More on NGC 1316

Contributed by
Nov 21, 2006

So yesterday I wrote about two supernovae in NGC 1316. This galaxy is way, way cool, and I wrote so much in the first draft (yes, I edit) that it was taking away from the supernovae. So I split off this bit.

To remind you, NGC 1316 is an elliptical galaxy, more or less, but it's got some issues. It has another, smaller galaxy just north of it, and the two are in the very slow process of colliding. The dark dust lanes across its middle attest to that:

That's a Hubble image of the central part of the galaxy. Those streamers of dust are pretty odd, and are a big clue that NGC 1316 started interacting with that other galaxy 100 million years ago or so. Elliptical galaxies don't have a lot of dust, so that much sitting brazenly in the galaxy means it's been visiting the galactic buffet table.

When a big galaxy eats a smaller one, sometimes there can be a shake up in the big galaxy. Gas and dust get tossed around, and a lot of it can fall into the central regions of the big galaxy. But as we all learned when we watched "Monster of the Milky Way", every big galaxy has a supermassive black hole in the middle. And even though you may think that black holes eat everything up around them, they actually don't. As matter falls in, it forms a big disk and gets very, very hot. This can collimate (focus) twin beams of matter and energy that scream out of the vicinity at speeds approaching that of light.

These beams can do a lot of damage on their way out. Eventually, though, they lose energy as they ram their way through the gas and junk between galaxies, and they billow out, forming two huge Q-tip shaped lobes of matter. As it slows and cools, it emits radio waves, and so using radio is the best way to see them.

NGC 1316 is the poster child for this phenomenon. The latest collision dumped a lot of crap onto the central black hole, which responded by belching out a vast amount of gas. In radio waves, the picture is slightly different than the Hubble one:

This image is a composite of radio (in orange) and visible light images, and shows a lot more of the region around NGC 1316 than the Hubble image does. That Hubble image would only be a few pixels across in this image. The radio source from NGC 1316 has its own name: Fornax A.

I'll note that this sort of thing is very common with interacting galaxies. In fact, many times when you see these twin lobes, it's a sign that some cannibal is a messy eater.

The radio image makes this all very clear, but there is some indication of it in visible light too. But you have to take a way deep exposure. I found one:

Cripes, what a mess.

Like I said, there's a lot going on in this system. Those two Type I supernovae, as amazing as they are, I think are pretty much unrelated to the rest of all this. It's just a coincidence that such an active, violent galaxy has produced two supernovae that we see at the same time. We see lots of other galaxies just like this one-- or worse-- without simultaneous supernovae.

Also, those two supernovae may be thousands of light years apart; one blew up a long time after the other, but the other one was farther away. From our viewpoint, the light from the farther one caught up with the first one just as it blew up (think of it this way: it might have been 1000 light years farther away, but blew up 1000 years earlier). So it's all just one big coincidence.

All in all, the only conclusion I can draw is that NGC 1316 pretty much hit the weirdness jackpot.

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