Transcript multilambda
Multiwavelength Astronomy What do different wavelength regimes allow astronomers to “see”? Temperature vs. peak wavelength 10-9 m 1 micron 100 microns 1 cm 50 K 0.5 K 1m Increasing wavelength 5x106 K 5000 K Increasing temperature • Recall Wien’s Law: object’s temperature determines the wavelength at which most of its electromagnetic radiation emerges A temperature-dependent “hierarchy” of states of matter • Coldest (<100 K): dense molecular gas, icecoated dust • “Warm” (100-1,000 K): warm dust & molecules • Hotter: (1,000 - 10,000 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 infrared optical radio A noisy “neighbor” galaxy The “starburst” galaxy M 82 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 +30 3639 Optical Infrared X-ray (Hubble Space Telescope) (Gemini 8-meter telescope) (Chandra) New discoveries of X-rays from planetary nebulae Chandra (left) and HST (right) images of NGC 6543 (The Cat’s Eye Nebula) Chandra (left) and HST (right) images of NGC 7027