Blogs / Bad Astronomy

For the first time ever, an extrasolar planet has been detected due to its physically slinging around its parent star.

Artiost’s impression of the planet orbiting VB10. Image credit: NASA/JPL-Caltech

Imagine two children, one big and one small, facing each other and holding hands. They swing around each other, each making a circle. The bigger kid makes a smaller circle, and the smaller kid makes a larger circle. If you stand off to the side, you’ll see each child alternately approaching and receding from you as they make their circles on the ground.

In effect, this is how we’ve been finding most of the planets orbiting other stars. As a planet orbits its parent star it tugs on that star gravitationally, and we see a very slight Doppler shift in the light of that star as it approaches and recedes from us.

If only we could magnify the system hugely, then we would actually see the star make a little circle as the planet orbited it. Well, this new discovery did just that!

The star is called VB10, and lies about 20 light years away. That’s close! Only a handful of stars are closer. It’s a very small, faint star: classified as an M8 dwarf, it’s barely massive enough to maintain the pressure and temperature in its core needed to fuse hydrogen into helium. If it were any less massive it would be a brown dwarf, a starlike object that is not actively fusing elements in its core.

The planet is massive, about six times the mass of Jupiter. All of these things together — the close distance, the low mass of the star, and the high mass of the planet — combined happily for this discovery. The massive planet tugs on its star, which is low mass so it makes a relatively big circle, and the nearby location makes it easier to see that motion.

Astronomers watched the system very carefully for 12 years. As the star was swung around by the planet, the physical motion was seen as a wobble in the location of the star. The position of the star had to be measured with exacting precision, which ain’t easy. Even a slight warp in the detector itself can throw off the measurements, as can a hundred other possible errors. I’ve done work like this myself — not exactly like this, but trying to get very high-precision positions on a detector — and it’s frustratingly difficult. This discovery is an amazing achievement.

Comparison chart of the sizes of the star and planet. Click to embiggen.

And the system itself is pretty interesting. For one thing, although the star is far more massive than the planet, physically they are about the same size! When a planet gets to be about as massive as Jupiter, its size remains the same as mass is added to it; instead of getting bigger it gets denser. So if you took two Jupiters and smashed them together, you’d get one planet with twice the mass and twice the density, but about the same size as the original planets.

The star is very dense, so even though it’s much more massive than its planet, they are about the same size. That would have to look pretty weird if you were there.

VB10b, the planet, orbits the star pretty close in, about 50 million km (30 million miles) out… closer than Mercury orbits the Sun! The star is so dim, though, that the planet would only be about room temperature at its cloud tops. It’s possible there are other, less massive planets closer in yet, though I doubt it. The gravity of the super-Jupiter would probably disrupt their orbits.

As it happens, VB 10 is a flare star; it sometimes erupts in ginormous X-ray flares so violent we can detect them here on Earth, 200 trillion kilometers away! So any planet orbiting that star would be cooked to a crisp. It’s ironic that such dim bulbs can produce such enormous blasts of energy, but the eruptions are magnetic in nature, much like the Sun’s own solar flares. These kinds of stars can have powerful magnetic fields, capable of much violence.

Perhaps the most remarkable thing about this system is that VB10 is the lowest mass star known to have a planet. It may keep that record for some time; there aren’t too many stars with a lower mass, or else they wouldn’t be stars at all!

So no mater how you look at this, it’s a pretty cool discovery. And it adds another arrow in our quiver of methods to detect other planets. It’s a difficult one to be sure, and it takes a lot of patience, but now we know it works.

M82 is a weird galaxy. Deep images of it show vast amounts of gas obviously screaming out from it, as if the galaxy itself is exploding. For a long time it was thought that exploding stars were driving the gas out of the galaxy, but now we know that M82 is a starburst galaxy, where huge numbers of stars are being born. There are so many young, hot, massive stars being made that their fierce stellar winds are driving out the material seen.

But those kinds of stars are exactly the types that live short furious lives, dying after only a few million years in titanic supernovae explosions. And now, astronomers are reporting that one has been seen… but the thing is, it can’t be seen.

Uh, say what?

SN2008iz in M82. Embiggen by clicking.

OK, here’s the deal. Newly formed stars produce a lot of dust, complex molecules that are really good at absorbing visible light. M82 is lousy with new stars, so it’s choked with that dust, which blocks the visible light coming from the galaxy’s heart. However, infrared and radio light can go right through the dust. So the newly discovered supernova was seen using radio telescopes; it’s completely invisible in visible light. M82 is close, only 12 million light years away; if it weren’t for all that dust the supernova would have been visible in binoculars!

The supernova, called SN2008iz, was only just discovered. It was seen in some older data from last year, but is not seen in data taken before then. The size of the object — 20 light days, about 500 billion km, or very roughly 50 times the size of our solar system — is pretty good evidence of it being the expanding debris from an exploding star, and the circular shape is also pretty conclusive; that’s just what you expect from an expanding shell of gas.

By combining the power of several radio telescopes, astronomers can see this object in some detail, even though from our distance it looks very small. Better yet, as the debris grows larger we can watch it expand, giving information on the energy of the explosion and what sort of material surrounds it as well, just as we did for a supernova that happened in 1987.

Supernovae create the heavy elements in the Universe, including iron and calcium which are in our bones and blood. I think that’s enough to make them worthy of study all by itself… but they are also just so freakin’ cool. Unimaginably, impossibly violent explosions due to a star ending its life not with a whimper but with a bang that can outshine entire galaxies… and even that mighty light can be hidden, shrouded by the expulsions of stars just being born.

I’d say it’s ironic, but since iron is actually involved that seems somehow wrong. Still. It’s cool. And that’s ironic too.

Whoa.

Hard on the heels of The Big Picture’s homage to Hubble comes this one at Geenstijl. These are gorgeous shots. My only complaint? There are only two pix of STIS; one is fuzzy and the other is blocked by the astronauts! Oh well.

Tom’s Astronomy Blog (you follow his blog, right? Right?) has a picture with an unusual view of Saturn:

Saturn, from Cassini. Click to embiggen

This takes some ’splainin’! But fasten your seat belt; this one is a bit of a wild ride.

First off, in this picture from Cassini we’re looking down on the rings from about a 41° angle. The sunlight is coming from the left, in a direction from below the rings as seen here. The part of the planet itself we see here is actually in shadow! That’s obvious from the top half of Saturn’s disk, which is dark. However, the bottom part of the disk is being softly illuminated by reflected light from the rings (rather like moonlight can illuminate the Earth). In that case, sunlight came from the left, hit the underside of the rings (underside as seen from this angle that is), reflected off, hit the planet, which then reflected that light back to Cassini’s camera.

The top half isn’t completely dark, though. Light from the Sun is passing through the rings, too. It gets scattered and diffused, and some of it hits the dark part of Saturn at the top of the picture. So we can see that as a faint illumination.

There’s more! The rings look like they’ve been sliced clean; that’s the planet itself blocking sunlight from the rings, so think of that as the shadow of Saturn on the rings. But if you look to the right of that cut, you can see still the rings! They look dark and thin, and you can only see them against the planet’s disk. Some of the light reflected off the planet’s southern hemisphere (which itself was reflected from the rings as mentioned above) backlights the rings where they are in shadow, so you can see them silhouetted against Saturn’s disk.

Wow. What a tortuous way to light an image! But it’s very cool that we have Cassini-on-the-spot to send us lovely images like this. We can simply enjoy their beauty, of course, or we can unravel the pieces of the puzzle (to mix a metaphor) to see what’s really going on here. Both are fun, and both are worth spending time doing.

I’m fascinated by clouds. Most astronomers I know are interested in meteorology — in much the same way sky divers are interested in gravity — but in my case it’s more than that. I love interesting clouds, ones with unusual shapes, coloring, patterns. Mrs. BA is sick of me grabbing her and saying, "Look at that one!" all the time, if that gives you a clue of how often I do this.

Yesterday we had an odd cloud formation over my house; a layer with puffy cells in it that looked convective (that is, due to hot air rising and cool air sinking), and the lines between the darker puffs were bright, giving the whole thing the look and feel of a medical X-ray. I posted the image on Twitter and got lots of comments…

…but the one from BATweep Ted_Rex was special, because he mentioned the Cloud Appreciation Society. It’s a website devoted to weirdos like me who like clouds. It has incredible pictures of clouds, and they’re archived in categories like cloud taxonomy (nimbus, stratus, and so on) as well as ones that look like other things… my favorite that I saw was the one shown here, which is astonishing.

There are places to talk about clouds and upload your own pictures. All in all, it’s a fine way to spend a little time… so you should save it away. For a sunny day.

No shocker here: The Big Picture has a feature on the Hubble servicing mission. Know what else isn’t shocking? It’s fantastic!

Awesome. But I also like picture #6, showing the tools the astronauts used for the repair. You can see the drill that looks like a Star Trek phaser! Appropriate, since the astronauts on the Space Station got a special upload of the new movie so they could watch it.

Yesterday, the European Space Agency successfully launched the space observatories Herschel and Planck. Today, they released two cool videos of the event: one was taken by the spacecraft itself and shows the Planck payload moving away from Herschel.

The other video was taken by a one-meter tracking ’scope in the Canary Islands, and shows the two spacecraft together with the Sylda launch vehicle gliding across the sky a few hours after the two observatories separated from the vehicle:

Whoa, that’s cool. The two bright objects are Herschel and Planck, and the dimmer one is the Sylda.

I love love love that this type of imagery is becoming available. It certainly helps engineers on the ground characterize the launch and trajectory of the spacecraft, but it’s also a visceral reminder that humanity has left its footprint in space. May many more join them.