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| Piú viste - The Universe in Super Definition |
NGC-6240-PIA11828.jpgNGC 6240 - Colliding Galaxies58 visiteThis image of a pair of colliding galaxies called NGC 6240 shows them in a rare, short-lived phase of their evolution just before they merge into a single, larger galaxy. The prolonged, violent collision has drastically altered the appearance of both galaxies and created huge amounts of heat turning NGC 6240 into an "InfraRed Luminous" Active Galaxy.
A rich variety of active galaxies, with different shapes, luminosities and radiation profiles exist. These galaxies may be related astronomers have suspected that they may represent an evolutionary sequence. By catching different galaxies in different stages of merging, a story emerges as one type of active galaxy changes into another. NGC 6240 provides an important "missing link" in this process.
This image was created from combined data from the infrared array camera of NASA's Spitzer Space Telescope at 3.6 and 8.0 microns (red) and Visible Light from NASA's Hubble Space Telescope (green and blue).MareKromium
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M-033-PIA11970.jpgM 33 - Spiral Galaxy58 visiteOne of our closest galactic neighbors shows its awesome beauty in this new image from NASA's Spitzer Space Telescope.
M 33, also known as the "Triangulum Galaxy", is a member of what's known as our Local Group of galaxies. Along with our own Milky Way, this group travels together in the universe, as they are gravitationally bound.
In fact, M 33 is one of the few galaxies that is moving toward the Milky Way despite the fact that space itself is expanding, causing most galaxies in the universe to grow farther and farther apart.
When viewed with Spitzer's InfraRed eyes, this elegant spiral galaxy sparkles with color and detail. Stars appear as glistening blue gems (many of which are actually foreground stars in our own galaxy), while dust in the spiral disk of the galaxy glows pink and red. But not only is this new image beautiful, it also shows M 33 to be surprising large —bigger than its Visible-Light appearance would suggest.
With its ability to detect cold, dark dust, Spitzer can see emission from cooler material well beyond the visible range of M 33's disk. Exactly how this cold material moved outward from the galaxy is still a mystery, but winds from giant stars or supernovas may be responsible.
M 33 is located about 2,9 MLY away in the constellation Triangulum. This composite image was taken by Spitzer's InfraRed Array Camera (a.k.a.: IRAC). The color blue indicates InfraRed Light of 3.6 microns, green shows 4.5-micron light, and red 8.0 microns.MareKromium
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MACS-J0717_5+3745-hs-2009-17-a-print.jpgMACS J0717.5+3745 (Galaxy Cluster)58 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 Affair58 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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30-Doradus.jpg30 Doradus and R-13658 visiteThe massive, young stellar grouping, called R136, is only a few million years old and resides in the 30 Doradus Nebula, a turbulent star-birth region in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. Many of the stars are among the most massive known. Several of them are over 100 times more massive than our Sun. These hefty stars are destined to become supernovae in a few million years.
The image, taken by Hubble's Wide Field Camera 3, spans about 100 light-years. The nebula is close enough to Earth that Hubble can resolve individual stars, giving astronomers important information about the stars' birth and evolution.
The brilliant stars are carving deep cavities in the surrounding material by unleashing a torrent of ultraviolet light, and hurricane-force stellar winds (streams of charged particles), which are etching away the enveloping hydrogen gas cloud in which the stars were born. The image reveals a fantasy landscape of pillars, ridges, and valleys, as well as a dark region in the center that roughly looks like the outline of a holiday tree. Besides sculpting the gaseous terrain, the brilliant stars can also help create a successive generation of offspring. When the winds hit dense walls of gas, they create shocks, which may be generating a new wave of star birth.
The movement of the LMC around the Milky Way may have triggered the massive cluster's formation in several ways. The gravitational tug of the Milky Way and the companion Small Magellanic Cloud may have compressed gas in the LMC. Also, the pressure resulting from the LMC plowing through the Milky Way's halo may have compressed gas in the satellite. The cluster is a rare, nearby example of the many super star clusters that formed in the distant, early universe, when star birth and galaxy interactions were more frequent. Previous Hubble observations have shown astronomers that super star clusters in faraway galaxies are ubiquitous. The LMC is located 170,000 light-years away and is a member of the Local Group of Galaxies, which also includes the Milky Way.
The Hubble image was taken at infrared wavelengths (1.1 microns and 1.6 microns). Hubble sees through the dusty nebula, revealing many stars that cannot be seen in visible light. The large bright star just above the center of the image is in the 30 Doradus nebula. The Hubble observations of 30 Doradus were made October 20-27, 2009.MareKromium
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NGC-2976.jpgNGC 2976 - Galaxy or "Galactic Star-Factory"?58 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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M 74-PIA08533_fig1.jpgM 74 and Supernova SN2003gd57 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)57 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.jpgM 74 - Spiral Galaxy57 visite
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M 42-PIA08656.jpgOrion's "Sword"57 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 Orion57 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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NGC-2535-PIA09106.jpgNGC 2535 and NGC 2536 (alias Arp 82)57 visiteA pair of interacting galaxies might be experiencing the galactic equivalent of a mid-life crisis. For some reason, the pair, called Arp 82, didn't make their stars early on as is typical of most galaxies. Instead, they got a second wind later in life -- about 2 billion years ago -- and started pumping out waves of new stars as if they were young again.
Arp 82 is an interacting pair of galaxies with a strong bridge and a long tail. NGC 2535 is the big galaxy and NGC 2536 is its smaller companion. The disk of the main galaxy looks like an eye, with a bright "pupil" in the center and oval-shaped "eyelids." Dramatic "beads on a string" features are visible as chains of evenly spaced star-formation complexes along the eyelids. These are presumably the result of large-scale gaseous shocks from a grazing encounter. The colors of this galaxy indicate that the observed stars are young to intermediate in age, around 2 million to 2 billion years old, much less than the age of the universe (13.7 billion years).
The puzzle is: why didn't Arp 82 form many stars earlier, like most galaxies of that mass range? Scientifically, it is an oddball and provides a relatively nearby lab for studying the age of intermediate-mass galaxies.
This picture is a composite captured by Spitzer's infrared array camera with light at wavelength 8 microns shown in red, NASA's Galaxy Evolution Explorer combined 1530 and 2310 Angstroms shown in blue, and the Southeastern Association for Research in Astronomy Observatory light at 6940 Angstroms shown in green.
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