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| Piú viste - The Universe in Super Definition |
Galaxies-HST.jpgGalaxies!65 visiteThese images taken with NASA's Hubble Space Telescope are close-up views of four galaxies from a large survey of nearby galaxies.
The galaxies have very different masses and sizes and showcase the diversity of galaxies found in the ANGST study. Although the galaxies are separated by many light-years, they are presented as if they are all at the same distance to show their relative sizes.
The images, taken with Hubble's Advanced Camera for Surveys, reveal rich detail in the stellar populations and in the interstellar dust scattered between the stars. Hubble's sharp views reveal the colors and brightnesses of individual stars, which astronomers used to derive the history of star formation in each galaxy.
In the composite image at the top, NGC 253 is ablaze with the light from thousands of young, blue stars. The spiral galaxy is undergoing intense star formation. The image demonstrates the sharp "eye" of the Advanced Camera, which resolved individual stars. The dark filaments are clouds of dust and gas. NGC 253 is the dominant galaxy in the Sculptor Group of galaxies and it resides about 13 million light-years from Earth.
In the view of the spiral galaxy NGC 300, second from top, young, blue stars are concentrated in spiral arms that sweep diagonally through the image. The yellow blobs are glowing hot gas that has been heated by radiation from the nearest young, blue stars. NGC 300 is a member of the Sculptor Group of galaxies and it is located 7 million light-years away.
The dark clumps of material scattered around the bright nucleus of NGC 3077, the small, dense galaxy at bottom, left, are pieces of wreckage from the galaxy's interactions with its larger neighbors. NGC 3077 is a member of the M81 group of galaxies and it resides 12.5 million light-years from Earth.
The image at bottom, right, shows a swarm of young, blue stars in the diffuse dwarf irregular galaxy NGC 4163. NGC 4163 is a member of a group of dwarf galaxies near our Milky Way and is located roughly 10 million light-years away.
These galaxies are part of a detailed survey called the ACS Nearby Galaxy Survey Treasury program (ANGST). In the census, Hubble observed roughly 14 million stars in 69 galaxies. The survey explored a region called the "Local Volume," and the galaxy distances ranged from 6.5 million light-years to 13 million light-years from Earth. The Local Volume resides beyond the Local Group of galaxies, an even nearer collection of a few dozen galaxies within about 3 million light-years of our Milky Way Galaxy.
The natural-color images were constructed using observations taken in infrared, visible, and blue light. The observations of NGC 253 and NGC 300 were taken in September 2006; of NGC 3077 in November 2006; and of NGC 4163 in December 2006.
Object Names: NGC 253, NGC 300, NGC 3077, NGC 4163
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Epsilon_Eridani-PIA11376.JPGSolar Systems65 visiteThis artist's diagram compares the Epsilon Eridani System to our own Solar System. The two systems are structured similarly, and both host asteroids (brown), comets (blue) and planets (white dots).
Epsilon Eridani is our closest known planetary system, located about 10 LY away in the constellation Eridanus. Its central star is a younger, fainter version of our Sun, and is about 800 million years old — about the same age of our Solar System when life first took root on Earth.
Observations from NASA's Spitzer Space Telescope show that the System hosts two Asteroid Belts, in addition to previously identified candidate planets and an Outer Comet Ring.
Epsilon Eridani's inner Asteroid Belt is located at about the same position as ours, approximately 3 AU from its star (aone AU is the distance between Earth and Sun). The system's second, denser Belt lies at about the same place where Uranus orbits in our Solar System, or 20 AU from the star.
In the same way that Jupiter lies just outside our Asteroid Belt, shepherding its rocky debris into a ring, Epsilon Eridani is thought to have planets orbiting near the rims of its two Belts. The first of these planets was identified in 2000 via the Radial Velocity Technique.
Called "Epsilon Eridani b", it orbits at an average distance of 3,4 AU — placing it just outside the System's inner Asteroid Belt.
The second planet orbiting near the rim of the outer Asteroid Belt at 20 AU was inferred when Spitzer discovered the belt.
A third planet might orbit in Epsilon Eridani at the inner edge of its outermost Comet Ring, which lies between 35 and 90 AU. This planet was first hinted at in 1998 due to observed lumpiness in the Comet Ring.
The outer Comet Ring around Epsilon Eridani is denser than our Comet Ring, called Kuiper Belt, because the system is younger.
Over time, Epsilon Eridani's ring will become wispier like the Kuiper Belt. Its comets will collide with each other and break up, or get pushed out of the ring by the gravitational influences of the planets. MareKromium
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MACS-J0717_5+3745-hs-2009-17-a-print.jpgMACS J0717.5+3745 (Galaxy Cluster)65 visiteThis composite image shows the massive Galaxy Cluster MACS J0717.5+3745 (MACS J0717, for short), where four separate Galaxy Clusters have been involved in a collision — the first time such a phenomenon has been documented. Hot gas is shown in an image from NASA's Chandra X-ray Observatory, and galaxies are shown in an optical image from NASA's Hubble Space Telescope.
The hot gas is color-coded to show temperature, where the coolest gas is reddish purple, the hottest gas is blue, and the temperatures in between are purple.
The repeated collisions in MACS J0717 are caused by a 13 MLY-long stream of galaxies, gas, and dark matter — known as a "Filament" — pouring into a region already full of matter. A collision between the gas in two or more clusters causes the hot gas to flow down. However, the massive and compact galaxies do not slow down as much as the gas does, and so move ahead of it. Therefore, the speed and direction of each cluster's motion — perpendicular to the line of sight — can be estimated by studying the offset between the average position of the galaxies and the peak in the hot gas.
MACS J0717 is located about 5,4 BLY from Earth. It is one of the most complex Galaxy Clusters ever seen. Other well-known Clusters, like the Bullet Cluster and MACS J0025.4-1222, involve the collision of only two galaxy clusters and show much simpler geometry.MareKromium
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From_HST-2009-19-a-print.jpgStarbursts in Dwarf Galaxies are a Global Affair65 visiteBursts of star making in a galaxy have been compared to a Fourth of July fireworks display: They occur at a fast and furious pace, lighting up a region for a short time before winking out.
But these fleeting starbursts are only pieces of the story, astronomers say. An analysis of archival images of small, or dwarf, galaxies taken by NASA's Hubble Space Telescope suggests that starbursts, intense regions of star formation, sweep across the whole galaxy and last 100 times longer than astronomers thought. The longer duration may affect how dwarf galaxies change over time, and therefore may shed light on galaxy evolution.
"Our analysis shows that starburst activity in a dwarf galaxy happens on a global scale", explains Kristen McQuinn of the University of Minnesota in Minneapolis and leader of the study. "There are pockets of intense star formation that propagate throughout the galaxy, like a string of firecrackers going off". According to McQuinn, the duration of all the starburst events in a single dwarf galaxy would total 200 to 400 MYs.
These longer timescales are vastly more than the 5 to 10 MYs proposed by astronomers who have studied star formation in dwarf galaxies. "They were only looking at individual clusters and not the whole galaxy, so they assumed starbursts in galaxies lasted for a short time".
Dwarf galaxies are considered by many astronomers to be the building blocks of the large galaxies seen today, so the length of starbursts is important for understanding how galaxies evolve.
"Astronomers are really interested to find out the steps of galaxy evolution", McQuinn says. "Exploring these smaller galaxies is important because, according to popular theory, large galaxies are created from the merger of smaller, dwarf galaxies. So understanding these smaller pieces is an important part of filling in that scenario".
McQuinn's team analyzed archival Advanced Camera for Surveys data of three dwarf galaxies, NGC 4163, NGC 4068 and IC 4662. Their distances range from 8 to 14 MLYs away. The trio is part of a survey of starbursts in 18 nearby dwarf galaxies. Hubble's superb resolution allowed McQuinn's team to pick out individual stars in the galaxies and measure their brightness and color, two important characteristics astronomers use to determine stellar ages.
By determining the ages of the stars, the astronomers could reconstruct the starburst history in each galaxy.
Two of the galaxies, NGC 4068 and IC 4662, show active, brilliant starburst regions in the Hubble images. The most recent starburst in the third galaxy, NGC 4163, occurred 200 MYs ago and has faded from view. The team looked at regions of high and low densities of stars, piecing together a picture of the starbursts. The galaxies were making a few stars, when something, perhaps an encounter with another galaxy, pushed them into high star-making mode. Instead of forming eight stars every thousand years, the galaxies started making 40 stars every thousand years, which is a lot for a small galaxy, McQuinn says. The typical dwarf is 10 to 30.000 LYs wide. By comparison, a normal-sized galaxy such as our Milky Way is about 100.000 LYs wide.
About 300 to 400 MYs ago star formation occurred in the outer areas of the galaxies. Then it began migrating inward as explosions of massive stars triggered new star formation in adjoining regions. Starbursts are still occurring in the inner parts of NGC 4068 and IC 4662.
The total duration of starburst activity depends on many factors, including the amount of gas in a galaxy, the distribution and density of the gas, and the event that triggered the starburst. A merger or an interaction with a large galaxy, for example, could create a longer starburst event than an interaction with a smaller system.
McQuinn plans to expand her study to a larger sample of more than 20 galaxies. "Studying nearby dwarf galaxies, where we can see the stars in great detail, will help us interpret observations of galaxies in the distant universe, where starbursts were much more common because galaxies had more gas with which to make stars".
McQuinn's results appeared in the April 10 issue of The Astrophysical Journal.MareKromium
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NGC-2976.jpgNGC 2976 - Galaxy or "Galactic Star-Factory"?65 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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Spectrum-PIA09199.jpgSpectrum of an Alien World64 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 189733b, 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.
Astronomers were perplexed when they first saw the infrared spectrum above. It doesn't look anything like what theorists had predicted. Theorists thought the spectra of hot, Jupiter-like planets like this one would be filled with the signatures of molecules in the planets' atmospheres. But the spectrum doesn't show any molecules, and is instead what astronomers call "flat." For example, theorists thought there'd be a strong signature of water in the form of a big drop in the wavelength range between 7 and 10 microns. The fact that water is not detected may indicate that it is hidden underneath a thick blanket of high, dry clouds. The average brightness of the spectrum is also a bit lower than theoretical predictions, suggesting that very high winds are rapidly moving the terrific heat of the noonday sun from the day side of HD 189733b to the night side.
This spectrum was produced by Dr. Carl Grillmair of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena, Calif., and his colleagues. The data were taken by Spitzer's infrared spectrograph on November 22, 2006.
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NGC-2237-PIA09267.jpgNGC 2237 - The "Rosette Nebula", and Globular Star Cluster NGC 224464 visiteThis infrared image from NASA's Spitzer Space Telescope shows the Rosette nebula, a pretty star-forming region more than 5,000 light-years away in the constellation Monoceros. In optical light, the nebula looks like a rosebud, or the "rosette" adornments that date back to antiquity.
But lurking inside this delicate cosmic rosebud are so-called planetary "danger zones" (see spheres illustrations in figure 1). These zones surround super hot stars, called O-stars (blue stars inside spheres), which give off intense winds and radiation. Young, cooler stars that just happen to reside within one of these zones are in danger of having their dusty planet-forming materials stripped away.
While O-star danger zones were known about before, their parameters were not. Astronomers used Spitzer's infrared vision to survey the extent of the five danger zones shown here. The results showed that young stars lying beyond 1.6 light-years, or 10 trillion miles, of any O-stars are safe, while young stars within this zone are likely to have their potential planets blasted into space.
Radiation and winds from the super hot stars have collectively blown layers of dust (green) and gas away, revealing the cavity of cooler dust (red). The largest two blue stars in this picture are in the foreground, and not in the nebula itself.
This image shows infrared light captured by Spitzer's infrared array camera. Light with wavelengths of 24 microns is red; light of 8 microns is green; and light of 4.5 microns is blue.
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NGC-2808-0.jpgNGC 2808 - Globular Star Cluster64 visiteAstronomers have long thought that globular star clusters had a single "baby boom" of stars early in their lives and then settled into a quiet existence.
New observations by NASA's Hubble Space Telescope, however, are showing that this idea may be too simple. The Hubble analysis of the massive globular cluster NGC 2808 provides evidence that star birth went "boom, boom, boom," with three generations of stars forming very early in the cluster's life.
"We had never imagined that anything like this could happen," said Giampaolo Piotto of the University of Padova in Italy and leader of the team that made the discovery. "This is a complete shock."
Globular clusters are the homesteaders of our Milky Way Galaxy, born during our galaxy's formation. They are compact swarms of typically hundreds of thousands of stars held together by gravity.
"The standard picture of a globular cluster is that all of its stars formed at the same time, in the same place, and from the same material, and they have co-evolved for billions of years," said team member Luigi Bedin of the European Space Agency, the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in Garching, Germany, and the Space Telescope Science Institute in Baltimore, Md. "This is the cornerstone on which much of the study of stellar populations has been built. So we were very surprised to find several distinct populations of stars in NGC 2808. All of the stars were born within 200 million years very early in the life of the 12.5-billion-year-old massive cluster."
Finding multiple stellar populations in a globular cluster so close to home has deep cosmological implications, the researchers said.
"We need to do our best to solve the enigma of these multiple generations of stars found in these Hubble observations so that we can understand how stars formed in distant galaxies in our early universe," Piotto explained.
The astronomers used Hubble's Advanced Camera for Surveys to measure the brightness and color of the cluster stars. Hubble's exquisite resolution allowed the astronomers to sort out the different stellar populations. The Hubble measurements showed three distinct populations, with each successive generation appearing slightly bluer. This color difference suggests that successive generations contain a slightly different mix of some chemical elements.
"One assumption, although we have no direct proof," said team member Ivan King of the University of Washington in Seattle, "is that the successively bluer color of the stellar populations indicates that the amount of helium increases with each generation of stars. Perhaps massive star clusters like NGC 2808 hold onto enough gas to ignite a rapid succession of stars."
The star birth would be driven by shock waves from supernovae and stellar winds from giant stars, which compress the gas and make new stars, King explained. The gas would be increasingly enriched in helium from previous generations of stars more massive than the Sun.
Astronomers commonly assume that globular clusters produce only one stellar generation, because the energy radiating from the first batch of stars would clear out most of the residual gas needed to make more stars. But a hefty cluster like NGC 2808, which is two to three times more massive than a typical globular cluster, may have enough gravity to hang onto that gas, which has been enriched by helium from the first stars. Of the about 150 known globular clusters in our Milky Way Galaxy, NGC 2808 is one of the most massive, containing more than 1 million stars.
Another possible explanation for the multiple stellar populations is that NGC 2808 may only be masquerading as a globular cluster. The stellar grouping may have been a dwarf galaxy that was stripped of most of its material due to gravitational capture by our galaxy.
Omega Centauri, the only other stellar system Piotto's group found to have multiple generations of stars, is suspected to be the remnant core of a dwarf galaxy, Bedin said.
Although the astronomers' search is only in its infancy, they say multiple stellar populations may be a typical occurrence in other massive clusters.
"No one would make the radical step of suggesting that previous work on other clusters is no longer valid," King said. "But this discovery shows that the study of stellar populations in globular clusters now opens up in a new direction."
The team plans to use ESO's Very Large Telescope in Chile to make spectroscopic observations of the chemical abundances in NGC 2808, which may offer further evidence that the stars were born at different times and yield clues to how they formed. They also will use Hubble to hunt for multiple generations of stars in about 10 more hefty globular clusters.
The team's results have been accepted for publication in the Astrophysical Journal Letters.
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NGC-2264.jpgNGC 2264 - The "Snowflake Cluster" versus the "Cone Nebula"64 visiteCaption NASA:"Strange shapes and textures can be found in the neighborhood of the Cone Nebula.
These patterns result from the tumultuous unrest that accompanies the formation of the open cluster of stars known as NGC 2264, the Snowflake Cluster. To better understand this process, a detailed image of this Region was taken in two colors of infrared light by the orbiting Spitzer Space Telescope (SST). Bright stars from the Snowflake cluster dot the field. These stars soon heat up and destroy the gas and dust mountains in which they formed. One such dust mountain is the famous Cone Nebula, visible in the above image on the left, pointing toward a bright star near the center of the field.
The entire NGC 2264 Region is located about 2500 LY away toward the constellation of the Unicorn (Monoceros)".MareKromium
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M-081-PIA09579.jpgThe M 81 Galaxy is "Pretty in Pink"64 visiteThe perfectly picturesque Spiral Galaxy known as Messier 81, or M81, looks sharp in this new composite from NASA's Spitzer (SST) and Hubble Space Telescopes (HST) and NASA's Galaxy Evolution Explorer.
M81 is a "grand design" spiral galaxy, which means its elegant arms curl all the way down into its center. It is located about 12 MLY away in the Ursa Major Constellation and is one of the brightest galaxies that can be seen from Earth through telescopes.
The colors in this picture represent a trio of light wavelengths: blue is ultraviolet light captured by the Galaxy Evolution Explorer; yellowish white is visible light seen by Hubble; and red is infrared light detected by Spitzer.
The blue areas show the hottest, youngest stars, while the reddish-pink denotes lanes of dust that line the spiral arms. The orange center is made up of older stars. MareKromium
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NGC-0362-PIA09653.jpgNGC 362 - Globular Star Cluster64 visiteThe Galaxy Evolution Explorer's ultraviolet eyes have captured a globular star cluster, called NGC 362, in our own Milky Way galaxy. In this new image, the cluster appears next to stars from a more distant neighboring galaxy, known as the Small Magellanic Cloud.
Globular clusters are densely packed bunches of old stars scattered in galaxies throughout the universe. NGC 362, located 30,000 light-years away, can be spotted as the dense collection of mostly yellow-tinted stars surrounding a large white-yellow spot toward the top-right of this image. The white spot is actually the core of the cluster, which is made up of stars so closely packed together that the Galaxy Evolution Explorer cannot see them individually.
The light blue dots surrounding the cluster core are called extreme horizontal branch stars. These stars used to be very similar to our sun and are nearing the end of their lives. They are very hot, with temperatures reaching up to about four times that of the surface of our sun (25,000 Kelvin or 45,500 degrees Fahrenheit).
A star like our sun spends most of its life fusing hydrogen atoms in its core into helium. When the star runs out of hydrogen in its core, its outer envelope will expand. The star then becomes a red giant, which burns hydrogen in a shell surrounding its inner core. Throughout its life as a red giant, the star loses a lot of mass, then begins to burn helium at its core. Some stars will have lost so much mass at the end of this process, up to 85 percent of their envelopes, that most of the envelope is gone. What is left is a very hot ultraviolet-bright core, or extreme horizontal branch star.
Blue dots scattered throughout the image are hot, young stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way located approximately 200,000 light-years away. The stars in this galaxy are much brighter intrinsically than extreme horizontal branch stars, but they appear just as bright because they are farther away. The blue stars in the Small Magellanic Cloud are only about a few tens of millions of years old, much younger than the approximately 10-million-year-old stars in NGC 362.
Because NGC 362 sits on the northern edge of the Small Magellanic Cloud galaxy, the blue stars are denser toward the south, or bottom, of the image.
Some of the yellow spots in this image are stars in the Milky Way galaxy that are along this line of sight. Astronomers believe that some of the other spots, particularly those closer to NGC 362, might actually be a relatively ultraviolet-dim family of stars called "blue stragglers." These stars are formed from collisions or close encounters between two closely orbiting stars in a globular cluster.
This image is a false-color composite, where light detected by the Galaxy Evolution Explorer's far-ultraviolet detector is colored blue, and light from the telescope's near-ultraviolet detector is red.
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PIA09955_fig1.jpgFearsome Foursome (Figure 1)64 visiteOne of the biggest galaxy collisions ever observed is taking place at the center of this image. The four yellow blobs in the middle are large galaxies that have begun to tangle and ultimately merge into a single gargantuan galaxy. The yellowish cloud around the colliding galaxies contains billions of stars tossed out during the messy encounter. Other galaxies and stars appear in yellow and orange hues.
NASA's Spitzer Space Telescope spotted the four-way collision, or merger, in a giant cluster of galaxies, called CL0958+4702, located nearly 5 BLY away.
The dots in the picture are a combination of galaxies in the cluster; background galaxies located behind the cluster; and foreground stars in our own Milky Way galaxy.
Infrared data from Spitzer are colored red in this picture, while visible-light data from a telescope known as WIYN are green. Areas where green and red overlap appear orange or yellow.
Since most galaxies in the cluster contain old stars that are visible to Spitzer and WIYN, those galaxies appear orange.
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