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Sparkling sphere of ancient stars

Messier 55

Messier 55 is a huge ball of very old stars, about 17,000 light-years from Earth.

A NEW IMAGE of Messier 55 from the European Southern Observatory’s (ESO) VISTA infrared survey telescope shows tens of thousands of stars crowded together like a swarm of bees. Besides being packed into a relatively small space, these stars are also among the oldest in the Universe. Astronomers study Messier 55 and other ancient objects like it, called globular star clusters, to learn how galaxies evolve and stars age.

Globular clusters are held together in a tight spherical shape by gravity. In Messier 55, the stars certainly do keep close company—approximately one hundred thousand stars are packed within a sphere with a diameter of only about 25 times the distance between the Sun and the nearest star system, Alpha Centauri.

About 160 globular clusters have been spotted encircling our galaxy, the Milky Way, mostly toward its bulging centre. The largest galaxies can have thousands of these rich collections of stars in orbit around them.

Wide-angle view of Messier 55

A wider view of Messier 55 at visible light wavelengths. It's easy to see how these vast collections of stars got their name…"globular star clusters". Courtesy ESO and Digitised Sky Survey 2.

Observations of globular clusters’ stars reveal that they originated around the same time—more than 10 billion years ago—and from the same cloud of gas. As this formative period was just a few billion years after the Big Bang, nearly all of the gas on hand was the simplest, lightest and most common in the cosmos—hydrogen, along with some helium and much smaller amounts of heavier chemical elements such as oxygen and nitrogen.

Being made mostly from hydrogen distinguishes globular cluster residents from stars born in later eras, like our Sun, that are infused with heavier elements formed in earlier generations of stars. The Sun lit up some 4.6 billion years ago, making it only about half as old as the elderly stars in most globular clusters.

The new image was obtained in infrared light by the 4.1-metre Visible and Infrared Survey Telescope for Astronomy (VISTA) at ESO’s Paranal Observatory in northern Chile.

As well as the stars of Messier 55, this VISTA image also records many galaxies lying far beyond the cluster. A particularly prominent edge-on spiral galaxy appears like a thin, red smudge to the upper right of the centre of the picture.

Adapted from information issued by ESO / J. Emerson / VISTA. Acknowledgment: Cambridge Astronomical Survey Unit.

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Hidden star groups uncovered

Star clusters discovered using VISTA

Using data from the VISTA infrared survey telescope, astronomers have discovered 96 new 'open' star clusters hidden behind dust in the Milky Way, 30 of which are shown in this mosaic.

  • Almost 100 star clusters found hiding behind dust in the Milky Way
  • Uncovered using the dust-penetrating power of infrared
  • There could be 30,000 more clusters still waiting to be found

NINETY-SIX PREVIOUSLY UNKNOWN ‘open star clusters’ have been found hiding behind dust in the Milky Way.

These tiny and faint groupings were invisible to previous surveys, but they could not escape the sensitive infrared detectors VISTA—an infrared survey telescope at the European Southern Observatory’s (ESO) Paranal Observatory in Chile—which can peer through the dust.

This result comes just one year after the start of the VISTA Variables in the Via Lactea programme (VVV), one of the six surveys running on the new telescope. (‘Via Lactea’ is the Latin name for the Milky Way.)

Invisible to most telescopes

Most stars that weigh more than half as much as our Sun form in groups, called open star clusters. These clusters are the building blocks of galaxies and vital for the formation and evolution of galaxies such as our own.

However, stellar clusters form in very dusty regions that absorb most of the visible light that the young stars emit, making them invisible to most telescopes, but not to VISTA.

In order to spot the youngest star clusters, the astronomers concentrated their search towards known star-forming areas. They found that regions that looked empty in previous visible-light surveys, actually held lots of clusters.

VISTA telescope

VISTA is an infrared survey telescope at the European Southern Observatory in Chile.

No wonder they were hidden

By using carefully tuned computer software, the team was able to remove the foreground stars appearing in front of each cluster in order to count the genuine cluster members.

Afterwards, they made visual inspections of the images to measure the cluster sizes, and for the more populous clusters they made other measurements such as distance, and the age of the stars.

“We found that … the dust in front of these clusters makes them appear 10,000 to 100 million times fainter in visible light,” explains Radostin Kurtev, another member of the team. “It’s no wonder they were hidden.”

Tip of the iceberg

Only 2,500 open clusters are known so far in the Milky Way, but astronomers think there might be as many as 30,000 still hiding behind the dust and gas.

These new 96 open clusters might be only the tip of the iceberg.

“We’ve just started to use more sophisticated automatic software to search for less concentrated and older clusters,” adds Jura Borissova, lead author of the study. “I am confident that many more are coming soon.”

Adapted from information issued by ESO. Images courtesy ESO / J. Borissova / Steven Beard (UKATC).

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Diving into the Lagoon

Infrared and visible light views of the Lagoon Nebula

Comparison of infrared (top) and visible light (bottom) views of the Lagoon Nebula (Messier 8). In the infrared, the dust clouds become more transparent and the gas clouds less conspicuous. A whole host of cool red stars that are otherwise invisible are revealed.

  • Lagoon Nebula is a “stellar nursery” where stars are born
  • Located 4,000 to 5,000 light-years from Earth
  • New image taken by the world’s biggest survey telescope

A NEW INFRARED IMAGE of the Lagoon Nebula was captured as part of a five-year study of the Milky Way using ESO’s VISTA telescope at the Paranal Observatory in Chile.

This is a small piece of a much larger image of the region surrounding the nebula, which is, in turn, only one part of a huge sky survey.

Astronomers are currently using ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) to scour the Milky Way’s central regions for variable objects and map its structure in greater detail than ever before.

This huge survey is called VISTA Variables in the Via Lactea (VVV). (Via Lactea means Milky Way in  Latin.) The new infrared image presented here was taken as part of this survey. It shows the stellar “nursery” called the Lagoon Nebula (also known as Messier 8), which is about 4,000-5,000 light-years away.

Infrared observations allow astronomers to peer through the veil of dust that prevents them from seeing celestial objects in visible light. This is because visible light, which has a wavelength that is about the same size as the dust particles, is strongly scattered, but the longer wavelength infrared light can pass through the dust largely unscathed.

VISTA, with its 4.1-metre-diameter mirror—the largest survey telescope in the world—is dedicated to surveying large areas of the sky at near-infrared wavelengths deeply and quickly. It is therefore ideally suited to studying star birth.

Watch a video zooming in on the Lagoon:

Stellar nursery

Stars typically form in large molecular clouds of gas and dust, which collapse under their own weight. The Lagoon Nebula, however, is also home to a number of much more compact regions of collapsing gas and dust, called Bok globules. These dark clouds are so dense that, even in the infrared, they can block the starlight from background stars.

But the most famous dark feature in the nebula, for which it is named, is the lagoon-shaped dust lane that winds its way through the glowing cloud of gas. Hot, young stars, which give off intense ultraviolet light, are responsible for making the nebula glow brightly.

But the Lagoon Nebula is also home to much younger stellar infants. Newborn stars detected in the nebula are so young that they are still surrounded by their natal accretion discs.

Such newborn stars occasionally eject jets of matter from their poles. When this ejected material ploughs into the surrounding gas short-lived bright streaks called Herbig-Haro objects are formed, making the newborns easy to spot.

In the last five years, several Herbig-Haro objects have been detected in the Lagoon Nebula, so the baby boom is clearly still in progress here.

Adapted from information issued by ESO / VVV / Cambridge Astronomical Survey Unit. The science team for VVV includes Dante Minniti (Universidad Catolica, Chile), Phil Lucas (University of Hertfordshire, UK), Ignacio Toledo (Universidad Catolica), and Maren Hempel (Universidad Catolica).

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Unicorn cloud reveals its inner self

Monoceros R2

Infrared image of the nearby star formation region Monoceros R2, located 2,700 light-years away in the constellation Monoceros (the Unicorn).

  • Infrared images can look through dust clouds
  • VISTA telescope designed for infrared sky surveys
  • Image penetrates into the heart of region called Monoceros R2

A new infrared image from the European Southern Observatory’s (ESO) VISTA survey telescope reveals a scene of glowing tendrils of gas, dark dust clouds and young stars within the constellation Monoceros (the Unicorn).

Known as Monoceros R2, this star-forming region is embedded within a huge dark cloud rich in molecules and dust and hiding an active stellar “nursery”.

VISTA telescope

The enclosure of the VISTA survey telescope at the ESO Paranal Observatory in northern Chile.

At “normal”, visible light wavelengths (see comparison images below), a grouping of massive hot stars can be seen amidst a beautiful collection of “reflection nebulae”, where bluish starlight is scattered from parts of the foggy outer layers of a cloud of molecular gas.

Most of the newborn massive stars in the nursery remain hidden at visible light wavelengths, as the thick dust clouds strongly absorb and block the stars’ ultraviolet and visible light from reaching us.

But spectacular detail pops out at VISTA’s infrared wavelengths. See the full-size, high-resolution version here (0.7MB, new window)

Taken from ESO’s Paranal Observatory in northern Chile, the VISTA image shows how the dark curtain of cosmic dust is penetrated to reveal in detail the folds, loops and filaments sculpted from the dusty interstellar matter by the intense particle winds and radiation emitted by hot young stars.

“When I first saw this image I just said, ‘Wow!’” says Jim Emerson, of Queen Mary, University of London and leader of the VISTA consortium. “I was amazed to see all the dust streamers so clearly around the Monoceros R2 cluster, as well as the jets from highly embedded young stellar objects.”

Stars form in a process that typically lasts few million years and which takes place inside large clouds of interstellar gas and dust, hundreds of light-years across.

Interstellar dust blocks visible light wavelengths but lets infrared and radio wavelengths through… so observations at the latter wavelengths are crucial in the understanding of the earliest stages of the stellar evolution.

Visible light wavelength image of Monoceros R2

A visible light wavelength image of Monoceros R2. Compare this to the infrared image at the top of the page. At infrared wavelengths, the thick, rich dust clouds that cover much of the image become nearly transparent and a whole host of young stars and associated outflows become apparent.

Home to newborn stars

Since dust is largely transparent at infrared wavelengths, many young stars that cannot be seen in visible-light images become apparent in Monoceros R2. The most massive of these stars are less than 10 million years old.

At the centre of the image lies Monoceros R2 dense core, no more than two light-years in extent, which is packed with very massive young stars, as well as a cluster of bright infrared sources, which are typically newborn massive stars still surrounded by dusty clouds.

The rightmost of the bright clouds in the centre is called NGC 2170, the brightest reflection nebula in this region. In visible light, the nebulae appear as bright, light blue islands in a dark ocean, while infrared reveals their interiors where hundreds of massive stars are coming into existence.

NGC 2170—faintly visible through a small telescope—was discovered from England in 1784 by astronomer William Herschel.

Although Monoceros R2 appears close in the sky to the more familiar Orion Nebula it is actually almost twice as far from Earth, at a distance of about 2,700 light-years. The width of VISTA’s field of view is equivalent to about 80 light-years at this distance.

With its 4.1-metre primary mirror, VISTA is the largest survey telescope in the world and is equipped with the largest infrared camera on any telescope, with 67 million pixels. It is dedicated to sky surveys.

By mapping the southern sky systematically, VISTA will gather some 300 gigabytes per night, providing a huge amount of information on those regions that will be studied in greater detail by the Very Large Telescope (VLT), the Atacama Large Millimetre/submillimetre Array (ALMA) and, in the future, by the European Extremely Large Telescope (E-ELT).

Adapted from information issued by ESO / J. Emerson / VISTA / Cambridge Astronomical Survey Unit.

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Cosmic grandeur: the Sculptor Galaxy

Infrared view of galaxy NGC 253

NGC 253 is one of the closest galaxies to our own. At infrared wavelengths shown here, dust clouds in the galaxy’s spiral arms become nearly transparent and a host of cool, red stars can be seen.

  • Sculptor Galaxy, also known as NGC 253
  • 13 million light-years from Earth
  • “Starburst” galaxy, in the throes of massive star formation

A new image of the Sculptor Galaxy (NGC 253) has been taken with the European Southern Observatory (ESO) VISTA telescope at the Paranal Observatory in Chile as part of one of its first major observational campaigns.

By observing in infrared light, VISTA’s view is less affected by dust in the galaxy, and reveals a myriad of cooler, red stars, as well as a prominent elongated belt of stars across the central region.

NGC 253 is one of the brightest galaxies in the sky. It is prominent enough to be seen with good binoculars and was discovered by Caroline Herschel from England in 1783.

A spiral galaxy that lies about 13 million light-years away, it is the brightest member of a small collection of galaxies called the Sculptor Group, one of the closest such groupings to our own Local Group of galaxies.

Part of its visual prominence comes from its status as a “starburst galaxy”, one in the throes of rapid star formation.

Infrared and visible light views of galaxy NGC 253

Comparison of the infrared (top) and visible light (bottom) views.

NGC 253 is also very dusty, which obscures the view of many parts of the galaxy. Seen from Earth, the galaxy is almost edge on, with the spiral arms clearly visible in the outer parts, along with a bright core at its centre.

See the full-size image here.

As VISTA works at infrared wavelengths it can see right through most of the dust that is such a prominent feature of the Sculptor Galaxy when viewed in visible light. Huge numbers of cooler stars that are barely detectable with visible-light telescopes suddenly can be seen.

The VISTA view reveals most of what was hidden by the thick dust clouds in the central part of the galaxy and allows a clear view of a prominent elongated section, or “bar”, of stars across the nuclear region — a feature that is not seen in visible light pictures. The majestic spiral arms now spread over the whole disc of the galaxy.

Astronomers are peeling away some of the mysteries of the Sculptor Galaxy. They are studying the myriad cool, red giant stars in the halo that surrounds the galaxy, measuring the composition of some of NGC 253’s small dwarf satellite galaxies, and searching for as yet undiscovered new objects such as globular clusters and ultra-compact dwarf galaxies that would otherwise be invisible without the deep VISTA infrared images.

Adapted from information issued by ESO / J. Emerson / VISTA / Cambridge Astronomical Survey Unit.