Take a look at the image displayed here [click to redshiftenate]. Every object you see there is a galaxy, a collection of billions of stars. See that one smack dab in the middle, the little red dot? The light we see from that galaxy traveled for 12.9 billion years before reaching the ESO’s Very Large Telescope in Chile. And when astronomers analyzed the light from it, and from a handful of other, similarly distant galaxies, they were able to pin down the timing of a pivotal event in the early Universe: when the cosmic fog cleared, and the Universe became transparent.

This event is called reionization, when radiation pouring out of very young galaxies flooded the Universe and stripped electrons off of their parent hydrogen atoms. An atom like this is said to be ionized. Before this time, the hydrogen gas was neutral: every proton had an electron around it. After this: zap. Ionized. This moment for the Universe was important because it changed how light flowed through space, which affects how we see it. The critical finding here is that reionization happened about 13 billion years ago, and took less time than previously thought, about 200 million years. Not only that, the culprit behind reionization may have been found: massive stars.

OK, those are the bullet points. Now let me explain in a little more detail.

Young, hot, dense, and chaotic

Imagine the Universe as it was 13.7 billion years ago. A thick, dense soup of matter permeates space, formed in the first three minutes after the Big Bang. The Universe was expanding, too, and cooling: as it got bigger, it got less dense, so the temperature dropped. During this time, electrons and protons were whizzing around on their own. Any time an electron would try to bond with a proton to form a neutral hydrogen atom, a high-energy photon (a particle of light) would come along and knock it loose again.

During this period, the Universe was opaque. Electrons are really good at absorbing photons, so light wouldn’t get far before being sucked up by an electron. But over time, things changed. All those photons lost energy as things cooled. Eventually, they didn’t have enough energy to prevent electrons combining with protons, so once an electron got together with a proton they stuck together. Neutral hydrogen became stable. This happened all over the Universe pretty much at the same time, and is called recombination. It occurred about 376,000 years after the Big Bang.

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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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The largest structures in the Universe are superclusters: not just clusters of galaxies, but clusters of clusters. They can stretch for millions of light years and be composed of thousands of galaxies.

Abell 2744, at a distance from Earth of about 3.5 billion light years, is one such megastructure (if you want to sound fancy, astronomers call it "large-scale structure"). Astronomers have been studying Abell 2744 with an arsenal of telescopes, and have discovered that it’s actually the result of the ongoing collision of four galaxies clusters. If you’ve ever wondered what 400 trillion solar masses of material slamming into each other looks like, well, it’s more than a bit of a mess:

[Click to enclusternate.]

Yeah, like I said, it’s a mess.

First off, this picture is a combination of observations from Hubble (in visible light, colored blue, green, and red), the Very Large Telescope (also blue, green, and red), and the Chandra X-Ray Observatory (X-rays, colored pinkish). In visible light you can see literally hundreds of galaxies, probably more, dotting the supercluster. The pink glow is from very hot gas between galaxies; it started its life as gas inside of galaxies that got stripped off and heated to millions of degrees as the galaxies plow through the space around them (I like to think of it as opening a car window to let a noxious smell out — the wind from the car’s motion pushes the air inside the car out the windows).

The blue glow is perhaps the most interesting bit here: it’s a map of the location of dark matter. This type of exotic matter neither emits nor reflects light — hence the name — but it has mass, and that means it has gravity. As I described when this method was used to trace dark matter in the Bullet Cluster, gravity bends space, and light follows that curve. Galaxies farther away get their light distorted by the gravity from dark matter, and that distortion can be measured and used to trace the location of dark matter. The blue glow in the image above maps that.

The thing about dark matter is that it doesn’t interact with normal matter (electron, protons, you, me, lip balm, oranges, whatever). But all that gas between galaxies shown in pink is normal matter, so when one galaxy cluster slams into another at a few thousand kilometers per second that gas gets compressed, mixed-up, and heated. But dark matter just blows right on through. So by comparing the location of the galaxies, the dark matter, and the hot gas, a lot of the cluster’s history can be unraveled.

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When it comes to black holes, there are some things we know a lot about them — in general. How they form, how they affect space around them, how they eat matter.

The details, though, are maddening. We know, for example, that black holes spin — as odd as that may sound — but how they get that spin and how spin changes over time is elusive knowledge.

A new study has given us an idea of that now, though. Here’s how this works: we see that as matter falls into them, some black holes generate twin beams, called jets, which shoot away from their poles. We see this from black holes that form when stars explode, and we see them in the supermassive black holes that inhabit the centers of all big galaxies, too. We know that various physical features of the jets are tied to the rate at which the black holes spin, and this new study makes this connection more clear. The astronomers used computer models to correlate spin to the jets, and observations appear to confirm these models.

Two very interesting results came out of the study. (more…)

The Wide-field Infrared Survey Explorer was turned off a few months ago, but the science it did lives on. NASA just released a gallery of nine spiral galaxy images taken by WISE, and they’re lovely:

[Click to galactinate.]

Several of my favorite big, grand design spirals are there, like M51, M81, and M83. Note that since WISE only sees infrared light, these are false color images; the colors used are blue for 3.4 micron IR light, cyan for 4.6 microns, green for 12 microns, and red for 22 microns. The reddest light a human eye can see is very roughly 0.75 microns, to give you a comparison. In the images, star-forming regions are yellowish and/or pink, dust (in the form of long-chain organic molecules called polycyclic aromatic hydrocarbons) is green, and old stars are blue.

While looking over the images, I actually recognized the name of the one in the lower right: IC 342 (here’s a full-res WISE shot of it). This is part of a small group of galaxies near our Milky Way that is heavily obscured by dust in our galaxy. (more…)

[This is a gallery of gorgeous images, my favorites, from the orbiting infrared observatory called the Spitzer Space Telescope. Click the thumbnail picture to get a bigger picture and more information, click the big pictures to go to my original blog posts about the pictures, and scroll through the gallery using the left and right arrows.]

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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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