern hemisphere. At the same time, the southern hemisphere is receiving less light and warmth, and experiences winter. (Note: Earth is NOT closer to the Sun during this time.)

Solstice happens because as Earth makes its yearly trip around the Sun, spinning its axis, the perceived position of the Sun changes. NOT just the east-west motion we see every day, but also north-south. The Sun appears to move farther north in the sky from December to June, as the tilt of our axis brings more of the Northern Hemisphere into more sunlight. Then, from June to December, the Sun appears to move back to the south. It reaches its northernmost point in the sky on June 21, where that slow northward motion seems to stop for a day or two. Then, as the planet continues on its trip around the Sun, the tilt slowly changes, and the Sun appears to head south again.

In the southern hemisphere on June 21, the Sun is also at its northernmost point, which means that half of the planet is getting less warmth, less sunlight, and things get cold.

On December 20, the date of the other solstice when the Sun appears to “stand still” at its southernmost point in the sky, the northern hemisphere is getting less sunlight and has lower temperatures. In the southern hemisphere on the same day, it’s warmer and summer is in full bloom.

The ancients, who watched the sky pretty closely for a variety of reasons, noted that “stoppage” with the term “solstice.” Since it seemed to coincide with warm weather, a good growing season, and increased amounts of food, solstice time seemed a great time to celebrate.