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There are days — and for me it's pretty much every day — when we can all use a spectacular shot of a magnificent spiral galaxy.
Is today such a day for you? Then I'm glad to help.
But first, a brief description …
M61 is a nearly face-on spiral galaxy about 52 million light years away. It's one of a couple of thousand galaxies that co-habitate in the Virgo Cluster, the closest galaxy cluster to the Milky Way (in fact, the Local Group, our own small neighborhood of galaxies, and the Virgo Cluster are all part of the much larger Virgo Supercluster, which itself is part of the Laniakea Supercluster). These galaxies are close enough that on a May night a decent set of binoculars will reveal a dozen or more of them, if you happen to be at a dark, moonless site.
So when you point the Hubble Space Telescope and Very Large Telescope at it, what you get is detail on a brain-stunning level. Behold!
That image is a composite of Hubble and VLT observations (as well as some amateur images to fill in the gaps) created by the talents of astrophotographers Robert Gendler and Roberto Colombari. The spiral structure is, um, fairly obvious, with massive, luminous blue stars tracing the arms, and long lanes of opaque dust intertwining them.
The central part of this galaxy is really interesting. The spiral goes right down to the very center, which is unusual. There's also a bar, a yellowish-red Tic-Tac-shaped structure surrounding the nucleus (nearly vertical, but tipped slightly clockwise) containing older stars. Such bars are common in disk galaxies; the Milky Way has a big one, too.
At the very center you can see a bluish mini-spiral; right in the middle of the galaxy is a super star cluster, a huge collection of newly born stars. Many of these stars are massive, and blast out visible light as well as ultraviolet, illuminating gas around it. Keep that in mind a sec …
Also right in the exact center is a circular blob of light as well. That is the location of M61's supermassive black hole, one with a mass of about 5 million times the Sun's. That's fairly meager as central black holes go; most galaxies have far more massive ones. It's actually about the same mass as the one at the center of the Milky Way, and in fact both galaxies are about the same diameter, too (roughly 100,000 light years across). So we're pretty similar.
Except M61's black hole is actively feeding on material! As a black hole like this draws in matter it piles up in a disk around it, and that matter gets incredibly hot, glowing across the electromagnetic spectrum. We call galaxies like this active galaxies, and M61 is an example. But it's a weak one; the black hole isn't all that sloppy an eater, so the light it emits is relatively dim.
In fact, the ultraviolet light coming from the core is only partly due to the black hole, maybe only 1/6th of it or so. The rest is coming from that super star cluster! That's pretty neat. Some active galaxies have cores so bright from the hot matter around the black hole that they're intensely luminous, the most powerful and brightest objects in the whole Universe! But in this case M61's central monster is being outshone by stars. That's unexpected, which is always fun.
Reading up on M61, finding these images, and writing about them makes me want to go out and observe it myself! Unfortunately right now it's far too low to the west once the Sun is down low enough; it sets around the time it gets dark. I missed my shot for this year (unless I want to get up before sunrise in a few months to try, which is … unlikely). But when spring comes around next year I may haul out the 'scope and give it a shot. These images are amazing, and the science is incredible. But having those photons hit your own eyes after traveling for over 50 million years … that quite literally brings it home.