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The Universe in the Infrared

The Universe in the Infrared. Intro to IR. What can we learn from infrared light and how do we see it?. Images courtesy NASA/JPL - Caltech. Funded by NASA’s Spitzer Science Center. Outline. The electromagnetic spectrum Atmospheric windows The c o l o r s of infrared light

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The Universe in the Infrared

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  1. The Universe in the Infrared Intro to IR What can we learn from infrared light and how do we see it? Images courtesy NASA/JPL - Caltech Funded by NASA’s Spitzer Science Center

  2. Outline • The electromagnetic spectrum • Atmospheric windows • The colors of infrared light • Sources of infrared light • Detecting IR light • Infrared telescopes • Distances The Universe in the Infrared

  3. Light Understanding the electromagnetic spectrum The Universe in the Infrared

  4. The Electromagnetic Spectrum • Infrared (IR) is a form of light (or electromagnetic radiation) • IR light is found between visible light and radio waves • Wavelengths extending from 1 to 200 mm (microns) • A micron is one-millionth of a meter, and is abbreviated as µm The Universe in the Infrared

  5. What does “electromagnetic” mean? • Properties of waves • speed (distance per second) • wavelength (length) • frequency (cycles per second) speed of light = wavelength x frequency The Universe in the Infrared

  6. speed = wavelength x frequency • speed – 300,000 km per second (3 x 108 meters per second) • frequency – say, one billion cycles per second (109 cycles per second) • What is the wavelength? • What kind of light is this? 3 x 108 m/sec = l x 109 /sec The Universe in the Infrared

  7. Terminology Microns and nanometers… decameter 101 meters hectometer 102 meters kilometer 103 meters decimeter 10-1 meters centimeter 10-2 meters millimeter 10-3 meters micrometer 10-6 meters nanometer 10-9 meters Visible light has wavelengths between 400 and 700 nanometers The Universe in the Infrared

  8. The Colors of Infrared Light • Astronomers refer to different types of infrared light • The precise wavelength ranges are somewhat arbitrary Near IR: 1-5 mm Mid IR: 5-30 mm Far IR: 30-200 mm The Universe in the Infrared

  9. Atmospheric Windows At different wavelengths of light, the Earth’s atmosphere can be either transparent or opaque • Some near-IR light reaches mountain-top observatories. • Clear IR windows are centered at 1.25, 1.65, 2.2, 3.5, 4.8 microns. • High-flying airplanes and balloons get above most of the atmosphere • Only space-borne infrared telescopes provide an unimpeded view of the infrared universe. Earth from GOES-8 @6.7 mm The Universe in the Infrared

  10. Sources of IR Light Stars Gas Dust The Universe in the Infrared

  11. All matter glows with light Cool matter glows primarily with radio or infrared light Warmer matter glows with higher energy light Matter at about 10,000 degrees centigrade glows white hot Even hotter matter glows blue hot The Universe in the Infrared

  12. Black Body Radiation The glow of matter because of its temperature Blackbodies emit light at all wavelengths Cooler object peak at longer wavelengths (redder) Hotter objects peak at shorter wavelengths (bluer) The higher the temperature, the shorter the peak wavelength Very cool objects peat at radio wavelengths and very hot objects peak at ultraviolet, x-ray, or gamma-ray wavelengths The Universe in the Infrared

  13. Stars as Black Bodies A very cool star will peak in the infrared, but we will see it as a red star A very hot star will peak in the ultraviolet, but we will see it as a blue star The Universe in the Infrared

  14. Black Body Spectrum • “Black bodies” glow at ALL wavelengths • The wavelength at which the black body is brightest tells us the temperature (hotter = shorter wavelength) • As the temperature increases, the blackbody radiation also gets BRIGHTER Black Body Radiation Applet The Universe in the Infrared

  15. Wien’s Law We can determine the surface temperature from the wavelength of the peak brightness for any star The sun is brightest at a wavelength of 520 nanometers. What is the temperature at the surface of the Sun? 3,000,000 / 520 = 5770 K The Universe in the Infrared

  16. Temperature Matters! To be bright in the infrared, cool sources must be BIG • The energy emitted is directly proportional to T4 • As stars get hotter, their energy output increases quickly! • A star 10 times hotter than Sun has 10,000 times more energy output The Universe in the Infrared

  17. Temperature – The Kelvin Scale • Named after Lord (William Thompson) Kelvin • 19th century Scottish physicist • a one degree difference on the Kelvin (K) scale is the same as for the Celsius (or centigrade) scale • The zero-point is defined to be absolute zero • the coldest possible temperature • atomic and molecular motion ceases • no negative temperatures • Note: no degree symbol (°) with the Kelvin scale The Universe in the Infrared

  18. Radio < 0.03K Microwave 0.03-30K Interstellar Space Infrared 30-4100K Humans Visible 4100-7300K Sun UV 7300-3 x 106K Hottest Stars X-ray 3x106-3x108K Neutron stars Gamma Ray > 3x108K Black holes Temperature and peak brightness The Universe in the Infrared

  19. Scattering and Extinction • Dust also scatters starlight Dust clouds block visible light but are transparent to infrared light T.A.Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA) The Universe in the Infrared

  20. The Pleiades – Optical & IR A dust cloud passing near the Pleiades scatters blue starlight in this visible light image. The dust radiates in the infrared. 24 mm Visible The Universe in the Infrared

  21. Why infrared? • Near-infrared (1-5 mm) • stars • warm gas • dust is transparent • Mid-infrared (3-30 mm) • dust warmed by starlight • protoplanetary disks • Far-infrared (30-200 mm) • cold gas & dust Dust is more transparent to infrared light. We can see what’s hidden in the dust. Cold gas and dust is invisible in visible light, but glows in infrared light. The Universe in the Infrared

  22. Detecting Infrared Light • Single-pixel bolometers, 1960’s • first semi-conductor arrays, 32x32 pixels, in early 1980’s Top left: 58 X 62 pixels, 1987 Middle left: 256 X 256 pixels, 1991 (SIRTF, IRAC) Lower left: 1024 X 1024 pixels (1 Mega Pixel), 1996 Right: 2048 X 2048 pixels (4 Mega Pixel) 2001 InSb array detectors by Raytheon (SBRC). Courtesy Univ. of Rochester Astronomy The Universe in the Infrared

  23. Observing at Nonvisible Wavelengths • Astronomical objects radiate in wavelengths other than visible (blackbody radiation) • Stars • Hot, warm and cold gas • Dust • Telescopes for each wavelength region • Require their own unique design • All collect and focus radiation and resolve details • False-color pictures to show images • Some wavelengths must be observed from space The Universe in the Infrared

  24. Infrared Telescopes • Space-Based Advantages • No atmospheric blurring • No atmospheric absorption • No atmospheric emission • Ground-Based Advantages • Larger collecting area • Better spatial resolution • Equipment easily updated • Ground-Based Considerations • Weather, humidity, and haze • Atmospheric transparency The Universe in the Infrared

  25. False Color • Astronomical images begin as black & white (grayscale) digital data from a single spectral region, often using wavelengths outside of the range of human vision • A "true" color image or photograph recreates what our eyes would see in visible light under natural conditions • To create a color image from data at other wavelengths, astronomers represent it in "false" colors • Three of grayscale images from different wavelengths may be mapped to red, green, and blue and overlaid to form a color image The Universe in the Infrared

  26. More false color • Astronomers also “colorize” black and white images to highlight certain aspects. The Universe in the Infrared

  27. Inverse Square Law If we know a star’s apparent AND absolute brightness, we can calculate its distance brightness = 1/distance2 The inverse square law describes how the brightness of a source light (a star!) diminishes with distance For nearby stars, stellar parallaxes provide a way to measure distance The Universe in the Infrared

  28. What is a Parsec??? Parsec: the distance to an object with a stellar parallax of one arc second A star at a distance of 1 parsec shows a parallax of 1 arc second How big is one arc second? The size of a dime at a distance of 2.3 miles! 1 parsec = 3.26 light years A parallax of ~0.001 arc seconds is the smallest we can measure The parallax of Alpha Centauri = 0.76 arcseconds The Universe in the Infrared

  29. Wrapping Up • The electromagnetic spectrum • Atmospheric windows • The colors of infrared light • Sources of infrared light • Detecting IR light • Infrared telescopes • Distances The Universe in the Infrared

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