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Sunday, January 6, 2019

Planetary Nebula Abell 33 - A Cosmic Gem

Planetary Nebula Abell 33
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Created when an aging star blew off its outer layers, this beautiful blue bubble is, by chance, aligned with a foreground star, and bears an uncanny resemblance to a diamond engagement ring. This cosmic gem is unusually symmetric, appearing to be almost perfectly circular on the sky. Most stars with masses similar to that of our Sun will end their lives as white dwarfs - small, very dense, and hot bodies that slowly cool down over billions of years. On the way to this final phase of their lives the stars throw their atmospheres out into the space and create planetary nebulae, colourful glowing clouds of gas surrounding the small, bright stellar relics. This image shows the remarkably round planetary nebula Abell 33, located roughly 2500 light-years from Earth. Being perfectly round is uncommon for these objects – usually something disturbs the symmetry and causes the planetary nebula to display irregular shapes.
The strikingly bright star located along the rim of the nebula creates a beautiful illusion in this image. This is just a chance alignment – the star, named HD 83535, lies in the foreground of the nebula, between Earth and Abell 33, in just the right place to make this view even more beautiful. Together, HD 83535 and Abell 33 create a sparkling diamond ring. The remnant of Abell 33's progenitor star, on its way to becoming a white dwarf, can be seen just slightly off-center inside the nebula, visible as a tiny white pearl. It is still bright – more luminous than our own Sun – and emits enough ultraviolet radiation to make the bubble of expelled atmosphere glow. Abell 33 is just one of the 86 objects included in astronomer George Abell's 1966 Abell Catalogue of Planetary Nebulae. Abell also scoured the skies for galaxy clusters, compiling the Abell Catalogue of over 4000 of these clusters in both the northern and southern hemispheres of the sky.
Image Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Absorption Nebula LDN 673

Absorption Nebula LDN 673
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This image was obtained with the wide-field view of the Mosaic camera on the Mayall 4-meter telescope at Kitt Peak National Observatory. LDN 673 is part of a giant cloud of dust and gas in the constellation of Aquilla. It is fragmented into many pieces, inside of which are forming stars. Some of these stars are illuminating parts of the nebula, such as in the upper-left and upper-right corners. The image was generated with observations in B (blue), V (cyan), I (orange) and H-alpha (red) filters. In this image, North is left, East is down.
Image Credit: T.A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF)
Image enhancement: Jean-Baptiste Faure

Saturday, January 5, 2019

Planetary Nebula ESO 378-1

Planetary Nebula ESO 378-1
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This extraordinary bubble, glowing like the ghost of a star in the haunting darkness of space, may appear supernatural and mysterious, but it is a familiar astronomical object: a planetary nebula, the remnants of a dying star. This is the best view of the little-known object ESO 378-1 yet obtained and was captured by ESO's Very Large Telescope in northern Chile.
Image Credit: ESO
Image enhancement: Jean-Baptiste Faure

A view of the planet orbiting Proxima Centauri

A view of the planet orbiting Proxima Centauri
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This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image to the upper-right of Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.
Image Credit: ESO/M. Kornmesser

Galaxy Cluster Abell S1063

Galaxy Cluster Abell S1063
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Abell S1063, a galaxy cluster, was observed by the Hubble Space Telescope as part of the Frontier Fields programme. The huge mass of the cluster – containing both baryonic matter and dark matter – acts as cosmic magnification glass and deforms objects behind it. In the past astronomers used this gravitational lensing effect to calculate the distribution of dark matter in galaxy clusters. A more accurate and faster way, however, is to study the intracluster light (visible in blue), which follows the distribution of dark matter.
In recent decades astronomers have tried to understand the true nature of the mysterious substance that makes up most of the matter in the Universe – dark matter – and to map its distribution in the Universe. Intracluster light is a byproduct of interactions between galaxies. In the course of these interactions, individual stars are stripped from their galaxies and float freely within the cluster. Once free from their galaxies, they end up where the majority of the mass of the cluster, mostly dark matter, resides.
Currently, all that is known about dark matter is that it appears to interact with regular matter gravitationally, but not in any other way. To find that it self-interacts would place significant constraints on its identity.
Image Credit: NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia)
Image enhancement: Jean-Baptiste Faure

Globular Cluster NGC 1866

Globular Cluster NGC 1866
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Star clusters are common structures throughout the Universe, each made up of hundreds of thousands of stars all bound together by gravity. This star-filled image, taken with the Hubble Space Telescope's Wide Field Camera 3 (WFC3), shows one of them: NGC 1866. NGC 1866 is found at the very edges of the Large Magellanic Cloud, a small galaxy located near to the Milky Way. The cluster was discovered in 1826 by Scottish astronomer James Dunlop, who catalogued thousands of stars and deep-sky objects during his career.
However, NGC 1866 is no ordinary cluster. It is a surprisingly young globular cluster situated close enough to us that its stars can be studied individually – no mean feat given the mammoth distances involved in studying the cosmos! There is still debate over how globular clusters form, but observations such as this have revealed that most of their stars are old and have a low metallicity. In astronomy, ‘metals’ are any elements other than hydrogen and helium; since stars form heavier elements within their core as they carry out nuclear fusion throughout their lifetimes, a low metallicity indicates that a star is very old, as the material from which it formed was not enriched with many heavy elements. It's possible that the stars within globular clusters are so old that they were actually some of the very first to form after the Big Bang.
In the case of NGC 1866, though, not all stars are the same. Different populations, or generations, of stars are thought to coexist within the cluster. Once the first generation of stars formed, the cluster may have encountered a giant gas cloud that sparked a new wave of star formation and gave rise to a second, younger, generation of stars – explaining why it seems surprisingly youthful.
Image Credit: ESA/Hubble and NASA
Image enhancement: Jean-Baptiste Faure

Spiral Galaxy M100 as seen by Hubble

Spiral Galaxy M100 as seen by Hubble
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This stunning spiral galaxy is Messier 100 in the constellation Coma Berenices, captured here by the Hubble Space Telescope – not for the first time. Among Hubble's most striking images of M100 are a pair taken just over a month apart, before and after Servicing Mission 1, which took place 25 years ago in December 1993. After Hubble was launched, the astronomers and engineers operating the telescope found that the images it returned were fuzzy, as if it were out of focus. In fact, that was exactly what was happening. Hubble's primary mirror functions like a satellite dish; its curved surface reflects all the light falling on it to a single focal point. However, the mirror suffered from a defect known as a spherical aberration, meaning that the light striking the edges of the mirror was not travelling to the same point as the light from the center. The result was blurry, unfocused images. To correct this fault, a team of seven astronauts undertook the first Servicing Mission in December 1993. They installed a device named COSTAR (Corrective Optics Space Telescope Axial Replacement) on Hubble, which took account of this flaw of the mirror and allowed the scientific instruments to correct the images they received. The difference between the photos taken of M100 before and after shows the remarkable effect this had, and the dramatic increase in image quality.
COSTAR was in place on Hubble until Servicing Mission 4, by which time all the original instruments had been replaced. All subsequent instrumentation had corrective optics built in. This new image of Messier 100 taken with Hubble's Wide Field Camera 3 (WFC3), demonstrates how much better the latest generation of instruments is compared to the ones installed in Hubble after its launch and after Servicing Mission 1.
Image Credit: NASA, ESA
Image enhancement: Jean-Baptiste Faure