Picture of the Week

Also see our pictures of the week on eso.org.
22 December 2014

The beautiful side of IC 335

This new NASA/ESA Hubble Space Telescope image shows the galaxy IC 335 in front of a backdrop of distant galaxies. IC 335 is part of a galaxy group containing three other galaxies, and located in the Fornax Galaxy Cluster 60 million light-years away.

As seen in this image, the disc of IC 335 appears edge-on from the vantage point of Earth. This makes it harder for astronomers to classify it, as most of the characteristics of a galaxy’s morphology — the arms of a spiral or the bar across the centre — are only visible on its face. Still, the 45 000 light-year-long galaxy could be classified as an S0 type.

These lenticular galaxies are an intermediate state in galaxy morphological classification schemes between true spiral and elliptical galaxies. They have a thin stellar disc and a bulge, like spiral galaxies, but in contrast to typical spiral galaxies they have used up most of the interstellar medium. Only a few new stars can be created out of the material that is left and the star formation rate is very low. Hence, the population of stars in S0 galaxies consists mainly of aging stars, very similar to the star population in elliptical galaxies.

As S0 galaxies have only ill-defined spiral arms they are easily mistaken for elliptical galaxies if they are seen inclined face-on or edge-on as IC 335 here. And indeed, despite the morphological differences between S0 and elliptical class galaxies, they share a some common characteristics, like typical sizes and spectral features.

Both classes are also early-type galaxies, as they are evolving passively. However, elliptical galaxies may be passively evolving when we observe them, but they had violent interactions with other galaxies in their past. Whereas S0 galaxies are either aging and fading spiral galaxies, which never had any interactions with other galaxies, or they are the aging result of a single merger between two spiral galaxies in the past. The exact nature of these galaxies is still a matter of debate.

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15 December 2014

A messy star factory

This sprinkle of cosmic glitter is a blue compact dwarf galaxy known as Markarian 209. Galaxies of this type are blue-hued, compact in size, gas-rich, and low in heavy elements. They are often used by astronomers to study star formation, as their conditions are similar to those thought to exist in the early Universe.

Markarian 209 in particular has been studied extensively. It is filled with diffuse gas and peppered with star-forming regions towards its core. This image captures it undergoing a particularly dramatic burst of star formation, visible as the lighter blue cloudy region towards the top right of the galaxy. This clump is filled with very young and hot newborn stars.

This galaxy was initially thought to be a young galaxy undergoing its very first episode of star formation, but later research showed that Markarian 209 is actually very old, with an almost continuous history of forming new stars. It is thought to have never had a dormant period — a period during which no stars were formed — lasting longer than 100 million years.

The dominant population of stars in Markarian 209 is still quite young, in stellar terms, with ages of under 3 million years. For comparison, the Sun is some 4.6 billion years old, and is roughly halfway through its expected lifespan.

The observations used to make this image were taken using Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys, and span the ultraviolet, visible, and infrared parts of the spectrum. A scattering of other bright galaxies can be seen across the frame, including the bright golden oval that could, due to a trick of perspective, be mistaken as part of Markarian 209 but is in fact a background galaxy.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.

Links:


8 December 2014

All that glitters

This striking new NASA/ESA Hubble Space Telescope image shows a glittering bauble named Messier 92. Located in the northern constellation of Hercules, this globular cluster — a ball of stars that orbits a galactic core like a satellite — was first discovered by astronomer Johann Elert Bode in 1777.

Messier 92 is one of the brightest globular clusters in the Milky Way, and is visible to the naked eye under good observing conditions. It is very tightly packed with stars, containing some 330 000 stars in total. As is characteristic of globular clusters, the predominant elements within Messier 92 are hydrogen and helium, with only traces of others. It is actually what is known as an Oosterhoff type II (OoII) globular cluster, meaning that it belongs to a group of metal-poor clusters — to astronomers, metals are all elements heavier than hydrogen and helium.

By exploring the composition of globulars like Messier 92, astronomers can figure out how old these clusters are. As well as being bright, Messier 92 is also old, being one of the oldest star clusters in the Milky Way, with an age almost the same as the age of the Universe.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Gilles Chapdelaine.

Links


1 December 2014

This is no supermodel spiral

The NASA/ESA Hubble Space Telescope observes some of the most beautiful galaxies in our skies — spirals sparkling with bright stellar nurseries (heic1403), violent duos ripping gas and stars away from one another as they tangle together (heic1311), and ethereal irregular galaxies that hang like flocks of birds suspended in the blackness of space (heic1114, heic1207).

However, galaxies, like humans, are not all supermodels. This little spiral, known as NGC 4102, has a different kind of appeal, with its tightly-wound spiral arms and understated, but charming, appearance.

NGC 4102 lies in the northern constellation of Ursa Major (The Great Bear). It contains what is known as a LINER, or low-ionization nuclear emission-line region, meaning that its nucleus emits particular types of radiation — specifically, emission from weakly-ionised or neutral atoms of certain elements. Even in this sense, NGC 4102 is not special; around one third of all nearby galaxies are thought to be LINER galaxies.

Many LINER galaxies also contain intense regions of star formation. This is thought to be intrinsically linked to their centres but just why is still a mystery for astronomers — either the starbursts pour fuel inwards to fuel the LINERs, or this active central region triggers the starbursts. NGC 4102 does indeed contain a starburst region towards its centre, where stars are being created at a rate much more furious than in a normal galaxy. This star formation is taking place within a small rotating disc, around 1000 light-years in diameter and with a mass some three billion times the mass of the Sun.

This image uses infrared and visible observations taken using Hubble’s Wide Field Planetary Camera 2. A version of this image was submitted to the Hubble's Hidden Treasures image processing competition by contestant Renaud Houdinet.

A team of astronomers led by Stephen Smartt of Queen's University Belfast, the Principal Investigator for the observations making up this image, have spent the last 15 years searching for the progenitor stars of supernovae in galaxy images like this. A recent review article explores some of the results from such studies.

Link


24 November 2014

A slashing smudge across the sky

The galaxy cutting dramatically across the frame of this NASA/ESA Hubble Space Telescope image is a slightly warped dwarf galaxy known as UGC 1281. Seen here from an edge-on perspective, this galaxy lies roughly 18 million light-years away in the constellation of Triangulum (The Triangle).

The bright companion to the lower left of UGC 1281 is the small galaxy PGC 6700, officially known as 2MASX J01493473+3234464. Other prominent stars belonging to our own galaxy, the Milky Way, and more distant galaxies can be seen scattered throughout the sky.

The side-on view we have of UGC 1281 makes it a perfect candidate for studies into how gas is distributed within galactic halos — the roughly spherical regions of diffuse gas extending outwards from a galaxy’s centre. Astronomers have studied this galaxy to see how its gas vertically extends out from its central plane, and found it to be a quite typical dwarf galaxy. However, it does have a slightly warped shape to its outer edges, and is forming stars at a particularly low rate.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Luca Limatola.

Links


17 November 2014

A spiral in a furnace

This new Hubble image is a snapshot of NGC 986 — a barred spiral galaxy discovered in 1828 by James Dunlop. This close-up view of the galaxy was captured by Hubble’s Wide Field and Planetary Camera 2 (WFPC2).

NGC 986 is found in the constellation of Fornax (The Furnace), located in the southern sky. NGC 986 is a bright, 11th-magnitude galaxy sitting around 56 million light-years away, and its golden centre and barred swirling arms are clearly visible in this image.

Barred spiral galaxies are spiral galaxies with a central bar-shaped structure composed of stars. NGC 986 has the characteristic S-shaped structure of this type of galactic morphology. Young blue stars can be seen dotted amongst the galaxy’s arms and the core of the galaxy is also aglow with star formation.

To the top right of this image the stars appear a little fuzzy. This is because a gap in the Hubble data was filled in with data from ground-based telescopes. Although the view we see in this filled in patch is accurate, the resolution of the stars is no match for Hubble’s clear depiction of the spiral galaxy.


10 November 2014

Hubble reveals a super-rich galactic neighbourhood

This new image from the NASA/ESA Hubble Space Telescope shows the super-rich galaxy cluster Abell 1413. Located between the constellations of Leo (The Lion) and Coma Berenices, the cluster is over 2 billion light-years from Earth. This image is dominated by a large and highly elliptical galaxy called MCG+04-28-097, with a halo of stars extending for more than 6.5 million light-years [1].

Abell 1413 is part of the Abell catalogue, a collection of over 4000 rich clusters of galaxies fairly close to Earth — at least from a cosmological perspective — their light took less than 3 billion years to reach us. The clusters are called rich due to the huge number of galaxies they play host to. Abell 1413 is observed to contain more than 300 galaxies held together by the immense gravity of the cluster.

The strong interactions between these galaxies cause the material in the cluster to be heated to extremely high temperatures of almost 100 million degrees. Because of this, the cluster emits very strong X-ray radiation.

Visible distortions in the image can be seen in the form of arcs, caused by gravitational lensing [2].

This image was created from optical and near-infrared exposures taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys (ACS). A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.

Notes

[1] The galaxies at the centre of Abell 1413 are found to be very highly elliptical whereas those at the periphery are more spherical.

[2] Gravitational lensing occurs when the intense gravity of the cluster bends space-time around it, causing a range of bizarre and beautiful optical phenomena for galaxies located in the background.


3 November 2014

A hazy nebula

This new image from Hubble’s Wide Field Planetary Camera 2 showcases NGC 1501, a complex planetary nebula located in the large but faint constellation of Camelopardalis (The Giraffe).

Discovered by William Herschel in 1787, NGC 1501 is a planetary nebula that is just under 5000 light-years away from us. Astronomers have modelled the three-dimensional structure of the nebula, finding it to be a cloud shaped as an irregular ellipsoid filled with bumpy and bubbly regions. It has a bright central star that can be seen easily in this image, shining brightly from within the nebula’s cloud. This bright pearl embedded within its glowing shell inspired the nebula’s popular nickname: the Oyster Nebula.

While NGC 1501's central star blasted off its outer shell long ago, it still remains very hot and luminous, although it is quite tricky for observers to spot through modest telescopes. This star has actually been the subject of many studies by astronomers due to one very unusual feature: it seems to be pulsating, varying quite significantly in brightness over a typical timescale of just half an hour. While variable stars are not unusual, it is uncommon to find one at the heart of a planetary nebula.

It is important to note that the colours in this image are arbitrary.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Marc Canale.

Links


27 October 2014

A galaxy on the edge

This spectacular image was captured by the NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys (ACS). The bright streak slicing across the frame is an edge-on view of galaxy NGC 4762, and a number of other distant galaxies can be seen scattered in the background.

NGC 4762 lies about 58 million light-years away in the constellation of Virgo (The Virgin). It is part of the Virgo Cluster, hence its alternative designation of VCC 2095 for Virgo Cluster Catalogue entry. This catalogue is a listing of just over 2000 galaxies in the area of the Virgo Cluster. The Virgo Cluster is actually prominently situated, and lies at the centre of the larger Virgo supercluster, of which our galaxy group, the Local Group, is a member.

Previously thought to be a barred spiral galaxy, NGC 4762 has since been found to be a lenticular galaxy, a kind of intermediate step between an elliptical and a spiral. The edge-on view that we have of this particular galaxy makes it difficult to determine its true shape, but astronomers have found the galaxy to consist of four main components — a central bulge, a bar, a thick disc and an outer ring.

The galaxy's disc is asymmetric and warped, which could potentially be explained by NGC 4762 violently cannibalising a smaller galaxy in the past. The remains of this former companion may then have settled within NGC 4762's disc, redistributing the gas and stars and so changing the disc's morphology.

NGC 4762 also contains a Liner-type Active Galactic Nucleus, a highly energetic central region. This nucleus is detectable due to its particular spectral line emission, which acts as a type of "atomic fingerprint", allowing astronomers to measure the composition of the region.


20 October 2014

The whirling disc of NGC 4526

This neat little galaxy is known as NGC 4526. Its dark lanes of dust and bright diffuse glow make the galaxy appear to hang like a halo in the emptiness of space in this new image from the NASA/ESA Hubble Space Telescope.

Although this image paints a picture of serenity, the galaxy is anything but. It is one of the brightest lenticular galaxies known, a category that lies somewhere between spirals and ellipticals. It has hosted two known supernova explosions, one in 1969 and another in 1994, and is known to have a colossal supermassive black hole at its centre that has the mass of 450 million Suns.

NGC 4526 is part of the Virgo cluster of galaxies. Ground-based observations of galaxies in this cluster have revealed that a quarter of these galaxies seem to have rapidly rotating discs of gas at their centres. The most spectacular of these is this galaxy, NGC 4526, whose spinning disc of gas, dust, and stars reaches out uniquely far from its heart, spanning some 7% of the galaxy's entire radius.

This disc is moving incredibly fast, spinning at more than 250 kilometres per second. The dynamics of this quickly whirling region were actually used to infer the mass of NGC 4526’s central black hole — a technique that had not been used before to constrain a galaxy’s central black hole.

This image was taken using Hubble’s Wide Field Planetary Camera 2. 

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt. Hidden Treasures was an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public.


13 October 2014

Turquoise-tinted plumes in the Large Magellanic Cloud

The brightly glowing plumes seen in this image are reminiscent of an underwater scene, with turquoise-tinted currents and nebulous strands reaching out into the surroundings.

However, this is no ocean. This image actually shows part of the Large Magellanic Cloud (LMC), a small nearby galaxy that orbits our galaxy, the Milky Way, and appears as a blurred blob in our skies. The NASA/ESA Hubble Space Telescope has peeked many times into this galaxy, releasing stunning images of the whirling clouds of gas and sparkling stars (opo9944a, heic1301, potw1408a).

This image shows part of the Tarantula Nebula's outskirts. This famously beautiful nebula, located within the LMC, is a frequent target for Hubble (heic1206, heic1402). 

In most images of the LMC the colour is completely different to that seen here. This is because, in this new image, a different set of filters was used. The customary R filter, which selects the red light, was replaced by a filter letting through the near-infrared light. In traditional images, the hydrogen gas appears pink because it shines most brightly in the red. Here however, other less prominent emission lines dominate in the blue and green filters.

This data is part of the Archival Pure Parallel Project (APPP), a project that gathered together and processed over 1000 images taken using Hubble’s Wide Field Planetary Camera 2, obtained in parallel with other Hubble instruments. Much of the data in the project could be used to study a wide range of astronomical topics, including gravitational lensing and cosmic shear, exploring distant star-forming galaxies, supplementing observations in other wavelength ranges with optical data, and examining star populations from stellar heavyweights all the way down to solar-mass stars.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Josh Barrington.


6 October 2014

A dusty spiral in Virgo

This magnificent new image taken with the NASA/ESA Hubble Space Telescope shows the edge-on spiral galaxy NGC 4206, located about 70 million light-years away from Earth in the constellation of Virgo.

Captured here are vast streaks of dust, some of which are obscuring the central bulge, which can just be made out in the centre of the galaxy. Towards the edges of the galaxy, the scattered clumps, which appear blue in this image, mark areas where stars are being born. The bulge, on the other hand, is composed mostly of much older, redder stars, and very little star formation takes place.

NGC 4206 was imaged as part of a Hubble snapshot survey of nearby edge-on spiral galaxies to measure the effect that the material between the stars — known as the interstellar medium — has on light as it travels through it. Using its Advanced Camera for Surveys, Hubble can reveal information about the dusty material and hydrogen gas in the cold parts of the interstellar medium. Astronomers are then able to map the absorption and scattering of light by the material — an effect known as extinction — which causes objects to appear redder to us, the observers.

NGC 4206 is visible with most moderate amateur telescopes at 13th magnitude. It was discovered by Hanoverian-born British astronomer, William Herschel on 17 April 1784.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.


29 September 2014

Snapshot of a shedding star

In this new Hubble image, the strikingly luminous star AG Carinae — otherwise known as HD 94910 — takes centre stage. Found within the constellation of Carina in the southern sky, AG Carinae lies 20 000 light-years away, nestled in the Milky Way.

AG Carinae is classified as a Luminous Blue Variable. These rare objects are massive evolved stars that will one day become Wolf-Rayet Stars — a class of stars that are tens of thousands to several million times as luminous as the Sun. They have evolved from main sequence stars that were twenty times the mass of the Sun.

Stars like AG Carinae lose their mass at a phenomenal rate. This loss of mass is due to powerful stellar winds with speeds of up to 7 million km/hour. These powerful winds are also responsible for the shroud of material visible in this image. The winds exert enormous pressure on the clouds of interstellar material expelled by the star and force them into this shape.

Despite HD 94910’s intense luminosity, it is not visible with the naked eye as much of its output is in the ultraviolet.

This image was taken with the Wide Field and Planetary Camera 2 (WFPC2), that was installed on Hubble during the Shuttle mission STS-61 and was Hubble’s workhorse for many years. It is worth noting that the bright glare at the centre of the image is not the star itself. The star is tiny at this scale and hidden within the saturated region. The white cross is also not an astronomical phenomenon but rather an effect of the telescope.


22 September 2014

Jets and explosions in NGC 7793

This new image from the NASA/ESA Hubble Space Telescope shows NGC 7793, a spiral galaxy in the constellation of Sculptor some 13 million light-years away from Earth. NGC 7793 is one of the brightest galaxies in the Sculptor Group, and one of the closest groups of galaxies to the Local Group — the group of galaxies containing our galaxy, the Milky Way and the Magellanic Clouds.

The image shows NGC 7793’s spiral arms and small central bulge. Unlike some other spirals, NGC 7793 doesn’t have a very pronounced spiral structure, and its shape is further muddled by the mottled pattern of dark dust that stretches across the frame. The occasional burst of bright pink can be seen in the galaxy, highlighting stellar nurseries containing newly-forming baby stars.

Although it may look serene and beautiful from our perspective, this galaxy is actually a very dramatic and violent place. Astronomers have discovered a powerful microquasar within NGC 7793 — a system containing a black hole actively feeding on material from a companion star. While many full-sized quasars are known at the cores of other galaxies, it is unusual to find a quasar in a galaxy’s disc rather than at its centre.

Micro-quasars are almost like scale models — they allow astronomers to study quasars in detail. As material falls inwards towards this black hole, it creates a swirling disc around it. Some of the infalling gas is propelled violently outwards at extremely high speeds, creating jets streaking out into space in opposite directions. In the case of NGC 7793, these jets are incredibly powerful, and are in the process of creating an expanding bubble of hot gas some 1000 light-years across.


15 September 2014

An interacting colossus

This picture, taken by the NASA/ESA Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2), shows a galaxy known as NGC 6872 in the constellation of Pavo (The Peacock). Its unusual shape is caused by its interactions with the smaller galaxy that can be seen just above NGC 6872, called IC 4970. They both lie roughly 300 million light-years away from Earth.

From tip to tip, NGC 6872 measures over 500 000 light-years across, making it the second largest spiral galaxy discovered to date. In terms of size it is beaten only by NGC 262, a galaxy that measures a mind-boggling 1.3 million light-years in diameter! To put that into perspective, our own galaxy, the Milky Way, measures between 100 000 and 120 000 light-years across, making NGC 6872 about five times its size.

The upper left spiral arm of NGC 6872 is visibly distorted and is populated by star-forming regions, which appear blue on this image. This may have been be caused by IC 4970 recently passing through this arm — although here, recent means 130 million years ago! Astronomers have noted that NGC 6872 seems to be relatively sparse in terms of free hydrogen, which is the basis material for new stars, meaning that if it weren’t for its interactions with IC 4970, NGC 6872 might not have been able to produce new bursts of star formation.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.


8 September 2014

A spattering of blue

Far beyond the stars in the constellation of Leo (The Lion) is irregular galaxy IC 559.

IC 559 is not your everyday galaxy. With its irregular shape and bright blue spattering of stars, it is a fascinating galactic anomaly. It may look like sparse cloud, but it is in fact full of gas and dust which is spawning new stars.

Discovered in 1893, IC 559 lacks the symmetrical spiral appearance of some of its galactic peers and not does not conform to a regular shape. It is actually classified as a “type Sm” galaxy — an irregular galaxy with some evidence for a spiral structure.

Irregular galaxies make up about a quarter of all known galaxies and do not fall into any of the regular classes of the Hubble sequence. Most of these uniquely shaped galaxies were not always so — IC 559 may have once been a conventional spiral galaxy that was then distorted and twisted by the gravity of a nearby cosmic companion.

This image, captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3, combines a wide range of wavelengths spanning the ultraviolet, optical, and infrared parts of the spectrum.


1 September 2014

Spiral in Serpens

This new NASA/ESA Hubble Space Telescope image shows a beautiful spiral galaxy known as PGC 54493, located in the constellation of Serpens (The Serpent). This galaxy is part of a galaxy cluster that has been studied by astronomers exploring an intriguing phenomenon known as weak gravitational lensing.

This effect, caused by the uneven distribution of matter (including dark matter) throughout the Universe, has been explored via surveys such as the Hubble Medium Deep Survey. Dark matter is one of the great mysteries in cosmology. It behaves very differently from ordinary matter as it does not emit or absorb light or other forms of electromagnetic energy — hence the term "dark".

Even though we cannot observe dark matter directly, we know it exists. One prominent piece of evidence for the existence of this mysterious matter is known as the "galaxy rotation problem". Galaxies rotate at such speeds and in such a way that ordinary matter alone — the stuff we see — would not be able to hold them together. The amount of mass that is "missing" visibly is dark matter, which is thought to make up some 27% of the total contents of the Universe, with dark energy and normal matter making up the rest. PGC 55493 has been studied in connection with an effect known as cosmic shearing. This is a weak gravitational lensing effect that creates tiny distortions in images of distant galaxies.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Judy Schmidt.

Links


25 August 2014

Light and dark

This new NASA/ESA Hubble Space Telescope image shows a variety of intriguing cosmic phenomena.

Surrounded by bright stars, towards the upper middle of the frame we see a small young stellar object (YSO) known as SSTC2D J033038.2+303212. Located in the constellation of Perseus, this star is in the early stages of its life and is still forming into a fully grown star. In this view from Hubble’s Advanced Camera for Surveys (ACS) it appears to have a murky chimney of material emanating outwards and downwards, framed by bright bursts of gas flowing from the star itself. This fledgling star is actually surrounded by a bright disc of material swirling around it as it forms — a disc that we see edge-on from our perspective.

However, this small bright speck is dwarfed by its cosmic neighbour towards the bottom of the frame, a clump of bright, wispy gas swirling around as it appears to spew dark material out into space. The bright cloud is a reflection nebula known as [B77] 63, a cloud of interstellar gas that is reflecting light from the stars embedded within it. There are actually a number of bright stars within [B77] 63, most notably the emission-line star LkHA 326, and its very near neighbour LZK 18.

These stars are lighting up the surrounding gas and sculpting it into the wispy shape seen in this image. However, the most dramatic part of the image seems to be a dark stream of smoke piling outwards from [B77] 63 and its stars — a dark nebula called Dobashi 4173. Dark nebulae are incredibly dense clouds of pitch-dark material that obscure the patches of sky behind them, seemingly creating great rips and eerily empty chunks of sky. The stars speckled on top of this extreme blackness actually lie between us and Dobashi 4173.

Link


18 August 2014

A silver needle in the sky

This stunning new image from the NASA/ESA Hubble Space Telescope shows part of the sky in the constellation of Canes Venatici (The Hunting Dogs).

Although this region of the sky is not home to any stellar heavyweights, being mostly filled with stars of average brightness, it does contain five Messier objects and numerous intriguing galaxies — including NGC 5195, a small barred spiral galaxy considered to be one of the most beautiful galaxies visible, and its nearby interacting partner the Whirlpool Galaxy (heic0506a). The quirky Sunflower Galaxy is another notable galaxy in this constellation, and is one of the largest and brightest edge-on galaxies in our skies.

Joining this host of characters is spiral galaxy NGC 4244, nicknamed the Silver Needle Galaxy, shown here in a new image from Hubble. This galaxy spans some 65 000 light-years and lies around 13.5 million light-years away. It appears as a wafer-thin streak across the sky, with its loosely wound spiral arms hidden from view as we observe the galaxy side on. It is part of a group of galaxies known as the M94 Group [1].

Numerous bright clumps of gas can be seen scattered across its length, along with dark dust lanes surrounding the galaxy’s core. NGC 4244 also has a bright star cluster at its centre. Although we can make out the galaxy’s bright central region and star-spattered arms, we cannot see any more intricate structure due to the galaxy’s position; from Earth, we see it stretched out as a flattened streak across the sky.

A number of different observations were pieced together to form this mosaic, and gaps in Hubble’s coverage have been filled in using ground-based data. The Hubble observations were taken as part of the GHOSTS survey, which is scanning nearby galaxies to explore how they and their stars formed to get a more complete view of the history of the Universe.

Notes

[1] Our home group, containing the Milky Way and many others, is known as the Local Group. M94 is relatively close to the Local Group.


11 August 2014

Galactic soup

This new NASA/ESA Hubble Space Telescope image shows a whole host of colourful and differently shaped galaxies; some bright and nearby, some fuzzy, and some so far from us they appear as small specks in the background sky.

The most prominent characters are the two galaxies on the left — 2MASX J16133219+5103436 at the bottom, and its blue-tinted companion SDSS J161330.18+510335 at the top. The latter is slightly closer to us than its partner, but the two are still near enough to one another to interact. Together, the two make up a galactic pair named Zw I 136.

Both galaxies in this pair have disturbed shapes and extended soft halos. They don’t seem to conform to our view of a “typical” galaxy — unlike the third bright object in this frame, a side-on spiral seen towards the right of the image.

Astronomers classify galaxies according to their appearance and their shape. The most famous classification scheme is known as the Hubble sequence, devised by its namesake Edwin Hubble. One of the great questions in galaxy evolution is how interactions between galaxies trigger waves of star formation, and why these stars then abruptly stop forming. Interacting pairs like this one present astronomers with perfect opportunities to investigate this.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Judy Schmidt.


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