450 million light years away are two interacting galaxies. Both spirals, they are caught in each other’s gravitational claws. Already distorted and bound, eventually, to merge into one larger galaxy in a few million years, the view we have of them from Earth is both amazing and lovely… and hey: they’re punctuating their own predicament!

[Click to exclamatenate.]

Looking a lot like an exclamation point, the two galaxies together are called Arp 302 (or VV 340). This image is a combination of pictures from the Chandra X-Ray Observatory (purple) and Hubble (red, green, and blue). The bottom galaxy is a face-on spiral, while the upper one is seen more edge-on, giving the pair their typographical appearance.

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One of the things I love about nearby galaxies is the incredible amount of detail we can get when we aim our best telescopes at them. For proof, I offer this amazingly intricate Hubble portrait of Centaurus A:

Isn’t that breathtaking? [Click to galactinate and see it in magnificent detail.]

Cen A (as those of us in the know call it) is pretty close by as galaxies go, a mere 11 million light years distant. For scale, our own galaxy is 100,000 light years across, and Andromeda, the closest big spiral galaxy, is a hair under 3 million light years away.

Cen A is a bit of a mess. It’s an elliptical galaxy, which are usually giant cotton balls in space. Calm, quiet, and sedate, they generally possess very little gas and dust and don’t form stars.

Obviously, Cen A hasn’t been keeping up with the neighborhood association rulebook.

In its defense, Cen A apparently suffered a recent collision with another galaxy, absorbing the intruder’s stars, gas, and dust. As you can see in the image here, the dust cuts across the bigger elliptical galaxy’s middle like a Texas cowboy’s belt, but with considerably more intricate scroll work. In the big image above you can also see the pink/red regions where stars are forming, lighting up the gas around them. The bright star in the middle is in our own galaxy, and happens to be in the way of our view of Cen A. Think of it as an intergalactic photobomb.

Another cool thing about this image is the number of sub-images that went into it. It’s a combination of no fewer than seven filtered images! Usually there are only three — one each for a red, green, and blue filter — which, when combined, mimic the way our eyes see color. But this image combines light from the ultraviolet all the way to the infrared, including some filters that only let through a very narrow slice of color, which sequesters out the light from hydrogen, oxygen, and sulfur — astrophysically interesting elements. They can tell us the density, temperature, and other physical properties of the gas emitting them.

All together, these images combine to create an amazing and impressive portrait of a weird and interesting galaxy, telling us a lot about its recent history… but also creating a beautiful piece of art.

Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: R. O’Connell (University of Virginia) [note: one of my PhD advisors!] and the WFC3 Scientific Oversight Committee

My love affair with spiral galaxies is well documented here on this blog. Of course, I’m biased: I live in one.

But some of them demand a little more attention than others, like the oddly off-kilter NGC 2442, aka the Meat Hook Galaxy:

That gorgeous image (click to galactinate, or grab the ginormous 6756 x 5687 pixel version) is from the MPG/ESO 2.2 meter telescope in Chile, and it definitely shows why NGC 2442 is a weird one. The one arm at the bottom is long and stretched out, the top one is thicker and dotted with pink star-forming regions, and the nucleus is way off-center. What the heck happened to this galaxy?

Perhaps a close-up by Hubble will help:

[Note: this image is rotated 180° from the one above.] Again, we see lots of red gas clouds glowing, fired up by massive stars forming in them. Interestingly, to me this view of the galaxy looks like a single bird feather, with the individual vanes arcing down. Those vanes are actually streamers of gas and dust pulled out like taffy from the main arm. Given all this, it’s pretty clear that NGC 2442 suffered a very close pass or even a collision with another galaxy sometime in the relatively recent past.

But what galaxy? (more…)

Happy 21st birthday, Hubble Space Telescope!

On this day, April 20, 1990, On April 24th, 1990, the Space Shuttle Discovery roared into space, carrying HST into orbit and into history. In honor of this anniversary, astronomers have released a new image of the interacting galaxies Arp 273, and it’s a beaut:

[Click to galactinate, or grab the cosmic4000 x 4000 pixel version -- and trust me, you want the bigger versions!]

Years ago, astronomer Halton Arp observed and cataloged a large number of oddly-shaped galaxies, and we now know these galaxies are interacting gravitationally, and some are colliding. These two galaxies, UGC 1810 (top) and UGC 1813 (bottom) are just such a pair. Collectively called Arp 273, they are in the early stages of a collision.

Most spiral galaxies are pretty close to being symmetric and circular, but UGC 1810 is offset and weird. That one arm is thick and sweeps out much farther than the others, making the nucleus of the galaxy decidedly off-center. The string of blue clumps on the top of the galaxy is a sign of furious star formation; massive, hot, blue stars are the culprit, and don’t live long, meaning they were born relatively recently. UGC 1813 is distorted as well, with its arms twisted oddly and gas flung every which-way.

These two galaxies probably passed very close to each other in the past few million years. (more…)

I’ve been posting a lot of nice astronomical images lately, but sometimes one comes along and blows me completely away. How fantastically gorgeous is this?

Holy Haleakala! [Click to galactinate.]

That spiral galaxy is NGC 6872, and as you can see in this image from the Gemini South telescope it’s getting its clock cleaned by the littler spiral — IC 4970 — just to the right. The two are undergoing a galactic collision, a colossal event playing out over hundreds of millions of years. NGC 6872 is currently the victim here; its spiral arms are clearly distorted and being flung wide by the gravitational interaction. However, the smaller IC 4970 will be the ultimate loser in this battle: it will fall into the bigger galaxy, be torn apart, and eventually consumed in its entirety, becoming a part of NGC 6872. Bigger galaxies do this to smaller ones all the time; the Milky Way is in the process of eating several small galaxies even as you read this (I have details in articles linked below; see Related Posts).

This pair has been observed by other telescopes, including the composite picture here of images by the Spitzer Space Telescope (which sees in the infrared), The Very Large Telescope (visible light), and Chandra (X-rays), which I rotated to match the Gemini shot and rescaled a bit.
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I have a morality tale to tell here, but first we have to do some science. The science is part of the moral, and it’s actually rather surprising and cool. And it was reading about the science that made me chuckle, because the moral to me — as a scientist myself — was pretty obvious, but I know to others it will be as opaque as black hole.

Speaking of which…

We know that at the heart of every big galaxy lies a supermassive black hole. There’s one at the center of our galaxy — tipping the cosmic scale at 4 million times the mass of the Sun! — and one in Andromeda. In fact, looking for these monsters^* was one of the key missions for building and launching the Hubble Space Telescope, a mission it had great success with.

There be monsters here. Click to supermassivate.

Why those black holes are there, and so huge, is a matter of some discussion. We’re pretty sure they formed at the same time as their host galaxies themselves, and in fact helped the galaxies grow at the same time the galaxies fed the black holes material. We also know that big galaxies like our Milky Way grew to their current enormous size by literally colliding with and eating other galaxies. This would inevitably lead to the doomed smaller galaxy’s black hole falling to the center of our galaxy, where the insatiable black hole already there would merge with it, growing bigger.

When this happens, so it’s thought, matter in the form of gas, dust, and stars would also fall into the center, feeding the black hole. The matter can pile up outside the hole and get incredibly hot — observations indicate it can reach many millions of degrees, blasting out light in the form of X-rays. Galaxies like these are called active, and we see them everywhere. And many of these active galaxies are weirdly shaped, distorted, indicating they may have recently undergone a big collision. Aha! That fits the idea that colliding galaxies feed black holes and make them active.

There have been so many observations of this that it has matured to become the standard assumption: most active galaxies have recently collided with another galaxy, dumping material into the core and triggering an outburst. I can’t tell you how many papers I’ve read about this, especially when I was working on the public outreach for the Fermi satellite, which was designed to look at active galaxies.

It’s a good story. The problem is, it looks like it’s wrong.

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The European Southern Observatory just released this lovely picture of NGC 520, two galaxies in the middle of the long, long process of colliding:

[Click to galactinate.]

NGC 520 is pretty far away, about 100 million light years. Still, even at a glance you can tell something is fishy^* about it. Colliding galaxies like NGC 520 are relatively common; hundreds of examples are known. These galactic train wrecks can take billions of years to unfold, and in this case the two galaxies have probably been at it for 300 million years or so. They’re well on their way to merging to become one much bigger galaxy, probably the size of the Milky Way: 100,000 light years across. We think our own galaxy grew over time in this way.

And if NGC 520 looks familiar to you, that may be because you’ve been reading this blog for more than a week. It was only a few days ago that I posted a stunning video showing a scientifically and mathematically-produced animation of how some scientists think two large galaxies collided and merged, forming the Andromeda Galaxy as we know it today.

Shown here is a still from that animation (flipped horizontally) which looks remarkably like NGC 520, don’t you think? (more…)