"The degree of the wobble told them how big the planet causing it was, the rate of wobble told them how far out the planet was orbiting, and the fact that there were multiple wobbles, each slightly different, told scientists how many planets there were," says Watson.
By watching the stars' spectrum, scientists could see a slight shift in where the elemental absorption lines are compared to where they should be, which told them a planet was making the star wobble. And objects moving away from you shift to longer frequencies, at the red end of the spectrum."Īstronomers used the Doppler effect to find the new solar system, says Watson.Īs planets orbit a star, they cause it to wobble ever so slightly. "In light waves, it causes things moving towards you to shift to shorter wavelengths at the blue end of the spectrum. "We hear it as the change in pitch of a train's horn as it passes us," says Watson. When something moves towards you it compresses the signal wavelength it emits, while if it's moving away from you, it stretches that waveform. Spectroscopy also lets you determine if an object is moving towards or away from you by the change in frequency of the wavelength - or the Doppler effect. (Source: KPNO 0.9-m Telescope, AURA, NOAO, NSF) O is the top line, followed by two lines for each of the remaining six spectra. When you look at the spectrum of a star, for example, you can see absorption lines because the star's outer atmosphere is cooler than the central part, explains Watson.Īstronomers divide stars into seven main spectral types OBAFGKM. There are also absorption lines that appear as dark marks dividing the spectrum at specific wavelengths.Ībsorption lines are created when light from something hot like a star passes through a cooler gas, cancelling out the emission lines the chemicals in the gas would normally create. When heated or when electrically charged, certain chemicals emit radiation at very specific colours or wavelengths called emission lines. From this you can work out all sorts of things," says Watson. "It lets you see the chemicals being absorbed or emitted by the light source. "You take the light from a star, planet or galaxy and pass it through a spectroscope, which is a bit like a prism letting you split the light into its component colours. Spectroscopy - the use of light from a distant object to work out the object is made of - could be the single-most powerful tool astronomers use, says Professor Fred Watson from the Australian Astronomical Observatory.
In fact, most of the roughly 500 planets so far found orbiting other stars, were detected by the same method. Like the very first exoplanet 51-Pegusus discovered in 1995, this new system was found using the science of spectroscopy. Just recently, astronomers discovered a distant solar system, 127 light years away with up to seven planets orbiting a Sun-like star called HD 10180.
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