If you’re wondering what all the buzz has been about the past few days over a NASA discovery, then wait no longer. No, it’s not aliens or an incoming asteroid. Instead, it’s still very cool: astronomers have found the youngest supernova in the Milky Way.

First, before I explain, here’s the photo of the newest galactic family member:

It kind of looks like a baby head swaddled in a blanket. Or a really bad drawing of Caesar. Anyway, seriously, this is a big deal. Why?

When a star like the Sun dies, it blows off a lot of its outer layers, leaving behind a dense hot object called a white dwarf (FYI, I have a more detailed description of all this here). If the star is binary — it has a companion — then the immense gravity of the white dwarf can draw material off its mate, and that matter will pile up on the surface of the dwarf. If enough piles up at just the right rate, it can ignite in a thermonuclear fire. This sets off a chain reaction, and the entire star self-destructs. This creates an immense amount of energy — as much energy is released every second as the Sun emits for billions of years — and an octillion tons of gas is launched violently into space at a large fraction of the speed of light.

The event is so titanic that it can be seen clear across the Universe, and of course you don’t want one to happen too close^*. But somewhat close is good: we can study them better.

We know how many stars like this there are in our galaxy (as well as massive stars which can also explode, although using a different mechanism), and we know roughly how long they live, so we should be able to predict how often one should go off. The answer is, about three per century, more or less.

But observationally, it’s been more less than more. That is, the last one we know of that blew up in the galaxy was over 400 years ago. That’s been a major pain for astronomers; statistically speaking, it’s a little weird that we haven’t seen one since the 1600s.

But that’s changed. After searching for literally decades, astronomers have found a supernova in our galaxy! It’s official name is G1.9+0.3, which doesn’t exactly make your heart sing, I know. But it’s very cool. It’s a remnant, the expanding gaseous debris from a supernova blast. It’s located very near the center of the galaxy, about 28,000 light years away, and it’s only at most about 140 years old.

The false-color image above shows the remnant as seen by the orbiting Chandra X-Ray Observatory, and the ground-based Very Large (radio) Array in New Mexico. To give you a sense of scale, the object is about 13 light years across, or 80 trillion miles end-to-end. The orange crinkly stuff is extremely hot — millions of degrees hot — X-ray emitting gas, generated by vast magnetic fields in the gas. The bluer material is smoother radio wave emission also dominated by magnetic forces.

Together, they paint an interesting picture of this explosion. For one thing, it looks like a ring, or a smoke bubble. That’s a clear sign that it’s actually a shell of material, and not a solid sphere. A filled sphere of gas would be brightest in the middle and fainter near the edges (because we’re seeing more bright material when we look through the center of a sphere as opposed to near the edge), but a shell has the opposite behavior.

For another, it’s asymmetric: the gas is not expanding in a perfect sphere. Either it’s slamming into gas that existed outside the star before it blew up, or the explosion wasn’t perfectly spherical. That tells astronomers quite a bit about the physics of the explosion mechanism.

How do we know it’s young? Ah, an excellent question! I love this part: we’ve seen this sucker expand!

Here are two radio images of the remnant taken 23 years apart:

See how it’s gotten bigger over time? By measuring that expansion and knowing the time elapsed between the two pictures, we can extrapolate backwards to see how old the object is. If you do the math, all that gas was in one point about 140 +/- 30 years ago. That’s actually an upper limit to the age: it may have been less than that, if the expansion is slowing over time due to the material slamming into gas floating in space. That’s likely; that region of the galaxy is pretty thick with dust and gas.

In other words, this thing went off around the time of the American Civil War.

So that’s how we know it’s the youngest we’ve ever seen. But there’s more! We know the distance to the remnant as well. The amount of dust and gas between us and it can be measured and compared to known maps of the galaxy, kind of like knowing how far away distant mountains are by the amount of haziness you see between you and them. Combining the distance with the expansion measured means we can get a real velocity for the gas, and it’s a whopper: 14,000 kilometers per second, or 5% the speed of light! That’s fast. The amount of energy released in a supernova is numbing.

So you may also ask, why didn’t anyone see this thing when it went off? All things being equal, at that distance it should have been as bright as Venus in our skies, visible even in daylight! But all things are not equal: all the gas and dust between us and it absorb visible light, making this object almost totally invisible. It might have been visible to someone using a good telescope a century or more ago when the explosion took place, but that astronomer would have had to have been looking at just the right spot, and noticed a very faint star that wasn’t there a few weeks before — and this object sits in a part of the sky loaded with faint stars. It would be like noticing a new grain of sand on the beach. Unlikely, and in fact no one did notice.

It can be seen now because we have more advanced instruments these days. X-rays and radio waves are not as affected by intervening glop in the galaxy, and pass right on through. That’s why we can see it at all; even in big optical telescopes G1.9+0.3 is totally invisible.

So there you go. This object will be heavily studied now, I’m sure, because it’s the youngest such explosion we can see up close. It may help us understand how white dwarfs explode, and what the environment is like near the center of the galaxy, and how gas behaves when it violently expands in such a place.

And, well, it’s just cool. It’s been a mystery for a long time why we haven’t seen any young remnants — we expect there to be 60 of them younger than 2000 years, but only 10 are known — and now that we’ve seen this one we know they’re out there, but really just a pain to detect. You can bet that astronomers will look even harder for more of them now that we know they exist.

The ways the Universe can deal out death are as numerous as they are terrifying. Asteroid impacts, nearby stars exploding, wandering black holes… I spent a year or so thinking of nearly every method of cosmic catastrophe I could while writing Death from the Skies!^*.

I wrote a whole chapter on what dangers lurk in our own Milky Way galaxy, and I was surprised to find out the Sun’s orbit around the center of the galaxy is a potential problem. The galaxy is flat, like a CD (in fact, the proportion is right if you stack about 4 CDs together). The Sun does not orbit the center of the galaxy in a nice, flat plane, like planets do around the Sun. Instead, it bobs up and down like a cork in water, making about four cycles for every one time it orbits the galaxy (which takes about 200 or so million years).

In my research, I came across the idea that when the Sun is at the apex of its bobbing, towards galactic north, it’s about 100 light years above the galactic plane. That’s far enough up that the magnetic fields of the galaxy are weaker, and it’s these fields that protect the Sun (and the planets, meaning us) from intergalactic cosmic rays, subatomic particles that zip around space between galaxies. When the Sun is up high, these cosmic rays can strike us, and we have to endure this particulate rain for millions of years. The radiation can do bad things, like damage the ozone layer or induce genetic mutations.

When researchers plotted the times of the Sun’s most northerly excursions (which happen every 64 or so million years), they lined up in time with many mass extinctions on Earth. Uh oh.

The good news is that this only happens at one part of the Sun’s orbit, so while we’re deep in the plane of the galaxy we’re protected and safe.

Or, actually, things get worse.

A new result has just been announced that says that when the Sun is in the thick of the Milky Way’s plane, tides from the galaxy can induce comets from the outer solar system to plunge down toward the Sun, meaning many will hit the Earth and potentially cause mass extinctions.

Well, nuts.

According to the new study, this happens every 35 - 40 million years, which is not too far off from the calculations in the older study. Since the Sun moves up and down in the plane, it actually plunges through the mid-plane twice each cycle. If it reaches its apex every 64 million years, then it should pass through the mid-plane every 32 million years, which is reasonably close to what the second study says.

So as if it’s not bad enough that we get irradiated at the top of the orbit, we get pummeled by comets twice as often!

Bummer.

So sure, having trillion ton chunks of rock and ice rain down every few 30 million years is bad and all, but that’s not the worst part! Horrifyingly, this news came too late for me to include in the book!

We have to keep our perspective on these things, after all.

On my live video chat the other day, I was asked a very cool question: if time slows down as you approach a black hole, how can they ever really form? Won’t they slow down to zero before they can actually be created?

I recorded my answer and put it on YouTube. Sorry about the jumpiness, but this was recorded off the live stream and the connection was laggy.

I love answering questions, so drop by the next time I do a live chat, and maybe yours will make it into the video!

I’m going to be heading to Michigan in May to attend the premier of — get this — the Bad Astronomy planetarium show!

I’ve been working with folks from the New Detroit Science Center for some time now on this project. Well, to be more honest, they’ve been working really hard, and I’ve been heckling them. Last year I flew to Detroit to film some segments for it, and from what I have seen the show will be funny, informative, silly, and perhaps with a slight hint of fromage. I have not seen the final product, so it’ll be as big a surprise to me as it is to everyone there.

I’ll be at the NDSC all day on May 10th from 10 a.m. to 6 p.m., and giving a talk at 1:00. They’re charging a nominal fee for this, seeing as how I’ll be a huge star after the premier. Click here for the flyer. I’ll be happy to sign books, too; they’ll have copies of my first book there for purchase. The second book, Death from the Skies!, won’t be out until October but as usual I’ll be shilling it mercilessly and without remorse.

While I’m in Michigan I’ll be giving a talk at the nearby Cranbrook Institute of Science, a nice museum outside of Detroit. The talk is on May 9th from 7:30 to 9:30 p.m., and tickets are $10 ($8 for members). They require pre-registration, so they know how many rotten tomatoes to stock.

I graduated from the University of Michigan, so it’ll be nice to be back in the land of harsh vowels, Vernor’s soda pop, and holding up your hand to show people where you’re from. And if you don’t get that last one, well, you’re just not from Meeechigan.

What happens when a smallish galaxy plows right through the center of a bigger one?

This:

Holy Haleakala. That’s Arp 148, and it’s magnificent. That elongated galaxy was probably not quite so stretchy before it hit, but the gravity of the other galaxy drew it out. In turn, its own gravity drew in stars and gas from the bigger galaxy, which then expanded as a ring as the smaller galaxy plunged on. It almost looks like a freeze-frame image of a bullet shattering a drum head.

If you like that, you’ll love this: Hubble has released 59 such images of galaxy collisions today (the US version of the release is here), celebrating Hubble’s 18th anniversary in space. It launched on April 24, 1990.

The galaxy pictures are stunning. The one on the left is Arp 256, two spiral galaxies interacting as they pass each other for the first time. Long tendrils are being drawn from both galaxies, and the blue regions indicate epic bursts of star formation (young, massive stars are blue and extremely luminous). Someday the Milky Way and Andromeda galaxies will look very much like this… a billion years from now, when they pass each other. I’d write more here, but golly, I have a book coming out in October with lots more details.

This one is even weirder: it’s a red elliptical galaxy and a bluish spiral interacting. The blue galaxy looks to be small to my eye; it’s getting totally disrupted by the elliptical. There’s some indications of dust getting blown every which-way in the elliptical too. This will be a very interesting system in about another 500 million years or so.

I’ll leave you with one more: NGC 6050.

Two magnificent spiral galaxies, each about the same size, slide toward one another and are just now beginning their slow dance. I can almost imagine them spinning like buzz saws into each other, tearing both to shreds (in fact, they look a whole lot like the animation of colliding galaxies used in my short astronomy video on Hulu — and yes, we’ll be posting that on internationally-accessible servers soon). The two spirals will no doubt merge completely into an elliptical… unless they’re moving too quickly. They are both part of the Hercules Cluster of galaxies, 650 million light years away (the press release says 450 million, but the 2MASS catalog says 650). Hercules has over 100 galaxies in it and is therefore pretty massive; all that mass means a lot of gravity, and that in turn means the component galaxies are screaming along at high velocity. It’s possible these two beauties will continue on their way, passing through each other, distorted, beaten, but surviving.

I wonder how that story will end; lover’s embrace or ships passing (literally) in the night? With images like these, astronomers will learn a lot more about how galaxies behave when they collide, and that will point the way to better, more detailed observations. Eventually we’ll know how the story goes, from start to finish.

Our own future is wrapped up in these images, writ large across the sky. As usual in astronomy, and in science as a whole, by looking outwards we learn more about ourselves.

Happy anniversary, Hubble.

BABloggee David Johnson tipped me off that a new mini-series just began filming in Canada. Called Impact, it will tell the incredibly realistic story of how a chunk of white dwarf will hit the Moon and set it hurtling toward Earth.

Uh, yeah.

You can’t make this stuff up. Wait! I mean, you have to make this stuff up:

Budgeted at $13 million, the effects-heavy “Impact” chronicles the aftermath of a meteor shower during which a piece of a dwarf star lodges itself in the moon. That triggers a series of anomalies on Earth, including cell phone service interruption, exaggerated tides and the occurrence of sporadic weightlessness.

Astrophysicist Alex Kinter (Elliott), with a help of a female astronomer, discover that the moon has been dislodged from its orbit and is on a collision course with Earth.

From the description, it’ll make Armageddon look like Shakespeare. I can’t wait to see it. I’ll tell Mrs. BA to remove all sharp object from the house first though, just to be safe.

If only I had included this scenario in my book! Golly, too late to add it. Shucks.

There has been news around the blogosphere this week about an ancient artifact that might indicate that Sumerians saw an asteroid impact… and that it might explain Sodom and Gemorrah. Pretty much everything about that press release set off my BA detector, and I was going to write about it. But then I saw that my friend and asteroid-namer-after Jeff Medkeff already tackled it with much gusto.

I’ll be very curious to see if more about this idea turns up any time soon.