Imagine yourself standing in a large open chamber like an aircraft hangar. If you clap your hands, you will be rewarded with a series of echoes reverberating through the building. These sound echoes are very much like a phenomenon astronomers have dubbed "light echoes." A sound echo occurs because of two basic properties of sound: it travels at a limited speed, and it will reflect off of many surfaces. In the case of an aircraft hangar, the walls are far enough away that a clapping sound will take some time to reach the walls, reflect, then return. As a result, a listener will hear a delay. Because the sound reflects off of walls at different distances, returning at different times, a listener will often hear many echoes. Light possesses the same properties as sound and thus can also produce echoes. However, since the speed of light is fantastically greater than the speed of sound, spaces as tiny as an aircraft hangar would not give rise to a noticeable light delay. For example, if a flash bulb goes off in even the largest hangar, only the most sensitive scientific instruments could detect the tiny delay, or light echo. In deep space, where distances between objects are measured in light-years, astronomers can directly observe echoes from cosmic flashes of light. The sequence of events associated with one such astronomical light echo are sketched out in this illustration. The stage is set in panel A, where a neutron star surrounded by dark, cold clouds of dust emits a brilliant burst of light. This flash travels out in all directions, but will still take years before it reaches the nearest dust cloud. Earth is towards the bottom of the page. Downward-pointing arrows in this figure indicate light rays that are headed toward Earth and the telescopes of astronomers. In panel B, light from the flash reaches the first, closest dust cloud, heating it up. The cloud, which was too cold to detect directly, begins warmly emitting infrared light. This infrared echo travels towards Earth, though it lags behind the original flash (which got a head start) and will arrive later. This can be seen in the relative positions of the arrows. Light from the flash continues to pass through and warm the first cloud in panel C. It has also just reached the second dust cloud and started a new echo there. Note that the arrow from the first light echo has progressed as far as the arrow from the new echo. This means the light from both of them will reach the Earth at the same time. In panel D the flash continues expanding outward, passing through the rest of the second cloud and now warming a third cloud as well. There are several groups of arrows indicating the continuing progress of these light echoes. The numbers on these Earth-bound light rays indicate the order in which they will arrive. The initial flash (1) will clearly arrive at Earth first. The first light echoes from all three clouds (2) will arrive next, all around the same time. Echoes from other parts of, the clouds (3) will arrive last. Panel E shows the astronomer's view of the light echo event as seen at the three times noted above. Initially, the telescope sees only the flash from the neutron star. At this point, the cold, dark clouds are nearly invisible. In the next time step, the light echoes begin to brilliantly light up these clouds, making them pop into view. Interestingly, all three echoes appear at the same time, even though the clouds are at different distances from the neutron star and from Earth. This is due to the particular geometry of this example, a viewer watching from some other direction would not see these echoes simultaneously. In the third time step, the echoes shift through the dust clouds, now lighting up different parts. This creates the illusion of small, rapidly-moving clumps of dust. In fact, there is no motion of the dust. It is only the expanding flash that brings different parts of stationary clouds into view. This illustration is a simplified explanation of what astronomers have seen in the space surrounding the Cassiopeia A supernova remnant. Two Spitzer Space Telescope images of the region around this object, taken a year apart, reveal such a light echo. The images appear to show many filaments and blobs moving outward at the speed of light. Astronomers, however, have determined this motion is actually due to a light echo from a recent explosion on the central neutron star dating back to 1953. The original supernova happened 325 years ago.
Blacker than Black
Title
Blacker than Black
Description
This artist's concept illustrates the hottest planet yet observed in the universe. The scorching ball of gas, a "hot Jupiter" called HD 149026b, is a sweltering 3,700 degrees Fahrenheit (2,040 degrees Celsius) -- about 3 times hotter than the rocky surface of Venus, the hottest planet in our solar system. The planet is so hot that astronomers believe it is absorbing almost all of the heat from its star, and reflecting very little to no light. Objects that reflect no sunlight are black. Consequently, HD 149026b might be the blackest known planet in the universe, in addition to the hottest. The temperature of this dark and balmy planet was taken with NASA's Spitzer Space Telescope. While the planet reflects no visible light, its heat causes it to radiate a little visible and a lot of infrared light. Spitzer, an infrared observatory, was able to measure this infrared light through a technique called secondary eclipse. HD 149026b is what is known as a transiting planet, which means that it crosses in front of and passes behind its star -- the secondary eclipse -- when viewed from Earth. By determining the drop in total infrared light that occurs when the planet disappears, astronomers can figure out how much infrared light is coming from the planet alone. The Spitzer observations of HD 149026b also suggest a hot spot in the middle of the side of the planet that always faces its star. Even though the planet is black, the spot would glow like a black lump of charcoal. HD 149026b is thought to be tidally locked, just as our moon is to Earth, such that one side of the planet is perpetually baked under the heat of its sun. Astronomers think that HD 149026b is probably blazing hot on its sunlit side, and much cooler on its dark side. A similar phenomenon was observed previously by Spitzer for the planet Upsilon Andromedae b. In the case of both planets, heat is not being evenly distributed across their surfaces. This is the opposite of what happens on Jupiter, where temperature differences are minimal all around. HD 149026b is located 256 light-years away in the constellation Hercules. It is the smallest known transiting planet, with a size similar to Saturn's and a suspected dense core 70 to 90 times the mass of Earth. It speeds around its star every 2.9 days.
Bursting with Stars and Blac
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Title
Bursting with Stars and Black Holes
Description
A growing black hole, called a quasar, can be seen at the center of a faraway galaxy in this artist's concept. Astronomers using NASA's Spitzer and Chandra space telescopes discovered swarms of similar quasars hiding in dusty galaxies in the distant universe. The quasar is the orange object at the center of the large, irregular-shaped galaxy. It consists of a dusty, doughnut-shaped cloud of gas and dust that feeds a central supermassive black hole. As the black hole feeds, the gas and dust heat up and spray out X-rays, as illustrated by the white rays. Beyond the quasar, stars can be seen forming in clumps throughout the galaxy. Other similar galaxies hosting quasars are visible in the background. The newfound quasars belong to a long-lost population that had been theorized to be buried inside dusty, distant galaxies, but were never actually seen. While some quasars are easy to detect because they are oriented in such a way that their X-rays point toward Earth, others are oriented with their surrounding doughnut-clouds blocking the X-rays from our point of view. In addition, dust and gas in the galaxy itself can block the X-rays. Astronomers had observed the most energetic of this dusty, or obscured, bunch before, but the "masses," or more typical members of the population, remained missing. Using data from Spitzer and Chandra, the scientists uncovered many of these lost quasars in the bellies of massive galaxies between 9 and 11 billion light-years away. Because the galaxies were also busy making stars, the scientists now believe most massive galaxies spent their adolescence building up their stars and black holes simultaneously. The Spitzer observations were made as part of the Great Observatories Origins Deep Survey program, which aims to image the faintest distant galaxies using a variety of wavelengths.
Size Comparisons
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Size Comparisons
Description
The artist's rendition shows the newly discovered planet-like object, dubbed "Sedna," in relation to other bodies in the Solar System, including Earth and its Moon, Pluto, and Quaoar, a planetoid beyond Pluto that was until now the largest known object beyond Pluto. The diameter of Sedna is slightly smaller than Pluto's but likely somewhat larger than Quaoar.
Comet Schwassmann-Wachmann 1
Title
Comet Schwassmann-Wachmann 1
Description
NASA's new Spitzer Space Telescope has captured an image of an unusual comet that experiences frequent outbursts, which produce abrupt changes in brightness. Periodic comet Schwassmann-Wachmann I (P/SW-1) has a nearly circular orbit just outside that of Jupiter, with an orbital period of 14.9 years. It is thought that the outbursts arise from the build-up of internal gas pressure as the heat of the Sun slowly evaporates frozen carbon dioxide and carbon monoxide beneath the blackened crust of the comet nucleus. When the internal pressure exceeds the strength of the overlying crust, a rupture occurs, and a burst of gas and dust fragments is ejected into space at speeds of 450 miles per hour (200 meters per second). This 24-micron image of P/SW-1 was obtained with Spitzer's multiband imaging photometer. The image shows thermal infrared emission from the dusty coma and tail of the comet. The nucleus of the comet is about 18 miles (30 kilometers) in diameter and is too small to be resolved by Spitzer. The micron-sized dust grains in the coma and tail stream out away from the Sun. The dust and gas comprising the comet's nucleus is part of the same primordial materials from which the Sun and planets were formed billions of years ago. The complex carbon-rich molecules they contain may have provided some of the raw materials from which life originated on Earth. Schwassmann-Wachmann 1 is thought to be a member of a relatively new class of objects called "Centaurs," of which 45 objects are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that Centaurs are recent escapees from the Kuiper Belt, a zone of small bodies orbiting in a cloud at the distant reaches of the solar system. Two asteroids, 1996 GM36 (left) and 5238 Naozane (right) were serendipitously captured in the comet image. Because they are closer to us than the comet and have faster orbital velocities, they appear to move relative to the comet and background stars, thereby producing a slight elongated appearance. The Spitzer data have allowed astronomers to use thermal measurements, which reduce the uncertainties of visible-light albedo (reflectivity) measurements, to determine their size. With radii of 1.4 and 3.0 kilometers, these are the smallest main-belt asteroids yet measured by infrared means.
Comet 'Bites the Dust' Aroun
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Title
Comet 'Bites the Dust' Around Dead Star
Description
This artist's concept illustrates a comet being torn to shreds around a dead star, or white dwarf, called G29-38. NASA's Spitzer Space Telescope observed a cloud of dust around this white dwarf that may have been generated from this type of comet disruption. The findings suggest that a host of other comet survivors may still orbit in this long-dead solar system. The white dwarf G29-38 began life as a star that was about three times as massive as our sun. Its death involved the same steps that the sun will ultimately undergo billions of years from now. According to theory, the G29-38 star became brighter and brighter as it aged, until it bloated up into a dying star called a red giant. This red giant was large enough to engulf and evaporate any terrestrial planets like Earth that happened to be in its way. Later, the red giant shed its outer atmosphere, leaving behind a shrunken skeleton of star, called a white dwarf. If the star did host a planetary system, outer planets akin to Jupiter and Neptune and a remote ring of icy comets would remain. The Spitzer observations provide observational evidence for this orbiting outpost of comet survivors. Astronomers speculate that one such comet was knocked into the inner regions of G29-38, possibly by an outer planet. As the comet approached very close to the white dwarf, it may have been torn apart by the star's tidal forces. Eventually, all that would be left of the comet is a disk of dust. This illustration shows a comet in the process of being pulverized: part of it still exists as a chain of small clumps, while the rest has already spread out into a dusty disk. Comet Shoemaker-Levy 9 broke apart in a similar fashion when it plunged into Jupiter in 1994.
Sowing the Seeds of Planets?
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Sowing the Seeds of Planets?
Description
This artist's concept shows microscopic crystals in the dusty disk surrounding a brown dwarf, or "failed star." The crystals, made up of a green mineral found on Earth called olivine, are thought to help seed the formation of planets. NASA's Spitzer Space Telescope detected the tiny crystals circling around five brown dwarfs, the cooler and smaller cousins of stars. Though crystallized minerals have been seen in space before -- in comets and around other stars -- the discovery represents the first time the little gem-like particles have been spotted around confirmed brown dwarfs. Astronomers believe planets form out of disks of dust that circle young brown dwarfs and stars. Over time, the various minerals making up the disks crystallize and begin to clump together. Eventually, the clumps collide and stick, building up mass like snowmen until planets are born.
A SWIRE Picture is Worth Bil
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Title
A SWIRE Picture is Worth Billions of Years
Description
These spectacular images, taken by the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy project, encapsulate one of the primary objectives of the Spitzer mission: to connect the evolution of galaxies from the distant, or early, universe to the nearby, or present day, universe. The larger picture (top) depicts one-tenth of the SWIRE survey field called ELAIS-N1. In this image, the bright blue sources are hot stars in our own Milky Way, which range anywhere from 3 to 60 times the mass of our Sun. The fainter green spots are cooler stars and galaxies beyond the Milky Way whose light is dominated by older stellar populations. The red dots are dusty galaxies that are undergoing intense star formation. The faintest specks of red-orange are galaxies billions of light-years away in the distant universe. The three lower panels highlight several regions of interest within the ELAIS-N1 field. The Tadpole galaxy (bottom left) is the result of a recent galactic interaction in the local universe. Although these galactic mergers are rare in the universe's recent history, astronomers believe that they were much more common in the early universe. Thus, SWIRE team members will use this detailed image of the Tadpole galaxy to help understand the nature of the "faint red-orange specks" of the early universe. The middle panel features an unusual ring-like galaxy called CGCG 275-022. The red spiral arms indicate that this galaxy is very dusty and perhaps undergoing intense star formation. The star-forming activity could have been initiated by a near head-on collision with another galaxy. The most distant galaxies that SWIRE is able to detect are revealed in a zoom of deep space (bottom right). The colors in this feature represent the same objects as those in the larger field image of ELAIS-N1. The observed SWIRE fields were chosen on the basis of being "empty" or as free as possible from the obscuring dust, gas, and stars of our own Milky Way. Because Earth is located within the Milky Way galaxy, there is always a screen of Milky Way objects blocking our view of the rest of the universe. In some places, our view of the larger universe is less obscured than others and for the most part is considered "empty." These are prime observing spots for astronomers interested in studying objects beyond the Milky Way. ELAIS-N1 is only one of six SWIRE survey fields. The full survey covers 49 square degrees of the sky, equivalent to the area covered by about 250 full moons. The SWIRE image is a 3-channel false-color composite, where blue represents visible green light (light that would appear to be blue/green to the human eye), green captures 3.6 microns, and red represents emissions at 8 microns. Interesting Note: From the Earth the SWIRE image (top image) can be seen in one square degree of sky, or a patch of sky that is approximately the size of a pea held out at arms length.
A SWIRE Picture is Worth Bil
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Title
A SWIRE Picture is Worth Billions of Years
Description
These spectacular images, taken by the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy project, encapsulate one of the primary objectives of the Spitzer mission: to connect the evolution of galaxies from the distant, or early, universe to the nearby, or present day, universe. The larger picture (top) depicts one-tenth of the SWIRE survey field called ELAIS-N1. In this image, the bright blue sources are hot stars in our own Milky Way, which range anywhere from 3 to 60 times the mass of our Sun. The fainter green spots are cooler stars and galaxies beyond the Milky Way whose light is dominated by older stellar populations. The red dots are dusty galaxies that are undergoing intense star formation. The faintest specks of red-orange are galaxies billions of light-years away in the distant universe. The three lower panels highlight several regions of interest within the ELAIS-N1 field. The Tadpole galaxy (bottom left) is the result of a recent galactic interaction in the local universe. Although these galactic mergers are rare in the universe's recent history, astronomers believe that they were much more common in the early universe. Thus, SWIRE team members will use this detailed image of the Tadpole galaxy to help understand the nature of the "faint red-orange specks" of the early universe. The middle panel features an unusual ring-like galaxy called CGCG 275-022. The red spiral arms indicate that this galaxy is very dusty and perhaps undergoing intense star formation. The star-forming activity could have been initiated by a near head-on collision with another galaxy. The most distant galaxies that SWIRE is able to detect are revealed in a zoom of deep space (bottom right). The colors in this feature represent the same objects as those in the larger field image of ELAIS-N1. The observed SWIRE fields were chosen on the basis of being "empty" or as free as possible from the obscuring dust, gas, and stars of our own Milky Way. Because Earth is located within the Milky Way galaxy, there is always a screen of Milky Way objects blocking our view of the rest of the universe. In some places, our view of the larger universe is less obscured than others and for the most part is considered "empty." These are prime observing spots for astronomers interested in studying objects beyond the Milky Way. ELAIS-N1 is only one of six SWIRE survey fields. The full survey covers 49 square degrees of the sky, equivalent to the area covered by about 250 full moons. The SWIRE image is a 3-channel false-color composite, where blue represents visible green light (light that would appear to be blue/green to the human eye), green captures 3.6 microns, and red represents emissions at 8 microns. Interesting Note: From the Earth the SWIRE image (top image) can be seen in one square degree of sky, or a patch of sky that is approximately the size of a pea held out at arms length.
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