Picture of the Week

Also see our pictures of the week on eso.org.
15 October 2012

Galaxy in a spin

NGC 3344 is a glorious spiral galaxy around half the size of the Milky Way, which lies 25 million light-years distant. We are fortunate enough to see NGC 3344 face-on, allowing us to study its structure in detail.

The galaxy features an outer ring swirling around an inner ring with a subtle bar structure in the centre. The central regions of the galaxy are predominately populated by young stars, with the galactic fringes also featuring areas of active star formation.

Central bars are found in around two thirds of spiral galaxies. NGC 3344’s is clearly visible here, although it is not as dramatic as some (see for example heic1202).

The high density of stars in galaxies’ central regions gives them enough gravitational influence to affect the movement of other stars in their galaxy. However, NGC 3344’s outer stars are moving in an unusual manner, although the presence of the bar cannot entirely account for this, leaving astronomers puzzled. It is possible that in its past NGC 3344 passed close by another galaxy and accreted stars from it, but more research is needed to state this with confidence.

The image is a combination of exposures taken in visible and near-infrared light, using Hubble’s Advanced Camera for Surveys. The field of view is around 3.4 by 3.4 arcminutes, or around a tenth of the diameter of the full Moon.


8 October 2012

A cosmic garden sprinkler

The Universe is filled with mysterious objects. Many of them are as strange as they are beautiful. Among these, planetary nebulae are probably one of the most fascinating objects to behold in the night sky. No other type of object has such a large variety of shapes and structures. The NASA/ESA Hubble Space Telescope provides us this week with a striking image of Hen 3-1475, a planetary nebula in the making.

Planetary nebulae — the name arises because most of these objects resembled a planet when they were first discovered through early telescopes — are expanding, glowing shells of gas coming from Sun-like stars at the ends of their lives. They glow brightly because of the radiation that comes from a hot, compact core, which remains after the outer envelope is ejected, and is powerful enough to make these gossamer shells shine.

Each planetary nebula is complex and unique. Hen 3-1475 is a great example of a planetary nebula in the making, a phase which is known to astronomers as a protoplanetary or preplanetary nebula.

Since the central star has not yet blown away its complete shell, the star is not hot enough to ionise the shell of gas and so the nebula does not shine. Rather, we see the expelled gas thanks to light reflected off it. When the star’s envelope is fully ejected, it will begin to glow and become a planetary nebula.

Hen 3-1475 is located in the constellation of Sagittarius around 18 000 light-years away from us. The central star is more than 12 000 times as luminous as our Sun. Its most characteristic feature is a thick torus of dust around the central star and two S-shaped jets that are emerging from the pole regions of the central star. These jets are long outflows of fast-moving gas travelling at hundreds of kilometres per second.

The formation of these bipolar jets has puzzled astronomers for a long time. How can a spherical star form these complex structures? Recent studies suggest that the object’s characteristic shape and the large velocity outflow is created by a central source that ejects streams of gas in opposite directions and precesses once every thousand years. It is like an enormous, slowly rotating garden sprinkler in the middle of the sky. No wonder astronomers also have nicknamed this object the “Garden-sprinkler Nebula”.

This picture was taken with Hubble’s Wide Field Camera 3, which provides significantly higher resolution than previous observations made with the Wide Field and Planetary Camera 2 (heic0308).

Links


1 October 2012

Cosmic riches

This dazzling image shows the globular cluster Messier 69, or M 69 for short, as viewed through the NASA/ESA Hubble Space Telescope. Globular clusters are dense collections of old stars. In this picture, foreground stars look big and golden when set against the backdrop of the thousands of white, silvery stars that make up M 69.

Another aspect of M 69 lends itself to the bejewelled metaphor: As globular clusters go, M 69 is one of the most metal-rich on record. In astronomy, the term “metal” has a specialised meaning: it refers to any element heavier than the two most common elements in our Universe, hydrogen and helium. The nuclear fusion that powers stars created all of the metallic elements in nature, from the calcium in our bones to the carbon in diamonds. Successive generations of stars have built up the metallic abundances we see today.

Because the stars in globular clusters are ancient, their metallic abundances are much lower than more recently formed stars, such as the Sun. Studying the makeup of stars in globular clusters like M 69 has helped astronomers trace back the evolution of the cosmos.

M 69 is located 29 700 light-years away in the constellation Sagittarius (the Archer). The famed French comet hunter Charles Messier added M 69 to his catalogue in 1780. It is also known as NGC 6637.

The image is a combination of exposures taken in visible and near-infrared light by Hubble’s Advanced Camera for Surveys, and covers a field of view of approximately 3.4 by 3.4 arcminutes.


24 September 2012

Hubble portrays a dusty spiral galaxy

The NASA/ESA Hubble Space Telescope has provided us with another outstanding image of a nearby galaxy. This week, we highlight the galaxy NGC 4183, seen here with a beautiful backdrop of distant galaxies and nearby stars. Located about 55 million light-years from the Sun and spanning about eighty thousand light-years, NGC 4183 is a little smaller than the Milky Way. This galaxy, which belongs to the Ursa Major Group, lies in the northern constellation of Canes Venatici (The Hunting Dogs).

NGC 4183 is a spiral galaxy with a faint core and an open spiral structure. Unfortunately, this galaxy is viewed edge-on from the Earth, and we cannot fully appreciate its spiral arms. But we can admire its galactic disc.

The discs of galaxies are mainly composed of gas, dust and stars. There is evidence of dust over the galactic plane, visible as dark intricate filaments that block the visible light from the core of the galaxy. In addition, recent studies suggest that this galaxy may have a bar structure. Galactic bars are thought to act as a mechanism that channels gas from the spiral arms to the centre, enhancing star formation, which is typically more pronounced in the spiral arms than in the bulge of the galaxy.

British astronomer William Herschel first observed NGC 4183 on 14 January 1778.

This picture was created from visible and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys. The field of view is approximately 3.4 arcminutes wide.

This image uses data identified by Luca Limatola in the Hubble's Hidden Treasures image processing competition.


17 September 2012

Glowing gas and dark dust in a side-on spiral

The NASA/ESA Hubble Space Telescope has produced a sharp image of NGC 4634, a spiral galaxy seen exactly side-on. Its disc is slightly warped by ongoing interactions with a nearby galaxy, and it is crisscrossed by clearly defined dust lanes and bright nebulae.

NGC 4634, which lies around 70 million light-years from Earth in the constellation of Coma Berenices, is one of a pair of interacting galaxies. Its neighbour, NGC 4633, lies just outside the upper right corner of the frame, and is visible in wide-field views of the galaxy. While it may be out of sight, it is not out of mind: its subtle effects on NGC 4634 are easy to see to a well-trained eye.

Gravitational interactions pull the neat spiral forms of galaxies out of shape as they get closer to each other, and the disruption to gas clouds triggers vigorous episodes of star formation. While this galaxy’s spiral pattern is not directly visible thanks to our side-on perspective, its disc is slightly warped, and there is clear evidence of star formation.

Along the full length of the galaxy, and scattered around parts of its halo, are bright pink nebulae. Similar to the Orion Nebula in the Milky Way, these are clouds of gas that are gradually coalescing into stars. The powerful radiation from the stars excites the gas and makes it light up, much like a fluorescent sign. The large number of these star formation regions is a telltale sign of gravitational interaction.

The dark filamentary structures that are scattered along the length of the galaxy are caused by cold interstellar dust blocking some of the starlight.

Hubble’s image is a combination of exposures in visible light produced by Hubble’s Advanced Camera for Surveys and the Wide Field and Planetary Camera 2.


10 September 2012

NGC 7090 — An actively star-forming galaxy

This image portrays a beautiful view of the galaxy NGC 7090, as seen by the NASA/ESA Hubble Space Telescope. The galaxy is viewed edge-on from the Earth, meaning we cannot easily see the spiral arms, which are full of young, hot stars.

However, our side-on view shows the galaxy’s disc and the bulging central core, where typically a large group of cool old stars are packed in a compact, spheroidal region. In addition, there are two interesting features present in the image that are worth mentioning.

First, we are able to distinguish an intricate pattern of pinkish red regions over the whole galaxy. This indicates the presence of clouds of hydrogen gas. These structures trace the location of ongoing star formation, visual confirmation of recent studies that classify NGC 7090 as an actively star-forming galaxy.

Second, we observe dust lanes, depicted as dark regions inside the disc of the galaxy. In NGC 7090, these regions are mostly located in lower half of the galaxy, showing an intricate filamentary structure. Looking from the outside in through the whole disc, the light emitted from the bright centre of the galaxy is absorbed by the dust, silhouetting the dusty regions against the bright light in the background.

Dust in our galaxy, the Milky Way, has been one of the worst enemies of observational astronomers for decades. But this does not mean that these regions are quite blind spots in the sky. At near-infrared wavelengths — slightly longer wavelengths than visible light — this dust is largely transparent and astronomers are able to study what is really behind it. At still longer wavelengths, the realm of radio astronomy, the dust itself can actually be observed, letting astronomers study the structure and properties of dust clouds and their relationship with star formation.

Lying in the southern constellation of Indus (The Indian), NGC 7090 is located about thirty million light-years from the Sun. Astronomer John Herschel first observed this galaxy on 4 October, 1834.

The image was taken using the Wide Field Channel of the Advanced Camera for Surveys aboard the Hubble Space Telescope and combines orange light (coloured blue here), infrared (coloured red) and emissions from glowing hydrogen gas (also in red).

A version of this image of NGC 7090 was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Rasid Tugral. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition is now closed and the list of winners is available here.


3 September 2012

Ancient orbs

This sparkling picture taken by the NASA/ESA Hubble Space Telescope shows the centre of globular cluster M 4. The power of Hubble has resolved the cluster into a multitude of glowing orbs, each a colossal nuclear furnace.

M 4 is relatively close to us, lying 7200 light-years distant, making it a prime object for study. It contains several tens of thousand stars and is noteworthy in being home to many white dwarfs — the cores of ancient, dying stars whose outer layers have drifted away into space.

In July 2003, Hubble helped make the astounding discovery of a planet called PSR B1620-26 b, 2.5 times the mass of Jupiter, which is located in this cluster. Its age is estimated to be around 13 billion years — almost three times as old as the Solar System! It is also unusual in that it orbits a binary system of a white dwarf and a pulsar (a type of neutron star).

Amateur stargazers may like to track M 4 down in the night sky. Use binoculars or a small telescope to scan the skies near the orange-red star Antares in Scorpius. M 4 is bright for a globular cluster, but it won’t look anything like Hubble’s detailed image: it will appear as a fuzzy ball of light in your eyepiece.

On Wednesday 5 September, the European Southern Observatory (ESO) will publish a wide-field image of M 4, showing the full spheroidal shape of the globular cluster. See it at www.eso.org on Wednesday.


27 August 2012

Spotting a supernova in NGC 5806

A new image from the NASA/ESA Hubble Space Telescope shows NGC 5806, a spiral galaxy in the constellation Virgo (the Virgin). It lies around 80 million light years from Earth. Also visible in this image is a supernova explosion called SN 2004dg.

The exposures that are combined into this image were carried out in early 2005 in order to help pinpoint the location of the supernova, which exploded in 2004. The afterglow from this outburst of light, caused by a giant star exploding at the end of its life, can be seen as a faint yellowish dot near the bottom of the galaxy.

NGC 5806 was chosen to be one of a number of galaxies in a study into supernovae because Hubble’s archive already contained high resolution imagery of the galaxy, collected before the star had exploded. Since supernovae are both relatively rare, and impossible to predict with any accuracy, the existence of such before-and-after images is precious for astronomers who study these violent events.

Aside from the supernova, NGC 5806 is a relatively unremarkable galaxy: it is neither particularly large or small, nor especially close or distant.

The galaxy’s bulge (the densest part in the centre of the spiral arms) is a so-called disk-type bulge, in which the spiral structure extends right to the centre of the galaxy, instead of there being a large elliptical bulge of stars present. It is also home to an active galaxy nucleus, a supermassive black hole which is pulling in large amounts of matter from its immediate surroundings. As the matter spirals around the black hole, it heats up and emits powerful radiation.

This image is produced from three exposures in visible and infrared light, observed by Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.3 by 1.7 arcminutes.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Andre van der Hoeven (who won second prize in the competition for his image of Messier 77). Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed.


20 August 2012

A collection of ancient stars

The NASA/ESA Hubble Space Telescope has produced this beautiful image of the globular cluster Messier 56 (also known as M 56 or NGC 6779), which is located about 33 000 light years away from the Earth in the constellation of Lyra (The Lyre). The cluster is composed of a large number of stars, tightly bound to each other by gravity.

However, this was not known when Charles Messier first observed it in January 1779.  He described Messier 56 as “a nebula without stars”, like most globular clusters that he discovered — his telescope was not powerful enough to individually resolve any of the stars visible here, making it look like a fuzzy ball through his telescope’s eyepiece. We clearly see from Hubble’s image how the development of technology over the years has helped our understanding of astronomical objects.

Astronomers typically infer important properties of globular clusters by looking at the light of their constituent stars. But they have to be very careful when they observe objects like Messier 56, which is located close to the Galactic plane. This region is crowded by “field-stars”, in other words, stars in the Milky Way that happen to lie in the same direction but do not belong to the cluster. These objects can contaminate the light, and hence undermine the conclusions reached by astronomers.  

A tool often used by scientists for studying stellar clusters is the colour-magnitude (or Hertzsprung-Russell) diagram. This chart compares the brightness and colour of stars – which in turn, tells scientists what the surface temperature of a star is.

By comparing high quality observations taken with the Hubble Space Telescope with results from the standard theory of stellar evolution, astronomers can characterise the properties of a cluster. In the case of Messier 56, this includes its age, which at 13 billion years is approximately three times the age of the Sun. Furthermore, they have also been able to study the chemical composition of Messier 56. The cluster has relatively few elements heavier than hydrogen and helium, typically a sign of stars that were born early in the Universe’s history, before many of the elements in existence today were formed in significant quantities.

Astronomers have found that the majority of clusters with this type of chemical makeup lie along a plane in the Milky Way’s halo. This suggests that such clusters were captured from a satellite galaxy, rather than being the oldest members of the Milky Way's globular cluster system as had been previously thought.

This image consists of visible and near-infrared exposures from Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.3 by 3.3 arcminutes.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Gilles Chapdelaine. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed and the results will be published soon.


13 August 2012

A lonely galactic island

In terms of intergalactic real estate, our Solar System has a plumb location as part of a big, spiral galaxy, the Milky Way. Numerous, less glamorous dwarf galaxies, keep the Milky Way company. Many galaxies, however, are comparatively isolated, without close neighbours. One such example is the small galaxy known as DDO 190, snapped here in a new image from the NASA/ESA Hubble Space Telescope.

DDO 190 is classified as a dwarf irregular galaxy as it is relatively small and lacks clear structure. Older, reddish stars mostly populate DDO 190’s outskirts, while some younger, bluish stars gleam in DDO 190’s more crowded interior. Some pockets of ionised gas heated up by stars appear here and there, with the most noticeable one shining towards the bottom of DDO 190 in this picture. Meanwhile, a great number of distant galaxies with evident spiral, elliptical and less-defined shapes glow in the background.

DDO 190 lies around nine million light-years away from our Solar System. It is considered part of the loosely associated Messier 94 group of galaxies, not far from the Local Group of galaxies that includes the Milky Way. Canadian astronomer Sidney van der Bergh was the first to record DDO 190 in 1959 as part of the DDO catalogue of dwarf galaxies. (“DDO” stands for the David Dunlap Observatory, now managed by the Royal Astronomical Society of Canada, where the catalogue was created).

Although within the Messier 94 group, DDO 190 is on its own. The galaxy’s nearest dwarf galaxy neighbour, DDO 187, is thought to be no closer than three million light-years away. In contrast, many of the Milky Way’s companion galaxies, such as the Large and Small Magellanic Clouds, reside within a fifth or so of that distance, and even the giant spiral of the Andromeda Galaxy is closer to the Milky Way than DDO 190 is to its nearest neighbour.

Hubble’s Advanced Camera for Surveys captured this image in visible and infrared light. The field of view is around 3.3 by 3.3 arcminutes

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Claude Cornen. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed and the results will be published soon.


6 August 2012

Close encounter with the Tarantula

Turning its 2.4-metre eye to the Tarantula Nebula, the NASA/ESA Hubble Space Telescope has taken this close-up of the outskirts of the main cloud of the Nebula.

The bright wispy structures are the signature of an environment rich in ionised hydrogen gas, called H II by astronomers. In reality these appear red, but the choice of filters and colours of this image, which includes exposures both in visible and infrared light, make the gas appear green.

These regions contain recently formed stars, which emit powerful ultraviolet radiation that ionises the gas around them. These clouds are ephemeral as eventually the stellar winds from the newborn stars and the ionisation process will blow away the clouds, leaving stellar clusters like the Pleiades.

Located in the Large Magellanic Cloud, one of our neighbouring galaxies, and situated at a distance of 170 000 light-years away from Earth, the Tarantula Nebula is the brightest known nebula in the Local Group of galaxies. It is also the largest (around 650 light-years across) and most active star-forming region known in our group of galaxies, containing numerous clouds of dust and gas and two bright star clusters. A recent Hubble image shows a large part of the nebula immediately adjacent to this field of view.

The cluster at the Tarantula nebula’s centre is relatively young and very bright. While it is outside the field of view of this image, the energy from it is responsible for most of the brightness of the Nebula, including the part we see here. The nebula is in fact so luminous that if it were located within 1000 light-years from Earth, it would cast shadows on our planet.

The Tarantula Nebula was host to the closest supernova ever detected since the invention of the telescope, supernova 1987A, which was visible to the naked eye.

The image was produced by Hubble’s Advanced Camera for Surveys, and has a field of view of approximately 3.3 by 3.3 arcminutes.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Judy Schmidt. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed and the results will be published soon.



30 July 2012

A ten billion year stellar dance

The NASA/ESA Hubble Space Telescope offers this delightful view of the crowded stellar encampment called Messier 68, a spherical, star-filled region of space known as a globular cluster. Mutual gravitational attraction amongst a cluster’s hundreds of thousands or even millions of stars keeps stellar members in check, allowing globular clusters to hang together for many billions of years.

Astronomers can measure the ages of globular clusters by looking at the light of their constituent stars. The chemical elements leave signatures in this light, and the starlight reveals that globular clusters' stars typically contain fewer heavy elements, such as carbon, oxygen and iron, than stars like the Sun. Since successive generations of stars gradually create these elements through nuclear fusion, stars having fewer of them are relics of earlier epochs in the Universe. Indeed, the stars in globular clusters rank among the oldest on record, dating back more than 10 billion years.

More than 150 of these objects surround our Milky Way galaxy. On a galactic scale, globular clusters are indeed not all that big. In Messier 68's case, its constituent stars span a volume of space with a diameter of little more than a hundred light-years. The disc of the Milky Way, on the other hand, extends over some 100 000 light-years or more.

Messier 68 is located about 33 000 light-years from Earth in the constellation Hydra (The Female Water Snake). French astronomer Charles Messier notched the object as the sixty-eighth entry in his famous catalogue in 1780.

Hubble added Messier 68 to its own impressive list of cosmic targets in this image using the Wide Field Camera of Hubble’s Advanced Camera for Surveys. The image, which combines visible and infrared light, has a field of view of approximately 3.4 by 3.4 arcminutes.


23 July 2012

A galaxy festooned with stellar nurseries

The galaxy NGC 4700 bears the signs of the vigorous birth of many new stars in this image captured by the NASA/ESA Hubble Space Telescope.

The many bright, pinkish clouds in NGC 4700 are known as H II regions, where intense ultraviolet light from hot young stars is causing nearby hydrogen gas to glow. H II regions often come part-and-parcel with the vast molecular clouds that spawn fresh stars, thus giving rise to the locally ionised gas.

In 1610, French astronomer Nicolas-Claude Fabri de Peiresc peered through a telescope and found what turned out to be the first H II region on record: the Orion Nebula, located relatively close to our Solar System here in the Milky Way. Astronomers study these regions throughout the Milky Way and those easily seen in other galaxies to gauge the chemical makeup of cosmic environments and their influence on the formation of stars.

NGC 4700 was discovered back in March 1786 by the British astronomer William Herschel who noted it as a “very faint nebula”. NGC 4700, along with many other relatively close galaxies, is found in the constellation of Virgo (The Virgin) and is classified as a barred spiral galaxy, similar in structure to the Milky Way. It lies about 50 million light-years from us and is moving away from us at about 1400 km/second due to the expansion of the Universe.


16 July 2012

An audience of stellar flashbulbs

The NASA/ESA Hubble Space Telescope has captured a crowd of stars that looks rather like a stadium darkened before a show, lit only by the flashbulbs of the audience’s cameras. Yet the many stars of this object, known as Messier 107, are not a fleeting phenomenon, at least by human reckoning of time — these ancient stars have gleamed for many billions of years.

Messier 107 is one of more than 150 globular star clusters found around the disc of the Milky Way galaxy. These spherical collections each contain hundreds of thousands of extremely old stars and are among the oldest objects in the Milky Way. The origin of globular clusters and their impact on galactic evolution remains somewhat unclear, so astronomers continue to study them through pictures such as this one obtained by Hubble.

As globular clusters go, Messier 107 is not particularly dense. Visually comparing its appearance to other globular clusters, such as Messier 53 or Messier 54 reveals that the stars within Messier 107 are not packed as tightly, thereby making its members more distinct like individual fans in a stadium's stands.

Messier 107 can be found in the constellation of Ophiuchus (The Serpent Bearer) and is located about 20 000 light-years from the Solar System.

French astronomer Pierre Méchain first noted the object in 1782, and British astronomer William Herschel documented it independently a year later. A Canadian astronomer, Helen Sawyer Hogg, added Messier 107 to Charles Messier's famous astronomical catalogue in 1947.

This picture was obtained with the Wide Field Camera of Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.4 by 3.4 arcminutes.


9 July 2012

A galactic disc, edge-on and up close

This image snapped by the NASA/ESA Hubble Space Telescope reveals an exquisitely detailed view of part of the disc of the spiral galaxy NGC 4565. This bright galaxy is one of the most famous examples of an edge-on spiral galaxy, oriented perpendicularly to our line of sight so that we see right into its luminous disc. NGC 4565 has been nicknamed the Needle Galaxy because, when seen in full, it appears as a very narrow streak of light on the sky.

The edgewise view into the Needle Galaxy shown here looks very similar to the view we have from our Solar System into the core of the Milky Way. In both cases ribbons of dust block some of the light coming from the galactic disc. To the lower right, the dust stands in even starker contrast against the copious yellow light from the star-filled central regions. NGC 4565’s core is off camera to the lower right. For a full view of NGC 4565 for comparison’s sake, see this wider field of view from ESO’s Very Large Telescope.

Studying galaxies like NGC 4565 helps astronomers learn more about our home, the Milky Way. At a distance of only about 40 million light-years, NGC 4565 is relatively close by, and being seen edge-on makes it a particularly useful object for comparative study. As spiral galaxies go, NGC 4565 is a whopper — about a third as big again as the Milky Way.

The image was taken with Hubble’s Advanced Camera for Surveys and has a field of view of approximately 3.4 by 3.4 arcminutes.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Josh Barrington. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed and the results will be published soon.


2 July 2012

Red giant blows a bubble

A bright star is surrounded by a tenuous shell of gas in this unusual image from the NASA/ESA Hubble Space Telescope. U Camelopardalis, or U Cam for short, is a star nearing the end of its life. As it begins to run low on fuel, it is becoming unstable. Every few thousand years, it coughs out a nearly spherical shell of gas as a layer of helium around its core begins to fuse. The gas ejected in the star’s latest eruption is clearly visible in this picture as a faint bubble of gas surrounding the star.

U Cam is an example of a carbon star. This is a rare type of star whose atmosphere contains more carbon than oxygen. Due to its low surface gravity, typically as much as half of the total mass of a carbon star may be lost by way of powerful stellar winds.

Located in the constellation of Camelopardalis (The Giraffe), near the North Celestial Pole, U Cam itself is actually much smaller than it appears in Hubble’s picture. In fact, the star would easily fit within a single pixel at the centre of the image. Its brightness, however, is enough to overwhelm the capability of Hubble’s Advanced Camera for Surveys making the star look much bigger than it really is.

The shell of gas, which is both much larger and much fainter than its parent star, is visible in intricate detail in Hubble’s portrait. While phenomena that occur at the ends of stars’ lives are often quite irregular and unstable (see for example Hubble’s images of Eta Carinae, potw1208a), the shell of gas expelled from U Cam is almost perfectly spherical.

The image was produced with the High Resolution Channel of the Advanced Camera for Surveys.


25 June 2012

A vapour of stars

Relatively few galaxies possess the sweeping, luminous spiral arms or brightly glowing centre of our home galaxy the Milky Way. In fact, most of the Universe's galaxies look like small, amorphous clouds of vapour. One of these galaxies is DDO 82, captured here in an image from the NASA/ESA Hubble Space Telescope. Though tiny compared to the Milky Way, such dwarf galaxies still contain between a few million and a few billion stars.

DDO 82, also known by the designation UGC 5692, is not without a hint of structure, however. Astronomers classify it as an Sm galaxy, or Magellanic spiral galaxy, named after the Large Magellanic Cloud, a dwarf galaxy that orbits the Milky Way. That galaxy, like DDO 82, is said to have one spiral arm.

In the case of DDO 82, gravitational interactions over its history seem to have discombobulated it so that this structure is not as evident as in the Large Magellanic Cloud. Accordingly, astronomers also refer to DDO 82 and others of a similar unshapely nature as dwarf irregular galaxies.       

DDO 82 can be found in the constellation of Ursa Major (the Great Bear) approximately 13 million light-years away. The object is considered part of the M81 Group of around three dozen galaxies. DDO 82 gets its name from its entry number in the David Dunlap Observatory Catalogue. Canadian astronomer Sidney van den Bergh originally compiled this list of dwarf galaxies in 1959.

The image is made up of exposures taken in visible and infrared light by Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.3 by 3.3 arcminutes.


18 June 2012

Globular Cluster M 10

Like many of the most famous objects in the sky, globular cluster Messier 10 was of little interest to its discoverer: Charles Messier, the 18th century French astronomer, catalogued over 100 galaxies and clusters, but was primarily interested in comets. Through the telescopes available at the time, comets, nebulae, globular clusters and galaxies appeared just as faint, diffuse blobs and could easily be confused for one another.

Only by carefully observing their motion — or lack of it — were astronomers able to distinguish them: comets move slowly relative to the stars in the background, while other more distant astronomical objects do not move at all.

Messier’s decision to catalogue all the objects that he could find and that were not comets, was a pragmatic solution which would have a huge impact on astronomy. His catalogue of just over 100 objects includes many of the most famous objects in the night sky. Messier 10, seen here in an image from the NASA/ESA Hubble Space Telescope, is one of them. Messier described it in the very first edition of his catalogue, which was published in 1774 and included the first 45 objects he identified.

Messier 10 is a ball of stars that lies about 15 000 light-years from Earth, in the constellation of Ophiuchus (The Serpent Bearer). Approximately 80 light-years across, it should therefore appear about two thirds the size of the Moon in the night sky. However, its outer regions are extremely diffuse, and even the comparatively bright core is too dim to see with the naked eye.

Hubble, which has no problems seeing faint objects, has observed the brightest part of the centre of the cluster in this image, a region which is about 13 light-years across.

This image is made up of observations made in visible and infrared light using Hubble’s Advanced Camera for Surveys. The observations were carried out as part of a major Hubble survey of globular clusters in the Milky Way.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant flashenthunder. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed and the results will be published soon.



11 June 2012

Compact blue dwarf can’t hide

The NASA/ESA Hubble Space Telescope has captured this view of the dwarf galaxy UGC 5497, which looks a bit like salt dashed on black velvet in this image.

The object is a compact blue dwarf galaxy that is infused with newly formed clusters of stars. The bright, blue stars that arise in these clusters help to give the galaxy an overall bluish appearance that lasts for several million years until these fast-burning stars explode as supernovae.

UGC 5497 is considered part of the M 81 group of galaxies, which is located about 12 million light-years away in the constellation Ursa Major (The Great Bear). UGC 5497 turned up in a ground-based telescope survey back in 2008 looking for new dwarf galaxy candidates associated with Messier 81.

According to the leading cosmological theory of galaxy formation, called Lambda Cold Dark Matter, there should be far more satellite dwarf galaxies associated with big galaxies like the Milky Way and Messier 81 than are currently known. Finding previously overlooked objects such as this one has helped cut into the expected tally — but only by a small amount.

Astrophysicists therefore remain puzzled over the so-called "missing satellite" problem.

The field of view in this image, which is a combination of visible and infrared exposures from Hubble’s Advanced Camera for Surveys, is approximately 3.4 by 3.4 arcminutes.


4 June 2012

A bright spark in a nearby spiral galaxy

This image, taken by the NASA/ESA Hubble Space Telescope, shows a detailed view of the spiral arms on one side of the galaxy Messier 99. Messier 99 is a so-called grand design spiral, with long, large and clearly defined spiral arms — giving it a structure somewhat similar to the Milky Way.

Lying around 50 million light-years away, Messier 99 is one of over a thousand galaxies that make up the Virgo Cluster, the closest cluster of galaxies to us. Messier 99 itself is relatively bright and large, meaning it was one of the first galaxies to be discovered, way back in the 18th century. This earned it a place in Charles Messier’s famous catalogue of astronomical objects.

In recent years, a number of unexplained phenomena in Messier 99 have been studied by astronomers. Among these is the nature of one of the brighter stars visible in this image. Catalogued as PTF 10fqs, and visible as a yellow-orange star in the top-left corner of this image, it was first spotted by the Palomar Transient Facility, which scans the skies for sudden changes in brightness (or transient phenomena, to use astronomers’ jargon). These can be caused by different kinds of event, including variable stars and supernova explosions.

What is unusual about PTF 10fqs is that it has so far defied classification: it is brighter than a nova (a bright eruption on a star’s surface), but fainter than a supernova (the explosion that marks the end of life for a large star). Scientists have offered a number of possible explanations, including the intriguing suggestion that it could have been caused by a giant planet plunging into its parent  star.

This Hubble image was made in June 2010, during the period when the outburst was fading, so PTF 10fqs’s location could be pinpointed with great precision. These measurements will allow other telescopes to home in on the star in future, even when the afterglow of the outburst has faded to nothing.

A version of this image of M 99 was entered into the Hubble’s Hidden Treasures Competition by contestant Matej Novak. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition is now closed and the winners will be announced soon.


« Previous 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 Next »
Showing 101 to 120 of 230