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Overview IR Astronomy Explore hidden universe , Cosmic dust, Cool objects , Dying stars, Forming stars, Early Universe Why IR? between wavelengths of about 1 and 300 microns The human eye detects only 1% of light at 0.69 microns, and 0.01% at 0.75 microns, and so effectively cannot see wavelengths longer than about 0.75 microns unless the light source is extremely bright. The Universe sends us a tremendous amount of information in the form of electromagnetic radiation . Much of this information is in the infrared, which we cannot see with our eyes or with visible light telescopes. All Sky Map of IRAS Point Sources IRAS (Infrared Astronomical Satellite), 1980 :The first IR satellite detected about 350,000 infrared sources, increasing the number of cataloged astronomical sources by about 70%. All Sky Map of IRAS Point Sources. The plane of our galaxy runs horizontally across the image A. Exploring the Hidden Universe study objects hidden by gas and dust in the infrared, Galactic Center Cygnus region Red : seeing the light from billions of stars, particularly the largest, brightest ones. The dark bands where vast clouds of dust block our view NIR : stars, but now it better traces the smaller, cooler ones. the lanes of dust have become partially transparent Far IR : stars hardly emit any light at all, almost everything we see is generated by the dust clouds themselves. B. Cosmic dust collections of just a few molecules to grains of 0.1 mm in size. Dust is important because we find lots of it around young stars. it helps them to form, and it is also the raw material from which planets like the Earth are formed. cosmic dust cycle. Dust is formed in stars and is then blown off in a slow wind or a massive star explosion. The dust is then 'recycled' in the clouds of gas and some of it is consumed when the next generation of stars begins to form. The dust converts the absorbed starlight into light at longer wavelengths. see the dust shining using special instruments sensitive to the far-infrared and submillimeter. Herschel is designed to work at these wavelengths, and see the dust shining at temperatures between 8 and 100 K. Clouds of dust in the far-infrared, this dust is seen to glow as it is heated by the young stars within. Rosette Nebula in visible light, seen by Herschel in the far-infrared. The Infrared Glow The extragalactic background is made up of radiation from distant objects beyond our own Milky Way. All the visible light from stars is plotted in the graph as the blue line. The infrared glow produced by cosmic dust which has been warmed by all the stars since the beginning of time is shown in red. This 'background glow' of the Universe tells us the total amount of energy released by stars. But this reveals a very surprising result: the amount of energy radiated by stars and dust is almost the same. C. Detecting Cool Objects cool stars, infrared galaxies, clouds of particles around stars, nebulae, interstellar molecules, brown dwarfs and planets. In the infrared, where planets have their peak brightness, the brightness of the star is reduced, making it possible to detect a planet in the infrared. Recently, an infrared survey of the Trapezium star cluster in the Orion Nebula revealed over 100 low mass objects which are brown dwarf candidates. C-1Brown Dwarf candidates Recently, an infrared survey of the Trapezium star cluster in the Orion Nebula revealed over 100 low mass objects which are brown dwarf candidates BD : stars with masses so low (about 8% of the Sun's) that they can not sustain nuclear hydrogen burning but be still massive enough to burn deuterium for energy, the deuterium burning limit : about 1.3% of the Sun's mass C-2 "free-floating planets" "free-floating planets" thirteen of the low mass objects show evidence of lying below even the deuterium burning limit, as little as 8 times as massive as Jupiter and likely formed along with the cluster stars a million or so years ago. They are detectable in the infrared BD & planets If the Trapezium is typical of young star clusters , then the survey results suggest that brown dwarfs and freefloating planets may be fairly common, but there are not enough to solve the mystery of dark matter in the Universe. D. Dying Stars Spitzer's view of the Cassiopiea A supernova remnant In death, extremely massive stars explode in a supernova, blasting their chemical creations into space, and seeding the universe for a new generation of stars to grow. medium mass stars like our Sun puff up to become red giants before sloughing off their outer layers, like snakes shedding their skin, sending newly-formed elements and molecules floating slowly off into space. IR study : solve the longstanding mystery of where the dust in our very young universe came from. pathways for massive stars and lower mass stars Low-mass stars Stars less than about eight times the mass of the Sun live for a long time (100 million to 10 billion years). At the end of its current middle-aged period, the Sun will become a Red Giant star, expanding by a factor of a hundred with its outer layers extending out to the orbit of Mars! Such stars puff away their outer layers, leaving behind the hot, dense core of the star. before they die stars actually lose most of their mass. This happens mostly in a period called the Asymptotic Giant Branch (AGB) phase, in which material is ejected in cycles, producing a series of shells around the star. These multiple shells are effectively a fossil record of the star’s mass-loss history. Shells the shells are too cold and faint to have been detected by previous infrared telescopes. Herschel’s sensitive submillimetre camera, SPIRE, is perfectly suited to seeing the cold dusty shells, revealing exactly how much mass has been lost. These shells are also rich in atoms and molecules which emit light at specific wavelengths that depend on their chemical make-up, and which will be examined by Herschel’s spectrometers. Herschel obs of shells looking at water molecules : for life, interesting compounds seen around dying stars : PAHs (Polycyclic Aromatic Hydrocarbons), made from hydrocarbon chains in a ring structure (see next inset), “bucky-ball” fullerene chain molecules, and amino acids, the building block of proteins. will tell us about the mass, temperature, and density of the gas, and what chemistry is going on. how stars evolve, how much mass they eject, how they make dust, what chemicals exist in their environments, and how this material influences the formation of new stars and planets. Polycyclic Aromatic Hydrocarbons Left: Polycyclic Aromatic Hydrocarbons in the Horsehead Nebula. Inset is an example of the structure of PAHs, this example includes a nitrogen atom (red). Right: Fingerprints of PAHs (spikes) seen in the spectrum of a star-forming region. Image credit: NASA/Spitzer. High-mass stars Stars more than eight times heavier than the Sun also enrich galaxies with cosmic dust and heavy elements. Near the end of their relatively short lives they go through several phases in which they eject material in intense winds, sometimes with speeds up to 6 million km/h, and with huge amounts of ejected material. The star eta Carinae is thought to have lost over 80 times the mass of our Sun in the last 1,000 years in the form of gas and dust. supernova explosions how much mass they lose before they explode, are largely unknown. find the colder ejected material to solve this problem Left: Cold dust bubble around an evolved massive star (RCW120). The submillimetre light is from cold dust (green) and visible light is shown for comparison (red and blue) (credit: ESO). Right: The massive star Eta Carinae in X-rays, visible light and submillimetre (credit: NASA/JCMT/H.Gomez et al.) supernova dust wondered if the supernova itself may create cosmic dust. Observations of supernova remnants with NASA’s Spitzer Space Telescope (below, left) and the ground-based SCUBA camera (below, right) indicate amounts of dust ranging from 10,000 Earth masses up to the mass of our Sun in dust alone! Left: Spitzer’s infrared image of the supernova remnant Cassiopeia A with argon gas (green), 10,000 Earth’s worth of warm cosmic dust (red) and silicon gas (blue) (credit: NASA/J.Rho et al.). Right: SCUBA submillimetre image of very cold dust in Cassiopeia A (credit: SCUBA/L.Dunne et al.). E. stellar embryos and infants Stars form like raindrops in space, from condensing clouds of gas and dust. The Fairy of Eagle Nebula Image Credit: The Hubble Heritage Team, (STScI/AURA), ESA, NASA The greater Eagle Nebula, M16, is actually a giant evaporating shell of gas and dust inside of which is a growing cavity filled with a spectacular stellar nursery currently forming an open cluster of stars. G. Exploring the Early Universe As a result of the Big Bang, the universe is expanding and most of the galaxies within it are moving away from each other. The light that galaxies emit are " redshifted ". The image to the right is an infrared view of some of the farthest galaxies ever seen. Image credit: RI Thompson (U. Arizona), NICMOS, HST, NASA) Missing Galaxies missing the galaxies which are hidden by lots of dust. Work with previous infrared and submillimetre telescopes showed that only a few billion years after the Big Bang there were lots of dusty galaxies that are so hidden by dust that they can barely be seen by optical telescopes. At the moment, it seems quite likely that these galaxies are the ancestors of elliptical-shaped galaxies we see around us today. The image on the right shows the SCUBA 'deep field'. This is the submillimetre view of the Hubble Deep field, the dusty view of the Universe. There are far fewer galaxies (seen as white blobs) in this sub-mm image than in the optical one left but these few galaxies alone are responsible for around a third of the total optical light in the Hubble picture. The amount of stars being born in these dusty galaxies is between 100 - 1000 times more than what we see in optical galaxies. H. Adding To Our Knowledge Of Visible Objects To get a complete picture of any object in the Universe we need to study all of the radiation that it emits. add a great deal to our knowledge about the Universe and the origins of our Solar System.