Blogs / Bad Astronomy

A science joke:

A woman is out walking and sees a kid on his hands and knees looking at the sidewalk. She asks the boy what he’s doing, and he says, "Looking for a quarter I lost." She asks him where he lost it, and he points across the street. Quizzically, she asks, "Then why are you looking here?" He replies, "The light’s better over here."

What’s this got to do with astronomy? I’m glad I asked.

Astronomers took a sample of 500 stars, 70 of which are known to have planets orbiting them, while the rest have no planets detected. They examined the spectra of the stars, looking specifically to see how much lithium was present. What they found, with good statistical significance, is that stars with planets had far less lithium than stars that did not have planets.

Somehow, having planets means a star loses its lithium. How the heck does that happen?

A brief digression. Lithium is a weird element. It’s the third lightest after hydrogen and helium, and unlike every other element after it on the periodic table, we don’t think it’s made inside stars. It’s too fragile; the nuclei get smashed up easily, and so it doesn’t last long in the cores of stars. That means that as far as we can tell, all the lithium in the Universe was created in the Big Bang.

Just because it gets wrecked in the cores of stars does not mean they have no lithium at all. Lithium created in the Big Bang would have been in clouds where stars formed, and if a lithium nucleus can avoid the core of the star by staying nearer the surface, it can survive. The Sun has lithium in it, for example, but at far less abundance (<1%) than what you see out in gas clouds. That means the Sun has destroyed a lot - but not all - of its lithium supply.

When astronomers look at other stars like the Sun, the amount of lithium they possess varies wildly. But now it appears that the amount of lithium in a Sun-like star depends on whether it has planets or not. Stars without planets have, on average, 10 times the lithium as stars with planets in the sample.

Weird.

It's possible to think of simple ways that a planet could affect the lithium abundance of a star. Maybe the gravitational tugging of the planet helps mix up the star's interior, letting the lithium get close enough to the core to get destroyed. Shortly after the star and planets form, the planets can migrate slowly toward the star over long periods of time, which might affect how rapidly the star rotates. That in turn will affect how deeply the star's outer convection layer can penetrate the interior (bringing lithium down with it, destroying the element; in fact, this is one scenario proposed by the team that made this discovery.

Or maybe it’s something else. Or maybe there is a third thing we haven’t thought of yet, something that both destroys lithium and allows the star to make planets. The presence of planets and depletion of lithium might be related, but not directly.

It’s a mystery, but astronomers love mysteries. More observations will no doubt uncover more clues, give us more data we can analyze to uncover yet more correlations.

And that brings me back to my joke at the start. The press release for this news story makes an interesting statement:

This finding does not only shed light on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.

I disagree with the philosophy of this conclusion. Sure, if you want to find stars with planets, it might make sense to concentrate on stars with depleted lithium abundance. But I think that’s not a great idea: you’re only looking where the light’s good. When planets were first discovered around sun-like stars, we were all surprised to find them very close to their parent stars, orbiting in days, not years. The reason they’d been missed for so long is that no one had thought to look for them in orbits that small! We’d been looking where the light was good (literally) and not where the planets really were.

I’m not saying it’s wrong to only look to lithium-poor stars when seeking planets, but I am saying that if you’re a planet hunter, you might want to open your criteria a bit. This lithium finding is very interesting, and may well play out to be a hard-and-fast law, but I think it’s still a little early to rule anything out just yet.

As always, the Universe knows what it’s doing. It’s our task to figure out just what that is.

Image credit: ESO/L. Calçada

The European Space Agency probe Rosetta is on its way to comet 67/P Churyumov-Gerasimenko (by way of asteroid 21 Lutetia next July), where it will arrive in May of 2014. It will be dropping a lander — the first ever attempted on a comet — and our knowledge of these fuzzy visitors will increase enormously.

But getting there is tough, and involves swinging by the Earth three times and Mars once. The final gravity assist will occur on November 13, with closest approach at 08:45 CET (over, roughly, the island of Java) when it’ll be moving past us at 13.3 km/sec (almost 30,000 mph). While it’s passing us by it will observe both the Earth and Moon, doing as much science as it can before heading out into deep space. Specifically, it will add its sensors to those already studying water on the Moon, as well as aurorae on Earth.

You can follow the action on the Rosetta blog. In fact, just the other day they posted this awesome shot of the Moon from Rosetta:

That was taken form a distance of 4.3 million kilometers (2.5 million miles), ten times the distance of the Moon from the Earth. The images as it gets closer will be even cooler.

So stay tuned! This is a very exciting mission, especially next year when it passes Lutetia! I can never see enough closeup pictures of asteroids.

Spacecraft image credit: ESA, image by AOES Medialab

The 128th Carnival of Space is online at AARTScope blog. It even comes with a quiz to see how well you scored on participating in the IYA 2009. My score? Astronomical.

For those of you in the upstate New York area, I’ll be giving my Death from the Skies! talk at Rensselaer Polytechnic Institute (RPI for those in the know) this Thursday, November 12, at 7:30 p.m. It’s free and open, which I guess means the public can come, but you might want to contact them about that.

I visited RPI many years ago (it was on my list of potential colleges when I was in high school, but that’s a long story), and it’s gorgeous. This time of year it’ll be spectacular, I bet, so I’m really looking forward to this!

When Galileo first turned his telescope to the sky, almost exactly 400 years ago, he could not possibly have known what he was starting.

Today, four centuries later, we’ve come a long, long way. To celebrate the anniversary of Galileo’s telescopic revolution, NASA’s Great Observatories — Hubble, Spitzer, and Chandra — have released a jaw-dropping mosaic of the very heart of the Milky Way galaxy. Behold!

[Oh yes, you want to click to embiggen that-- what I show here is a very compressed version. Or you can go here for a massive copy. You can also get wallpaper versions here.]

This image is nothing less than a heroic effort of astronomical artistry. It’s a chunk of the sky 38 x 14 arcminutes across, or about half the size of the full Moon, and it’s aimed right into the core of our galaxy. See the bright spot just to the right of the center? Buried in there behind light years of dust and gas is the monster of the Milky Way, a black hole with four million times the mass of the Sun. But even that is dwarfed by the 400 billion solar mass heft of the entire galaxy.

There is so much going on in this image it’s hard to know where to start. But first… the Hubble images are in the near-infrared, with a wavelength a little more than twice what the eye can see (1.87 microns for those playing at home). That’s represented in the image as yellow. Spitzer contributed observations in four infrared wavelengths (3.6, 4.5, 5.8, and 8.0 microns), and those are depicted in red. Chandra sees X-rays which are normally written as units of energy, but to remain consistent with the other two images, they were at wavelengths of 0.0005, 0.00025, and 0.00016 microns, and are shown in blue.

What does all this mean? Different objects emit light at different characteristic wavelengths. Warm dust, for example, emits strongly in the infrared. Stars and warm gas emit visible and near-infrared light. Violently heated gas, affected by huge magnetic fields or shocked by colossal collisions glows in X-rays. So this image is a polychromatic view of the crowded downtown region of a bustling city: our galaxy.

You might want to look at an annotated version of this image so you can get your bearings. It’s worth it!

The huge arches of gas on the left are actually the edges of gigantic molecular clouds (dense nebulae where stars are born), lit up by the torrential blast of light from a clutch of massive stars nearby. This clot of stars, called the Arches Cluster due to the arcs it excites, can be seen as a small spot glowing blue just to the left of center in the picture. Don’t be deceived by its diminutive appearance: the Arches cluster has thousands of superstars in it, each dwarfing our Sun, and each capable of sleeting out vast amounts of radiation that lights up the gas surrounding it. Were this cluster much closer than its 25,000+ light year distance, it would blaze in our sky like a beacon. Replace the Sun in our solar system with just one of those stars, and the Earth would be fried beyond the capability of any life to survive. You might as well try living in the flame of an arc-welder.

Below and just to the left of the Arches is a clumpier, more twisted arc of gas called the Sickle. That’s a giant cavity being carved out of dense gas by the Quintuplet cluster, the pinkish glow in its center. It’s another nursery of stars like the Arches cluster, which is also blasting out light and stellar winds which eat away at the gas enveloping it. The Pistol Star resides there, perhaps one of the most massive stars in the Milky Way.

And there’s more! The blue glow on the left is from an X-ray binary called 1E1743.1-2834, what is probably a massive star being orbited by either a neutron star or a black hole. Matter is being stripped from the star and piling up outside the collapsed companion, where it gets heated up to millions of degrees and emits X-rays.

Supernovae remnants dot the image, as do stars, filaments of gas, clouds of dust, and more. This picture is an astronomer’s dream, a map of everything someone might want to visit with a starship — as long as the shields are at full strength. This image is also a map of violence, turbulence, and unrest… a typical scene, so we think, of any normal spiral galaxy like ours. And our Galaxy’s center is considered quiet by astronomers! Some are far worse.

But this is home for us. It’s a place of unimaginable fury but also astonishing beauty… and we see it now as we do because we have dared to examine the world around us, to use tools we invent to peer closer, to magnify the tiny, to extend our eyes into realms we once didn’t even know existed. And every time we do — every single time — we find more questions, more puzzles, more things to examine.

And we find art. Galileo wasn’t the first to turn his telescope to the sky, nor was he the first to record what he saw. But he was the one who made everyone see what he did, and for that, all these years later, he is owed a debt of gratitude.

Today is Carl Sagan’s 75th birthday. It would be nice if he were still around to send him the greeting personally, but sadly, he died too young: in 1996 he succumbed to complications of myleodysplasia. As he himself noted, though, the progress of science — medical science in this case — kept him alive far longer than would otherwise have been possible. Up to the end, he was an evangelist of science.

And his legacy continues. His TV show "Cosmos" continues to inspire people, and the generation of astronomers who took up the cause due to Sagan’s exhortations are still looking up, looking out, and seeking what’s around the next corner. Because of Carl Sagan, we have many more scientists who not only love the field itself, but strive to express it to others. I include myself among the latter.

That’s why we celebrated Carl Sagan Day on Saturday, to honor the man and, in my opinion just as if not more importantly, to continue his work. James Randi knew Sagan personally; they were friends for many years, and so at the celebration Randi was the keynote speaker, relating stories about the man whom Randi knew as simply Carl. Below is video of Randi’s talk. It’s an hour long, but it’s more than worth your time. This was recorded off a live stream, so go ahead and click forward to about the 9:00 minute mark to get started.

This first Carl Sagan Day was a great success. We had a great audience at every talk, kids playing outside in the inflatable rocket ship bounce room, pictures from Hubble adorning the windows and walls of Broward College, and an overall sense that there is great work that has been done, with still a vast amount yet to do.

But that’s where the fun is. Sagan knew that, and I hope that you do too. And if you don’t — if you think science is stodgy, uninteresting, and doesn’t affect your life — then hopefully you have an amazing moment lying in wait for you. Maybe it’ll be a Cassini image of Saturn, or a tiny cell undergoing mitosis under your scrutiny through a microscope, or the sudden understanding from a news article about the Large Hadron Collider. There’s no way to know what precisely that trigger will be. But at some point there will come something that will jolt you, will shake you out of your complacence, and the scales will fall from your eyes.

At that moment you’ll experience what Carl Sagan did every moment of his life, that same sense of wonder and pure, undiluted joy about the Universe. I feel it too. It’s the blood in my veins, the calcium in my bones, the electricity of my eyes and ears as they relay what they detect to my brain. It’s the sense of connectedness with everything, and it’s real.

That’s what Carl Sagan taught us.

Somewhere, something incredible is waiting to be known.

The Big Picture.

Mars.

What else do you need to know? Go click.