Into the Eye of the Helix

his colour-composite image of the Helix Nebula (NGC 7293) was created from images obtained using the the Wide Field Imager (WFI), an astronomical camera attached to the 2.2-metre Max-Planck Society/ESO telescope at the La Silla observatory in Chile. The blue-green glow in the centre of the Helix comes from oxygen atoms shining under effects of the intense ultraviolet radiation of the 120 000 degree Celsius central star and the hot gas. Further out from the star and beyond the ring of knots, the red colour from hydrogen and nitrogen is more prominent. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. This image was created from images through blue, green and red filters and the total exposure times were 12 minutes, 9 minutes and 7 minutes respectively.



Helix Nebula Zoom-in



Pan over the Helix Nebula



Zoom and pan over the Helix Nebula

A deep new image of the magnificent Helix planetary nebula has been obtained using the Wide Field Imager at ESO's La Silla Observatory. The image shows a rich background of distant galaxies, usually not seen in other images of this object.

Friday, February 27, 2009

The Helix Nebula, NGC 7293, lies about 700 light-years away in the constellation of Aquarius (the Water Bearer). It is one of the closest and most spectacular examples of a planetary nebula. These exotic objects have nothing to do with planets, but are the final blooming of Sun-like stars before their retirement as white dwarfs. Shells of gas are blown off from a star’s surface, often in intricate and beautiful patterns, and shine under the harsh ultraviolet radiation from the faint, but very hot, central star. The main ring of the Helix Nebula is about two light-years across or half the distance between the Sun and its closest stellar neighbour.

Despite being photographically very spectacular the Helix is hard to see visually as its light is thinly spread over a large area of sky and the history of its discovery is rather obscure. It first appears in a list of new objects compiled by the German astronomer Karl Ludwig Harding in 1824. The name Helix comes from the rough corkscrew shape seen in the earlier photographs.

Although the Helix looks very much like a doughnut, studies have shown that it possibly consists of at least two separate discs with outer rings and filaments. The brighter inner disc seems to be expanding at about 100 000 km/h and to have taken about 12000 years to have formed.

Because the Helix is relatively close — it covers an area of the sky about a quarter of the full Moon — it can be studied in much greater detail than most other planetary nebulae and has been found to have an unexpected and complex structure. All around the inside of the ring are small blobs, known as “cometary knots”, with faint tails extending away from the central star. They look remarkably like droplets of liquid running down a sheet of glass. Although they look tiny, each knot is about as large as our Solar System. These knots have been extensively studied, both with the ESO Very Large Telescope and with the NASA/ESA Hubble Space Telescope, but remain only partially understood. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. Some of these seem to be gathered in separate galaxy groups scattered over various parts of the image.

IC 418: The "Spirograph" Nebula

IC 418, also known as Spirograph Nebula, is a planetary nebula in the Milky Way Galaxy.The name derives from the intricate pattern of the nebula, which resembles a pattern which can be created using the Spirograph, a toy which produces geometric patterns (specifically, hypotrochoids and epitrochoids) on paper.Only a few million years ago, IC 418 was probably a common red giant star.Since running out of nuclear fuel, though, the outer envelope has begun expanding outward leaving a hot remnant core destined to become a white dwarf star.IC 418 lies about 2000 light-years away and spans 0.3 light-years across.

Bok globule

An image of Bok globules in the H II region IC 2944, taken with the WFPC2 instrument on the Hubble Space Telescope

A Bok globule is a dark cloud of dense dust and gas in which star formation sometimes takes place. Bok globules are found within H II regions, and typically have a mass of about 2 to 50 solar masses contained within a region about a light year or so across. They contain molecular hydrogen (H2), carbon oxides and helium, and around 1% (by mass) of silicate dust. Bok globules most commonly result in the formation of double or multiple star systems.

Bok globules were first observed by astronomer Bart Bok in the 1940s. In a paper published in 1947, Bok and E.F. Reilly hypothesised that these clouds were 'similar to insect's cocoons' that were undergoing gravitational collapse to form new stars from which stars and star clusters were born.This hypothesis was difficult to verify due to the observational difficulties of establishing what was happening inside a dense dark cloud that obscured all visible light emitted from within it. An analysis of near infrared observations published in 1990 confirmed that stars were being born inside Bok globules.Further observations have revealed that some Bok globules contain embedded warm sources,some contain Herbig-Haro objects,and some show outflows of molecular gas.Millimetre-wave emission line studies have also provided evidence for the infall of material onto an accreting protostar.

Bok globules are still a subject of intense research. Known to be some of the coldest objects in the natural universe (as cold as 8 kelvins) their structure and density remains somewhat a mystery. Methods applied so far have relied on column density derived from near infrared extinction and even star counting in a bid to probe these objects further.

Variable nebula

A Hubble Space Telescope image of NGC 2261, a classic example of a variable nebula.

Variable nebula are reflection nebula that change in brightness because of changes in their star.

Orion - Infrared

Sunday, November 30, 2008

Credits: Infrared Processing and Analysis Center, Caltech/JPL

The familiar winter sky constellation Orion takes on a spectacular guise in the infrared, as seen in this false-color image constructed from data collected by IRAS--the Infrared Astronomical Satellite. This picture, covering about 30 degrees x 24 degrees is a composite of IRAS wavelength band data centered at 12 microns, 60 microns, and 100 microns. New processing techniques have been used to enhance faint details and remove the instrumental artifacts (stripes) seen in earlier IRAS images. The warmest features, e.g.~the stars, are brightest at 12 microns. This emission is coded blue. The interstellar dust is cooler and shines brighter at 60 microns (coded green) and 100 microns (coded red).

The bright yellow region in the lower right of the image is the Sword of Orion, containing the Great Orion Nebula (M42 and M43). Above it to the left is the nebulosity around the belt star Zeta Orionis which contains the often photographed Horsehead Nebula (barely visible as a small indentation on the right side). Higher and to the left is M78, a reflection nebula. The Rosette Nebula is the brightest object near the left margin of the picture.

Most of the visually bright stars of Orion are not prominent in the infrared. However, Betelgeuse can be easily seen in the upper center of the picture as a blue-white dot (the faint tail is an instrumental artifact). The large ring to the right of Betelgeuse is the remnant of a supernova explosion, centered around the star Lambda Orionis. These rings are quite common in the IRAS sky. Another one, fainter and larger, can be seen in the lower left quadrant of the image.

A Sparkling Spray of Stars

ESO PR Photo 48/08
NGC 2264 and the Christmas Tree cluster
Credit: ESO

The festive season has arrived for astronomers at the European Southern Observatory (ESO) in the form of this dramatic new image. It shows the swirling gas around the region known as NGC 2264 — an area of sky that includes the sparkling blue baubles of the Christmas Tree star cluster.

NGC 2264 lies about 2600 light-years from Earth in the obscure constellation of Monoceros, the Unicorn, not far from the more familiar figure of Orion, the Hunter. The image shows a region of space about 30 light-years across.

William Herschel discovered this fascinating object during his great sky surveys in the late 18th century. He first noticed the bright cluster in January 1784 and the brightest part of the visually more elusive smudge of the glowing gas clouds at Christmas nearly two years later. The cluster is very bright and can easily be seen with binoculars. With a small telescope (whose lenses will turn the view upside down) the stars resemble the glittering lights on a Christmas tree. The dazzling star at the top is even bright enough to be seen with the unaided eye. It is a massive multiple star system that only emerged from the dust and gas a few million years ago.

As well as the cluster there are many interesting and curious structures in the gas and dust. At the bottom of the frame, the dark triangular feature is the evocative Cone Nebula, a region of molecular gas flooded by the harsh light of the brightest cluster members. The region to the right of the brightest star has a curious, fur-like texture that has led to the name Fox Fur Nebula.

Much of the image appears red because the huge gas clouds are glowing under the intense ultra-violet light coming from the energetic hot young stars. The stars themselves appear blue as they are hotter, younger and more massive than our own Sun. Some of this blue light is scattered by dust, as can be seen occurring in the upper part of the image.

This intriguing region is an ideal laboratory for studying how stars form. The entire area shown here is just a small part of a vast cloud of molecular gas that is in the process of forming the next generation of stars. Besides the feast of objects in this picture there are many interesting objects hidden behind the murk of the nebulosity. In the region between the tip of the Cone Nebula and the brightest star at the top of the picture there are several stellar birthing grounds where young stars are forming. There is even evidence of the intense stellar winds from these youthful embryos blasting out from the hidden stars in the making.

This picture of NGC 2264, including the Christmas Tree Cluster, was created from images taken with the Wide Field Imager (WFI), a specialised astronomical camera attached to the 2.2-metre Max-Planck Society/ESO telescope at the La Silla observatory in Chile. Located nearly 2400 m above sea level, in the mountains of the Atacama Desert, ESO's La Silla enjoys some of the clearest and darkest skies on the whole planet, making the site ideally suited for studying the farthest depths of the Universe. To make this image, the WFI stared at the cluster for more than ten hours through a series of specialist filters to build up a full colour image of the billowing clouds of fluorescing hydrogen gas.

A Bubble in Cygnus

Image Credit & Copyright: Keith Quattrocchi, Mel Helm

Adrift in the rich star fields of the constellation Cygnus, this lovely, symmetric bubble nebula was only recently recognized and may not yet appear in astronomical catalogs.

In fact, amateur astronomer Dave Jurasevich identified it as a nebula on July 6 in his images of the complex Cygnus region that included the Crescent Nebula (NGC 6888). He subsequently notified the International Astronomical Union.

Only eleven days later the same object was independently identified by Mel Helm at Sierra Remote Observatories, imaged by Keith Quattrocchi and Helm, and also submitted to the IAU as a potentially unknown nebula.

Their final composite image is seen here, including narrow-band image data that highlights the nebula's delicate outlines. What is the newly recognized bubble nebula? Like the Crescent Nebula itself, this cosmic bubble could be blown by winds from a massive Wolf-Rayet star, or it could be a spherically-shaped planetary nebula, a final phase in the life of a sun-like star.

Integral locates origin of high-energy emission from Crab Nebula

photo: High-energy polarised emission from Crab Nebula

Thanks to data from ESA’s Integral gamma-ray observatory, scientists have been able to locate where particles in the vicinity of the rotating neutron-star in the Crab Nebula are accelerated to immense energies.

The discovery, resulting from more than 600 individual observations of the nebula, put in place another piece of the puzzle in understanding how neutron stars work.
Rotating neutron-stars, or pulsars, are known to accelerate particles to enormous energies, typically one hundred times more than the most powerful accelerators on Earth, but scientists are still uncertain exactly how these systems work and where the particles are accelerated.

A step forward in this understanding is now accomplished thanks to a team of researchers from the UK and Italy, led by Professor Tony Dean of the University of Southampton, who studied high-energy polarised light emitted by the Crab Nebula – one of the most dramatic sights in deep space.

The Crab Nebula is the result of a supernova explosion which was seen from Earth on 4 July 1054. The explosion left behind a pulsar with a nebula of radiating particles around it. The pulsar contains the mass of the Sun squeezed into a volume of about 10 km radius, rotating very fast – about 30 times a second – thereby generating very powerful magnetic fields and accelerating particles. A highly collimated jet, aligned with the spin axis of the pulsar and a bright radiating ‘donut’ structure (or torus) around the pulsar itself, are also seen.

So, the Crab is known to accelerate electrons - and possibly other particles - to extremely high speed, and so produces high energy radiation. But where exactly are these particles accelerated?

Looking into the heart of the pulsar with Integral’s spectrometer (SPI), the researchers made a detailed study to assess the polarization – or the alignment - of the waves of high-energy radiation originating from the Crab.


They saw that this polarised radiation is highly aligned with the rotation axis of the pulsar. So they concluded that a significant portion of the electrons generating the high-energy radiation must originate from a highly-organised structure located very close to the pulsar, very likely directly from the jets themselves. The discovery allows the researchers to discard other theories that locate the origin of this radiation further away from the pulsar.

Professor Tony Dean of the University’s School of Physics and Astronomy commented that the discovery of such alignment – also matching with the polarisation observed in the visible band - is truly remarkable. “The findings have clear implications on many aspects of high energy accelerators such as the Crab,” he added.

"The detection of polarised radiation in space is very complicated and rare, as it requires dedicated instrumentation and an in-depth analysis of very complex data”, said Chris Winkler, Integral Project Scientist at ESA. “Integral’s ability to detect polarised gamma-radiation and, as a consequence, to obtain important results like this one, confirms it once more as a world-class observatory.”

Uncovering the Veil Nebula

Date: Thursday, August 02, 2007

NASA's Hubble Space Telescope photographed three magnificent sections of the Veil Nebula — the shattered remains of a supernova that exploded thousands of years ago. This series of images provides beautifully detailed views of the delicate, wispy structure resulting from this cosmic explosion. The Veil Nebula is one of the most spectacular supernova remnants in the sky. The entire shell spans about 3 degrees on the sky, corresponding to about 6 full moons.

The Veil Nebula is a prototypical middle-aged supernova remnant, and is an ideal laboratory for studying the physics of supernova remnants because of its unobscured location in our Galaxy, its relative closeness, and its large size. Also known as the Cygnus Loop, the Veil Nebula is located in the constellation of Cygnus, the Swan. It is about 1,500 light-years away from Earth.

Stars in our Galaxy, and in other galaxies, are born and then die. How long a star lives depends on how massive it is. The more massive the star, the shorter its life. When a star significantly more massive than our Sun runs out of fuel, it collapses and blows itself apart in a catastrophic supernova explosion. A supernova releases so much light that it can outshine a whole galaxy of stars put together. The exploding star sweeps out a huge bubble in its surroundings, fringed with actual stellar debris along with material swept up by the blast wave. This glowing, brightly colored shell of gas forms a nebula that astronomers call a "supernova remnant."

Such a remnant can remain visible long after the initial explosion fades away. Scientists estimate that the Veil supernova explosion occurred some 5,000 to 10,000 years ago.

The small regions captured in these Hubble images provide stunning close-ups of the Veil. Fascinating smoke-like wisps of gas are all that remain visible of what was once a star in our Milky Way Galaxy. The intertwined rope-like filaments of gas in the Veil Nebula result from the enormous amounts of energy released as the fast-moving debris from the explosion plows into its surroundings and creates shock fronts. These shocks, driven by debris moving at 600,000 kilometers per hour, heat the gas to millions of degrees. It is the subsequent cooling of this material that produces the brilliant glowing colors.

The Hubble images of the Veil Nebula are striking examples of how processes that take place hundreds of light-years away can sometimes resemble effects we see around us in our daily life. Although caused by different forces, the structures show similarities to the patterns formed by the interplay of light and shadow on the bottom of a swimming pool, rising smoke, or a ragged cirrus cloud.

Although only about one star per century in our Galaxy will end its life in this spectacular way, these explosions are responsible for making all chemical elements heavier than iron, as well as being the main producers of oxygen in the universe. Elements such as copper, mercury, gold, and lead are forged in these violent events. The expanding shells of supernova remnants mix with other clouds in the Milky Way and become the raw material for new generations of stars and planets. The chemical elements that constitute Earth, and indeed those of which we ourselves are made, were formed deep inside ancient stars and distributed by supernova explosions in nebulae like the one we see here.

The images were taken with Hubble's Wide Field Planetary Camera 2 (WFPC2) in November 1994 and August 1997. The color is produced by creating a composite of three different images. The colors indicate emission from different kinds of atoms excited by the shock: blue shows oxygen, green shows sulfur, and red shows hydrogen.

Planetary Nebula NGC 7293

Orion Nebula - Courtesy Nasa/Hubble Heritage

photo: If beauty is in the details, this is one of the most beautiful pictures ever made.

NASA's Hubble Space Telescope has captured one of the most detailed astronomical images in history. Released yesterday, the original of this Orion Nebula image is a mosaic of a billion pixels—nearly 5,000 times sharper than the 212,521-pixel version on this page.

Despite their stunning depiction of stars still forming in wombs of gas and dust (as well as thousands of heretofore unseen stars), these details aren't simply in the service of beauty.

Cat's Eye Nebula - NGC 6543

photo:
The Cat's Eye Nebula, one of the first planetary nebulae discovered, also has one of the most complex forms known to this kind of nebula. Eleven rings, or shells, of gas make up the Cat's Eye.

The Eagle Has Risen: Stellar Spire in the Eagle Nebula

photo: A billowing tower of gas and dust rises from the stellar nursery known as the Eagle Nebula. This small piece of the Eagle Nebula is 57 trillion miles long (91.7 trillion km).

Nebula DEM L 106

photo:
Within nebula DEM L 106 is a second nebula, N30B. The peanut-shaped cocoon of dust, called a reflection nebula, surrounds a cluster of young, hot stars. The bright, supergiant star at the top of the picture illuminates the dusty cocoon. Wispy filaments from DEM L 106 fill the rest of the image.

The Ghost Head Nebula - NGC 2028

photo:
This nebula is one of a chain of star-forming regions lying south of the 30 Doradus nebula in the Large Magellanic Cloud. The red and blue light comes from regions of hydrogen gas heated by nearby stars. The green light comes from glowing oxygen, illuminated by the energy of a stellar wind. The white center shows a core of hot, massive stars.

The Southern Ring Nebula (NGC 3132)

photo: This planetary nebula, also known as the "Eight-Burst" Nebula because of its figure-8 appearance through amateur astronomer telescopes, is visible in the southern hemisphere. NGC 3132 is nearly half a light year in diameter and 2,000 light years away. Gases are moving away from the dying star at its center at a speed of nine miles per second (14.4 km/s).

Nebula N83B

photo: Intense radiation from newly born, ultra-bright stars in nebula N83B, also known as NGC 1748, carve out a large cavity in the gas surrounding them. The "bubble" of vanished gas is 25 light years in diameter.

Lagoon Nebula

NGC 1512 - Courtesy Nasa/JPL

Black Widow Nebula - Courtesy Nasa/JPL