Early Galaxies – Clearing The “Cosmic Fog”

Scientists have used ESO’s Very Large Telescope to probe the early Universe at several different times as it was becoming transparent to ultraviolet light. This brief but dramatic phase in cosmic history — known as reionisation — occurred around 13 billion years ago. By carefully studying some of the most distant galaxies ever detected, the team has been able to establish a timeline for reionisation for the first time. They have also demonstrated that this phase must have happened quicker than astronomers previously thought.


The seasons are changing for both hemispheres and it’s not uncommon to wake up to wonderful, mysterious swirls of fog. What we experience here on Earth is water vapor, but the Universe was once filled with a fog of hydrogen gas. As the hours progress, the Sun slowly burns it off – quietly revealing trees, houses and the road ahead. In time after expansion began, the electrically neutral hydrogen gas was slowly swept away by the light of ultraviolet radiation from early galaxies…

Using the Very Large Telescope (VLT) like a “time machine”, a team of astronomers cut through the cosmic cloud layer to view some of the most distant galaxies recorded so far – a look back between 780 million and a billion years after the Big Bang. These antediluvian galaxies excited the gas, making it electrically charged (ionised), it gradually became transparent to ultraviolet light. While you may argue this process is technically known as reionization, there is theorized to be a brief timeline when hydrogen was also ionised.

“Archaeologists can reconstruct a timeline of the past from the artifacts they find in different layers of soil. Astronomers can go one better: we can look directly into the remote past and observe the faint light from different galaxies at different stages in cosmic evolution,” explains Adriano Fontana, of INAF Rome Astronomical Observatory who led this project. “The differences between the galaxies tell us about the changing conditions in the Universe over this important period, and how quickly these changes were occurring.”

As we know from spectroscopy, each element has its own signature – the emission lines – and the strongest in ultraviolet is the Lyman-alpha line generated from hydrogen. This bold spectral signature is easily recognizable – even at a vast distance. By observing the Lyman-alpha line for five very remote galaxies, the team was able to establish two critical factors: their distance through redshift and how soon they could be detected. Through this process, the astronomers were then able to establish how much the Lyman-alpha emission was reabsorbed by the neutral hydrogen fog and create a timeline… A whole lot like recording what minute each landmark reappears when terrestrial fog clears and seeing the long road ahead.

“We see a dramatic difference in the amount of ultraviolet light that was blocked between the earliest and latest galaxies in our sample,” says lead author Laura Pentericci of INAF Rome Astronomical Observatory. “When the Universe was only 780 million years old this neutral hydrogen was quite abundant, filling from 10 to 50% of the Universe’ volume. But only 200 million years later the amount of neutral hydrogen had dropped to a very low level, similar to what we see today. It seems that reionization must have happened quicker than astronomers previously thought.”

As always, there’s a bit more to the story. In this case, by understanding the rate at which the ancient absorbent obstruction began fading, scientists could also deduce the source of the powerful ultraviolet radiation. Could it be first generation stars – or even the work of primeval black holes?

“The detailed analysis of the faint light from two of the most distant galaxies we found suggests that the very first generation of stars may have contributed to the energy output observed,” says Eros Vanzella of the INAF Trieste Observatory, a member of the research team. “These would have been very young and massive stars, about five thousand times younger and one hundred times more massive than the Sun, and they may have been able to dissolve the primordial fog and make it transparent.”

To prove anything, it’s going to take a lot more research and some very accurate measurements – ones that are already in the planning stage for the future ESO European Extremely Large Telescope. But, in the meantime, the team used the great light-gathering power of the 8.2-metre VLT to carry out spectroscopic observations, targeting galaxies first identified by the NASA/ESA Hubble Space Telescope and in deep images from the VLT.

Original Story Source: ESO Press Release. For Further Reading: Probing The Earliest Galaxies And The Epoch Of Reionization.

Free Range Brown Dwarfs

Brown dwarfs in the young star cluster NGC 1333. This photograph combines optical and infrared images taken with the Subaru Telescope. Brown dwarfs newly identified by the SONYC Survey are circled in yellow, while previously known brown dwarfs are circled in white. The arrow points to the least massive brown dwarf known in NGC 1333; it is only about six times heftier than Jupiter. Credit: SONYC Team/Subaru Telescope


Using two of the world’s largest optical-infrared telescopes, the Subaru Telescope in Hawaii and the Very Large Telescope (VLT) in Chile, an international team of astronomers has discovered more than two dozen brown dwarf stars floating around in two galactic clusters. During the Substellar Objects in Nearby Young Clusters (SONYC) survey, these “failed stars” came to their attention by showing up in extremely deep images of the NGC 1333 and rho Ophiuchi star clusters at both optical and infrared wavelengths. To make the findings even more exciting, these stellar curiosities outnumbered the “normal” stars in one cluster!

“Our findings suggest once again that objects not much bigger than Jupiter could form the same way as stars do. In other words, nature appears to have more than one trick up its sleeve for producing planetary mass objects,” says Professor Ray Jayawardhana, Canada Research Chair in Observational Astrophysics at the University of Toronto and leader of the international team. Their discovery will be published in two upcoming papers in the Astrophysical Journal and will be presented this week at a scientific conference in Garching, Germany.

Spectra of several brown dwarfs in the young star cluster NGC1333, taken with the FMOS instrument on the Subaru Telescope. The spectra show a characteristic peak around 1670nm. Water steam in a brown dwarf's atmosphere absorbs radiation on both sides of the peak. The plot shows that the strength of the water absorption increases in cooler objects (from 3000 to 2200K). FMOS allows astronomers to take spectra for many objects simultaneously, a crucial advantage for the SONYC Survey. Credit: SONYC Team/Subaru Telescope

Using spectroscopy, the researchers were able to separate candidate brown dwarfs by their red color. But there’s more to the story than just hues. In this case, it’s the identification of one that’s only about six times more massive than Jupiter. Located in NGC 1333, it is the smallest known free-floating object to date. What does that mean? “Its mass is comparable to those of giant planets, yet it doesn’t circle a star. How it formed is a mystery,” said Aleks Scholz of the Dublin Institute for Advanced Studies in Ireland, lead author of the first paper.

Brown dwarfs are indeed unusual. They walk a fine line between planet and star – and may have once been in stellar orbit, only to be ejected at some point in time. But in this circumstance, all of the brown dwarfs found in this particular cluster have very low mass – only about twenty times that of Jupiter. “Brown dwarfs seem to be more common in NGC 1333 than in other young star clusters. That difference may be hinting at how different environmental conditions affect their formation,” said Koraljka Muzic of the University of Toronto in Canada, lead author of the second paper.

“We could not have made these exciting discoveries if not for the remarkable capabilities of Subaru and the VLT. Instruments that can image large patches of the sky and take hundreds of spectra at once are key to our success,” said Motohide Tamura of the National Astronomical Observatory of Japan.

Free-range brown dwarfs? I’ll take mine over easy…

Original Story Source: Subaru Telescope News.

Studying Saturn’s Super Storm

Three views of Saturn's northern storm. ESO/University of Oxford/L. N. Fletcher/T. Barry


First seen by amateur astronomers back in December, the powerful seasonal storm that has since bloomed into a planet-wrapping swath of churning clouds has gotten some scrutiny by Cassini and the European Southern Observatory’s Very Large Telescope array situated high in the Chilean desert.

The image above shows three views of Saturn acquired on January 19: one by amateur astronomer Trevor Barry taken in visible light and the next two by the VLT’s infrared VISIR instrument – one taken in wavelengths sensitive to lower atmospheric structures one sensitive to higher-altitude features. 

Cassini image showing dredged-up ammonia crystals in the storm. NASA/JPL/Univ. of Arizona.

While the storm band can be clearly distinguished in the visible-light image, it’s the infrared images that really intrigue scientists. Bright areas can be seen along the path of the storm, especially in the higher-altitude image, marking large areas of upwelling warmer air that have risen from deep within Saturn’s atmosphere.

Normally relatively stable, Saturn’s atmosphere exhibits powerful storms like this only when moving into its warmer summer season about every 29 years. This is only the sixth such storm documented since 1876, and the first to be studied both in thermal infrared and by orbiting spacecraft.

The initial vortex of the storm was about 5,000 km (3,000 miles) wide and took researchers and astronomers by surprise with its strength, size and scale.

“This disturbance in the northern hemisphere of Saturn has created a gigantic, violent and complex eruption of bright cloud material, which has spread to encircle the entire planet… nothing on Earth comes close to this powerful storm.”

– Leigh Fletcher, lead author and Cassini team scientist at the University of Oxford in the United Kingdom.

The origins of Saturn’s storm may be similar to those of a thunderstorm here on Earth; warm, moist air rises into the cooler atmosphere as a convective plume, generating thick clouds and turbulent winds. On Saturn this mass of warmer air punched through the stratosphere, interacting with the circulating winds and creating temperature variations that further affect atmospheric movement.

The temperature variations show up in the infrared images as bright “stratospheric beacons”. Such features have never been seen before, so researchers are not yet sure if they are commonly found in these kinds of seasonal storms.

“We were lucky to have an observing run scheduled for early in 2011, which ESO allowed us to bring forward so that we could observe the storm as soon as possible. It was another stroke of luck that Cassini’s CIRS instrument could also observe the storm at the same time, so we had imaging from VLT and spectroscopy of Cassini to compare. We are continuing to observe this once-in-a-generation event.”

– Leigh Fletcher

A separate analysis using Cassini’s visual and infrared mapping spectrometer confirmed the storm is very violent, dredging up larger atmospheric particles and churning up ammonia from deep in the atmosphere. Other Cassini scientists are studying the evolving storm and a more extensive picture will emerge soon.

Read the NASA article here, or the news release from ESO here.


The leading edge of Saturn's storm in visible RGB color from Cassini raw image data taken on February 25, 2011. (The scale size of Earth is at upper left.) NASA / JPL / Space Science Institute. Edited by J. Major.

Awe-Inspiring View of the Milky Way

The Milky Way as seen near the Very Large Telescope in the Atacama Desert. Credit: ESO/Y. Beletsky


The Chilean Atacama Desert boasts some of the darkest skies on Earth – which is why it is home to several telescopes, including the Very Large Telescope. This beautiful panoramic image was taken there, showing the VLT’s Unit Telescope 1, and across on the other side of the image are the Large and Small Magellanic Clouds glowing brightly. Like an arch in between is plane of our Milky Way galaxy. This awe-inspiring image was taken by ESO Photo Ambassador Yuri Beletsky. These photographers specialize in taking images of not only the night sky, but also the large telescopes that give us eyes to see across the great distances of our Universe.

See this ESO page for a larger version of this image.

A Galaxy With a Big “S” on Its Chest

Super galaxy, NGC 157. Credit: ESO


Can galaxy NGC 157 leap tall buildings in a single bound, stop a speeding bullet or bend steel in it’s bare hands? This relatively mild-mannered galaxy has a central sweep of stars that resembles a giant “S”, almost just like the comic book hero Superman’s symbol. The image was taken by the HAWK-I (High-Acuity Wide-field K-band Imager) on the Very Large Telescope in Chile. HAWK-I looks in infrared light, allowing us to peer through the gas and dust that normally obscures our view and see parts of NCG 157 that otherwise is hidden from our optical view.

Looking at this and other galaxies like it, astronomers can learn about star formation, as the same processes that are coalescing material and creating stars in NGC 157 also took place around 4.5 billion years ago in the Milky Way to form our own star, the Sun.

NGC 157 is faint — about magnitude 11, but can be seen bigger amateur telescopes. It is located within the constellation of Cetus (the Sea Monster).

For those interested in observing this object, see this post on WikiSky.

And just in case you don’t get the Superman references:

Source: ESO

Hidden Companion Responsible for Surprising Disk Around Strange Supergiant Star

3D images of HD 62623, obtained with the VLTI (left), compared to the model of a rotating disk (right). In the boxes, the gas kinematics is shown (3rd dimension): blue-coloured gas approaches the observer, while red-coloured gas recedes from the observer. The size of the inner gas disk of approx. 2 milli-arcseconds corresponds to 1.3 astronomical units (distance Earth-Sun), while the outer dust ring seen in the images has a radius corresponding to 4 astronomical units, assuming 2100 light years as distance to HD 62623. Images: F. Millour et al.


For several years, astronomers have been trying to get a good look at a peculiar supergiant star that is surrounded by a disk of gas and dust. The star, HD 62623, is one of the very few known supergiant stars to have such a disk. These disks are generally only associated with smaller, young stars, as supergiants have strong stellar winds that would blow away any surrounding plasma and debris. Now, using long-baseline stellar interferometry with the “Amber” instrument at ESO’s Very Large Telescope interferometer, a team of astronomers were able to capture, for the first time, a 3-D view of this strange star and its surrounding environment, which revealed a hidden secret: a companion star is likely responsible for the surrounding disk.

“Thanks to our interferometric observations with Amber we could synthetize a 3-D image of HD 62623 as seen through a virtual 130 m-diameter telescope”, says Florentin Millour, leading author of the study, from Observatoire de la Côte d’Azur. “The resolution is an order of magnitude higher compared with the world’s largest optical telescopes of 8-10 m diameter.”

HD 62623 is an exotic, hot, supergiant star. Supergiants are the most massive stars out there, ranging between 10 to 70 solar masses, and can range in brightness from 30,000 to hundreds of thousands of times the output of our Sun. They have very short lifespans, living from 30 million down to just a few hundred thousand years. Supergiants seem to always detonate as Type II supernovae at the end of their lives.

“Our new 3D image locates the dust-forming region around HD 62623 very precisely, and it provides evidence for the rotation of the gas around the central star,” said co-author Anthony Meilland from Max Planck Institute for Radio Astronomy. “This rotation is found to be Keplerian, the same way the Solar system planets rotate around the Sun.”

The companion star, although not seen directly because its light couldn’t be resolved among the brightness of HD62623, was detected by a central cavity between the gas disk and HD 62623. The companion is thought to be approximately the mass of our Sun, and its presence would explain the exotic characteristics of HD 62623, which has many similar characteristics to a monster among the old stars within our Galaxy, Eta Carinae.

HD 62623 is located in the constellation Cygnus near another bright supergiant, Deneb of the summer triangle. Deneb however, like most other supergiants, has no surrounding disk.

Four domes of the 1.8 m Auxiliary Telescopes (AT), utilized for the Very Large Telescope Interferometer (VLTI). ESO, Cerro Paranal, Chile. Image: F. Millour, OCA, Nice, France.

The images obtained with the Amber instrument combines spatial and velocity information, showing not only the shape of the close environment of HD 62623, but also its kinematics or motion. Up to now, the necessary kinematics information was missing in such images.

The astronomers were able to “disentangle” the dust and gas emission in the HD 62623 circumstellar disc, and measure the dusty disc inner rim. They also constrained the inclination angle and the position angle of the major-axis of the disc.

The new 3D imaging technique used by the team is equivalent to integral-field spectroscopy, but gives access to a 15 times larger angular resolution or capacity to detect fine details in the images. “With these new capacities, the VLTI will be able to provide a better comprehension of many sky targets, too small to be resolved by the largest telescopes,” said Millour. “We could aim at young stellar disks or jets, or even the central regions of active galaxies.”

Read the team’s paper: “Imaging the spinning gas and dust in the disc around the supergiant A[e] star HD62623,” Florentin Millour, Anthony Meilland, Olivier Chesneau, Philippe Stee, Samer Kanaan, Romain Petrov, Denis Mourard, Stefan Kraus, 2011, Astronomy & Astrophysics, Vol. 526, A107.

Source: Max Planck Institute for Astronomy

HAWK-I Hunts Down Spiral Galaxies in Stunning Detail

Six spectacular spiral galaxies are seen in a clear new light in images from ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile. Credit: ESO


Just like its ornithological namesake, the HAWK-I imager on the Very Large Telescope uses its piercing eyesight to hunt down its prey. But the High-Acuity Wide-field K-band Imager draws on its infrared vision to provide new insights into the spiral structures of galaxies. Today, ESO released six stunning new images of bright galaxies, showing exquisite detail with a clarity that is only possible by observing in the infrared.
Usually, dust in the arms of spiral galaxies blocks out much of the detail from our view, but observing in infrared light, much of the obscuring dust becomes transparent to its detectors. Compared to another VLT infrared camera called ISAAC, HAWK-I has sixteen times as many pixels to cover a much larger area of sky in one shot and, by using newer technology than ISAAC, it has a greater sensitivity to faint infrared radiation.

The six galaxies are part of a study of spiral structure led by Preben Grosbøl at ESO. Because HAWK-I can study galaxies stripped bare of the confusing effects of dust and glowing gas it is ideal for studying the vast numbers of stars that make up spiral arms, as well as helping astronomers to understand the complex and subtle ways in which the stars in these systems form into such perfect spiral patterns.

NGC 5247. Credit: ESO

The first image shows NGC 5247, a spiral galaxy dominated by two huge arms, located 60–70 million light-years away. The galaxy lies face-on towards Earth, thus providing an excellent view of its pinwheel structure. It lies in the zodiacal constellation of Virgo (the Maiden).

Messier 100, also known as NGC 4321. Credit: ESO

The galaxy in the second image is Messier 100, also known as NGC 4321, which lies about 55 million light-years from Earth in the Virgo Cluster of galaxies. It is an example of a “grand design” spiral galaxy — a class of galaxies with very prominent and well-defined spiral arms.

NGC 1300. Credit: ESO

The third image is of NGC 1300, a spiral galaxy with arms extending from the ends of a spectacularly prominent central bar. It is considered a prototypical example of barred spiral galaxies and lies at a distance of about 65 million light-years, in the constellation of Eridanus (the River).

NGC 4030. Credit: ESO

The spiral galaxy in the fourth image, NGC 4030, lies about 75 million light-years from Earth, in the constellation of Virgo.

NGC 2997. Credit: ESO

The fifth image, NGC 2997, is a spiral galaxy roughly 30 million light-years away in the constellation of Antlia. NGC 2997 is the brightest member of a group of galaxies of the same name in the Local Supercluster of galaxies. Our own Local Group, of which the Milky Way is a member, is itself also part of the Local Supercluster.

NGC 1232. Credit: ESO

Last but not least, NGC 1232 is a beautiful galaxy some 65 million light-years away in the constellation of Eridanus (the River). The galaxy is classified as an intermediate spiral galaxy — somewhere between a barred and an unbarred spiral galaxy.

Source: ESO

Galaxy Growth Not Always Result of Violent Collisions

Artist’s impression of a young galaxy accreting material. Credit: ESO/L. Calçada


Until recently, it was thought the galactic equivalent of a motorway pile-up was the only way galaxies got bigger. But startling new evidence from a European team of astronomers suggests that violent galactic collisions are not the only way that galaxies evolve and grow, and instead there seems to be something else happening that has affected the majority of galaxies — a kinder, gentler action which is not quite so disruptive.

For some years, astronomers have struggled to understand why the mass of galaxies seems to have increased dramatically just a few billion years after the Big Bang. We know from observation that galaxies collide but this is an incredibly violent activity and one that is not particularly common.

A new study using the Very Large Telescope (VLT) at the European Southern Observatory (ESO), by a team led by Giovanni Cresci, looked for evidence that galaxies might be accreting material from the hydrogen and helium gas that filled the early Universe and permeates the space between the galaxies. We know that they are surrounded by halos of unseen material but Cresci’s team wanted to see if there was any evidence of material being sucked into the galaxy from the surrounding environment.

Their study focused on a group of distant galaxies which would represent those in the early Universe, about 2 billion years after the big bang, to see if they could detect any evidence of this gas accretion.

Using the SINFONI (Spectrograph for Integral Field Observation in the Near Infrared) attached to the VLT, Cresci and his team mapped the distribution of elements within the target galaxies. Their findings showed that instead of heavier elements being concentrated around the core as we find in today’s galaxies, the core was surprisingly abundant of the lighter elements hydrogen and helium. This can only be as a result of accretion of lighter elements from the surrounding area boosting the rate of star formation in the core. The accretion process itself relies on cool gas being transferred directly into the core of the galaxy.

“The primordial gas in the halo of galaxies, especially at great distances, is mostly shock heated and therefore very hot,” Cresci told Universe Today. “To be accreted it has to be cooled and this is not an efficient process. Recent theoretical models have shown that narrow streams of cold gas can form, and that they are able to penetrate the hot gas and to provide fresh gas to the centre of the galaxy. Unlike more destructive and violent mergers between galaxies, the streams are likely to keep the rotating disk configuration intact, although turbulent.”

This new discovery means astronomers have perhaps found an answer to a long standing question but with the major consequence of needing to rewrite our current theories of the evolution of the Universe.

Source: ESO, email exchange with Cresci

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Dramatic Moonset — Amazing Sight on Cerro Paranal

Moonset on Cerro Paranal. Credit: ESO


Need a new desktop image? Usually the Very Large Telescope on Cerro Paranal in Chile provides us with stunning views of the cosmos. This image, however, is a gorgeous view of the observatory itself. As the Moon was setting after a long night of observing, ESO staff member Gordon Gillet welcomed the new day by capturing this stunning image from 14 km away. This image is not a montage or computer-generated (such as the infamous ‘Moon and Sun over the North Pole‘ urban legend)

The ESO website explains:

The Moon appears large because it is seen close to the horizon and our perception is deceived by the proximity of references on the ground. In order to get this spectacular close view, a 500-mm lens was necessary. The very long focal length reduces the depth of field making the objects in focus appear as if they were at the same distance. This effect, combined with the extraordinary quality of this picture, gives the impression that the Moon lies on the VLT platform, just behind the telescopes, even though it is in fact about 30,000 times further away.

Interestingly, Gillet took the image from the road leading to the nearby Cerro Armazones, the peak recently chosen by the ESO Council as the preferred location for the planned 42-meter European Extremely Large Telescope (E-ELT), which should be open for business by 2018.

Source: ESO

Hail to His Spiralness, M83

M83. Credit: ESO/M. Gieles. Acknowledgement: Mischa Schirmer


ESO released a beautiful image today of M83, a classic spiral galaxy. The image was taken by the HAWK-I instrument on ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile. The picture shows the galaxy in infrared light and the combination of the huge mirror of the VLT, the large field of view and great sensitivity of the HAWK –I and the superb observing conditions at ESO’s Paranal Observatory makes this one of the sharpest and most detailed pictures of Messier 83 ever taken from the ground. M83 is perhaps a mirror to how our own Milky Way galaxy looks, could we step outside and take a look.

Messier 83 is located about 15 million light-years away in the constellation of Hydra. It is famous for its many supernovae: over the last century, six supernovae have been observed in Messier 83 — a record number that is matched by only one other galaxy. Even without supernovae, Messier 83 is one of the brightest nearby galaxies, visible using just binoculars.

Check out this article by our resident astronomer Tammy Plotner to find out how you can spot M83 in the night sky.

Source: ESO