Picture of The Week
Invisible X-rays
Mon, 18 Mar 2019 06:00:00 +0100

This fuzzy orb of light is a giant elliptical galaxy filled with an incredible 200 billion stars. Unlike spiral galaxies, which have a well-defined structure and boast picturesque spiral arms, elliptical galaxies appear fairly smooth and featureless. This is likely why this galaxy, named Messier 49, was discovered by French astronomer Charles Messier in 1771. At a distance of 56 million light-years, and measuring 157 000 light-years across, M49 was the first member of the Virgo Cluster of galaxies to be discovered, and it is more luminous than any other galaxy at its distance or nearer.

Elliptical galaxies tend to contain a larger portion of older stars than spiral galaxies and also lack young blue stars. Messier 49 itself is very yellow, which indicates that the stars within it are mostly older and redder than the Sun. In fact, the last major episode of star formation was about six billion years ago — before the Sun was even born!

Messier 49 is also rich in globular clusters; it hosts about 6000, a number that dwarfs the 150 found in and around the Milky Way. On average, these clusters are 10 billion years old. Messier 49 is also known to host a supermassive black hole at its centre with the mass of more than 500 million Suns, identifiable by the X-rays pouring out from the heart of the galaxy (as this Hubble image comprises infrared observations, these X-rays are not visible here).

Nebulous, but no nebula
Mon, 11 Mar 2019 06:00:00 +0100

This Hubble Picture of the Week shows Messier 28, a globular cluster in the constellation of Sagittarius (The Archer), in jewel-bright detail. It is about 18 000 light-years away from Earth.

As its name suggests, this cluster belongs to the Messier catalogue of objects — however, when astronomer Charles Messier first added Messier 28 to his list in 1764, he catalogued it incorrectly, referring to it as a “[round] nebula containing no star”. While today we know nebulae to be vast, often glowing clouds of interstellar dust and ionised gases, until the early twentieth century a nebula represented any astronomical object that was not clearly localised and isolated. Any unidentified hazy light source could be called a nebula. In fact, all 110 of the astronomical objects identified by Messier were combined under the title of the Catalogue of Nebulae and Star Clusters. He classified many objects as diverse as star clusters and supernova remnants as nebulae. This includes Messier 28, pictured here — which, ironically, is actually a star cluster.

Messier’s mistake is understandable. Whilst Messier 28 is easily recognisable as a globular stellar cluster in this image, it is far less recognisable from Earth. Even with binoculars it is only visible very faintly, as the distorting effects of the Earth’s atmosphere reduce this luminous ancient cluster to a barely visible smudge in the sky. One would need larger telescopes to resolve single stars in Messier 28. Fortunately, from space Hubble allows Messier 28 to be seen in all its beauty — far more than a faint, shapeless, nebulous cloud.

Colliding galaxies
Mon, 04 Mar 2019 06:00:00 +0100

Located in the constellation of Hercules, about 230 million light-years away, NGC 6052 is a pair of colliding galaxies. They were first discovered in 1784 by William Herschel and were originally classified as a single irregular galaxy because of their odd shape. However, we now know that NGC 6052 actually consists of two galaxies that are in the process of colliding. This particular image of NGC 6052 was taken using the Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope.

A long time ago gravity drew the two galaxies together into the chaotic state we now observe. Stars from within both of the original galaxies now follow new trajectories caused by the new gravitational effects. However, actual collisions between stars themselves are very rare as stars are very small relative to the distances between them (most of a galaxy is empty space). Eventually things will settle down and one day the two galaxies will have fully merged to form a single, stable galaxy.

Our own galaxy, the Milky Way, will undergo a similar collision in the future with our nearest galactic neighbour, the Andromeda Galaxy. Although this is not expected to happen for around 4 billion years so there is nothing to worry about just yet.

This object was previously observed by Hubble with its old WFPC2 camera. That image was released in 2015.

The two mysterious populations of NGC 2419
Mon, 25 Feb 2019 06:00:00 +0100

Globular clusters like NGC 2419, visible in this image taken with the NASA/ESA Hubble Space Telescope, are not only beautiful, but also fascinating. They are spherical groups of stars which orbit the centre of a galaxy; in the case of NGC 2419, that galaxy is the Milky Way. NGC 2419 can be found around 300 000 light-years from the Solar System, in the constellation Lynx (the Lynx).

The stars populating globular clusters are very similar to one another, with similar properties such as metallicity. The similarity of these stellar doppelgängers is due to their formation early in the history of the galaxy. As the stars in a globular cluster all formed at around the same time, they tend to display reasonably homogeneous properties. It was believed that this similarity also extended to the stellar helium content; that is, it was thought that all stars in a globular cluster would contain comparable amounts of helium.

However, Hubble’s observations of NGC 2419 have shown that this is not always the case. This surprising globular cluster turns out to be made up of two separate populations of red giant stars, one of which is unusually helium-rich. Other elements within the different stars in NGC 2419 vary too — nitrogen in particular. On top of this, these helium-rich stars were found to be predominantly in the centre of the globular cluster, and to be rotating. These observations have raised questions about the formation of globular clusters; did these two drastically different groups of stars form together? Or did this globular cluster come into being by a different route entirely?

A storm is coming
Mon, 18 Feb 2019 06:00:00 +0100

Since Pluto’s status-change from fully-fledged planet to dwarf planet, Neptune holds the title of outermost planet in the Solar System. This new image of the planet was made during Hubble’s Outer Planet Atmosphere Legacy (OPAL) programme, under which it has observed the four outermost planets, including Neptune, on a yearly basis since 2014.

The observations of Neptune carried out in September and November 2018 show the first evidence of a huge storm brewing, with the discovery of a new northern Great Dark Spot (visible here to the upper left of the planet’s disc, partially overlapping a large patch of white). This new dark storm is of a similar size and shape to the storm discovered in 1989 by the Voyager 2 space probe.

While the future evolution of the storm will be tracked through the continued yearly Hubble observations and also by ground-based telescopes, older OPAL observations from Hubble show that its appearance was preceded by increased cloud activity throughout the region. There are hints of the storm forming in images from as early as 2015. This slow origin process indicates that the storm developed deep within Neptune's atmosphere, pulling up dark material from its depths, and only became visible once the top of it reached higher altitudes.

Adding to Uranus’s legacy
Mon, 11 Feb 2019 06:00:00 +0100

One of the NASA/ESA Hubble Space Telescope’s many scientific objectives is to study the planets within the Solar System — and in past years, our system’s outer planets have been observed several times as part of Hubble’s Outer Planet Atmosphere Legacy (OPAL) programme.

This programme has given us this new image of the planet Uranus, the seventh planet in the Solar System in order of increasing distance from the Sun. Past observations of Uranus using Hubble have led to many interesting insights about the cold ice giant; in 2006 the telescope managed to capture a shot in which the moon Ariel and its accompanying shadow were traversing the face of Uranus, and in 2011 Hubble was able to spot faint auroras in its atmosphere.

Observations made over the course of several years also allowed astronomers to study the planet’s faint ring system as its inclination changed with respect to Earth’s orbit. This new image, taken with Hubble’s Wide Field Camera 3, adds to the legacy of images already taken and will provide scientists with even more new insights into our distant neighbour.

The darkness within?
Mon, 04 Feb 2019 06:00:00 +0100

This atmospheric image shows a galaxy named Messier 85, captured in all its delicate, hazy glory by the NASA/ESA Hubble Space Telescope. Messier 85 slants through the constellation of Coma Berenices (Berenice’s Hair), and lies around 50 million light-years from Earth. It was first discovered by Charles Messier’s colleague Pierre Méchain in 1781, and is included in the Messier catalogue of celestial objects.

Messier 85 is intriguing — its properties lie somewhere between those of a lenticular and an elliptical galaxy, and it appears to be interacting with two of its neighbours: the beautiful spiral NGC 4394, located out of frame to the upper left, and the small elliptical MCG 3-32-38, located out of frame to the centre bottom.

The galaxy contains some 400 billion stars, most of which are very old. However, the central region hosts a population of relatively young stars of just a few billion years in age; these stars are thought to have formed in a late burst of star formation, likely triggered as Messier 85 merged with another galaxy over four billion years ago. Messier 85 has a further potentially strange quality. Almost every galaxy is thought to have a supermassive black hole at its centre, but from measurements of the velocities of stars in this galaxy, it is unclear whether Messier 85 contains such a black hole.

This image combines infrared, visible and ultraviolet observations from Hubble’s Wide Field Camera 3.

Wading through water
Mon, 28 Jan 2019 06:00:00 +0100

This striking image combines data gathered with the Advanced Camera for Surveys, installed on the NASA/ESA Hubble Space Telescope and data from the Subaru Telescope in Hawaii. It shows just a part of the spectacular tail emerging from a spiral galaxy nicknamed D100.

Tails such as these are created by a process known as ram-pressure stripping. Despite appearances, the space between galaxies in a cluster is far from empty; it is actually filled with superheated gas and plasma, which drags and pulls at galaxies as they move through it, a little like the resistance one experiences when wading through deep water. This can be strong enough to tear galaxies apart, and often results in objects with peculiar, bizarre shapes and features — as seen here.

D100’s eye-catching tail of gas, which stretches far beyond this image to the left, is a particularly striking example of this phenomenon. The galaxy is a member of the huge Coma cluster. The pressure from the cluster’s hot constituent plasma (known as the intracluster medium) has stripped gas from D100 and torn it away from the galaxy’s main body, and drawing it out into the plume pictured here.

Densely populated clusters such as Coma are home to thousands of galaxies. They are thus the perfect laboratories in which to study the intriguing phenomenon of ram-pressure stripping, which, as well as producing beautiful images such as this, can have a profound effect on how galaxies evolve and form new generations of stars.

Links

Peering into the past
Mon, 21 Jan 2019 06:00:00 +0100

This picture showcases a gravitational lensing system called SDSS J0928+2031. Quite a few images of this type of lensing have been featured as Pictures of the Week in past months, as NASA/ESA Hubble Space Telescope data is currently being used to research how stars form and evolve in distant galaxies.

Gravitational lensing can help astronomers study objects that would otherwise be too faint or appear too small for us to view. When a massive object — such as a massive cluster of galaxies, as seen here — distorts space with its immense gravitational field, it causes light from more distant galaxies to travel along altered and warped paths. It also amplifies the light, making it possible for us to observe and study its source.

In this image, we see two dominant elliptical galaxies near the centre of the image. The gravity from the galaxy cluster that is the home of these galaxies is acting as the aforementioned gravitational lens, allowing us to view the more distant  galaxies sitting behind them. We see the effects of this lensing as narrow, curved streaks of light surrounding both of the large galaxies.

This image was observed by Hubble as part of the Sloan Giant Arcs Survey programme.

Messier Monday
Mon, 14 Jan 2019 06:00:00 +0100

This huge ball of stars — around 100 billion in total — is an elliptical galaxy located some 55 million light-years away from us. Known as Messier 89, this galaxy appears to be perfectly spherical; this is unusual for elliptical galaxies, which tend to be elongated ellipsoids. The apparently spherical nature of Messier 89 could, however, be a trick of perspective, and be caused by its orientation relative to the Earth.

Messier 89 is slightly smaller than the Milky Way, but has a few interesting features that stretch far out into the surrounding space. One structure of gas and dust extends up to 150 000 light-years out from the galaxy’s centre, which is known to house a supermassive black hole. Jets of heated particles reach out to 100 000 light-years from the galaxy, suggesting that Messier 89 may have once been far more active — perhaps an active quasar or radio galaxy — than it is now. It is also surrounded by an extensive system of shells and plumes, which may have been caused by past mergers with smaller galaxies — and implies that Messier 89 as we know it may have formed in the relatively recent past.

Messier 89 was discovered by astronomer Charles Messier in 1781, when Messier had been cataloguing astronomical objects for 23 years — ever since he mistook a faint object in the sky for Halley’s Comet. Upon closer inspection, he realised the object was actually the Crab Nebula. To prevent other astronomers from making the same error, he decided to catalogue all the bright, deep-sky objects that could potentially be mistaken for comets. His methodical observations of the night sky led to the first comprehensive catalogue of astronomical objects: the Messier catalogue! Messier 89 holds the record for being the last ever giant elliptical to be found by Messier, and the most perfectly spherical galaxy in the entire catalogue of 110 objects.

The heart of the Lion
Mon, 07 Jan 2019 06:00:00 +0100

It might appear featureless and unexciting at first glance, but NASA/ESA Hubble Space Telescope observations of this elliptical galaxy — known as Messier 105 — show that the stars near the galaxy’s centre are moving very rapidly. Astronomers have concluded that these stars are zooming around a supermassive black hole with an estimated mass of 200 million Suns! This black hole releases huge amounts of energy as it consumes matter falling into it and causing the centre to shine far brighter than its surroundings. This system is known as an active galactic nucleus.

Hubble also surprised astronomers by revealing a few young stars and clusters in Messer 105, which was thought to be a “dead” galaxy incapable of star formation. Messier 105 is now thought to form roughly one Sun-like star every 10 000 years. Star-forming activity has also been spotted in a vast ring of hydrogen gas encircling both Messier 105 and its closest neighbour, the lenticular galaxy NGC 3384.

Messier 105 was discovered in 1781, lies about 30 million light-years away in the constellation of Leo (The Lion), and is the brightest elliptical galaxy within the Leo I galaxy group.

The smoking gun of a newborn star
Mon, 31 Dec 2018 06:00:00 +0100

In this image the NASA/ESA Hubble Space Telescope has captured the smoking gun of a newborn star, the Herbig–Haro objects numbered 7 to 11 (HH 7–11). These five objects, visible in blue in the top centre of the image, lie within NGC 1333, a reflection nebula full of gas and dust found about a thousand light-years away from Earth.

Herbig-Haro objects like HH 7–11 are transient phenomena. Travelling away from the star that created them, at a speed of up to 250 000 kilometres per hour they disappear into nothingness within a few tens of thousands of years. The young star that is the source of HH 7-11 is called SVS 13 and all five objects are moving away from SVS 13 toward the upper left. The current distance between HH 7 and SVS 13 is about 20 000 times the distance between Earth and the Sun.

Herbig–Haro objects are formed when jets of ionised gas ejected by a young star collide with nearby clouds of gas and dust at high speeds. The Herbig-Haro objects visible in this image are no exception to this and were formed when the jets from the newborn star SVS 13 collided with the surrounding clouds. These collisions created the five brilliant clumps of light within the reflection nebula.

Climbing the cosmic distance ladder
Mon, 24 Dec 2018 06:00:00 +0100

This image from the NASA/ESA Hubble Space Telescope reveals an ancient, glimmering ball of stars called NGC 1466. It is a globular cluster — a gathering of stars all held together by gravity — that is slowly moving through space on the outskirts of the Large Magellanic Cloud, one of our closest galactic neighbours.

NGC 1466 certainly is one for extremes. It has a mass equivalent to roughly 140 000 Suns and an age of around 13.1 billion years, making it almost as old as the Universe itself. This fossil-like relic from the early Universe lies some 160 000 light-years away from us.

Nestled within this ancient time capsule are 49 known RR Lyrae variable stars, which are indispensable tools for measuring distances in the Universe. These variable stars have well-defined luminosities, meaning that astronomers know the total amount of energy they emit. By comparing this known luminosity to how bright the stars appear in the sky, their distance can be easily calculated. Astronomical objects such as this are known as standard candles, and are fundamental to the so-called cosmic distance ladder.

Hubble opens its eye again
Mon, 17 Dec 2018 06:00:00 +0100

For three weeks in October, Hubble’s eyes on the Universe closed. On the evening of Friday 5 October, the orbiting observatory put itself into safe mode after one of its gyroscopes failed. The telescope stopped making science observations, oriented its solar panels toward the Sun, and waited for further instructions from the ground. Within hours the ground control team had activated a backup gyroscope. However, when that gyroscope did not work correctly, the long, hard work to get the telescope exploring the Universe once again began in earnest.

The Hubble team had either to figure out how to get this backup gyroscope working, or to turn to a previously developed and tested one-gyroscope mode, which is proven to work. It took weeks of creative thinking, repeated tests, and minor setbacks to solve the problem of the misbehaving gyroscope.

Members of the Hubble operations team and of the review board suspected there might be some sort of obstruction in the gyroscope affecting its readings. Attempting to dislodge such a blockage, the team repeatedly tried switching the gyroscope between different operational modes and rotating the spacecraft by large amounts. In response, the extremely high rotation rates from the gyroscope gradually fell until they were close to normal. Encouraged but cautious, the team uploaded new software safeguards to Hubble to protect the telescope in case the gyroscope should again report unduly high rates, and then sent the telescope through some practice manoeuvres to simulate real science observations. They kept a close watch to make sure everything on the spacecraft performed correctly. It did.

In the early morning of 27 October Hubble captured its first image since slipping into safe mode at the beginning of the month. The observations targeted star-forming galaxies 11 billion light-years away in the constellation Pegasus. Astronomers hope to use observations like this to answer the question of how the Universe was reionised between 150 million and one billion years after the Big Bang.

Links:

25 years of stunning definition
Mon, 10 Dec 2018 06:00:00 +0100

This stunning spiral galaxy is Messier 100 in the constellation Coma Berenices, captured here by the NASA/ESA Hubble Space Telescope — not for the first time. Among Hubble’s most striking images of Messier 100 are a pair taken just over a month apart, before and after Servicing Mission 1, which took place 25 years ago in December 1993.

After Hubble was launched, the astronomers and engineers operating the telescope found that the images it returned were fuzzy, as if it were out of focus. In fact, that was exactly what was happening. Hubble’s primary mirror functions like a satellite dish; its curved surface reflects all the light falling on it to a single focal point. However, the mirror suffered from a defect known as a spherical aberration, meaning that the light striking the edges of the mirror was not travelling to the same point as the light from the centre. The result was blurry, unfocused images.

To correct this fault, a team of seven astronauts undertook the first Servicing Mission in December 1993. They installed a device named COSTAR (Corrective Optics Space Telescope Axial Replacement) on Hubble, which took account of this flaw of the mirror and allowed the scientific instruments to correct the images they received. The difference between the photos taken of Messier 100 before and after shows the remarkable effect this had, and the dramatic increase in image quality.

COSTAR was in place on Hubble until Servicing Mission 4, by which time all the original instruments had been replaced. All subsequent instrumentation had corrective optics built in.

This new image of Messier 100 taken with Hubble’s Wide Field Camera 3 (WFC3), demonstrates how much better the latest generation of instruments is compared to the ones installed in Hubble after its launch and after Servicing Mission 1.

Links

Clusters within clusters
Mon, 03 Dec 2018 06:00:00 +0100

This image, from the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), reveals thousands of globular clusters lying at the core of a galaxy cluster. It was created by a Hubble survey that drew on data from three of the telescope’s separate observing programmes to explore the centre of the Coma cluster, a huge gathering of over 1000 galaxies, about 320 million light-years away, all bound together by gravity.

Astronomers spotted over 22 000 globular clusters, some of which had formed a bridge connecting a pair of well-known interacting galaxies (NGC 4889 and NGC 4874). A globular cluster is a spherical group of stars that usually orbits a galaxy as a self-contained satellite. However, the globular clusters studied here are of a different type, intracluster globular clusters. Specifically, these are globular clusters that are not bound to an individual galaxy, but to a galaxy cluster — in this case, Coma.

While globular clusters orbiting our Milky Way reveal themselves as sparkling spherical assemblies of densely packed stars, at the distance of the Comla cluster, they only appear as tiny dots of light, even to Hubble's advanced vision. However, a characteristic feature of globular clusters is their colour; since the stars in any given cluster all formed at around the same time and from the same “stuff”, they usually have a consistent colour. In this way, the astronomers were able to identify the clusters — and rule out background galaxies lying in the same region of sky — by analysing their colour and size, painting a beautiful family portrait of Coma and its clusters.

With the help of the identified globular clusters astronomers can map the distribution of matter and — even more important — of dark matter in the Coma cluster. The Coma Cluster was one of the first places where observed gravitational anomalies indicated the existence of dark matter.

Links

Tangled — cosmic edition
Mon, 26 Nov 2018 06:00:00 +0100

This dark, tangled web is an object named SNR 0454-67.2. It formed in a very violent fashion — it is a supernova remnant, created after a massive star ended its life in a cataclysmic explosion and threw its constituent material out into surrounding space. This created the messy formation we see in this NASA/ESA Hubble Space Telescope image, with threads of red snaking amidst dark, turbulent clouds.

SNR 0454-67.2 is situated in the Large Magellanic Cloud, a dwarf spiral galaxy that lies close to the Milky Way. The remnant is likely the result of a Type Ia supernova explosion; this category of supernovae is formed from the death of a white dwarf star, which grows and grows by siphoning material from a stellar companion until it reaches a critical mass and then explodes.

As they always form via a specific mechanism — when the white dwarf hits a particular mass — these explosions always have a well-known luminosity, and are thus used as markers (standard candles) for scientists to obtain and measure distances throughout the Universe.

Different generations
Mon, 19 Nov 2018 06:00:00 +0100

Star clusters are common structures throughout the Universe, each made up of hundreds of thousands of stars all bound together by gravity. This star-filled image, taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), shows one of them: NGC 1866.

NGC 1866 is found at the very edges of the Large Magellanic Cloud, a small galaxy located near to the Milky Way. The cluster was discovered in 1826 by Scottish astronomer James Dunlop, who catalogued thousands of stars and deep-sky objects during his career.

However, NGC 1866 is no ordinary cluster. It is a surprisingly young globular cluster situated close enough to us that its stars can be studied individually — no mean feat given the mammoth distances involved in studying the cosmos! There is still debate over how globular clusters form, but observations such as this have revealed that most of their stars are old and have a low metallicity. In astronomy, ‘metals’ are any elements other than hydrogen and helium; since stars form heavier elements within their core as they carry out nuclear fusion throughout their lifetimes, a low metallicity indicates that a star is very old, as the material from which it formed was not enriched with many heavy elements. It’s possible that the stars within globular clusters are so old that they were actually some of the very first to form after the Big Bang.

In the case of NGC 1866, though, not all stars are the same. Different populations, or generations, of stars are thought to coexist within the cluster. Once the first generation of stars formed, the cluster may have encountered a giant gas cloud that sparked a new wave of star formation and gave rise to a second, younger, generation of stars — explaining why it seems surprisingly youthful.

Of bent time and jellyfish
Mon, 12 Nov 2018 06:00:00 +0100

At first glance, a bright blue crescent immediately jumps out of this NASA/ESA Hubble Space Telescope image: is it a bird? A plane? Evidence of extraterrestrial life? No — it’s a galaxy.

The shape of this galaxy admittedly appears to be somewhat bizarre, so confusion would be forgiven. This is due to a cosmic phenomenon called gravitational lensing. In this image, the gravitational influence of a massive galaxy cluster (called SDSS J1110+6459) is causing its surroundings spacetime to bend and warp, affecting the passage of any nearby light. This cluster to the lower left of the blue streak; a few more signs of lensing (streaks, blobs, curved lines, distorted shapes) can be seen dotted around this area.

This image also features a rare and interesting type of galaxy called a jellyfish galaxy, visible just right next to the cluster and apparently dripping bright blue material. These are galaxies that lose gas via a process called galactic ram pressure stripping, where the drag caused by the galaxy moving through space causes gas to be stripped away.

Feeling blue
Mon, 05 Nov 2018 06:00:00 +0100

This captivating image from the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 shows a lonely dwarf galaxy, a staggering 100 million light-years away from Earth. This image depicts the blue compact dwarf galaxy ESO 338-4, which can be found in the constellation of Corona Australis (the Southern Crown).

Blue compact dwarf galaxies take their name from the intensely blue star-forming regions that are often found within their cores. One such region can be seen embedded in ESO 338-4, which is populated with bright young stars voraciously consuming hydrogen. These massive stars are doomed to a short existence, as despite their vast supplies of hydrogen fuel. The nuclear reactions in the cores of these stars will burn through these supplies in only millions of years — a mere blink of an eye in astronomical terms.

The young blue stars nestled within a cloud of dust and gas in the centre of this image are the result of a recent galaxy merger between a wandering galaxy and ESO 388-4. This galactic interaction disrupted the clouds of gas and dust surrounding ESO 338-4 and led to the rapid formation of a new population of stars.

Helping Hubble
Mon, 29 Oct 2018 06:00:00 +0100

The NASA/ESA Hubble Space Telescope doesn’t usually get much assistance from its celestial subjects — but to take this image, the telescope opted for teamwork and made good use of a fascinating cosmic phenomenon known as gravitational lensing.

This effect works when the gravitational influence of a massive object, such as the galaxy cluster in the centre of this image, is so colossal that it warps the surrounding space, causing nearby light to travel along distorted paths. The massive object is effectively turned into a giant magnifying glass, bending and amplifying the light travelling from more distant galaxies lying behind it.

In this particular case, astronomers used the foreground galaxy cluster (named SDSS J0915+3826) to study star formation in galaxies lying so far away that their light has taken up to 11.5 billion years to reach our eyes. These galaxies formed at a very early stage in the lifetime of the Universe, giving astronomers a rare glimpse into the beginning of the cosmos. Despite their distance, the lensing effects of SDSS J0915+3826 allowed astronomers to work out the sizes, luminosities, star formation rates, and stellar populations of individual star-forming clumps within these galaxies — quite an achievement!

A galaxy with a bright heart
Mon, 22 Oct 2018 06:00:00 +0200

This Picture of the Week shows the unbarred spiral galaxy NGC 5033, located about 40 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The galaxy is similar in size to our own galaxy, the Milky Way, at just over 100 000 light-years across. Like in the Milky Way NGC 5033’s spiral arms are dotted with blue regions, indicating ongoing star formation. The blue patches house hot, young stars in the process of forming, while the older, cooler stars populating the galaxy’s centre cause it to appear redder in colour.

In contrast to the Milky Way NGC 5033 is missing a central bar. Instead it has a bright and energetic core called an active galactic nucleus, which is powered by a supermassive black hole. This active nucleus gives it the classification of a Seyfert galaxy. Due to the ongoing activity the core of NGC 5033 shines bright across the entire electromagnetic spectrum. This released energy shows that the central black hole is currently devouring stars, dust and gas getting to close to it. As this matters falls onto the supermassive black hole, it radiates in many different wavelengths.

While its relative proximity to Earth makes it an ideal target for professional astronomer to study its active nucleus in more detail, its big apparent size on the night sky and its brightness also makes it a beautiful target for amateur astronomers.

On the hunt for newborn stars
Mon, 15 Oct 2018 06:00:00 +0200

This image, taken with the NASA/ESA Hubble Space Telescope's Wide Field Camera 3 (WFC3), shows a patch of space filled with galaxies of all shapes, colours, and sizes. WFC3 is able to view many such galaxies at an unprecedented resolution — high enough to locate and study regions of star formation in a bid to understand how new stars spring to life throughout the cosmos.

Stars are born within giant clouds of gas. These massive clouds, or stellar nurseries, grow unstable and begin to collapse under gravity, becoming the seeds that will grow into new stars. By analysing the luminosity, size, and formation rate of different stellar nurseries, scientists hope to learn more about the processes that can lead to the formation of a newborn star. Studying nurseries within different galaxies will provide information about star formation at different points in time and space throughout the Universe.

Just below centre in this image is a formation of galaxies akin to a smiling face! Two yellow-hued blobs hang atop a sweeping arc of light, forming a celestial object known as SDSSJ0952+3434. The lower, arc-shaped galaxy has the characteristic shape of a galaxy that has been gravitationally lensed — its light has passed near to a massive object en route to us, causing it to become distorted and stretched out of shape.

Rings upon rings
Mon, 08 Oct 2018 06:00:00 +0200

This image from the NASA/ESA Hubble Space Telescope reveals a spiral galaxy named Messier 95 (also known as M95 or NGC 3351). Located about 35 million light-years away in the constellation of Leo (The Lion), this swirling spiral was discovered by astronomer Pierre Méchain in 1781, and catalogued by French astronomer Charles Messier just four days later. Messier was primarily a comet hunter, and was often left frustrated by objects in the sky that resembled comets but turned out not to be. To help other astronomers avoid confusing these objects in the future, he created his famous catalogue of Messier objects.

Most definitely not a comet, Messier 95 is actually a barred spiral galaxy. The galaxy has a bar cutting through its centre, surrounded by an inner ring currently forming new stars. Also our own Milky Way is a barred spiral.

As well as hosting this stellar nursery, Messier 95 is a known host of the dramatic and explosive final stages in the lives of massive stars: supernovae. In March 2016 a spectacular supernova named SN 2012aw was observed in the outer regions of one of Messier 95’s spiral arms. Once the light from the supernova had faded, astronomers were able to compare observations of the region before and after the explosion to find out which star had “disappeared” — the progenitor star. In this case, the star was an especially huge red supergiant up to 26 times more massive than the Sun.

Celestial fairy lights
Mon, 01 Oct 2018 06:00:00 +0200

 

This glittering ball of stars is the globular cluster NGC 1898, which lies towards the centre of the Large Magellanic Cloud — one of our closest cosmic neighbours. The Large Magellanic Cloud is a dwarf galaxy that hosts an extremely rich population of star clusters, making it an ideal laboratory for investigating star formation.

Discovered in November 1834 by British astronomer John Herschel, NGC 1898 has been scrutinised numerous times by the NASA/ESA Hubble Space Telescope. Today we know that globular clusters belong to the oldest known objects in the Universe and that they are relics of the first epochs of galaxy formation. While we already have a pretty good picture on the globular clusters of the Milky Way — still with many unanswered questions — our studies on globular clusters in nearby dwarf galaxies just started. The observations of NGC 1898 will help to determine if their properties are similar to the ones found in the Milky Way, or if they have different features, due to being in a different cosmic environment.

This image was taken by Hubble’s Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). The WFC3 observes light ranging from near-infrared to near-ultraviolet wavelengths, while the ACS explores the near-infrared to the ultraviolet.


rssfeedwidget.com