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💫AM 0644-741


Resembling a diamond-encrusted bracelet, a ring of brilliant blue star clusters wraps around the yellowish nucleus of what was once a normal spiral galaxy in this new image from the NASA/ESAHubble Space Telescope (HST). This image is being released to commemorate the 14th anniversary of Hubble's launch on April 24, 1990 and its deployment from the space shuttle Discovery on April 25, 1990.

The sparkling blue ring is 150,000 light-years in diameter, making it larger than our entire home galaxy, the Milky Way. The galaxy, cataloged as AM 0644-741, is a member of the class of so- called "ring galaxies." It lies 300 million light-years away in the direction of the southern constellation Dorado.

Credit:
NASA, ESA, and The Hubble Heritage Team (AURA/STScI)


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💫Wide field image of Abell 2218

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An international team of astronomers may have set a new record in discovering what is the most distant known galaxy in the Universe. Located an estimated 13 billion light-years away, the object is being viewed at a time only 750 million years after the big bang, when the Universe was barely 5 percent of its current age. The primeval galaxy was identified by combining the power of the NASA/ESA Hubble Space Telescope and CARA's W. M. Keck Telescopes on Mauna Kea in Hawaii. These great observatories got a boost from the added magnification of a natural 'cosmic gravitational lens' in space that further amplifies the brightness of the distant object. The newly discovered galaxy is likely to be a young galaxy shining during the end of the so-called "Dark Ages" - the period in cosmic history which ended with the first galaxies and quasars transforming opaque, molecular hydrogen into the transparent, ionized Universe we see today. The new galaxy was detected in a long exposure of the nearby cluster of galaxies Abell 2218, taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. This cluster is so massive that the light of distant objects passing through the cluster actually bends and is amplified, much as a magnifying glass bends and magnifies objects seen through it. Such natural gravitational 'telescopes' allow astronomers to see extremely distant and faint objects that could otherwise not be seen. The extremely faint galaxy is so far away its visible light has been stretched into infrared wavelengths, making the observations particularly difficult.



"As we were searching for distant galaxies magnified by Abell 2218, we detected a pair of strikingly similar images whose arrangement and colour indicate a very distant object," said astronomer Jean-Paul Kneib (Observatoire Midi-Pyrénées and California Institute of Technology), who is lead author reporting the discovery in a forthcoming article in the Astrophysical Journal. Analysis of a sequence of Hubble images indicate the object lies between a redshift of 6.6 and 7.1, making it the most distant source currently known. However, long exposures in the optical and infrared taken with spectrographs on the 10-meter Keck telescopes suggests that the object has a redshift towards the upper end of this range, around redshift 7. Redshift is a measure of how much the wavelengths of light are shifted to longer wavelengths. The greater the shift in wavelength toward the redder regions of the spectrum, the more distant the object is. "The galaxy we have discovered is extremely faint, and verifying its distance has been an extraordinarily challenging adventure," said Dr. Kneib. "Without the 25 x magnification afforded by the foreground cluster, this early object could simply not have been identified or studied in any detail at all with the present telescopes available. Even with aid of the cosmic lens, the discovery has only been possible by pushing our current observatories to the limits of their capabilities!" Using the combination of the high resolution of Hubble and the large magnification of the cosmic lens, the astronomers estimate that this object, although very small - only 2,000 light-years across - is forming stars extremely actively.


However, two intriguing properties of the new source are the apparent lack of the typically bright hydrogen emission line and its intense ultraviolet light which is much stronger than that seen in star-forming galaxies closer by. "The properties of this distant source are very exciting because, if verified by further study, they could represent the hallmark of a truly young stellar system that ended the Dark Ages" added Dr. Richard Ellis, Steele Professor of Astronomy at Caltech, and a co-author in the article. The team is encouraged by the success of their technique and plans to continue the search for more examples by looking through other cosmic lenses in the sky. Hubble's exceptional resolution makes it ideally suited for such searches. "Estimating the abundance and characteristic properties of sources at early times is particularly important in understanding how the Universe reionized itself, thus ending the Dark Ages," said Mike Santos, a former Caltech graduate student, now a postdoctoral researcher at the Institute of Astronomy, Cambridge, UK. "The cosmic lens has given us a first glimpse into this important epoch. We are now eager to learn more by finding further examples, although it will no doubt be challenging." "We are looking at the first evidence of our ancestors on the evolutionary tree of the entire Universe," said Dr. Frederic Chaffee, director of the W. M. Keck Observatory, home to the twin 10-meter Keck telescopes that confirmed the discovery. "Telescopes are virtual time machines, allowing our astronomers to look back to the early history of the cosmos, and these marvellous observations are of the earliest time yet."


Credit: European Space Agency, J.-P. Kneib (Observatoire Midi-Pyrénées) and DSS2


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💫Wide field galaxy cluster CL0024+1654


Clusters of galaxies are the largest stable systems in the Universe. They are like laboratories for studying the relationship between the distributions of dark and visible matter. In 1937, Fritz Zwicky realised that the visible component of a cluster (the thousands of millions of stars in each of the thousands of galaxies) represents only a tiny fraction of the total mass. About 80-85% of the matter is invisible, the so-called 'dark matter'. Although astronomers have known about the presence of dark matter for many decades, finding a technique to view its distribution is a much more recent development. Led by Drs Jean-Paul Kneib (from the Observatoire Midi-Pyrénées, France/Caltech, United States), Richard Ellis and Tommaso Treu (both Caltech, United States), the team used the NASA/ESA Hubble Space Telescope to reconstruct a unique 'mass map' of the galaxy cluster CL0024+1654. It enabled them to see for the first time on such large scales how mysterious dark matter is distributed with respect to galaxies. This comparison gives new clues on how such large clusters assemble and which role dark matter plays in cosmic evolution. Tracing dark matter is not an easy task because it does not shine. To make a map, astronomers must focus on much fainter, more distant galaxies behind the cluster.

The shapes of these distant systems are distorted by the gravity of the foreground cluster. This distortion provides a measure of the cluster mass, a phenomenon known as "weak gravitational lensing". To map the dark matter of CL0024+1654, more than 120 hours observing time was dedicated to the team. This is the largest amount of Hubble time ever devoted to studying a galaxy cluster. Despite its distance of 4.5 thousand million light-years (about one third of the look-back time to the Big Bang) from Earth, this massive cluster is wide enough to equal the angular size of the full Moon. To make a mass map that covers the entire cluster required observations that probed 39 regions of the galaxy cluster. The investigation has resulted in the most comprehensive study of the distribution of dark matter in a galaxy cluster so far and extends more than 20 million light-years from its centre, much further than previous investigations. Many groups of researchers have tried to perform these types of measurements with ground-based telescopes. However, the technique relies heavily on finding the exact shapes of distant galaxies behind the cluster. The sharp vision of a space telescope such as NASA-ESA's Hubble is superior. The study reveals that the density of dark matter on large scales drops sharply with distance from the cluster centre.

This confirms a picture that has emerged from recent detailed computer simulations. As Richard Ellis says: 'Although theorists have predicted the form of dark matter in galaxy clusters from numerical simulations based on the effects of gravity alone, this is the first time we have convincing observations to back them up. Some astronomers had speculated clusters might contain large reservoirs of dark matter in their outermost regions. Assuming our cluster is representative, this is not the case.' The team noticed that dark matter appears to clump together in their map. For example, they found concentrations of dark matter associated with galaxies known to be slowly falling into the system. Generally, the researchers found that the dark matter traces the cluster galaxies remarkably well and over an unprecedented range of physical scales. 'When a cluster is being assembled, the dark matter will be smeared out between the galaxies where it acts like a glue,' says Jean-Paul Kneib. 'The overall association of dark matter and 'glowing matter' is very convincing evidence that structures like CL0024+1654 grow by merging of smaller groups of galaxies that were already bound by their own dark matter components.'

Credit:
European Space Agency, NASA, Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) and the Canada France Hawaii Telescope


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💫Helix Nebula Detail

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This ESA/NASA Hubble Space Telescope image shows a fine web of filamentary 'bicycle-spoke' features embedded in the colourful red and blue gas ring, which is one of the nearest planetary nebulae to Earth. The nebula is nearby so it is nearly half the size of the diameter of the full Moon. Hubble astronomers took several exposures with the Advanced Camera for Surveys to capture most of it. They then combined Hubble views with a wider photo taken by Kitt Peak's Mosaic Camera. The result is a breathtaking look down a tunnel of glowing gases that is a million million kilometres long. The fluorescing tube is pointed nearly directly at Earth, so it looks more like a bubble than a cylinder. Thousands of comet-like filaments embedded along the inner rim of the nebula point back toward the central star, which is a small but superhot white dwarf. These tentacles formed when a hot stellar 'wind' of gas ploughed into colder shells of dust and gas previously ejected by the doomed star. Astronomers have known about these comet-like filaments from ground-based telescopes for decades but have never before seen them in so much detail. The filaments may lie in a disc around the hot star, like a collar. During the November 2002 Leonid meteor storm, to protect the spacecraft and Hubble's precise mirror, controllers turned Hubble's tail end towards the meteor stream for about half a day. Fortunately, the Helix Nebula was almost exactly in the opposite direction of the meteor stream, so Hubble used nine orbits to photograph the nebula while it waited out the storm.



To capture the nebula, Hubble had to take nine separate snapshots. Astronomers at the Space Telescope Science Institute assembled these images into a mosaic. Experts then blended the mosaic with a wider photograph taken by the Mosaic Camera on the National Science Foundation's 0.9-metre telescope at Kitt Peak National Optical Astronomy Observatory, United States. The radiant colours correspond to glowing hydrogen and nitrogen (red) and oxygen (blue). Planetary nebulae like the Helix are sculpted late in a Sun-like star's life by a torrential gush of gases escaping from the dying star. They have nothing to do with planet formation, but get their name because they look like planetary disks in a small telescope. With higher magnification, astronomers can resolve the classic 'doughnut-hole' in the middle of a planetary nebula. Given the nebula's distance of 650 light-years, its angular size corresponds to a huge ring diameter of nearly 3 light-years across. This distance is approximately three-quarters of the distance between our Sun and the nearest star. The Helix Nebula is a popular target for amateur astronomers. Viewed through binoculars, it appears as a ghostly, green-coloured cloud in the constellation Aquarius. Larger amateur telescopes can resolve the ring-shaped nebula, but only the largest ground-based telescopes can resolve the radial streaks. After careful analysis, astronomers conclude that this nebula is a cylinder that happens to be pointed toward Earth, rather than a bubble.


Credit: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO)


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💫Dumbbell Nebula


This excellent image of the Dumbbell Nebula (M27, NGC6853), a planetary nebula in the constellation of Vulpecula, was taken at the 3.5-meter WIYN telescope using the mini-mosaic imager (described in an NOAO newsletter article). The nebula was formed when an evolved, red giant star ejected its outer envelope near the end of its lifetime. The expanding cloud of gas becomes visible once the hot core of the star, visible near the center, is exposed and the high-energy, ultraviolet light from the core ionizes the cloud. This makes the nebula emit mostly a strong emission-line spectrum. This color image was obtained by combining three separate pictures, each one taken through a narrow filter centered at the emission wavelengths of Hydrogen (H alpha, red, 656 nm), doubly ionized Oxygen (OIII, green, 501 nm), and neutral Oxygen (OI, blue, 630 nm). It is physically very interesting that neutral gas can survive in a region right next to highly ionized gas, and this image shows how, as the blue component is concentrated in very dense clumps which act to protect the neutral oxygen from the intense ultraviolet radiation which has ionized the other gas components.

Credit:
G. Jacoby, WIYN / NOAO / NSF


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💫Cygnus X-1

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Wide-field, ground-based image showing the visible light component of Cygnus X-1 (centre).


A rich source of X-rays in the constellation of Cygnus, the Swan.


Credit: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)


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