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SYFY WIRE Bad Astronomy

Galactic Archipelago

By Phil Plait
M64, the Black Eye galaxy. Credit: NASA/ESA and The Hubble Heritage Team (AURA/STScI)

Our galaxy, the Milky Way, is a flat-disked spiral galaxy, a collection of dark matter, gas, dust, and a couple of hundred billion stars all held together by their own gravity. We venture through this Universe not alone; we are part of a small clump of other galaxies called the Local Group, a few dozen mostly very tiny galaxies, with two others of decent size (the Andromeda and Triangulum galaxies).

But our group is also not alone. It lies on the distant outskirts of a much larger collection of something like 2000 galaxies called the Virgo Cluster. Named after the constellation in which it lies, the biggest and brightest of these galaxies are visible through binoculars, and have been favorites of amateur astronomers for over a century.

Most of the images I see of the Virgo Cluster are tight close-ups of its galactic denizens. Finding a deep, wide-angle view is surprisingly difficult. But then my friend — and master astrophotographer — Rogelio Bernal Andreo comes to the rescue. Behold, Virgo!

The Virgo Cluster and more. Credit: Rogelio Bernal Andreo

Yeah, I know, right?

There’s a lot to see here, but I want to point out just a few things. First, I rotated this image to fit the highest-res version I could on your monitor; the original version Rogelio put on Flickr is simply magnificent.

But let’s take a look at a few things. On the left, just above center, is an elongated, fuzzy galaxy called M87. That’s the most massive galaxy in the Virgo Cluster, and its gravitational heart. It’s bigger than the Milky Way, but also note that it’s roughly a sphere, so it’s far more massive, at least twice as massive as our home galaxy. I’ve written about it many times. It’s about 55 million light-years away; the Virgo Cluster is pretty big, so some galaxies are closer and others farther, but this is a decent guess at its average distance.

Just below M87 is an unusual structure: Markarian’s Chain, a grouping of a dozen or more galaxies along a gentle curve (this image may help you spot it). Two of the galaxies in it, M84 and M86, were first spotted in 1781 (by Charles Messier, which is where the M comes from in the galaxy names), and others were catalogued a century later. In the 1960s, Armenian astronomer Benjamin Markarian measured their velocities and found many of them apparently moving together, indicating they are physically associated with one another, and not just randomly aligned as seen from Earth as they move around the cluster.

Closeup on M64 near (but not in) the Virgo Cluster. Credit: Rogelio Bernal Andreo

Now journey to the far side of the image, all the way over to the right. That brownish, feathery structure is called galactic cirrus: dust strewn inside our Milky Way and lit by ambient starlight (another name for these features is Integrated Flux Nebulae, which is also rather prosaically poetic, if I may oxymoronate the situation). Such structures are incredibly faint, so this one is quite the catch.

Just under that cloud is the wonderful spiral M64, also called the Black Eye Galaxy. In this shot, you can see it looks odd, like a ring with a deep dark spot in it. It’s hard to tell from this wide-angle shot, but this is actually a dark dust lane around much of the galaxy’s center, the result of a galactic collision. This Hubble shot should clear that up:

M64, the Black Eye galaxy. Credit: NASA/ESA and The Hubble Heritage Team (AURA/STScI)

Yegads. M64 is actually much closer to us than the Virgo Cluster, only about 17 or 18 million light-years away, and Rogelio’s huge image captures it as well.

There’s one more thing to show you. Look straight up in the image, above M64. See the two fuzzy blobs? Those are both globular clusters, roughly spherical collections of thousands to hundreds of thousands of stars. The one nearest the corner is NGC 5053, and the brighter one near it is M53. Both are about 57 – 58,000 light-years from Earth,. There are over 150 globulars orbiting our Milky Way, strewn all over the near volume of galactic space. Having two so close together is suspicious (they'd be just a few thousand light-years apart in space); are they connected in some way? I read that there may be a “tidal tail” of stars between them, stars ripped out of the clusters by their mutual gravity after a near pass.

The magnificent globular cluster M53. Credit: ESA/Hubble & NASA

One final comment. Most of the objects you see in this image are stars in our galaxy (some appear slightly elongated or have lines through them; those are diffraction spikes caused by Rogelio’s telescope optics). We’re inside the Milky Way, so we have to see past those stars to look out into intergalactic space. I like to think of it as sitting at home and looking out a window with smudges on it to the mountains beyond.

If we could travel, oh, say, 10,000 light-years toward Virgo, we’d see very much this same view, but minus all those stars (and the galactic cirrus). That distance, vast as it is (100 quadrillion kilometers!), is but a step in the long walk to the far more remote galaxies. When we see images like this, it’s like a deep, long cone, the apex here at Earth, and the broad opening expanding ever outward into the Universe.

The farther we look out, the more our vision encompasses. I find that comforting, and inspiring. The more we see, the more there is to see.