Less Lithium means more planets

These guys found a correlation between the amount of lithium and planets around a star. So if there’s less lithium then the star is more likely to have planets. The correlation is strong and makes for a very good predictor.

• Lithium clue for planet-hunters (BBC 11/11/09)
• Study

In addition to the articles, you might be interested in how the science is done. I’ll leave it to the articles to tell you how planets get rid of lithium. But I can tell you how they find planets and how they find lithium.

Funny enough, both are accomplished using spectroscopy. Just like a prism, a spectroscope breaks light up into a spectrum and then measures the brightness all through the rainbow. Chemical elements near the star absorb light and leave dark lines in the spectrum. Each element leaves a different set of lines. So it’s easy to tell which elements are around the star. The most common are hydrogen and helium. They’re the lightest elements. (Think balloons and blimps.) Lithium is also light but it’s less common, which makes the absorption line lighter. The lightness is used to measure the amount of lithium.

It’s hard to actually see a planet through a telescope. So astronomers have figured out better ways. The best is to see if a star wobbles. Planets make stars wobble as they go around. If you’ve ever seen the hammer throw in the Olympics then you might have noticed that the athlete has to lean back while spinning. That’s to counterbalance the pull of the hammer. Well stars do the same thing to counterbalance the gravitational pull of the planet. If things are lined up right, then the star moves closer and farther from us.

That movement causes the absorption lines in the spectrum to shift. That shifting is called the Doppler Effect. If you’ve ever noticed the pitch of a siren change as a police car passes by, then you’ve heard the Doppler Effect. As the car is heading toward you, the sound waves bet pushed together and sound higher. As the car goes away, the waves get separated and sound deeper.

The same thing happens with light from a wobbling star. (Doppler Spectroscopy) As the star moves closer, the absorption lines get shifted toward the blue end. And as the star moves away, the lines shift toward the red. Astronomers track this information for months and years. 

There are other methods for finding planets but spectroscopy is has found the most. Another method is to see if a planet crosses in front of the star. (The transit method) It’s hard to do since few systems are lined up just right and you have to keep your telescope on the star all the time. Recently, NASA launched the Kepler Mission to watch a large field of stars for transits.

Quantum Gravity Test Fails

Light at very different frequencies both came from an explosion 7 billion years ago. They arrived here at nearly the same time.

Einstein’s theory of special relativity predicts that light travels at a particular speed, no more, no less. That goes for the light we can see and other forms such as radio, micro waves, x-rays and gamma rays. Quantum mechanics, on the other hand, predicts that space is not as smooth as it appears to us once you get down to sizes far smaller than an atom. If a light wave is small enough, it might take longer to get through that bumpiness. So these 2 theories disagree. They disagree on several issues. For one, quantum mechanics is not as good at explaining gravity. That bumpiness is an important part of one theory that tries to incorporate gravity into quantum mechanics. Gamma rays have the highest frequency of light we know of. Several waves fit in an atom. We can detect gamma ray bursts from billions of light-years away. Plus they last a very short time. The experiment is to find the peak of the burst at various wavelengths. If the peak occurs later for gamma rays, then they might have been going slower. Well that didn’t happen. All the peaks were reasonably close together. So quantum gravity as a theory becomes a little less likely.

This is what makes science so different from some other ways of finding the truth. Science is not just theories but also predictions. If the prediction turns out to be wrong when tested, the theory must be fixed or die. If a theory cannot be tested, then it is not science. If the prediction proves true, it does not mean the theory becomes fact. It only means that the theory becomes more reliable for making other predictions.

http://www.nytimes.com/2009/10/29/science/space/29light.html

Supersonic Vapor Cone in NASA Ares

Associated Press

Cool cone! That’s a test flight of the Ares rocket that will replace the shuttle. And that cone is called a Prandtl–Glauert singularity better known as a vapor cone or a shock collar. You usually see it on fighters. It occurs when the rocket reaches the sound barrier and causes a sonic boom.  It’s caused by pressure waves that collect together and are all moving along with the rocket at the speed of sound (Mach 1). The waves cause high air pressure and just behind the waves is low air pressure. The drop in pressure causes a temperature drop and that’s where condensation forms. Vapor cones are usually not too icecream cone shaped. That’s because the shock wave moves along in a straight line next to the rocket at the speed of sound. (See #4 in the Mach 1 diagram.)

The Space-Time Diagram

You can tell that the right guns were fired first because the circle around them is bigger. As time goes on, the circles get bigger. A space-time diagram can show how that works. 

 In this diagram, the blast starts at the bottom tip of the cone. It show how the circle gets bigger. A space-time diagram isn’t usually this fancy. Usually, it just show distance over time. That makes it flatter and easier to draw.

In the case of light, it’s common to use 45 degrees for the speed of light. For every year, light travels a light year. So a year is the same length as a light year.

No Special Speed in the Universe

That title is a twist on the Copernican Principal that we hold no special place in the universe. It led Copernicus to conclude that the Earth is not the center of the solar system. Nine decades later (1543-1632), Galileo stated his principal of invariance. Basically, the laws of physics stay the same even if you’re moving. We hold no special speed. That means you can juggle in a jet. Galileo used a ship for his example.

Still, that’s no reason to think the Galilean Invariance principle holds at speeds approaching the speed of light. That is until the most famous failed experiment: the Michelson-Morley experiment in 1887. At the time, the speed of light wasn’t known. These guys came up with an ingenious way to measure even the slightest change in the speed caused by our orbit. It failed! There was no change in the speed of light no matter which direction or when. How can that be unless the earth really isn’t moving?