X-ray Astronomy

    We can see planets, stars, and some fuzzy objects - nebulae and galaxies - in the night sky with our own eyes. But our eyes are sensitive only to light that has a wavelength in a narrow range. X rays are a type of light that has a much shorter wavelength than visible light. In the last 40 years or so, astronomers have begun to study X rays from the cosmos: this is X-ray astronomy. Suzaku is a satellite that is designed to advance X-ray astronomy in one particular direction. It will distinguish "colors" of X rays very precisely. This is like using a prism on sunlight to reveal a rainbow of colors, which we call a spectrum. Suzaku will work like the X-ray equivalent of a prism, splitting X rays into a spectrum and allowing astronomers to do "X-ray spectroscopy." Spectroscopy is the study of spectra, the plural of a spectrum.

    X-ray Spectroscopy

    Have you ever been caught speeding by a police officer using a radar gun? If you have, you've experienced the power of spectroscopy first hand. That radar gun analyzes radio waves bouncing off your car and determines how fast you are moving.

    Spectroscopy is the study of light's fingerprint, and it is a powerful tool. Scientists use it to determine the speed of stars and other celestial objects in the same way the police use it to nab speeders. The answers are encoded in the light waves. Through spectroscopy, scientists can even determine the temperature and contents of objects trillions of millions away. It's like reaching out deep into space to collect a sample of a star.

    NASA's Hubble Space Telescope and Chandra X-ray Observatory are known for the images they create. That's their bread and butter, but they do a fair share of spectroscopy too. The new Suzaku mission, however, will excel in X-ray spectroscopy. This will be the best tool astronomers have to study the properties of massive, sprawling regions in space such as clusters of galaxies, and hot gas surrounding massive and dense objects such as black holes.

    Here's how spectroscopy works. Light is energy. Picture the rainbow with its colors from red and orange through blue and violet. Blue light has more energy than red light; that's why a blue part of a flame is hotter. Each chemical element shines brightly at certain energies. Neon gas, for example, glows red. Scientists can analyze the light from a certain star or gas cloud, make a graph of all the energies it contains, and determine all the elements it contains. And there's more. Hydrogen gas swirling at a million miles per hour is more energetic than hydrogen gas swirling at 10,000 mph. Understanding the change in energy is one of the ways scientists can determine speed.

    X rays are more energetic than the colors of the rainbow. X rays are invisible. The wavelengths are shorter and of a higher frequency. In fact, light waves are analogous to sound waves, with their high and low frequencies and musical notes. Visible light is like the middle C range. X rays are at a higher octave, well beyond the soprano range. Strike a chord. A chord is a collection of distinct notes, maybe C, F and G. These notes are of a specific frequency, so an instrument that can analyze notes can determine that that sound was C, F and G. Likewise, a spectrograph reveals the elements sounding off at certain frequencies -- hydrogen, carbon and iron. Heat the elements, and that chord once heard in the "middle C" optical range is now detected somewhere in a higher-octave (higher energy) X-ray range.

    Motion, like temperature, also shifts frequency. You hear this all the time with the sound of a passing car, going eeeeeeyyyyoooom. Objects moving toward you have a higher pitch than the same object moving away. This is called Doppler shifting (and is the same science behind Doppler radar scans). The same thing applies in space. Light from stars moving toward us -- and all the "notes" or elements in that stellar orchestra -- gets shifted to higher energies. Through spectroscopy, scientists study the contents and temperature of a celestial symphony in motion.

    Suzaku will study some of the hottest tunes in the universe. These include star explosions hurling high-speed gas into space and heating it up to millions of degrees. All the elements needed for life, such as oxygen and nitrogen, are made in stars and star explosions. Also on the playlist is gas spiraling into a black hole. Previous X-ray telescopes could record the loudest notes, but Suzaku will allow us to discern the weaker notes that are mixed in. The key instrument on Suzaku is the X-ray Spectrometer (XRS).

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