Here’s the latest report from ESO (European Southern Observatory):

A Cosmic Rose With Many Names

This new image of the rose-coloured star forming region Messier 17 was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. It is one of the sharpest images showing the entire nebula and not only reveals its full size but also retains fine detail throughout the cosmic landscape of gas clouds, dust and newborn stars.

The nebula pictured here may have had more names bestowed upon it over the ages than any other object of its kind. Although officially known as Messier 17, its nicknames include: the Omega Nebula, the Swan Nebula, the Checkmark Nebula, the Horseshoe Nebula and — lest those with more of a more marine bent miss out — the Lobster Nebula.

This zoom video sequence takes us from a broad vista of the bright central parts of the Milky Way right into a close-up view of the bright star formation region Messier 17. The final detailed view is from the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Credit: ESO, N. Risinger (skysurvey.org), DSS. Music: Johan Monell (www.johanmonell.com)

Messier 17 is located about 5500 light-years from Earth near the plane of the Milky Way and in the constellation of Sagittarius (The Archer). The object spans a big section of the sky — its gas and dust clouds measure about 15 light-years across. This material is fueling the birth of new stars and the wide field of view of the new picture reveals many stars in front of, in, or behind Messier 17.

The nebula appears as a complex red structure with some graduation to pink. Its colouring is a signature of glowing hydrogen gas. The short-lived blue stars that recently formed in Messier 17 emit enough ultraviolet light to heat up surrounding gas to the extent that it begins to glow brightly. In the central region the colours are lighter, and some parts appear white. This white colour is real — it arises as a result of mixing the light from the hottest gas with the starlight reflected by dust.

This video gives us a close-up view of the rose-coloured star forming region Messier 17. The picture was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. It is one of the sharpest images showing the entire nebula and not only reveals its full size but also retains fine detail throughout the cosmic landscape of gas clouds, dust and newborn stars. Credit: ESO, Music: Johan Monell (www.johanmonell.com)

The gas in the nebula is estimated to have more than 30 000 times the mass of the Sun. Messier 17 also contains an open star cluster of 35 stars, which is known as NGC 6618 [1]. The total number of stars in the nebula, however, is much higher — there are almost 800 stars in the centre with even more forming in its outer regions.

Throughout this rosy glow, the nebula shows a web of darker regions of dust that obscure the light. This obscuring material is also glowing and — although these areas are dark in this visible-light image — they look bright when observed using infrared cameras.

The nebula owes its official name to the French comet hunter Charles Messier who included the nebula as the seventeenth object in his famous astronomical catalogue in 1764 [2]. But even with a name as bland as Messier 17, this flowery nebula still looks dazzling.

This picture comes from the ESO Cosmic Gems programme [3].

Notes

[1] This designation is also sometimes used for the entire star formation region.

[2] The astronomer Jean Philippe de Chéseaux discovered the object in 1745, but his discovery did not receive widespread attention. Thus, Messier independently rediscovered and catalogued it almost 20 years later.

[3] The ESO Cosmic Gems programme is an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

ESO (European Southern Observatory) releases a new report:

A Shy Galactic Neighbour

The Sculptor Dwarf Galaxy, pictured in this new image from the Wide Field Imager camera, installed on the 2.2-metre MPG/ESO telescope at ESO’s La Silla Observatory, is a close neighbour of our galaxy, the Milky Way. Despite their close proximity, both galaxies have very distinct histories and characters. This galaxy is much smaller and older than the Milky Way, making it a valuable subject for studying both star and galaxy formation in the early Universe. However, due to its faintness, studying this object is no easy task.

The Sculptor Dwarf Galaxy — also known as the Sculptor Dwarf Elliptical or the Sculptor Dwarf Spheroidal — is a dwarf spheroidal galaxy, and is one of the fourteen known satellite galaxies orbiting the Milky Way [1]. These galactic hitchhikers are located close by in the Milky Way’s extensive halo, a spherical region extending far beyond our galaxy’s spiral arms. As indicated by its name, this galaxy is located in the southern constellation of Sculptor and lies about 280 000 light-years away from Earth. Despite its proximity, the galaxy was only discovered in 1937, as its stars are faint and spread thinly across the sky.

Although difficult to pick out, the Sculptor Dwarf Galaxy was among the first faint dwarf galaxies found orbiting the Milky Way. The tiny galaxy’s shape intrigued astronomers at the time of its discovery, but nowadays dwarf spheroidal galaxies play a more important role in allowing astronomers to dig deeply into the Universe’s past.

The Milky Way, like all large galaxies, is thought to have formed from the build-up of smaller galaxies during the early days of the Universe. If some of these small galaxies still remain today, they should now contain many extremely old stars. The Sculptor Dwarf Galaxy fits the bill as a primordial galaxy, thanks to a large number of ancient stars, visible in this image.

Astronomers can determine the age of stars in the galaxy because their light carries the signatures of only a small quantity of heavy chemical elements. These heavy elements accumulate in galaxies with successive generations of stars. A low level of heavy elements thus indicates that the average age of the stars in the Sculptor Dwarf Galaxy is high.

This quantity of old stars makes the Sculptor Dwarf Galaxy a prime target for studying the earliest periods of star formation. In a recent study, astronomers combined all the data available for the galaxy to create the most accurate star formation history ever determined for a dwarf spheroidal galaxy. This analysis revealed two distinct groups of stars in the galaxy. The first, predominant group is the older population, which is lacking in heavier elements. The second, smaller population, in contrast, is rich with heavy elements. Like young people crowding into city centres, this youthful stellar population is concentrated toward the galaxy’s core.

This video zoom takes a closer look at the Sculptor Dwarf Galaxy, pictured in new image from the Wide Field Imager camera, installed on the 2.2-metre MPG/ESO telescope at ESO’s La Silla Observatory. This elusive galaxy is a close neighbour of our galaxy, the Milky Way. Despite their proximity, both galaxies have very distinct histories and characters. This galaxy is much smaller, fainter and older than the Milky Way. It appears here as a rich cloud of faint stars at the centre of the image at the start, and completely fills the frame later on. Here and there much more distant galaxies can be spotted between the stars of the Sculptor Dwarf.

Credit: DSS, ESO. Music: Johan Monell (www.johanmonell.com)

The stars within dwarf galaxies like the Sculptor Dwarf Galaxy can exhibit complex star formation histories. But as most of these dwarf galaxies’ stars have been isolated from each other and have not interacted for billions of years, each collection of stars has charted its own evolutionary course. Studying the similarities in dwarf galaxies’ histories, and explaining the occasional outliers, will help to explain the development of all galaxies, from the most unassuming dwarf to the grandest spirals. There is indeed much for astronomers to learn from the Milky Way’s shy neighbours.

Notes

[1] This faint galaxy should not be confused with the much brighter Sculptor Galaxy (NGC 253) in the same constellation

An announcement from the Hubble Space Telescope program.

Astronomers find galaxy cluster with bursting heart
Hubble, Spitzer, and the Canada-France-Hawaii Telescope
join forces for rare cosmic find

An international team of astronomers has discovered a gargantuan galaxy cluster with a core bursting with new stars — an incredibly rare find. The discovery, made with the help of the NASA/ESA Hubble Space Telescope, is the first to show that gigantic galaxies at the centres of massive clusters can grow significantly by feeding off gas stolen from other galaxies.

Galaxy clusters are vast families of galaxies bound together by gravity. Our own galaxy, the Milky Way resides within a small galaxy group known as the Local Group, which itself is a member of the massive Laniakea supercluster.

Galaxies at the centres of clusters are usually made of stellar fossils — old, red or dead stars. However, astronomers have now discovered a giant galaxy at the heart of a cluster named SpARCS1049+56 that seems to be bucking the trend, instead forming new stars at an incredible rate.

“We think the giant galaxy at the centre of this cluster is furiously making new stars after merging with a smaller galaxy,” explained Tracy Webb of McGill University, Montreal, Canada, lead author of a new paper accepted for publication in The Astrophysical Journal.

The galaxy was initially discovered using NASA’s Spitzer Space Telescope and the Canada-France-Hawaii Telescope, located on Mauna Kea in Hawai`i and confirmed using the W.M. Keck Observatory, also on Mauna Kea. Follow-up observations using the NASA/ESA Hubble Space Telescope allowed the astronomers to explore the galaxy’s activity.

The SpARCS1049+56 cluster is so far away that its light took 9.8 billion years to reach us. It houses at least 27 galaxies and has a combined mass equal to 400 trillion Suns. It is a truly unique cluster in one aspect — its vibrant heart of new stars. The cluster’s brightest galaxy [1] is rapidly spitting out 800 new stars per year. The Milky Way forms two stars per year at most!

“The Spitzer data showed us a truly enormous amount of star formation in the heart of this cluster, something that has rarely been seen before, and certainly not in a cluster this distant,” commented co-author Adam Muzzin of the University of Cambridge, UK.

Spitzer picks up infrared light, so it can detect the warm glow of hidden, dusty regions of starbirth. Follow-up studies with Hubble in visible light helped to pinpoint what was fuelling the new star formation. It appears that a smaller galaxy has recently merged with the monster in the middle of the cluster, lending its gas to the larger galaxy and igniting a furious episode of new starbirth.

“Building on our other observations, we used Hubble to explore the galaxy in depth — and we weren’t disappointed,”added Muzzin. “Hubble found a trainwreck of a merger at the centre of this cluster. We detected features that looked like beads on a string.”

Beads on a string (heic1414) are telltale signs of something known as a wet merger. Wet mergers occur when gas-rich galaxies collide — this gas is converted quickly into new stars.

The new discovery is one of the first known cases of a wet merger at the core of a galaxy cluster. Hubble had previously discovered another closer galaxy cluster containing a wet merger, but it was not forming stars as vigorously. Other galaxy clusters grow in mass through dry mergers [2], or by siphoning gas towards their centres. For example, the mega galaxy cluster known as the Phoenix Cluster grows in size by sipping off gas that flows into its centre.

The astronomers now aim to explore how common this type of growth mechanism is in galaxy clusters. Are there other “messy eaters” out there similar to SpARCS1049+56, which also munch on gas-rich galaxies? SpARCS1049+56 may be an outlier — or it may represent an early time in our Universe when messy eating was the norm.

Notes

[1] At the core of most galaxy clusters lies a hulking galaxy called the brightest cluster galaxy, or BCG. This newly discovered starbursting galaxy is the BCG in SpARCS1049+56.

[2] Dry mergers involve the coming together of two galaxies lacking in gas. The two just mix their existing stars, rather than causing the birth of any new ones.

The latest ESO (European Southern Observatory) report:

Cosmic Recycling

Dominating this image is part of the gigantic nebula Gum 56, illuminated by the hot bright young stars that were born within it. For millions of years stars have been created out of the gas in this nebula, material which is later returned to the stellar nursery when the aging stars either expel their material gently into space or eject it more dramatically as supernova explosions. This image was taken with the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile as part of ESO’s Cosmic Gems programme.

Deeply immersed in this huge stellar nursery are three clusters of hot young stars — only a few million years old — which glow brightly in ultraviolet light. It is the light from these stars that causes the nebula’s gas clouds to glow. The radiation strips electrons from atoms — a process known as ionisation — and when they recombine they release energy in the form of light. Each chemical element emits light in characteristic colours and the large clouds of hydrogen in the nebula are the cause of its rich red glow.

Gum 56 — also known as IC 4628 or by its nickname, the Prawn Nebula — is named after the Australian astronomer Colin Stanley Gum, who, in 1955, published a catalogue of H II regions. H II regions such as Gum 56 are huge, low density clouds containing a large amount of ionised hydrogen.

This video sequence starts with a view of the rich central parts of the Milky Way and then closes in on a spectacular region of star formation known as the Prawn Nebula (also known as Gum 56 and IC 4628) in the constellation of Scorpius (The Scorpion). The final close up view is a very sharp image taken using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Credit: ESO/Nick Risinger (skysurvey.org). Music: Johan B Monell

A large portion of the ionisation in Gum 56 is done by two O-type stars, which are hot blue–white stars, also known as blue giants because of their colour [1]. This type of star is rare in the Universe as the very large mass of blue giants means that they do not live for long. After only roughly a million years these stars will collapse in on themselves and end their lives as supernovae, as will many of the other massive stars within the nebula.

Besides the many newborn stars nestled in the nebula, this large region is still filled with enough dust and gas to create an even newer generation of stars. The regions of the nebula giving birth to new stars are visible in the image as dense clouds. The material forming these new stars includes the remains of the most massive stars from an older generation that have already ended their lives and ejected their material in violent supernova explosions. Thus the cycle of stellar life and death continues.

Given the two very unusual blue giants in this area and the prominence of the nebula at infrared and radio wavelengths, it is perhaps surprising that this region has been comparatively little studied as yet by professional astronomers. Gum 56 has a diameter of around 250 light-years, but despite its huge size it has also often been overlooked by visual observers due to its faintness, and because most of the light it emits is at wavelengths not visible to the human eye.

The nebula is at a distance of about 6000 light-years from Earth. In the sky it can be found in the constellation Scorpius (The Scorpion) where it has a projected size which is four times the size of the full Moon [2].

This image, which only captures a part of the nebula, was taken with the 2.2-metre MPG/ESO telescope using the Wide Field Imager (WFI) camera as part of the ESO Cosmic Gems programme. The programme makes use of telescope time that cannot be used for science observations to produce images of interesting, intriguing or visually attractive objects. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

Notes

[1] Note that these stars fall outside the field of view of this particular image and do not appear in the picture.

[2] A wide-angle view of the Prawn Nebula taken by the VLT Survey Telescope was published earlier (eso1340a).