Our Milky Way galaxy is a sprawling collection of gas, dust, and hundreds of billions of stars, arrayed in a more-or-less flat disk. In the very center of the galaxy – just as in countless other large galaxies like ours – lies a hidden monster: a black hole. And not just any black hole, but one with four million times the Sun’s mass.
It’s called a supermassive black hole for a reason.
Usually, it’s not doing a whole lot except sitting there being black and holey. But sometimes it gets a little snack, and when it does it can let out a cosmic-sized belch. A very, very, very hot belch. Like it did in July 2012:
[Click to schwarzschildenate.]
These images were taken with NASA’s newest X-ray satellite, NuSTAR (more on that in a sec). NuSTAR can detect high-energy X-rays coming from space, and happened to be pointed toward the black hole when it erupted. On the left is an overview of the region near the center of our galaxy. The whitish area is the stuff immediately surrounding the black hole (the pink glow is most likely from a supernova, a star that exploded in centuries past). On the right is a series of three images showing that region getting very bright in X-rays, then fading away: a flare.
OK, so I know what you’re thinking. How can a black hole – famous for gobbling down everything nearby, even light – get bright and emit so much energy?
Basically, it doesn’t. The stuff around it does.
A black hole by itself is dark. But if a gas cloud gets near, very interesting things happen. The gravity from the black hole stretches out the cloud, because the part of the cloud nearer the hole gets pulled by the gravity harder than the part of the cloud farther away. Also, the cloud probably doesn’t just fall straight it; like an orbiting planet around the Sun it has some sideways motion. This means the hole whips it around, pulling out a long tendril which then spirals ever closer to the Point Of No Return.
This video may help. It shows a star getting torn apart by a black hole, but the principle is the same.
So some of the stuff may get flung away, but a lot of it falls toward the black hole. As it nears the hole, it forms a flat disk, called an accretion disk. The material in this disk is tortured by unbelievable forces: the inner part of the disk is whirling madly around the black hole, while the outer part is moving more slowly. The gas is literally heated up by friction as the different parts of the disk rub against each other (other forces like magnetism play a role too). The heating can be HUGE: the gas can reach temperatures of hundreds of millions of degrees!
Gas that hot emits X-rays, which is how this flare was seen by NuSTAR. Probably, a smallish cloud found itself too close to the black hole, got torn apart, and flew down into it. As it did it got extremely hot and blasted out X-rays. But when the whole thing was gobbled down, the X-rays stopped… because there was nothing left to emit them.
So maybe saying this was a belch is a bit misleading, since you do that after you eat something. This is more like your food screaming loudly and incoherently and flailing around while you’re actually eating it. Is that better?
This is a pretty cool observation. For one thing, our local big black hole is usually pretty quiet, so even getting a chance to see something like this is pretty nifty. Second, it can tell us what the environment is like near the black hole. And also, it helps us understand what happens right before some unfortunate object takes The Final Plunge. As I mentioned, every big galaxy has a supermassive black hole – ours is actually rather paltry compared to others; the one in the center of the Andromeda Galaxy is probably ten times more massive than ours – so anytime we can observe something going on with ours, we learn more about how they behave in other galaxies, too.
Also, I’m proud of NuSTAR. I worked on the project for a while, as part of the Education and Public Outreach team. I wrote quite a bit about the mission at the time, and was very pleased when it launched in June. It almost never got off the ground; the mission was actually canceled at one point, but was eventually reinstated.
I’m very glad it was! Now we can watch black holes in our galaxy (and others) as they eat and act rudely. Maybe it’s impolite to stare, but c’mon. When one puts on a fun show like this, it would be wrong not to.
- Astronomers see ANOTHER star ripped apart by a black hole! (including this original post and this followup)
- NuSTAR opens its X-ray eye
- The long reach of the Centaur’s dark heart
- Desktop Project Part 22: A black hole belches out a hurricane
Every now again I get surprised by a photo, showing me something I didn’t know about. And I love it even more when that surprise is from an object I thought I knew!
So check out this incredible image of the nearby galaxy Centaurus A, a nearby galaxy harboring a whole slew of surprises:
[Click to galactinate, or get the 4000 x 4000 pixel version, or, if you're feeling frisky, cram this onto your hard drive: an image that's 8500 x 8400 pixels and 29 Mb in size! And trust me: you want to.]
Isn’t that stunning? This picture was taken by the MPG/ESO 2.2 meter telescope in Chile, and once you get over its beauty you’ll realize this galaxy is, frankly, seriously messed up.
Cen A is about 12 million light years away and has roughly the same mass as our Milky Way, containing a few hundred billion stars. The underlying glow of those stars is what makes that round background fuzz in the image, and takes on the familiar elliptical shape of many such galaxies. [Note: All the individual stars you see here are in our on galaxy, since we're inside the Milky Way looking out to Cen A. Also, the little circles next to bright stars are reflections inside the camera itself, and aren't real.]
But check out that wide swath of dark stuff across the middle! That blocks the light from stars behind it, so it’s a cold certainty that’s a dust lane: a thick, flat disk of complex molecules commonly seen in galaxies. But… it’s commonly seen in spiral galaxies like ours, not elliptical ones like Cen A. So something’s weird right off the bat. And note how the ends of the disk seem bent in opposite directions; on the right it’s bent down, and on the left it’s bent up.
Most likely, this is because Cen A ate another galaxy. Literally: a galaxy collided with it in the recent past — well, like in the past few dozen million years — and that galaxy was probably more like our own, rich with dust. As it was absorbed, the dust was stripped from it and settled into that disk. The warping at the ends is a gravitational effect, most likely a distortion from the collision itself. We see it in other galaxies that have nearby companions.
When you observe Cen A using a radio telescope it gets weirder: two huge jets of material are being shot out of the core. The image here shows those jets (click to embiggen). Cen A is a very strong emitter of radio waves; in fact that’s why it’s called Cen A: the brightest radio source in the constellation of Centaurus.
The source of those jets is a gigantic black hole in the core of the galaxy. Read More
Last year, astronomers saw the violent death throes of a star as it was literally torn apart by a black hole (see here, and links within). And now, they’ve seen it again: observations across the electromagnetic spectrum caught another star that wandered too close to a supermassive black hole, and suffered the ultimate fate.
These observations show the before-and-after (left versus right) of the event. The top two are from GALEX, a satellite that observes the skies in the ultraviolet, and the bottom using Pan-STARRS1, a powerful telescope (located on which mountain, you ask? Why, Haleakala in Hawaii, of course) that scans the entire night sky looking for transients, things that change brightness.
The light from the star’s violent demise reached us in June of 2010. The event happened in the heart of a distant galaxy, 2.7 billion light years away. At the center of that galaxy is a black hole with millions of times the Sun’s mass, comparable to the black hole in the center of our own Milky Way galaxy. The star apparently orbited the black hole in an elliptical orbit. Over millions or billions of years, the star evolved, and turned into a red giant. Over time, its orbit tightened, and one day it got too close. The enormous tides of the black hole tore the star apart.
The flare happened when the stellar material spiraled into the hole. It formed a flattened disk right before the Ultimate Plunge, which got very hot and blasted out high-energy light — the ultraviolet light from this galaxy flared 350 times brighter than it was before! Some of the material from the star was also flung away into space. Astronomers put together a nifty video simulating what happened:
[We're in the home stretch of my Desktop Project: going through all the pictures on my computer's desktop and posting one a day until they're gone. Only a few left now...]
This is the only one of my Desktop Project pictures that’s not actually a picture: it’s an illustration. It’s still pretty neat:
[Click to Schwarzschildenate.]
This drawing shows the binary star IGR J17091−3624, which is actually a normal star in the clutches of a black hole. They orbit each other, and the fierce gravity of the black hole is drawing material off the other star. This matter doesn’t fall straight into the black hole, however. Because the two stars orbit each other, the material coming off the normal star has some sideways velocity (technically, angular momentum) which causes it to spiral around the black hole and form a disk called the accretion disk.
This disk is hot. Very way incredibly yikes hot: probably something like 10 million degrees Celsius (27 million F). The heat comes from lots of forces including magnetism and plain old friction as particles rub against each other pretty violently before The Final Plunge.
Stuff that hot emits X-rays, and this binary is blasting them out. What’s so very interesting is that astronomers studying this black hole found that something was absorbing X-rays from the disk. Their best guess is that this is vaporized iron blasting away from the disk in a kind of black hole wind, and it’s hauling butt: the material is expanding at a speed upwards of 9300 km/sec — that’s 5800 miles per second, fast enough to cross the US in less than the tick of a watch. Want another unit? That means the wind is blowing at a brisk 0.03 times the speed of light!
I love black holes. They’re many things, but one they aren’t is subtle.
Another thing they are is ironic: although most people think of them as being able to suck down everything, including light, they power the most luminous objects in the Universe. This black hole probably is small, a few times the mass of the Sun. But much bigger ones exist, with millions or even billions of times the mass of the Sun. Those are in the centers of galaxies, and can have so much material falling into them and heating up that they can shine brighter than all the stars in the galaxy combined! It’s not the black hole itself that’s glowing, but it’s the center, the engine, behind that raw fury.
And that wind may be more than bright: there’s some evidence that the mighty gale from a galaxy’s central black hole affects the overall state of the galaxy itself. It may be tied to the way stars form in the galaxy, and even the size of the galaxy itself. Mind you, even a black hole with a billion times the Sun’s mass is still only as small fraction of a galaxy, which might have hundreds of billions of stars! So while you might think of something like that as a monster, it’s actually more amazing to me that something so tiny can be so influential on such a huge scale.
Illustration credit: NASA/CXC/M.Weiss
In late March of 2011, an extraordinary event occurred: a black hole in a distant galaxy tore apart and ate a whole star (I wrote about this twice at the time; here’s the original post, and a followup article including a Hubble image of the event).
Now, there’s more info: the black hole, lying at the center of a galaxy nearly 4 billion light years away, has about 8 million times the mass of the Sun. When it tore the star apart, about half the mass of the star swirled around the black hole, forming twin beams of matter and energy that blasted outward at a large fraction of the speed of light. The folks at NASA’s Goddard Space Flight Center made a great animation to show this:
The star was ripped apart by tides. The thing about black holes is, they’re small: this one was probably about 15 million kilometers across. A typical star is about a million km across (the Sun is 1.4 million kilometers in diameter, for comparison). This means the star could get really close to the black hole, and that’s why it was doomed. The force of gravity drops with distance, so as the star approached, the side of it facing the black hole felt a far greater force than the size facing away. That stretched the star, and the stretching increased as the star got closer. At some point, the force was so great it exceeded the star’s own gravity, and it could no longer hold on to its material. The black hole won — as they usually do.
I recently wrote about a mind-boggling event: astronomers capturing what are apparently the final moments in a star’s life as it was literally torn apart by a black hole.
Today, NASA has released some new pictures of the event, including this Hubble Space Telescope shot:
[Click to embiggen.]
I know, it may not look like much at first. But remember what you’re seeing: the violent death of a star ripped apart by the gravity of a black hole… and it’s happening 3.8 billion light years away! That’s about 40,000,000,000,000,000,000,000 kilometers, so the fact that we can see it at all is pretty amazing. And terrifying.
In this false-color Hubble image, the galaxy and explosion are marked. Pretty much everything you see in the picture is a distant galaxy, a billion of more light years away. Normally, the host galaxy itself would appear as a dot, at best with some small amount of fuzz around it, the glow of billions of stars reduced by the incredible distance. But the dying light of the star increased the galaxy’s brightness by a lot. A whole lot.
This image (click to greatly embiggen!) is a combination of visible light (white), ultraviolet (purple), and X-rays (yellow and red) from NASA’s Swift observatory, the satellite that first detected the explosion. While the spikes are not real — they’re just an optical effect from the telescope itself — it still speaks to the drama of what we’re seeing.
And so just what are we seeing?
On March 28, 2011, NASA’s Swift satellite caught a flash of high-energy X-rays pouring in from deep space. Swift is designed to do this, and since its launch in 2004 has seen hundreds of such things, usually caused by stars exploding at the ends of their lives.
But this time was hardly "usual". It didn’t see a star exploding as a supernova, it saw a star literally getting torn apart as it fell too close to a black hole!
The event was labeled GRB 110328A –a gamma-ray burst seen in 2011, third month (March) on the 28th day (in other words, last week). Normal gamma-ray bursts are when supermassive stars collapse (or ultra-dense neutron stars merge) to form a black hole. This releases a titanic amount of energy, which can be seen clear across the Universe.
And those last two characteristics are certainly true of GRB 110328A; it’s nearly four billion light years away*, and the ferocity of its final moments is not to be underestimated: it peaked at a solid one trillion times the Sun’s brightness!
Yegads. I’m rather glad this happened so far away. That’s not the kind of thing I’d like to see up close.
Although initially cataloged as a GRB, followup observations indicated this was no usual event. The way the light grew and faded seemed to fit better with a star getting torn apart. And what can do that to an entire star? A black hole. So instead of the star in question forming a black hole, it apparently literally fell victim to one!
The observations indicate the black hole in question may have as much as half a million times the mass of the Sun, meaning it’s very probably a supermassive black hole in the very center of a distant galaxy. Hubble Space Telescope observations (not yet released to the public) also place the event very near the center of a galaxy, which is consistent with this scenario.
So what happened?
Astronomers have just announced something that took me by surprise: the dwarf irregular galaxy named Henize 2-10 has a fairly beefy supermassive black hole in it! Here’s a picture of the galaxy:
[Click to unendwarfenate.]
The image is a composite of images from Hubble (red, green, and blue), radio images from the Very Large Array in New Mexico (yellow), and X-rays from the Chandra Observatory (purple). The cross marks the location of the black hole.
Henize 2-10 is pretty dinky, only about 3000 light years across — the Milky Way is 100,000 for comparison. It’s about 30 million light years away, which is kinda sorta close by, at least close enough to get a decent look at it. Now, we know that big galaxies like ours have these monster black holes in their very centers; the Milky Way’s is about 4 million times the mass of the Sun. Many galaxies have much larger ones, like Andromeda which harbors one 35 times as massive as ours.
Astronomers using the Chandra X-Ray Observatory may have found evidence for a young black hole: it was born in a titanic explosion just 31 years ago.
Black holes form when massive stars explode. The core of the star collapses, and if it’s massive enough (more than about 3 times the mass of the Sun), the gravity of the core can crush it down into a black hole.
Enter Supernova 1979c, a star that exploded in the nearby galaxy M100. About 50 million light years away, M100 is a lovely face-on spiral galaxy in the constellation Coma Berenices. SN1979c was discovered in — duh — 1979, and has been heavily studied for years since it was so bright, making it easy to see.
SN1979c was an interesting event, even for something as mind-numbingly violent as a supernova. The star that exploded was right on the edge of being massive enough to create a black hole; the total mass of the star was about 20 times the mass of the Sun, with a core of just about 3 solar masses. The question is, was the star big enough to create a black hole, or would the core collapse to form an incredibly dense neutron star?
Chandra observations may have answered this question. Read More
My friend Erin McCarthy works at Popular Mechanics. We met at Comic Con last year, and at this year’s nerdfest we chatted briefly about me possibly writing an article for them some day.
That day has come. On their website they’ve posted my short but deadly "Top 5 Ways the Universe Could Wipe Out Humankind". I wrote it a bit tongue-in-cheek — the topic sure lends itself to snark, doesn’t it? — but I had to scratch my head about it a wee bit. After all, what are the Top 5 ways? So I picked one that was statistically likely, two that weren’t, and two that were inevitable.
I bet you can figure out which was which. Anyway, they generously plugged my show in the article, and even embedded the teaser clip in the section about asteroid impacts.
I hope you like it. And thanks, Erin!