How powerful is spectroscopy?

Credit: ESO

Spectroscopy has revealed the expansion of the Universe, the chemical composition of stars and nebulae, and the existence of exoplanets.

Galaxies galore: Each vertical strip in this image contains the faint spectrum of an individual galaxy, while the bright horizontal lines in each strip come from the Earth’s atmosphere.
Credit: ESO
Atmospheric fingerprints: When an exoplanet transits in front of its host star, gases in the planet’s atmosphere produce tell-tale lines in the star’s spectrum.
Credit: ESO/M. Kornmesser

Taking the spectrum of a single astronomical object used to be a very time-consuming process. But with the advent of sensitive electronic detectors and ingenious multi-object spectrographs, spectroscopy has become a much more powerful technique. The latest generation of instruments can even provide spectral information for every single pixel of an astronomical image. Astronomers expect spectroscopy to detect biosignatures – possible indicators of biological activity – in the atmospheres of Earth-like exoplanets.

Musings on spectroscopy: The Multi Unit Spectroscopic Explorer (MUSE) at ESO’s Very Large Telescope provides spectroscopic information for every pixel in its field of view.
Credit: A. Tudorica/ESO
Lining up: Hot, glowing gas produces bright emission lines, but cooler gases leave dark absorption lines in the spectrum of a luminous background object.
Credit: ESO

A selfie made by your friend may look nice, but their DNA can tell you more about her. Likewise, the spectrum of a star or galaxy contains more information than a beautiful photograph.