Blogs / Bad Astronomy

This will be my last post from the actual physical location of the American Astronomical Society meeting; I’ve preloaded this entry to go up when I’ll be on a plane winging it back to Boulder. I’ll have some wrap-up stuff later (oh, just you wait) but since I’m heading back, I want to leave you with a really cool supernova remnant image. But I can’t… so instead I’ll leave you with two!

This object looks like a single nebula with two lobes, but new studies show that it’s actually two separate object next to each other in the sky! This Gemini telescope image is of DEM L316, and it was always assumed to be what’s called a bipolar nebula, a single object blowing bubbles of gas in opposite directions. However, it’s now understood to be the expanding gas (called the remnant) from two separate exploding stars. The two stars blew up in the Large Magellanic Cloud, a small galaxy orbiting our Milky Way galaxy.

X-ray observations support the idea that these are two distinct objects: the X-ray emission indicates the chemical composition (the relative amount of iron, oxygen, and so on) are different in the two objects. In fact, it looks like these were two different types of supernovae altogether: the smaller lobe on the left is probably from the detonation of a white dwarf star, while the bigger one on the right is from the explosion of a star more like the Sun (though with substantially more mass — the Sun can’t go supernova). While both explosions probably happened around the same time (give or take a few tens of thousands of years), the stars were much different ages when they blew: the white dwarf was probably billions of years old, while the massive star was only a few million years old. The two stars were almost certainly totally unrelated to each other.

But through a cosmic coincidence, they both chose the same epoch of the Universe to light up the skies around them. And from our perspective they form a pretty, if somewhat lopsided, example of just how pretty death and destruction on an epic scale can be.

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When I worked on Hubble data, lo these many years ago, some of the most fun I had was working on protoplanetary disks. Stars form when local bits of an interstellar cloud collapses. Random eddies and whorls amplify as the blob shrinks under its own gravity. The swirling junk forms a disk, and the central region compresses and forms the nascent star. The outer part of the disk spins around the central star and forms planets. As you can imagine, the disk can be pretty big, many billions of miles across. That means that even from light years away, telescopes like Hubble can see them fairly clearly. They come in many shapes, but usually they are relatively symmetric and round. However, one was recently found around the nearby star HD 61005 (which is about 100 light years away), and it was a bit of a surprise:

It’s squished! The astronomers who found it call it "The Moth". It’s extended on the sides, almost as if it’s being swept back by something.. and it turns, it is. The whole system is moving through the galaxy, and as it sweeps through the thin gas between the stars, the pressure pushes on the disk, giving it those graceful arcs. Here’s an annotated version of that image showing what’s what.

As you can see, the disk is plowing through space pretty much face-on, which is why it’s warped. Just so’s you know, the part labeled "coronographic hole" is where a small piece of metal block out the light from the star, which is far brighter than the disk, allowing us to see the much fainter circumstellar material. The scale is huge; the size of Neptune’s orbit is shown for comparison. The wings of The Moth are 35 billion kilometers across! The disk is probably in the middle of forming planets now, and it’s unclear how this will affect whatever planets are being born. It’s quite possible planet formation will be suppressed, and eventually the disk will blow away entirely… which, I hope, explains the title of this post.

I’ll note that the astronomers who made these observations — Dean Hines and Glenn Schneider — are friends of mine. I worked with Glenn in particular on several very cool protoplanetary disks. They were fun for a lot of reasons: they were interesting scientifically, they were pretty, and I just plain enjoyed working on the images where the coronograph was blocking the starlight and letting the disk light through. Plus it was simply a true and clear joy to gaze upon the light from planets and stars in the throes of birth, knowing that there was literally a bright future ahead of them for the next few billion years.

Fraser, Pamela and I have been whining remarking to each other that there is a huge amount of news coming from this meeting, and we’re having a heckuva time keeping up. Some is worth a long writeup, while others can probably be handled with a short post. Below are a few of the stories that are worth noting briefly.

And as a reminder: if you like what you’re seeing here, Digg the articles! Click the button at the top of the post, and it’ll help spread the word. Thanks!

1) The bigger the telescope the better, right? So what if your scope is the size of the Earth?

A technique called interferometry combines the light from telescopes that are widely separated, and with it you can make a virtual telescope that’s the same size as the distance between the physical telescopes. If those ’scopes are on opposite sides of the Earth, you get a telescope thousands of miles across. Using this technique, astronomers have made phenomenal measurements, including actually seeing the rotation of the galaxy M33 as well as its physical motion across the sky; something that had never been done before. They have been able to see the effects of the Sun’s motion around the Milky Way’s center, even though a full orbit takes 240 million years!

2) One long-standing mystery in astronomy is an apparent fountain of antimatter streaming out from the center of the Galaxy. What’s causing it? Most astronomers assumed it was coming from the giant supermassive black hole there, but now observations indicate it’s actually being accelerated by binary stars, where one of the two orbiting stars is a neutron star or black hole.

The cloud of antimatter is detected because it gives off gamma rays, which are a very high energy form of light. The gamma rays from the Galactic center are not centered on the center (hmmm, remember to edit that line), but extend a little bit more on the western side. This matches the distribution of the black hole or neutron star binaries. These binaries can generate antimatter when regular matter from the normal (sunlike) star swirls around the denser object.

I wrote about this in my book, so now I might have to do some editing. Nuts.

3) The most luminous objects in the Universe are, ironically and paradoxically, the faintest.

Huh?
Black holes can generate fantastic amounts of light as matter falling in to the hole first forms a disk around it. The disk is hot, and magnetic forces (along with friction and gravity) can make it extremely bright, as bright as billions of stars like the Sun. Supermassive black holes in the centers of galaxies are big, and have proportionately big disks which can outshine the rest of the galaxy in which it sits. We call these active galaxies, and there are different kinds (quasars, blazars, Seyferts) depending on the various characteristics of the galaxy.

It turns out, though, that in many cases our view of these black holes is blocked by tick gas and dust in the galaxy. The folks at the Sloan Digital Sky Survey have figured out a way to detect a fingerprint of these obscured galaxies, and found 887 hidden quasars that were previously unknown, by far the largest such sample ever made. What this means is that we have to be careful in the future about what objects we can and cannot see — astronomers may say "We expect to see XXX of these kind of galaxies and see none, which means our cosmology is wrong," we can take it with a judicious grain of salt.

Because he reads my blog.