| Piú viste - The Universe in Super Definition |
NGC-2976.jpgNGC 2976 - Galaxy or "Galactic Star-Factory"?54 visiteGalaxies throughout the Universe are ablaze with star birth. But for a nearby, small spiral galaxy, the star-making party is almost over. Astronomers were surprised to find that star-formation activities in the outer regions of NGC 2976 have been virtually asleep because they shut down millions of years ago. The celebration is confined to a few die-hard partygoers huddled in the galaxy's inner region.
The explanation, astronomers say, is that a raucous interaction with the neighboring M 81 group of galaxies ignited star birth in NGC 2976.
Now the star-making fun is beginning to end. Images from NASA's Hubble Space Telescope show that star formation in the galaxy began fizzling out in its outskirts about 500 MY ago as some of the gas was stripped away and the rest collapsed toward the center. With no gas left to fuel the party, more and more regions of the galaxy are taking a much-needed nap. The star-making region is now confined to about 5000 LY around the core.
NGC 2976 does not look like a typical Spiral Galaxy, as this Hubble image shows. In this view of the oddball galaxy's inner region, there are no obvious spiral arms. Dusty filaments running through the disk show no clear spiral structure. Although the gas is centrally concentrated, the galaxy does not have a central bulge of stars. Astronomers pieced together the galaxy's star-formation story with the help of Hubble's sharp vision. The galaxy's relatively close distance to Earth allowed Hubble's Advanced Camera for Surveys (ACS) to resolve hundreds of thousands of individual stars. What look like grains of sand in the image are actually individual stars.
Studying the individual stars allowed astronomers to determine their color and brightness, which provided information about when they formed. The astronomers combined the Hubble results with a map, made from radio observations, showing the current distribution of hydrogen across the galaxy. By analyzing the combined data, the Hubble research team then reconstructed the star-making history for large areas of the galaxy. The Hubble observations are part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. The map is part of The HI Nearby Galaxy Survey by the National Radio Astronomy Observatory's Very Large Array in New Mexico.
The blue dots are fledgling blue giant stars residing in the remaining active star-birth regions. NGC 2976 resides on the fringe of the M 81 Group of Galaxies, located about 12 MLY away in the constellation Ursa Major.MareKromium
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Large Magellanic Cloud-1.jpgThe Large Cloud of Magellan (HR)53 visiteAn alluring sight in dark Southern skies, the Large Magellanic Cloud (LMC) is seen here through a narrow filter that transmits only the red light of Hydrogen Atoms. Ionized by energetic starlight, a Hydrogen Atom emits the characteristic red H-alpha light as its single electron is recaptured and transitions to lower energy states. As a result, this image of the LMC seems covered with shell-shaped clouds of Hydrogen gas surrounding massive, young stars. Sculpted by the strong stellar winds and ultraviolet radiation, the glowing Hydrogen clouds are known as "H-II" (such as Ionized Hydrogen) Regions. This HR mosaic view was recorded in 6 segments, each with 200 minutes of exposure time. Itself composed of many overlapping shells, the Tarantula Nebula, is the large star forming Region near top center. A satellite of our Milky Way Galaxy, the LMC is about 15,000 light-years across and lies a mere 180.000 LY away in the constellation known as Dorado.
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M 45 - PIA08260.jpgM 45 - The "Seven Sisters", from Cassini53 visiteCaption NASA originale:"The stars of the Pleiades cluster, also known by the names "M 45" and "The Seven Sisters," shine brightly in this view from the Cassini spacecraft. The cluster is comprised of hundreds of stars, a few of which are visible to the unaided eye on Earth as a brilliant grouping in the constellation Taurus.
Some faint nebulous material is seen here. This reflection nebula is dust that reflects the light of the hot, blue stars in the cluster.
The monochrome view was made by combining 49 clear filter images of the Pleiades taken with the Cassini spacecraft wide-angle camera on Aug. 1, 2006. The images were taken as a part of a sequence designed to help calibrate the camera electronics".
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PIA07854.jpgA beautiful "Asteroid Belt"53 visiteThis artist's animation illustrates a massive asteroid belt in orbit around a star the same age and size as our Sun. Evidence for this possible belt was discovered by NASA's Spitzer Space Telescope when it spotted warm dust around the star, presumably from asteroids smashing together.
The view starts from outside the belt, where planets like the one shown here might possibly reside, then moves into to the dusty belt itself. A collision between two asteroids is depicted near the end of the movie. Collisions like this replenish the dust in the asteroid belt, making it detectable to Spitzer.
The alien belt circles a faint, nearby star called HD 69830 located 41 light-years away in the constellation Puppis. Compared to our own solar system's asteroid belt, this one is larger and closer to its star - it is 25 times as massive, and lies just inside an orbit equivalent to that of Venus. Our asteroid belt circles between the orbits of Mars and Jupiter.
Because Jupiter acts as an outer wall to our asteroid belt, shepherding its debris into a series of bands, it is possible that an unseen planet is likewise marshalling this belt's rubble. Previous observations using the radial velocity technique did not locate any large gas giant planets, indicating that any planets present in this system would have to be the size of Saturn or smaller.
Asteroids are chunks of rock from "failed" planets, which never managed to coalesce into full-sized planets. Asteroid belts can be thought of as construction sites that accompany the building of rocky planets.
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M 74-PIA08533_fig1.jpgM 74 and Supernova SN2003gd53 visiteThis image is the galaxy M 74, as seen by SST's infrared array camera. The white box to the left of the Galaxy's center identifies the location of the Supernova Remnant. In all the images, the blue dots represent hot gas and stars. The galaxy's cool dust is shown in red.
Astronomers using NASA's SST have spotted a "dust factory" 30 MLY away in the spiral galaxy M 74. The factory is located at the scene of a massive star's explosive death, or supernova.
While astronomers have suspected for years that supernovae could be producers of cosmic dust particles, the technology to confirm this suspicion has only recently become available.
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M 74-PIA08533_fig2.jpgSupernova SN2003gd in July 2004 (1)53 visiteThe dust factory, also known as supernova SN 2003gd, is shown at the center of the two small insets from Spitzer's infrared array camera. A white arrow points to its exact location.
The yellow-green dot shown in the July 2004 inset (here) shows that the source's temperature is warmer than the surrounding material. This is because newly formed dust within the Supernova is just starting to cool.
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M 74-PIA08533_fig3.jpgSupernova SN2003gd in January 2005 (2)53 visiteBy January 2005, the dust had cooled and completely faded from the camera's view (here). However, it was still detected in January 2005 by another instrument aboard Spitzer called the Multiband Imaging Photometer.
All the images are false-color, infrared composites, in which 3,6-micron light is blue, 4,5-micron light is green, and 8-micron light is red.
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M 74-PIA08533.jpgM 74 - Spiral Galaxy53 visite
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M 42-PIA08656.jpgOrion's "Sword"53 visiteThis image composite outlines the region near Orion's sword that was surveyed by NASA's Spitzer Space Telescope (white box). The view on the left (figure 1) is from a visible-light telescope, and the view on the right (figure 2) shows infrared light captured by a previous infrared mission, the Infrared Astronomical Satellite.
The Orion nebula, our closest massive star-making factory, is the brightest spot near the hunter's sword. On a dark night, it can appear to the naked eye as a fuzzy star, and it looks like a ghostly blob through a pair of binoculars. The Orion constellation is one of the most prominent winter constellations, and can be seen from all northern latitudes starting in the fall.
Spitzer used its infrared eyes to probe the dusty clouds of a region called Orion cloud A. outlined here in the hockey stick-shaped box (see PIA08655). This giant cloud stretches almost a quarter of the length of the constellation, an area equivalent to 18 full moons. The small box within the hockey stick shows the location of another image released by Spitzer (see PIA08653), which mainly features the Orion nebula itself.
The bright spot that shows up in the infrared view in the area of Orion's belt is known as Orion cloud B. Together, Orion clouds A and B make up the Orion cloud complex. In a survey of this entire complex, Spitzer unearthed 2,300 stars circled by disks of planet-forming dust and 200 stellar embryos too young to have developed disks.
The Infrared Astronomical Satellite was a joint effort between NASA, the Science and Engineering Research Council, United Kingdom and the Netherlands Agency for Aerospace Programmes, the Netherlands. Spitzer has extended the legacy of the satellite by providing much better resolution and sensitivity.
The visible-light image comes courtesy of Howard McCallon of the Infrared Processing and Analysis Center at the California Institute of Technology of Pasadena.
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M 42-PIA08655-ed.jpgThe "Great Cloud" around Orion53 visiteThis image composite shows a part of the Orion constellation surveyed by NASA's Spitzer Space Telescope. The shape of the main image was designed by astronomers to roughly follow the shape of Orion cloud A, an enormous star-making factory containing about 1,800 young stars. This giant cloud includes the famous Orion nebula (bright circular area in "blade" part of hockey stick-shaped box at the bottom), which is visible to the naked eye on a clear, dark night as a fuzzy star in the hunter constellation's sword.
The region that makes up the shaft part of the hockey stick box stretches 70 light-years beyond the Orion nebula. This particular area does not contain massive young stars like those of the Orion nebula, but is filled with 800 stars about the same mass as the sun. These sun-like stars don't live in big "cities," or clusters, of stars like the one in the Orion nebula; instead, they can be found in small clusters (right inset), or in relative isolation (middle insert).
In the right inset, developing stars are illuminating the dusty cloud, creating small wisps that appear greenish. The stars also power speedy jets of gas (also green), which glow as the jets ram into the cloudy material.
Since infrared light can penetrate through dust, we see not only stars within the cloud, but thousands of stars many light-years behind it, which just happen to be in the picture like unwanted bystanders. Astronomers carefully separate the young stars in the Orion cloud complex from the bystanders by looking for their telltale infrared glow.
The infrared image shows 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.
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M-016-PIA09109.jpgM 16 - The "Eagle Nebula"53 visiteThis image composite highlights the pillars of the Eagle Nebula, as seen in infrared light by NASA's Spitzer Space Telescope (bottom) and visible light by NASA's Hubble Space Telescope (top insets).
The top right inset focuses on the 3 famous pillars, dubbed the "Pillars of Creation", which were photographed by Hubble in 1995. Hubble's optical view shows the dusty towers in exquisite detail, while Spitzer's infrared eyes penetrate through the thick dust, revealing ghostly transparent structures. The same effect can be seen for the pillar outlined in the top left box.
In both cases, Spitzer's view exposes newborn stars that were hidden inside the cocoon-like pillars, invisible to Hubble. These stars were first uncovered by the European Space Agency's Infrared Satellite Observatory. In the Spitzer image, two embedded stars are visible at the tip and the base of the left pillar, while one star can be seen at the tip of the tallest pillar on the right.
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M-016-PIA09108.jpgThe many colors of the Eagle53 visiteThis set of images from NASA's Spitzer Space Telescope shows the Eagle Nebula in different hues of infrared light. Each view tells a different tale. The left picture shows lots of stars and dusty structures with clarity. Dusty molecules found on Earth called polycyclic aromatic hydrocarbons produce most of the red; gas is green and stars are blue.
The middle view is packed with drama, because it tells astronomers that a star in this region violently erupted, or went supernova, heating surrounding dust (orange). This view also reveals that the hot dust is shell shaped, another indication that a star exploded.
The final picture highlights the contrast between the hot, supernova-heated dust (green) and the cooler dust making up the region's dusty star-forming clouds and towers (red, blue and purple).
The left image is a composite of infrared light with the following wavelengths: 3.6 microns (blue); 4.5 microns (green); 5.8 microns (orange); and 8 microns (red). The right image includes longer infrared wavelengths, and is a composite of light of 4.5 to 8.0 microns (blue); 24 microns (green); and 70 microns (red). The middle image is made up solely of 24-micron light.
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