“This is the way I wanna die. Torn apart by angry fans who want me to play a different song.” –Regina Spektor
You’re familiar with the classic picture of a black hole: a dark, dense region at the center from which no light can escape, surrounded by an accretion disk of matter that constantly feeds it, shooting off relativistic jets in either direction.
This is a pretty accurate picture of active black holes. But most black holes aren’t active, and of the ones that are, they aren’t active most of the time!
Most people think of black holes as marauders, gobbling up whatever poor stars happen to get in their way. You very likely have a picture of a black hole as though it behaves like a great cosmic vacuum cleaner, sucking up anything that dares get too close to it.
I can’t fault you for thinking that; this is a genuine NASA video, and the picture that some very smart people have been painting for you for a long time. But that isn’t quite how the Universe works.
So, how does it work? When any object falls in close to a black hole, it experiences different forces on different parts of the object. We call these forces tidal forces, because they’re the same types of gravitational forces that cause the tides we experience here on Earth!
Only, in the vicinity of a black hole, the tidal forces are much stronger than we experience on Earth. They are, in fact, much stronger than Jupiter’s innermost moon, Io, experiences, and those forces are powerful enough to constantly tear Io apart, making it the only volcanically active moon in the Solar System!
No, when you get close to a black hole, you get stretched at either end so severely, and compressed in the middle so thinly, we call the process spaghettification, one of the greatest astrophysics words ever invented!
But “falling in” to a black hole, like illustrated above, practically never happens! Space is simply too big, and even for supermassive black holes — like the multi-million-solar-mass behemoth at the Milky Way’s center — the event horizon is too small. Most stars and objects that pass nearby to a black hole simply do what all other objects in the Universe do.
Gravitate! (Ha ha ha ha haaaaa!)
Remember that space is huge, and that getting within a paltry 0.001 light years of our galaxy’s supermassive black hole won’t even disrupt the passing star, much less “vacuum it up,” as you might have thought.
“But what if the star does get close enough,” you ask, “then what happens?”
Note how, first, the star gets completely ripped apart by these intense tidal forces! But rather than acting like a vacuum cleaner and sucking it all up, most of the mass from this star doesn’t get devoured at all; quite to the contrary, most of it gets ejected back out into the space around the black hole! It’s only a small fraction of the original that gets swallowed, but that’s totally sufficient to take a quiet, supermassive black hole, and bring it back to life!
And we know this, because we just observed a super distant galaxy — more than 2 billion light years distant — just become ultra bright thanks to its supermassive black hole sneaking a bite out of an unlucky passerby! Let’s take a before-and-after look.
The above images, from GALEX (in the Ultraviolet) and Pan-STARRS (in the visible/IR), show this distant galaxy shortly before it started snacking on its newly accreted material. The images are low-resolution because GALEX and Pan-STARRS focus on grabbing very wide fields-of-view; when you’re looking for very rare occurrences like this, you need to grab as much of the deep sky as possible!
So, that was 2009. But the next year…
The galaxy has brightened by a factor of around 350 in the Ultraviolet, and the visible/IR image has turned much bluer, an indication of the extraordinarily high energies being belched out by this suddenly noisy galaxy!
Taking a look at the before-and-after images together, you can really see the difference.
But don’t be fooled by the vacuum cleaner description; it’s not eating the entire thing that ran into it! This is, in fact, something that we may see happening for much smaller black holes that are much closer to us; the nearby galaxy Messier 83 just had a very similar outburst from a much smaller black hole!
Black holes aren’t giant leviathans, devouring anything that comes nearby, but nor are they dainty, steady nibblers on objects that orbit. Rather, black holes are wild, violent and inevitable, tearing anything that dares approach too closely into shreds, but coming away with a snack-sized meal whose first bite makes quite an impression!
Now, if you’ll excuse me, all this black hole talk has made me hungry! Where did I put the spaghetti…