Not Always

If you know anything about black holes (and you probably have at least heard that these bad boys suck up pretty much anything that wanders past their event horizons), then it might surprise you to learn that young stars can form near black holes. Now, this seems counter-intuitive, since, if the black hole is gobbling all the stuff up (including the stuff that makes stars), there wouldn’t be any (or at least enough) left to make stars.

Not so fast, says a team of astronomers and astrophysicists at the University of St. Andrews and University of Edinburgh in Scotland, U.K. It turns out that, through a set of computer simulations (left) of giant clouds of gas being sucked into black holes, the scientists have solved the mystery of how stars could be formed in the blustery, dangerous, and not completely hospitable environment near a black hole

The discovery of hundreds of high-mass young stars orbiting the black hole at the center of our own Milky Way was probably one of the most exciting in recent times. But, it begged the question of how they could have formed near the hungry maw of the black hole. And survived!

The series of images at  left show the evolution of a 10,000 solar-mass molecular cloud falling toward a supermassive black hole. Although the cloud is disrupted by the black hole, some of the material is captured to form an eccentric disc that quickly forms numerous stars. The stars that form retain the eccentricity of the captured gas and those that form very close to be the black hole tend to be very massive. These results match the two primary properties of the young stars that have formed in the center of the Milky Way Galaxy. They have high mass and they follow eccentric orbits around the supermassive black hole. Not only does this simulation set help us understand the black hole at OUR galaxy’s heart (and the formation of stars nearby), but they should be quite valuable when astronomers look to the hearts of other galaxies and find newborn stars orbiting close to the hungry maws of supermassive black holes.

The Power of Magnetic Fields in Space

Yesterday this amazing picture came rumbling through the Intarwebs from the folks at Hubble Space Telescope. It’s from the Advanced Camera for Surveys and shows the galaxy NGC 1275 seemingly surrounded by what looks like a spiderweb of stuff.

Now, there’s a lot going on here, so let’s break it down. First, the galaxy is in the center of the Perseus Cluster of galaxies, and the whole region is permeated with hot gas — REALLY hot — around 100 million degrees. The red stringy things are filaments of cooler hydrogen gas and they’re threaded on magnetic field lines that extend throughout the region.

Magnetic field lines?  Yes, this is indeed true. The actions of a supermassive black hole and its associated jet at the core of the galaxy are the source of very strong magnetic fields that extend quite far out from the core. Gas near the center of the galaxy gets superheated by all the hoopla surrounding the black hole and jet, and that blows bubbles of material out into surrounding space. Those expanding bubbles plow into cooler regions of hydrogen gas, and the expansion carries some of that gas out along with it. The red filaments are the hydrogen gas that looks like it’s draped on the magnetic field lines. Those filaments are actually a very important clue to astronomers. They are the biggest visible-light evidence for some “invisible” (i.e. not visible to our eyes) interactions between NGC 1275’s central black hole and the hot gas that permeates the surrounding interstellar and intergalactic spaces.

Now, the filaments look really delicate, and you’d think that the huffing and puffing of material blasting out from the center of the galaxy via the jet would destroy the hydrogen gas threads. What’s saving them are the magnetic fields. Those lines of force hold the gas in place and help it resist the outward blasts from the core of the galaxy. They also keep the gas from clumping up to form newborn stars, making them a disruptive as well as a unifying force.

For anybody who thought that intergalactic space might be empty and boring, this image and another one taken with multiple instruments (left), reveals just how frenetic the environment in galaxy clusters can be.

While we may not be able to see those magnetic fields, images like these show us the effects that such fields have on the ordinary matter they thread through.

For more information, surf on over to the Space Telescope Science Institute’s HubbleSite page.

They’re SO Misunderstood

How many of you have seen ANY movie or read a bad science fiction story that featured a black hole that had people somehow flying into a black hole and managing to get out again? I remember this really awful movie from Disney called (imaginatively enough) “The Black Hole” that pretty much ignored most physical laws and violated more than a few storytelling rules. It seems like black holes suck more than gas and dust and stars into their maws. They also have the strange ability to remove a writer’s common sense when it comes to a) tellling a credible story, and b) respecting that black holes have rules they must follow and that you can’t bend those rules just so that the hero can get the girl in the end.

Let’s face it. If you’re in a spacecraft anywhere NEAR a black hole, you’re going to feel its effects. Its gravitational pull will tug at you. The radiation environment will kill you, unless your spacecraft is really well-shielded. And even then, there’s a good chance that you’re never going to father (or mother) children after the encounter (provided you survive it). If you happen to stray too close to the black hole, you’re toast. You’re going in and you’re going to be swirling down the celestial tidy bowl for a LONG time (from the perspective of an outside observer). From YOUR perspective, it’s going to be a short, nasty, brutish trip into the universe’s ultimate trash compactor. And, no matter how much a producer or writer or art director or second assistant key grip wants to see your spacecraft escape the black hole, it ain’t gonna happen. You won’t have a droid up there in the control booth trying to turn off the compactor at the last second. You. Are. Toast.

So, you might ask me if you’re one of those writers who just HAS to have a black hole in your show to keep the sponsors happy, what CAN be written about? IS there a viable, exciting story about these things that could hold an audience’s interest?

Of course I have an answer to that, mostly because I DID write such a story some years ago for a planetarium show. I had the spacecraft go not quite close enough to the singularity’s event horizon and the pilot pulled out just in time… but not before a few hair-raising, nail-biting moments when both the crew and the audience weren’t sure if they’d get out in time. I had twenty minutes to get them out TO the black hole’s vicinity (all the while explaining how we can detect these dudes), and then about five minutes to put them in danger and get them out again. By standards of a movie or network TV, that’s pretty short, but it kept me intellectually honest, and I told a good story with accurate science and emotional affect (as they like to say in the business).

So, it can be done. And black holes, if you respect them and what they’re about, can give you fodder for a LOT of good stories.

But the Matter Surrounding It? That’s Another Issue…

Black holes, as the old bumper sticker said, suck. They also don’t have any hair, as Stephen Hawking once said. They gobble up stuff like stars and gas and dust, and they don’t give anything back. You can’t tell anything about them by simply looking at them, although you can infer their masses by the gravitational influence they have on material around them. And, you can tell that one is around by the heat and x-rays and other signals given off by the material that spirals into a black hole. And, if the supermassive black hole has a jet, you can detect THAT. But, all of the mass they take in stays there and the information about it stays secret forever. It’s a sort of cosmic version of “what happens in Vegas stays in Vegas.”

It turns out there are some other interesting things about black holes besides the fact that they suck. For one thing, for a while, astronomers thought that there was a correlation between size of a galaxy’s central bulge (if it has one) and the size/mass of its central supermassive black hole. The more massive the black hole, the larger the bulge of stars at the center of a galaxy would be. That makes sense, since supermassive black holes have to have a lot of matter to eat to keep them hefty and massive, and big galaxy bulges would have a lot of stars and gas and dust to feed them.

Well, this relationship seems to work for some galaxies, but not all of them. Some galaxies, like M33 in Triangulum, have massive black holes, but don’t have central bulges. So, maybe there’s something else influencing black hole growth. Something as mysterious as a black hole: like, dark matter.

Now, that’s not to say that there are dark-matter-munching black holes out there in skinny galaxies. The relationship is something far more complex and so far, astronomers are still figuring out what it is.

Dark matter exists, but you can’t see it. You CAN, however (if you have the right methods) measure its influence on regular matter. It has a gravitational influence. And, how much influence it has depends on how much of it there is. So, maybe there are galaxies out there with huge dark matter components; some of them with bulges and some without. And, maybe all that dark matter is having some influence on the growth of the black holes at the hearts of those galaxies, whether they have bulges or not. Maybe the dark matter is influencing the bulge. And, maybe the black hole’s growth rate and size is telling us something about the dark matter surrounding it. If so, it may be the only message we get about matter from a black hole!

What Do You Feed Your Inner Supermassive Black Hole?

Remember that black hole at the center of our galaxy I talked about in the last entry? It feeds off of stars, gas and dust that happens to get too close. This happens at the center of any galaxy with a supermassive black hole. Where does all that black hole “food” material come from? And, if a supermassive black hole at the center of a galaxy has a supermassive appetite to match, won’t it clear out its neighborhood quickly? And if so, and it continues to grow, what’s feeding it?

In the case of some types of galaxies that are different from ours–such as those with extra-bright cores (called Seyfert galaxies), their central black holes may be getting the cosmic equivalent of a Big Mac with fries whenever two of these galaxies interact with each other. When such a close encounter takes place, the interaction stirs up gas, which brings more material within the reach of the central black hole of one of the galaxies.

Now, this isn’t something you can see easily with an optical telescope. But, if you scan the sky with a radio telescope and trace out the emissions from hydrogen gas in the interacting galaxies, you find something interesting: a transfer of material from one galaxy to the other’s supermassive black hole. That’s what a Cheng-Yo Kuo, a graduate student at University of Virginia did, using the Very Large Array (VLA) radio telescope in Socorro, New Mexico. He looked at several sets of nearby Seyfert galaxies that appear to be snacking on each other. As the galaxies interact, the gas and dust goes goes from one to the other, on a sort of death spiral into the hungry maw of the black hole. The material don’t go quietly; it’s heated (ionized) by friction and radiation, and slapped around by twisted magnetic fields. Those actions produce energy as the material is consumed. Depending on how rapidly the black hole is eating up its neighbor’s contribution to the cosmic picnic, the galaxy can show a wide range of activity. The most action is at the center, which is the brightest (and quite “loud” in radio wavelengths). Seyfert galaxies have the mildest version of this activity, while quasars and blazars are hundreds of times more powerful.

Astronomers can trace the flow of material between galaxies by looking for neutral hydrogen, which is pretty abundant in galaxies. It gives off emissions at a wavelength of 21 centimeters, which radio telescopes can detect. It also traces out the route that material is taking between the two galaxies into the heart of the black hole. That’s what this image from the NRAO press release illustrates, showing what a good tool neutral hydrogen can be when it comes to diagnosing the inevitable “heartburn” that follows when two galaxies interact and feed a supermassive black hole.