Introduction to the Universe
Introduction to the Universe ASTR 1000
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This 14 page Class Notes was uploaded by Adelia Adams on Monday October 12, 2015. The Class Notes belongs to ASTR 1000 at Georgia Southern University taught by James Higdon in Fall. Since its upload, it has received 20 views. For similar materials see /class/222011/astr-1000-georgia-southern-university in Astronomy at Georgia Southern University.
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Date Created: 10/12/15
Exam 3 is approaching Lecture 1 Overview 1 N onOptical Telescopes AM Rama FM I 1 1oquot 1aquotI 1n Most of the EM Spectrum is absorbed by the 39 Earth s atmosphere e g Xray Infrared Gamma rays Omufv Aimmvhsm Damn 5 IS ovauua Lecture 1 Overview 1 What are we missing The answer to all of these is YES Radio Astronomy Radio astronomy was discovered by accident in the 1930 s Lecture 1 Overview 1 Radio Astronomy J ansky found that thunderstorms produced almost all the radio static He also noticed that a constant radio static signal always came from the same part of the sky 7 near the constellation Sagittarius towards the Milky Way s center Jansky made the front page of the NY Times with this discovery 7 May 5 1933 7 Radio Telescopes Lecture 1 Overview 1 Two Radio Telescope Questions 1 Why are Radio Telescopes so large 2 Why are some Radio Telescopes arranged in groups Answer Radio Photons Carry Little Energy Radio NS go from l cm to several meters As a consequence 1 Radio signals are extremely weak Radio photons are pathetic Large telescope primary mirrors dishes are needed to collect enough energy photons from radio sources to be detected Lecture 1 Overview 1 Answer Radio Wavelengths Are Big 2 Large primary mirrors dishes are needed for good Angular Resolution Question How large must a radio mirror be such that AR is l at a wavelength of 20 cm Answer AR 167 arcsec Lecture 1 Overview 1 Improving Angular Resolution You have only two options 1 observe at smaller L 2 make the dish bigger somehow You can t make a steerable dish larger than d 100 rn m But you can simulate a much bigger dish with an array of smaller dishes This technique is called interferometry I 7 A rrays AR 1 at 7 20cm 36000 In for the VLA Lecture 1 Overview 1 Bigger Arrays Give Higher AR To get higher Angular Resolution radio astronomers have linked up radio dishes across countries or across continents 10 Using interferometer arrays it is possible to get AR rivaling that even of the HST 160 140 120 100 80 60 The Galaxy M82 Evidence suggests that it is forming stars unusually fast in its dusty central regions Radio observations peer through dust to show the presence of dozen stars that blew upernovas VLA 7 20cm I39MLlquot I 20712 9 18cm u an an wemm palmw owl1 Lecture 1 Overview 7 Neutral Hydrogen Gas Higdon el al 2008 9 Doppler shifts in the 21 cm emission line tell us how the gas is moving 17 Some galaxies look remarkably different in the radio NGC 1316 is one of the more un interesting galaxies at optical wavelengths But in the radio red the VLA shows Two gigantic lobes ofradio photons 600000 LY across What is going on here Lecture 1 Overview 1 Infrared Telescopes Infrared telescopes are configured much like optical re ecting telescopes However they must be kept very cold T 4 K to minimize their own IR emission to detect faint IR sources in space Sunahadog Secondary minor lnqwd helvumvonk anury quotMINDY Delector assembly 7 lnfmredzistronomy Satellite 1 9 The Orion Region in Optical amp the F ar IR 20 Lecture 1 Overview 1 Lecture 1 Overview Other Infrared Telescopes in Space S n itzer S n ace Telesco e Similar to IRAS but with much improved detectors and an IR Spectrograph Like IRAS the telescope amp instruments are cooled with liquid helium to T5 K It will work until it runs out of helium coolant Currently near the end of its 5year mission Data is streaming down 247 See webpages at ssc spitzer caltech edu 21 Spitzer Result Optically Invisible Galaxies Our team has discovered a class of sources in the sky that are bright in the IR ie A 24 pm but extremely faint essentially invisible at optical wavelengths We nd that these I Optically Invisible Sources are very distant galaxies that are hidden by lots of dust Higdon etal 20062008 22 1 XRay Telescopes Xrays are emitted by very hot T 110 million K gas Since the Earth s atmosphere absorbs Xrays completely Xray telescopes have to be in orbit above the atmosphere and away rom the Earth s radiation belts ii 3395 39 Chandra Xray telescope gives images AR l arcsec and spectra 3939 0 fl 39 Q 30 Chandra X ray Telescope prior to launch in 98 23 Xray Telescope Optics Revenge of the Refractors Xrays either pass through or are absorbed by materials 9 you can t build Xray mirrors or lenses Xrays are focused using grazing angle re ections from concentric mirrors This is very much the same way refracting telescopes work Only a few Xrays are captured per pixel but they have huge energies and pack a whallop CCDs are used to detect Xrays 24 Lecture 1 Overview 1 Xruy Sources Supernova Remnants 25 Xruy Sources Galaxy Clusters massive galaxy clusters may consist of 100 s of individual galaxies the space between galaxies is not empty it is filled with 10100 million degree gas Xray telescopes can make images of this hot gas Images obtained with Xray telescopes of distant galaxy clusters The galaxies are the small blue or red dots in both images The Xray emitting gas is shown as the red left or purple right extended emission 26 Lecture 1 Overview 1 Neutrino Telescopes Every once in a while one of the NI 014 solar neutrinos would interact with a molecule of the cleaning fluid C2Cl4 v gt C2Cl3 Ar Al is a radioactive argon atom is produced and can easily be detected amp counted The number of Ar atoms produced is proportional to the number of neutrinos passing through the tank each second Counting the Ar gives you the rate at which vare created in the sun s core a direc2t7check left image of the Sun in neutrinos from the Sudbury Neutrino telescope buried onemile underground in Canada right 1 Lecture 1 Overview 1
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