Emily Linden & Fiona Ward Interstellar Matter Emily Linden & Fiona Ward

Question Specify the radio techniques used to probe the nature of interstellar matter.

Book example Optical Spectral Analysis Requires -Background source of radiation -Stars viewed through clouds to be relatively close to earth (w/in a few thousand pcs) Low-energy Radio Emissions produced by the gas of the nebula itself is more versatile Astronomers examine hydrogen spin-rates to determine radio spectral lines Hydrogen 21-Centimeter Radiation

Book Example Hydrogen ground state spin patterns: parallel or antiparallel Antiparallel has slightly less energy than parallel All matter tends to achieve lowest possible energy state. When hydrogen atom drops down to antiparallel spin, a photon is emitted. High energy  low energy: Emitted photon is equal to energy lost Energy difference is very low, so energy of photon is very low Wavelength= 21.1 cm (radio portion) 21-centimeter radiation: the spectral line that results from this hydrogen-spin-flip process

Book Example Requires no visible light Can be used on any interstellar region that contains enough hydrogen gas to produce a detectable signal This includes low-density regions between dark clouds Wavelength much larger than typical interstellar dust particles Radio radiation reaches Earth unscattered by interstellar debris Can reach well beyond a few thousand parsecs Can reach in directions lacking background stars

Ultraviolet, Visible, and infrared http://hubblesite.org/newscenter/archive/releases/2003/30/image/a/ Ultraviolet, Visible, and infrared Hubble's Wide Field Planetary Camera 2 in 1994, 1995, and 2001 Color filters were used to isolate light emitted by hydrogen, oxygen, nitrogen, and sulfur atoms This nebula is an emission NGC 604 (Nicolas-Claude Fabri de Peiresc.) First noted by the English astronomer William Herschel

Gravitational Lens Radio signals will be sent out http://spectrevision.net/2013/05/31/interstellar-radio/ Gravitational Lens Radio signals will be sent out Usually up to five satellites in space Higher the frequency the father the distance

Reflection Nebula Gives off a blue color http://www.nasa.gov/multimedia/imagegallery/image_feature_701.html Reflection Nebula Gives off a blue color The star Rigel supplying the light Retains light from other source

Answer Book Example: Astronomers use Hydrogen 21-Centimeter Radiation to probe the nature of interstellar matter. Web Example: Astronomers use cameras from telescopes such as Hubble equipped with color filters and radio emissions to probe the nature of interstellar matter.