Starship Asterisk*

Sister tornados from a massive supercell outside of Simla, Colorado. Shot of a lifetime for me. I have been trying to get a shot like this for 6 years. I hope you enjoy!

[b][i]Credit: ESO / Manu Mejias[/i][/b]

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The Crab Nebula, which also goes by the names Messier 1, NGC 1952 and Taurus A, is one of the best studied astronomical objects in the sky. It is the remnant of a supernova explosion which was observed by Chinese astronomers in 1054. The tangled filaments visible in this image are the remains of the exploded star, which are still expanding outwards at about 1500 kilometres per second.

Although not visible to the naked eye due to foreground filaments of helium and hydrogen the heart of the nebula hosts two faint stars. It is one of these that is responsible for the nebula that we see today — a star that is known as the Crab Pulsar, or CM Tau. This is the small, dense, corpse of the original star that caused the supernova. It is now only about 20 kilometres in diameter and rotates around its axis 30 times every second!

The star emits pulses of radiation in all wavelengths, ranging from gamma rays — for which it is one of the brightest sources in the sky — to radio waves. The radiation from the star is so strong that it is creating a wave of material that is deforming the inner parts of the nebula. The appearance of these structures changes so fast that astronomers can actually observe how they reshape. This provides a rare opportunity as cosmic timescales are usually much too long for change to be observed to this extent.

The data from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile used to make this image were selected from the ESO archive by Manu Mejias as part of the Hidden Treasures competition.

[b][i]Credit: ESA/Hubble & NASA[/i][/b]

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There are many galaxies in the Universe and although there is plenty of room, they tend to stick together. The Milky Way, for example, is part of a large gathering of over fifty galaxies known as the Local Group. Galaxy groups like this come together to form even larger groups called clusters which can congregate further still to create mammoth superclusters.

The sphere of space surrounding our galaxy is known as the Local Volume, a region some 35 million light-years in diameter and home to several hundred known galaxies. The subject of this new NASA/ESA Hubble Space Telescope image, a beautiful dwarf irregular galaxy known as PGC 18431, is one of these galaxies.

This image shows PGC 18431 smudged across the sky, but it wasn’t imaged purely for its looks. These Hubble observations were gathered in order to probe how Local Volume galaxies cluster together and move around. Hubble’s high resolution allows astronomers to explore star populations within these moderately distant galaxies — specifically, stars known as tip of the red-giant branch stars — in order to get an idea of the galaxy’s composition and, crucially, its distance from us. Knowing galactic distances enables us to accurately map a galaxy sample in three dimensions, a method key to understanding more about our cosmic neighbours, and to dismiss perspective and line-of-sight illusions.

[img3="Credit: NASA, ESA, HST/LEGUS/WFC3, D. Calzetti (UMass), H. Ford (JHU),
and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration"]http://cdn.spacetelescope.org/archives/ ... c1513a.jpg[/img3][hr][/hr]

Although the Universe may seem spacious most galaxies are clumped together in groups or clusters and a neighbour is never far away. But this galaxy, known as NGC 6503, has found itself in a lonely position, shown here at the edge of a strangely empty patch of space called the Local Void. This new NASA/ESA Hubble Space Telescope image shows a very rich set of colours, adding to the detail seen in previous images.

NGC 6503 is only some 18 million light-years away from us in the constellation of Draco (The Dragon), making it one of the closest neighbours from our Local Group. It spans some 30 000 light-years, about a third of the size of the Milky Way. The galaxy’s lonely location led stargazer Stephen James O'Meara to dub it the “Lost-In-Space galaxy” in his 2007 book Hidden Treasures.

This galaxy does not just offer poetic inspiration; it is also the subject of ongoing research. The Hubble Legacy ExtraGalactic UV Survey (LEGUS) is exploring a sample of nearby galaxies, including NGC 6503, to study their shape, internal structure, and the properties and behaviour of their stars. This survey uses 154 orbits of time on Hubble; by contrast, a typical Hubble observing programme lasts from a few to a few tens of orbits.

The Local Void is a patch of space thought to be about 150 million light-years across that seems to be curiously devoid of galaxies. Astronomers using Hubble discovered that the emptiness of this region has quite an effect on the space around us — the Milky Way is being strongly pulled away from it by the gentle but relentless tug of other nearby galaxies.

NGC 6503 lies right on the edge of this void. It has an almost non-existent central bulge surrounded by a massive halo of gas. The galaxy’s central region is a good example of something known as a “low ionisation nuclear emission region”, or LINER. These are less luminous than some of the brightest galaxies. Emission from NGC 6503’s heart is believed to be the result of a starved black hole that is only just being kept active, receiving a very small amount of infalling gas to keep its large appetite at bay. ...

starsurfer wrote:NGC 4217
http://www.spacetelescope.org/images/potw1503a/
Copyright: ESA/Hubble & NASA
Acknowledgement: R. Schoofs

bystander wrote:

starsurfer wrote:NGC 4217
http://www.spacetelescope.org/images/potw1503a/
Copyright: ESA/Hubble & NASA
Acknowledgement: R. Schoofs

http://asterisk.apod.com/viewtopic.php?p=238370#p238370
http://asterisk.apod.com/viewtopic.php?p=239193#p239193

[img3="Credit: ESO, Babak Tafreshi (TWAN)"]http://cdn.eso.org/images/screen/potw1524a.jpg[/img3][hr][/hr]

ESO’s Paranal Observatory is one of the best places on Earth to take in the night sky.

This panorama of ESO’s Very Large Telescope (VLT) atop the platform of Chile’s Cerro Paranal was taken by Babak Tafreshi, one of the ESO Photo Ambassadors.

A mix of colours sweeps across the sky in this image. From the fiery red sunset up to the dusty purple band of the Milky Way.

Although the VLT site is one of the best places on Earth for astronomy, the telescope must still overcome the natural distortions caused by our atmosphere. This is done through a process known as adaptive optics. Astronomers can make use of an artificial star by shining a powerful laser — seen here projected from the telescope on the far right — to correct for the blurring caused by the atmosphere.

The VLT, as a flagship facility for European astronomy, has opened up a new golden age of discovery in astronomy by making use of the most state-of-the art technologies.

[img3="Credit: ESA/Hubble & NASA"]http://cdn.spacetelescope.org/archives/ ... w1524a.jpg[/img3][hr][/hr]

This NASA/ESA Hubble Space Telescope image shows a galaxy known as UGC 11411. It is a galaxy type known as an irregular blue compact dwarf (BCD) galaxy.

BCD galaxies are about a tenth of the size of a typical spiral galaxy such as the Milky Way, and are made up of large clusters of hot, massive stars that ionise the surrounding gas with their intense radiation. Because these stars are so hot they glow brightly with a blue hue, giving galaxies like UGC 11411 their characteristic blue tint. With these massive stars being less than 10 million years old, they are very young compared to stellar standards. They were created during a starburst, a galaxy-wide episode of furious star formation. UGC 11411 in particular has an extremely high star formation rate, even for a BCD galaxy.

Unusually for galaxies with such intense star-forming regions, BCDs don’t contain either a lot of dust, or the heavy elements that are typically found as trace elements in recently formed stars, making their composition very similar to that of the material from which the first stars formed in the early Universe. Because of this astronomers consider BCD galaxies to be good objects to study to improve our understanding of primordial star-forming processes.

The bright stars in the image are foreground stars in our own Milky Way galaxy.