| |
| Piú viste - The Universe in Super Definition |
HD189733b-PIA09200.jpgJust like Jupiter...63 visiteThis artist's concept shows a cloudy Jupiter-like planet that orbits very close to its fiery hot star. NASA's Spitzer Space Telescope was recently used to capture spectra, or molecular fingerprints, of two "hot Jupiter" worlds like the one depicted here. This is the first time a spectrum has ever been obtained for an exoplanet, or a planet beyond our solar system.
The ground-breaking observations were made with Spitzer's spectrograph, which pries apart infrared light into its basic wavelengths, revealing the "fingerprints" of molecules imprinted inside. Spitzer studied two planets, HD 209458b and HD 189733b, both of which were found, surprisingly, to have no water in the tops of their atmospheres. The results suggest that the hot planets are socked in with dry, high clouds, which are obscuring water that lies underneath. In addition, HD209458b showed hints of silicates, suggesting that the high clouds on that planet contain very fine sand-like particles.
Capturing the spectra from the two hot-Jupiter planets was no easy feat. The planets cannot be distinguished from their stars and instead appear to telescopes as single blurs of light. One way to get around this is through what is known as the secondary eclipse technique. In this method, changes in the total light from a so-called transiting planet system are measured as a planet is eclipsed by its star, vanishing from our Earthly point of view. The dip in observed light can then be attributed to the planet alone.
This technique, first used by Spitzer in 2005 to directly detect the light from an exoplanet, currently only works at infrared wavelengths, where the differences in brightness between the planet and star are less, and the planet's light is easier to pick out. For example, if the experiment had been done in visible light, the total light from the system would appear to be unchanged, even as the planet disappeared from view.
To capture spectra of the planets, Spitzer observed their secondary eclipses with its spectrograph. It took a spectrum of a star together with its planet, then, as the planet disappeared from view, a spectrum of just the star. By subtracting the spectrum of the star from the spectrum of the star and planet together, astronomers were able to determine the spectrum of the planet itself.
Neither of the parent stars for HD 209458b or HD 189733b can be seen with the naked eye. HD 209458b is located about 153 light-years away in the constellation Pegasus, while HD 189733b is about 62 light-years away in the constellation Vulpecula. Both planets zip around their stars in very tight orbits; HD 209458b circles once every 3.5 days, while HD 189733b orbits once every 2.2 days.
Of the approximately 200 known exoplanets, there are 12 besides HD 209458b and HD 189733b whose orbits are inclined in such a way that, from our point of view, they pass in front of their stars. At least three of these transiting exoplanets are bright enough to follow in the footsteps of HD 209458b and HD 189733 and reveal their infrared spectra to Spitzer. Astronomers hope to use Spitzer's spectrograph in the future to study HD 209458b and HD 189733b again in much greater detail, and to examine some of the other candidates for the first time.
|
|
Spectrum-PIA09197.jpgSpectrum of an Alien World63 visiteThis infrared data from NASA's Spitzer Space Telescope - called a spectrum - tells astronomers that a distant gas planet, a so-called "hot Jupiter" called HD 209458b, might be smothered with high clouds. It is one of the first spectra of an alien world.
A spectrum is created when an instrument called a spectrograph cracks light from an object open into a rainbow of different wavelengths. Patterns or ripples within the spectrum indicate the presence, or absence, of molecules making up the object.
Astronomers using Spitzer's spectrograph were able to obtain infrared spectra for two so-called "transiting" hot-Jupiter planets using the "secondary eclipse" technique. In this method, the spectrograph first collects the combined infrared light from the planet plus its star, then, as the planet is eclipsed by the star, the infrared light of just the star. Subtracting the latter from the former reveals the planet's own rainbow of infrared colors.
When astronomers first saw the infrared spectrum above, they were shocked. It doesn't look anything like what theorists had predicted. For example, theorists thought there'd be signatures of water in the wavelength ranges of 8 to 9 microns. The fact that water is not detected might indicate that it is hidden under a thick blanket of high, dry clouds.
In addition, the spectrum shows signs of silicate dust -- tiny grains of sand -- in the wavelength range of 9 to 10 microns. This suggests that the planet's skies could be filled with high clouds of dust unlike anything seen in our own solar system.
There is also an unidentified molecular signature at 7.78 microns. Future observations using Spitzer's spectrograph should be able to determine the nature of the mysterious feature.
This spectrum was produced by Dr. Jeremy Richardson of NASA's Goddard Space Flight Center, Greenbelt, Md. and his colleagues. The data were taken by Spitzer's infrared spectrograph on July 6 and 13, 2005.
|
|
NGC-2808-2.jpgTriple Stellar Evolution Epochs in NGC 280863 visiteLike a simplified version of the Hertzsprung-Russell (HR) Diagram and by using the original HST data, this graph schematically plots the brightness of the stars in Globular Cluster NGC 2808 (along the vertical axis) against stellar color and temperature (along the horizontal axis).
The cooler a star is, the redder it appears, and it diminishes in brightness.
The bluer stars are to the left; redder stars are to the right.
The brightest stars are near the top.
The 3 curves represent the 3 different populations of stars that are present in NGC 2808.MareKromium
|
|
M-042-PIA09412.jpgOut of Orion's Head (2)63 visiteThis image from NASA's SST shows infant stars "hatching" in the Head of the Hunter constellation, Orion. Astronomers suspect that shockwaves from a supernova explosion in Orion's head, nearly 3 MY ago, may have initiated this newfound birth
The Region featured in this Spitzer image is called Barnard 30.
It is located approximately 1300 LY away and sits on the right side of Orion's "Head" just North of the massive star Lambda Orionis. Wisps of red in the cloud are organic molecules called polycyclic aromatic hydrocarbons. These molecules are formed anytime carbon-based materials are burned incompletely. On Earth, they can be found in the sooty exhaust from automobile and airplane engines. They also coat the grills where charcoal-broiled meats are cooked.
This image shows infrared light captured by Spitzer's infrared array camera. Light with wavelengths of 8 and 5.8 microns (red and orange) comes mainly from dust that has been heated by starlight.
Light of 4.5 microns (green) shows hot gas and dust; and light of 3.6 microns (blue) is from starlight.
MareKromium
|
|
M-042-PIA09411.jpgOut of Orion's Head (1)63 visiteThis image from NASA's SST shows infant stars "hatching" in the Head of the Hunter constellation, Orion. Astronomers suspect that shockwaves from a supernova explosion in Orion's head, nearly 3 MY ago, may have initiated this newfound birth
The Region featured in this Spitzer image is called Barnard 30.
It is located approx. 1,300 LY away and sits on the right side of Orion's "Head" just North of the massive star Lambda Orionis.
Wisps of green in the cloud are organic molecules called polycyclic aromatic hydrocarbons. These molecules are formed anytime carbon-based materials are burned incompletely. On Earth, they can be found in the sooty exhaust from automobile and airplane engines. They also coat the grills where charcoal-broiled meats are cooked.
Tints of orange-red in the cloud are dust particles warmed by the newly forming stars. The reddish-pink dots at the top of the cloud are very young stars embedded in a cocoon of cosmic gas and dust. Blue spots throughout the image are background Milky Way along this line of sight.
This composite includes data from Spitzer's infrared array camera instrument, and multiband imaging photometer instrument. Light at 4.5 microns is shown as blue, 8.0 microns is green, and 24 microns is red.
MareKromium
|
|
HD_189733b-PIA09715_01.jpgExoplanet HD 189733b63 visiteCaption NASA:"This plot of data from NASA's Spitzer Space Telescope (SST) tells astronomers that a toasty gas exoplanet, or a planet beyond our Solar System, contains water vapor.
Spitzer observed the Planet, called HD 189733b, cross in front of its star at three different infrared wavelengths: 3,6; 4,5 and 8 microns (see lime-colored dots). For each wavelength, the Planet's Atmosphere absorbed different amounts of the starlight that passed through it. The pattern by which this absorption varies with wavelength matches known signatures of water, as shown by the theoretical model in blue".MareKromium
|
|
NGC-2237_and_NGC-2244.jpgHot Stars in the Rosette Nebula63 visiteWinds and radiation from massive hot stars in the Rosette Nebula have cleared the natal gas and dust from the center of the nearby star-forming region. They also pose a danger to planet forming disks around young, cooler stars in the neighborhood. This Spitzer Space Telescope (SST) infrared image of dust clouds near the Rosette's central region, shows the cleared-out cavity.
The view spans about 45 LY at the the nebula's estimated distance of 5.200 LY. MareKromium
|
|
Mira-PIA09961.jpgMira's Tail63 visiteCaption NASA:"NASA's Galaxy Evolution Explorer discovered an exceptionally long comet-like tail of material trailing behind Mira -- a star that has been studied thoroughly for about 400 years.
So, why had this tail gone unnoticed for so long? The answer is that nobody had scanned the extended region around Mira in ultraviolet light until now.
As this composite demonstrates, the tail is only visible in ultraviolet light (top), and does not show up in visible light (bottom). Incidentally, Mira is much brighter in visible than ultraviolet light due to its low surface temperature of about 3000 Kelvin (about 5000° Fahrenheit)".MareKromium
|
|
SN-Cassiopeia_A_-PIA10207.jpgCassiopeia "A": Dissecting the Wake of a Supernova Explosion63 visiteThe elements and molecules that flew out of the Cassiopeia A star when it exploded about 300 years ago can be seen clearly for the first time in this plot of data, called a Spectrum, taken by NASA's SST.
The Spectrum, which was created by splitting light into its basic components, reveals the composition of gas and dust that were synthesized in the explosion. It also provides some of the best evidence yet that stellar explosions, called Supernovae, were a significant source of fresh dust in the very young universe.
Prior to these observations, nobody was certain where this early dust — the same dust that ultimately made its way into future stars, planets and people — came from.
One of the most interesting features of the plot is a bump labeled Cassiopeia A Dust Feature. This bump is actually the signature of a collection of dust composed of proto-silicates, Silicon Dioxide and Iron Oxide. The Spectrum reveals that the brightness of the dust feature is correlated to that of Argon gas (yellow vertical line at left), known to have been expelled and synthesized during the star's explosion. The fact that the dust is associated with the expelled gas, or ejecta, tells astronomers that this Supernova manufactured new dust.
Each of the 3 lines of this plot represents a different layer of the Supernova remnant, with the top yellow and red line being the outermost layer.
Similar correlations between gas and dust are also seen in the middle layer (green line). For example, neon gas correlates with dust composed of Carbon and Aluminum Oxide.MareKromium
|
|
M-101-PIA11797.jpgM 10163 visiteIn 1609, Galileo improved the newly invented telescope, turned it toward the heavens, and revolutionized our view of the universe. In celebration of the 400th anniversary of this milestone, 2009 has been designated as the International Year of Astronomy.
Today, NASA's Great Observatories are continuing Galileo's legacy with stunning images and breakthrough science from the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory.
While Galileo observed the sky using visible light seen by the human eye, technology now allows us to observe in many wavelengths, including Spitzer's infrared view and Chandra's view in X-rays. Each wavelength region shows different aspects of celestial objects and often reveals new objects that could not otherwise be studied.
This image of the spiral galaxy Messier 101 is a composite of views from Spitzer, Hubble, and Chandra.
The red color shows Spitzer's view in infrared light. It highlights the heat emitted by dust lanes in the galaxy where stars can form.
The yellow color is Hubble's view in visible light. Most of this light comes from stars, and they trace the same spiral structure as the dust lanes.
The blue color shows Chandra's view in X-ray light. Sources of X-rays include million-degree gas, exploded stars, and material colliding around black holes.
Such composite images allow astronomers to see how features seen in one wavelength match up with those seen in another wavelength. It's like seeing with a camera, night vision goggles, and X-ray vision all at once.
In the four centuries since Galileo, astronomy has changed dramatically. Yet our curiosity and quest for knowledge remain the same. So, too, does our wonder at the splendor of the universe.
The International Year of Astronomy Great Observatories Image Unveiling is supported by the NASA Science Mission Directorate Astrophysics Division. The project is a collaboration between the Space Telescope Science Institute, the Spitzer Science Center, and the Chandra X-ray Center.
MareKromium
|
|
NGC-3242-PIA11968.jpgThe Extended Region around the Planetary Nebula NGC 324263 visiteThe unfortunate name of Planetary Nebula for this class of Celestial Objects is a historical legacy credited to William Herschel during the 18th Century — a time when telescopes where small and objects like these, at least the central region, looked very similar to gas-giant planets such as Saturn and Jupiter. In fact, NGC 3242 has no relation to Jupiter or any other planet.
Telescopes and their detectors have dramatically improved over the past few centuries. Our understanding of what Planetary Nebulae truly are has improved accordingly.
When stars with a mass similar to our Sun approach the end of their lives by exhausting supplies of Hydrogen and Helium fuel in their cores, they swell up into cool red-giant stars. In a last gasp before death, they expel the layers of gas in their Outer Atmosphere. This exposes the core of the dying star, a dense hot ball of Carbon and Oxygen called a "White Dwarf".
The White Dwarf is so hot that it shines very brightly in the UltraViolet Spectrum. The UltraViolet Light from the White Dwarf, in turn, ionizes the gaseous material expelled by the star causing it to glow. A Planetary Nebula is really the death of a low-mass star.
Although low-mass stars like our Sun live for billions of years, Planetary Nebulae only last for about ten thousand years. As the central white dwarf quickly cools and the UltraViolet Light dwindles, the surrounding gas also cools and fades.
In this image of NGC 3242 from the Galaxy Evolution Explorer, the Extended Region around the Planetary Nebula is shown in dramatic detail. The small circular white and blue area at the center of the image is the well-known portion of the famous Planetary Nebula. The precise origin and composition of the extended wispy white features is not known for certain. It is most likely material ejected during the star's red-giant phase before the White Dwarf was exposed.
However, it may be possible that the extended material is simply interstellar gas that, by coincidence, is located close enough to the White Dwarf to be energized by it, and induced to glow with UltraViolet Light.
NGC 3242 is located 1400 to 2500 Light-Years away in the constellation of Hydra. It was discovered by William Herschel in 1785.MareKromium
|
|
Sharpless308-Goldman.jpgSharpless 30863 visiteCaption NASA:"Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 308 it lies some 5200 LY away in the constellation Canis Major and covers over 2/3° on the sky (compared with 0,5° for the Full Moon). That corresponds to a diameter of 60 LY at its estimated distance. The massive star itself, a Wolf-Rayet Star, is the bright blue one near the center of the Nebula.
Wolf-Rayet Stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet Star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution.
The windblown nebula has an age of about 70.000 years. Relatively faint emission captured in the expansive image is dominated by the glow of Ionized Oxygen atoms mapped to bluish hues".MareKromium
|
|
| 157 immagini su 14 pagina(e) |
|
|
|
|
|
|
|
|
12 | |
|
|
|
