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Sunday, November 27, 2011

Hubble Space Telescope Imagery -2/2



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This image shows the edge of a giant gaseous cavity within the star-forming region called NGC 3324. The glowing nebula has been carved out by intense ultraviolet radiation and stellar winds from several hot, young stars. A cluster of extremely massive stars, located well outside this image in the center of the nebula, is responsible for the ionization of the nebula and excavation of the cavity. The image also reveals dramatic dark towers of cool gas and dust that rise above the glowing wall of gas. The dense gas at the top resists the blistering ultraviolet radiation from the central stars, and creates a tower that points in the direction of the energy flow. The high-energy radiation blazing out from the hot, young stars in NGC 3324 is sculpting the wall of the nebula by slowly eroding it away. Located in the Southern Hemisphere, NGC 3324 is at the northwest corner of the Carina Nebula (NGC 3372), home of the Keyhole Nebula and the active, outbursting star Eta Carinae. The entire Carina Nebula complex is located at a distance of roughly 7,200 light-years, and lies in the constellation Carina.




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A small region inside the massive globular cluster Omega Centauri which boasts nearly 10 million stars. The stars in Omega Centauri are about about 16,000 light-years from Earth, and are between 10 billion and 12 billion years old. The majority of the stars in the image are yellow-white, like our Sun. These are adult stars that are shining by hydrogen fusion. Toward the end of their normal lives, the stars become cooler and larger. These late-life stars are the orange dots in the image. Even later in their life cycles, the stars continue to cool down and expand in size, becoming red giants. These bright red stars swell to many times larger than our Sun's size and begin to shed their gaseous envelopes. After ejecting most of their mass and exhausting much of their hydrogen fuel, the stars appear brilliant blue. Only a thin layer of material covers their super-hot cores. These stars are desperately trying to extend their lives by fusing helium in their cores. At this stage, they emit much of their light at ultraviolet wavelengths. When the helium runs out, the stars reach the end of their lives. Only their burned-out cores remain, and they are called white dwarfs (the faint blue dots in the image). White dwarfs are no longer generating energy through nuclear fusion and have gravitationally contracted to the size of Earth. They will continue to cool and grow dimmer for many billions of years until they become dark cinders. All of the stars in the image are cozy neighbors. The average distance between any two stars in the cluster's crowded core is only about a third of a light-year, roughly 13 times closer than our Sun's nearest stellar neighbor, Alpha Centauri. Although the stars are close together, WFC3's sharpness can resolve each of them as individual stars. If anyone lived in this globular cluster, they would behold a star-saturated sky that is roughly 100 times brighter than Earth's sky. Hubble observed Omega Centauri on July 15, 2009, in ultraviolet and visible light.

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This image from NASA's Hubble Space Telescope shows the diverse collection of galaxies in the cluster Abell S0740 that is over 450 million light-years away in the direction of the constellation Centaurus. The giant elliptical ESO 325-G004 looms large at the cluster's center. The galaxy is as massive as 100 billion of our suns. Hubble resolves thousands of globular star clusters orbiting ESO 325-G004. At the galaxy's distance they appear as pinpoints of light contained within the diffuse halo. Other fuzzy elliptical galaxies dot the image. Some have evidence of a disk or ring structure that gives them a bow-tie shape. Several spiral galaxies are also present. The starlight in these galaxies is mainly contained in a disk and follows along spiral arms. This image was created by combining Hubble science observations taken in January 2005 with Hubble Heritage observations taken a year later to form a 3-color composite. The filters that isolate blue, red and infrared light were used with the Advanced Camera for Surveys aboard Hubble.



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The star cluster Pismis 24 lies in the core of the large emission nebula NGC 6357 that extends one degree on the sky in the direction of the Scorpius constellation. Part of the nebula is ionised by the youngest (bluest) heavy stars in Pismis 24. The intense ultraviolet radiation from the blazing stars heats the gas surrounding the cluster and creates a bubble in NGC 6357. The presence of these surrounding gas clouds makes probing into the region even harder. One of the top candidates for the title of "Milky Way stellar heavyweight champion" was, until now, Pismis 24-1, a bright young star that lies in the core of the small open star cluster Pismis 24 (the bright stars in the Hubble image) about 8,000 light-years away from Earth. Pismis 24-1 was thought to have an incredibly large mass of 200 to 300 solar masses. New NASA/ESA Hubble measurements of the star, have, however, resolved Pismis 24-1 into two separate stars, and, in doing so, have "halved" its mass to around 100 solar masses.


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In 2004, Hubble created the deepest visible-light image of the Universe and now, with its brand-new camera, it is seeing even farther in the same region. This image, taken by the HUDF09 team with the new WFC3/infrared camera on Hubble in late August 2009, during a total of four days of pointing for 173,000 seconds of total exposure time, is the deepest image of the universe ever taken in near-infrared light. Nearly every smudge and bit of light in this image is a separate galaxy made up of billions of stars. The faintest and reddest objects in the image are galaxies that formed 600 million years after the Big Bang. No galaxies have been seen before at such early times. The image was taken in the same region as the Hubble Ultra Deep Field (2004), and is roughly 2.4 arcminutes wide. Again, I invite you to step outside some dark night in the future and gaze up at the sky, knowing that every bit of apparent darkness above is really filled with the faint light of these billions of faraway galaxies.

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In January 2002, a dull star in an obscure constellation suddenly became 600,000 times more luminous than our Sun, temporarily making it the brightest star in our galaxy. The star, called V838 Monocerotis, has long since faded back to obscurity, but observations of a phenomenon called a "light echo" around the star have uncovered remarkable new features over the following years (this animation covers two years' time). The light echo is light from the earlier explosion echoing off dust surrounding the star. Light from the outburst traveled to the dust and then was reflected to Earth. Because of this indirect path, the light arrived at Earth months after light from the star that traveled directly from the star.




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Called I Zwicky 18, this galaxy - some 59 million light-years distant - has a youthful appearance that resembles galaxies typically found only in the early universe. Hubble has now found faint, older stars within this galaxy, suggesting that the galaxy may have formed at the same time as most other galaxies. I Zwicky 18 is classified as a dwarf irregular galaxy and is much smaller than our Milky Way Galaxy. The concentrated bluish-white knots embedded in the heart of the galaxy are two major starburst regions where stars are forming at a furious rate. The wispy blue filaments surrounding the central starburst regions are bubbles of gas that have been blown away by stellar winds and supernovae explosions from a previous generation of hot, young stars. A companion galaxy lies just above and to the left and may be interacting with I Zwicky 18.



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This object is a billowing tower of cold gas and dust rising from a stellar nursery called the Eagle Nebula. 7,000 light-years distant from us, the soaring tower is 9.5 light-years or about 90 trillion kilometers tall. Stars in the Eagle Nebula are born in clouds of cold hydrogen gas that reside in chaotic neighbourhoods, where energy from young stars sculpts fantasy-like landscapes in the gas. The tower may be a giant incubator for those newborn stars. A torrent of ultraviolet light from a band of massive, hot, young stars [off the top of the image] is eroding the pillar. The column is silhouetted against the background glow of more distant gas. The bumps and fingers of material in the center of the tower are examples of stellar birthing areas. These regions may look small but they are roughly the size of our solar system. The blue colour at the top is from glowing oxygen, the red color in the lower region is from glowing hydrogen. This image was taken in November 2004 with the Advanced Camera for Surveys.


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The "Retina Nebula" is in fact, a dying star named IC 4406. The left and right halves of the Hubble image are nearly mirror images of the other. If we could fly around IC 4406 in a starship, we would see that the gas and dust form a vast donut of material streaming outward from the dying star. From Earth, we are viewing the donut from the side. This side view allows us to see the intricate tendrils of dust that have been compared to the eye's retina. Gas on the inside of the donut is ionized by light from the central star and glows brightly. Light from oxygen atoms is rendered blue in this image; hydrogen is shown as green, and nitrogen as red. One of the most interesting features here is the irregular lattice of dark lanes that criss-cross the center of the nebula. These lanes are about 24 billion kilometers wide, and are like an open mesh veil that has been wrapped around the bright donut.





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"The Grasshopper", or UGC 4881, is a stunning system consisting of two colliding galaxies. It has a bright curly tail containing a remarkable number of star clusters. The galaxies are thought to be halfway through a merger - the cores of the parent galaxies are still clearly separated, but their discs are overlapping. A supernova exploded in this system in 1999 and astronomers believe that a vigorous burst of star formation may have just started. This notable object is located in the constellation of Lynx, some 500 million light-years away from Earth. UGC 4881 is the 55th galaxy in Arp's Atlas of Peculiar Galaxies. This image is part of a large collection of 59 images of merging galaxies taken by the Hubble Space Telescope and released on the occasion of its 18th anniversary on April 24th, 2008.





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Seen here is a very thin section of a supernova remnant caused by a stellar explosion that occurred more than 1,000 years ago. On or around May 1, 1006 A.D., observers around the world witnessed and recorded the arrival of light from what is now called SN 1006, a tremendous supernova explosion caused by the final death throes of a white dwarf star nearly 7,000 light-years away. The supernova was probably the brightest star ever seen by humans, and surpassed Venus as the brightest object in the night time sky, only to be surpassed by the moon. It was visible even during the day for weeks, and remained visible to the naked eye for at least two and a half years before fading away. Today we know that the shockwave of SN 1006 has a diameter of nearly 60 light-years, and it is still expanding at roughly 6 million miles per hour.



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This image is called the Hubble Ultra Deep Field, and it is by far my favorite Hubble image. Starting in late 2003, astronomers pointed Hubble at a tiny, relatively empty part of our sky (only a few stars from the Milky Way visible), and created an exposure nearly 12 days long over a four-month period. The result is this amazing image, looking back through time at thousands of galaxies that range from 1 to 13 billion light-years away from Earth. Some 10,000 galaxies were observed in this tiny patch of sky (a tenth the size of the full moon) - each galaxy a home to billions of stars. Go outside tonight, take a ball-point pen with you, and hold it up in front of the night sky at arm's length. The tip of your pen is about 1 millimeter wide, and at arm's length, it would cover the 10,000 galaxies seen in the Ultra Deep Field image. That's how unbelievably massive the visible universe is. By way of comparison, to really put us Earthlings in our place in the Grand Scheme, please have a look at another famous image, thePale Bule Dot - a photograph taken of the Earth (the tiny pale speck, top center) by Voyager 1 in 1990 from 4 billion miles away (about 6 light-hours). I will finish with the words of astronomer Carl Sagan about this Pale Blue Dot: "That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar", every "supreme leader", every saint and sinner in the history of our species lived there - on a mote of dust suspended in a sunbeam."

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