Blogs / Bad Astronomy

Astronomers using the Chandra X-Ray Observatory have just released an extraordinarily cool animation. Composed of images taken between 2000 and 2007, it shows the supernova remnant Cas A literally expanding as you watch it!

See the little white dot in the center? That used to be a star, a big one. About 330 years ago^*, that star blew up in a titanic supernova explosion. Several octillion tons of material screamed outward from the star at a good fraction of the speed of light, leaving behind an ultradense neutron star, the remains of the star’s core. So, that dot in the center? It’s an object a dozen kilometers across that has about the same mass as our entire Sun. It has a density of about 100 million tons per cubic centimeter. That’s roughly the mass of every single car in the United States, crushed into a cube the size of, oh, say, a mini marshmallow.

Yeah.

The outer layers of the explodey star are what you’re seeing here in this animation. Rushing outward at thousands of kilometers per second, they are heated by the explosion itself, by the decay of radioactive materials forged in the blast, and by magnetic processes when the spinning neutron star interacts with the gas. All of these together heat the gas to millions of degrees, and it glows in X-rays. The Chandra X-Ray Observatory can see these high-energy photons, and so astronomers use it to observe Cas A (so called because it is in the constellation of Cassiopaeia, and is also a radio source, which were traditionally named after letters in the alphabet).

In fact, Chandra observes this supernova remnant quite often, so the astronomers took the images made over the past 8 years and created this animation. It shows the expansion of the debris as the gas moves outward from the point in space where the original explosion happened. It’s like watching a nuclear blast in super duper slomo.

Still images showing the expansion. Credit: NASA/CXC/SAO/D.Patnaude et al.

But don’t be fooled by the apparent peacefulness and calm you see here. Supernovae explosions are among the most violent events in the Universe. If one were to happen within 20 light years of the Earth, it could cause a mass extinction through the destruction of our ozone layer. Happily, no star capable of blowing up is that close. Cas A is about 10,000 light years away, so we’re in no danger from it either.

The flip side of that is that the iron in our blood, the calcium in our bones, and even the gold in our jewelry is created in supernovae blasts. The incredible heat and pressure of the explosion forces the gas to undergo nuclear fusion, alchemically creating the heavy elements life is based on. A supernova could wipe out life on a nearby planet, but we literally owe our existence to such supernovae. I could go into some kind of "Lion King" Circle of Life speech, but I think you get my point.

An interesting tidbit: it’s been thought for years that high-energy particles that slam into our atmosphere all the time, called cosmic rays, were accelerated to their high speeds in supernovae remnants like Cas A. Interestingly, this animation indicates the gas is expanding more slowly than it should given how much energy is released in the explosion, which in turn means that lost energy is going somewhere. Astronomers think it’s going into the production of those cosmic rays, which eat up about 35% of the explosion energy.

Animations like this are more than just cool to look at (though they are very cool to look at). They can reveal a huge amount of information about the explosions as well. One of my favorite things about astronomy — and I have a lot of favorite things — is that we can create gorgeous images and movies, and they are a wonder to see… but they also teach us stuff. And not only that, the stuff we learn is fundamental to our very existence: information on how we got to be here, how the elements in our bodies were made, and even how the Universe itself changes over time.

How amazing is that?

Well, it’s that time of year again: the weblog awards have been announced, and the science category has this very blog listed. The usual suspects are there, including Pharyngula, as well as Neurologica, run by my pal Steve Novella from Skeptics’ Guide to the Universe.

I couldn’t help but notice that Climate Audit and Watt’s Up With That are there as well, just like last year. And those of you with long memories will remember much of the ugliness that happened last year, a situation I am loathe to repeat. Also, the sentiments I expounded upon in that linked post are still true today; these awards are not set up in a way that necessarily rewards truly good blogs. Instead, the sites that garner votes are the ones with the loudest voice, the biggest audience, or that generate the most controversy.

Two years ago it was fun to have the mock battle with PZ, an affair we still chuckle over when we get together. But last year… yeah. It wasn’t fun at all. So that’s why I will mention the awards here now, and that’s it. Vote if you’d like, vote for whom you’d like, vote against whom you’d like — you can vote once per day. And check out the other blogs, too; there are quite a few worth reading.

And my thanks to Miss Cellania. She knows why. I’ll note that she’s up for Best Large Blog. Hint hint.

And how the Law category doesn’t include Bob Loblaw’s Law Blog I’ll never know.

If you live in Toronto, you may notice something the next time you take the bus: someone’s trying to teach you astronomy.

That someone is Ray Jayawardhana, who has coordinated a public outreach campaign called Cool Cosmos to get the public interested in astronomy. Along with the Dunlap Institute for Astronomy and Astrophysics he has created a series of five posters that will go on buses, subways, and streetcars. They’re cute, simple, and feature a basic but cool fact. I like this one best:

It says, "Having a long day? It will only get longer. Tides caused by the Moon are slowing down the Earth’s spin, making each day a tiny bit longer than the one before."

How cool is that? The others are good too. This is a very clever campaign, and I think at the very least it’ll get people thinking about nifty ideas about the Universe. This is being done as a way to celebrate IYA 2009, too, and it’s an excellent endeavor.

My one complaint: they should’ve talked to the folks at Spitzer first about the name. D’oh!

I’ve been getting email and tweets about the American Astronomical Society meeting going on right now in Long Beach California, so I thought I’d make a coupla quick comments:

1) I am not there. Long story, but it just didn’t work out this year. I love going to the meetings — and I’ll be honest here — because it’s my annual chance to get together with a lot of friends, both new and old. I can’t believe I’ll miss the clubbing night this year… but anyway, I’m not there, and I’m doing any writing about it from home. I’ll preface each post title with "AAS #XX" to let you know it’s from the meeting.

2) You can participate vicariously in the press conferences by going to the Astronomy Cast live stream. Whenever there is a press conference (three times a day, usually) or some other live event, you can watch it there. They have a live chat room on that page as well, so you can actually participate!

That’s it. I’ll post what I can about the meeting, as well as the usual nonsense. But expect to hear a lot of astronomy news this week! And remember, those yellow Digg buttons at the tops of my posts work pretty well.

I’ll be on TV tonight and all this week: The History Channel is airing a show called "Seven Signs of the Apocalypse" at 21:00 Eastern (US) time (but check your local listings). I did what I call a "stand-up interview" for this show: me standing in front of some interesting background while I talk astronomy. In this case, it was asteroid impacts and gamma-ray bursts, two of my fave death-from-the-skies scenarios.

I’ve seen some of the graphics from the show, and they are spectacular. It should be pretty cool, even if couched in an "End Times" framework.

Astronomers using the Hubble and Spitzer Space Telescopes have just released an incredible image of the center of the Milky Way:

Hubble and Spitzer map of Milky Way Center. Credit: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst), Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech)

Wow. Click to get access to much higher-res versions that will embiggen your brain. They have HUGE versions too.

The image is in the infrared, showing piles of warm gas and dust that litter the galactic center. The weird structures are carved out by massive star winds, supernova explosions, bursts of star formation, and more. Lurking in this image, far too small to be seen, is the supermassive black hole at the heart of our galaxy. Even though our past and future are intertwined — the black hole formed around the same time the galaxy did, and evidence is that they helped shape each other — the black hole is invisible. It’s smaller than our solar system, and this map is millions of times wider (300 x 115 light years); the black hole is far smaller than a pixel on this scale.

To get an idea of the scale of this image, here’s a closeup on the lower left portion:

There’s so much to see! The fingers of stalagmite-looking gas on the left are actually columns of gas light years long being eroded by the winds of massive stars, probably that bright cluster to the right of the fingers. On the right is a bright star surrounded by a halo of gas. What’s that? I’m not sure; it’s probably another just-born massive star carving out a bubble of gas around it. That bubble is several light years across!

And just look at the sheer number of stars in the image! It’s hard to grasp just how big a number 200 billion is, but that’s how many stars are in the galaxy. There are countless thousands in this one image, and it represents a tiny, tiny fraction of our galaxy.

Wow.

1) Black holes succor!

So we live in a spiral galaxy, right? That means it’s a flat disk, with spiral arms, a bulge of stars in the middle, and right at the center sits a black hole — all big galaxies appear to have one. The monster in our middle tips the cosmic scales at over 4 million times the mass of the Sun. That sounds like a lot, but remember there are about 200 billion stars in the Milky Way, so in reality the black hole is 0.002% of the mass of the galaxy, more or less.

Artist’s concept of young stars near the galactic center. Credit: NASA, ESA, and A. Schaller (for STScI)

Near the black hole, you’d think the environment is not exactly nurturing. The gravity of the hole is enormous, of course. Stars can orbit it in stable paths that last for billions of years, but big objects like gas clouds can be shredded; the black hole pulls on one side more strongly than the other, which can tear the clouds apart.

So we don’t expect to see young stars near the very center of the Milky Way — yet that is precisely what astronomers have found using the radio telescopes in the Very Large Array in New Mexico!

Young stars being born cry out in radio wavelengths, and the VLA is exceptional at precisely pinpointing post-partum protostars. The astronomers found two such young stars still in the act of forming. Incredibly, this means their cocoon of gas must survive being so close to the black hole — in this case, just seven and ten light years away! Since most gas clouds are light years across, this means these clouds must be smaller and more dense than usual.

This study means that stars can form in relatively hostile environments, and that in turn tells more about how stars form, which is cool, and what things are like very close to the maw of the supermassive black hole lurking at the galactic center, which is very cool indeed.

2) Our Galaxy is beefier than thought

Sitting as we do off to one side of the Milky Way, it’s really hard to get a good census of it. Dust clouds block our view, for example, and the Sun is rushing around the center of the galaxy along with the hundreds of billions of others.

Map of the galaxy, showing the center, the arms, and the locations of the gas clouds used to get the data. Our location is the red dot. Credit: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF

However, astronomers have used a collection of radio telescopes strung across the Earth to get better data than ever before on our home galaxy. And what they found is pretty interesting: we thought the Sun was going around the center at about 220 km/sec, but it turns out we’re actually moving at closer to 270 km/sec!

The speed of the Sun depends on the combined mass of all the stars, gas, and dust between us and the center. The gravity of all that stuff is what determines our speed. If we’re moving faster than we thought, then the galaxy itself must be more massive. This increase in speed indicates the Milky Way is actually 50% more massive than we previously thought!

That’s a big difference. That means we’re the equal of the Andromeda Galaxy, which we thought was the big boy of the local collection of galaxies. Now we don’t have to hang our head in shame any more.

Even cooler, the astronomers discovered the Milky Way appears to have four spiral arms, and not just two!

So we’re as massive as Andromeda, and we have four arms. Hmmmm. The obvious conclusion: we can easily take Andromeda on and beat it up! In a couple of billion years, we’ll get our chance, when the two galaxies collide and eventually merge. Sadly, after that, we’ll most likely be an elliptical puffball galaxy, with no arms at all. But until then, it looks like we’re king of the hill.