Multiwavelength Astronomy What do different wavelength regimes allow astronomers to “see”?

Temperature vs. peak wavelength Ultraviolet (UV) X Rays Visible Light Infrared (IR) Microwaves Radio waves 1 micron1 m1 cm10 -9 m100 microns Increasing wavelength Increasing temperature Recall Wien’s Law: object’s temperature determines the wavelength at which most of its electromagnetic radiation emerges 5000 K50 K5x10 6 K0.5 K

A temperature-dependent “hierarchy” of states of matter Coldest (<100 K): dense molecular gas, ice- coated dust “Warm” (100-1,000 K): warm dust & molecules Hotter: (1, ,000 K): atomic gas (molecular bonds break down) Hotter still: (>10,000): ionized gas (electrons separated from nuclei; plasma)

Radio/microwave radiation Generally, probe of “coldest” matter: dense gas & dust –Afterglow of “Big Bang” (2.7 degrees K) Probe of molecular gas –long list of molecules that have been detected in interstellar space via their radio radiation carbon monoxide, water, hydrogen cyanide, ammonia, alcohol… Very penetrating –most matter is transparent to radio waves

Mid- to Far-infrared radiation Probe of “dust grains” –huge variety known, from giant molecules to grains of glass Most of the known dust in the universe shines in the mid- to far-IR –Dust forms around dying stars –Dust congeals into planetary systems now forming around young, recently formed stars –Dust surrounds the massive centers of many galaxies Planets emit most strongly in the mid- to far-IR Very penetrating

M17 star cluster: Optical Photograph + Far Infrared

Near-infrared radiation Probe of “hot” dust and molecular gas Somewhat penetrating –2 micron light penetrates matter 10 times easier than visible light Probe of stars that are cool and/or surrounded by dust clouds –this includes stars just formed and stars that are “kicking off”

Visible Near-Infrared

Hot molecules and dust Image mosaic of the NGC 6334 star formation region obtained with SPIREX/Abu at the South Pole

Visible light Stars dominate the visible-light universe –Starlight can be detected directly (the stars themselves) or can be seen in light reflected off dust grains located near stars –Stars represent a primary constituent of galaxies, so distant galaxies are usually first detected in visible or near-IR light Gas ionized by UV from hot stars (and heated to about 10,000 K) also emits brightly in the visible –case in point: the Great Nebula in Orion Easily blocked by dust clouds

Our Nearest (Galactic) Neighbor in visible light: a twin to the Milky Way? Andromeda Galaxy, Optical

Ultraviolet light Probe of the hottest stars and ionized gas Matter spiraling into a massive object (a collapsed star or the center of a massive galaxy) emits strongly in the UV as it gets heated to >10000 K Easily blocked by atomic gas and by dust clouds

X-rays Probe of cosmic “collisions” that produce plasma at temperatures in excess of 1,000,000 K –Example: gas ejected at high speed from a rapidly dying star hits gas that was ejected more slowly by the same star => gas heated to X-ray-emitting temperatures –Most stars, especially young stars, have a tenuous outer atmosphere (corona) hot enough to produce X-rays –Many compact, massive objects thought to be black holes display X-ray emission Highly penetrating; dust is almost transparent to X-rays

X-rays trace explosive events Supernova remnant Cassiopeia A

The many faces of the supernova remnant Casseopeia A X-ray optical infrared radio

The “starburst” galaxy M 82 A noisy “neighbor” galaxy

It takes images at a variety of wavelengths to find every newborn star Central Orion Nebula region: left, X-ray; right, infrared

Stars like the Sun don’t exactly go quietly into the night The planetary nebula BD Infrared (Gemini 8-meter telescope) Optical (Hubble Space Telescope) X-ray (Chandra)

New discoveries of X-rays from planetary nebulae Chandra (left) and HST (right) images of NGC 7027 Chandra (left) and HST (right) images of NGC 6543 (The Cat’s Eye Nebula)