Archive for the ‘Globular Clusters’ Category

A Cluster With A Secret

September 5, 2012 Leave a comment

The globular star cluster Messier 4

A new image from ESO’s La Silla Observatory in Chile shows the spectacular globular star cluster Messier 4. One of its stars has strange and unexpected properties, apparently possessing the secret of eternal youth.

New results for the stars in Messier 4 have been surprising. The stars in globular clusters are old and hence not expected to be rich in the heavier chemical elements. This is what is found, but one of the stars in a recent survey was also found to have much more of the rare light element lithium than expected. The source of this lithium is mysterious. Normally this element is gradually destroyed over the billions of years of a star’s life, but this one star amongst thousands seems to have the secret of eternal youth. It has either somehow managed to retain its original lithium, or it has found a way to enrich itself with freshly made lithium.

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Hubble Watches Star Clusters On A Collision Course

August 16, 2012 Leave a comment

Image Credit: NASA, ESA, and E. Sabbi (ESA/STScI)

Astronomers using data from NASA’s Hubble Space Telescope have caught two clusters full of massive stars that may be in the early stages of merging. The clusters are 170,000 light-years away in the Large Magellanic Cloud, a small satellite galaxy to our Milky Way.

What at first was thought to be only one cluster in the core of the massive star-forming region 30 Doradus (also known as the Tarantula Nebula) has been found to be a composite of two clusters that differ in age by about one million years.

Lead scientist Elena Sabbi of the Space Telescope Science Institute in Baltimore, Md., and her team began looking at the area while searching for runaway stars, fast-moving stars that have been kicked out of their stellar nurseries where they first formed. “Stars are supposed to form in clusters, but there are many young stars outside 30 Doradus that could not have formed where they are; they may have been ejected at very high velocity from 30 Doradus itself,” Sabbi said.

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Glittering Jewels of Messier 9

March 16, 2012 Leave a comment

Image Credit: NASA & ESA

Image Credit: NASA & ESA

The NASA/ESA Hubble Space Telescope has produced the most detailed image so far of Messier 9, a globular star cluster located close to the centre of the galaxy. This ball of stars is too faint to see with the naked eye, yet Hubble can see over 250 000 individual stars shining in it.

Messier 9, pictured here, is a globular cluster, a roughly spherical swarm of stars that lies around 25 000 light-years from Earth, near the centre of the Milky Way, so close that the gravitational forces from the galactic centre pull it slightly out of shape.

Globular clusters are thought to harbour some of the oldest stars in our galaxy, born when the Universe was just a small fraction of its current age. As well as being far older than the Sun — around twice its age — the stars of Messier 9 also have a markedly different composition, and are enriched with far fewer heavier elements than the Sun.

In particular, the elements crucial to life on Earth, like oxygen and carbon, and the iron that makes up our planet’s core, are very scarce in Messier 9 and clusters like it. This is because the Universe’s heavier elements were gradually formed in the cores of stars, and in supernova explosions. When the stars of Messier 9 formed, there were far smaller quantities of these elements in existence.

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Globular Star Clusters Survived 13-Gyr-Old Massacre

February 14, 2012 Leave a comment

Our Milky Way galaxy is surrounded by some 200 compact groups of stars, containing up to a million stars each. These globular clusters are almost as old as the universe itself and hold valuable information on how the first generations of stars and galaxies formed. Now a team of astronomers from Germany and the Netherlands have conducted a novel type of computer simulation that looked at how they were born – and they find that these giant clusters of stars are the only survivors of a 13 billion year-old massacre that destroyed many of their smaller siblings. The new work, led by Dr Diederik Kruijssen of the Max Planck Institute for Astrophysics in Garching appears in a paper in the journal Monthly Notices of the Royal Astronomical Society.

Globular star clusters have a remarkable characteristic: the typical number of stars they contain appears to be about the same throughout the Universe. This is in contrast to much younger stellar clusters, which can contain almost any number of stars, from fewer than 100 to many thousands. The team of scientists proposes that this difference can be explained by the conditions under which globular clusters formed early on in the evolution of their host galaxies.

The researchers ran simulations of isolated and colliding galaxies, in which they included a model for the formation and destruction of stellar clusters. When galaxies collide, they often generate spectacular bursts of star formation (“starbursts”) and a wealth of bright, young stellar clusters of many different sizes. As a result it was always thought that the total number of star clusters increases during starbursts. But the Dutch-German team found the opposite result in their simulations.

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First Low-Mass Star Detected in Globular Cluster

December 22, 2011 Leave a comment

Until now, it was merely assumed that low-mass and therefore extremely faint stars must exist. However, in view of the vast distances and weak luminosity of low-mass stars, even the most modern telescopes fail. Together with a Polish-Chilean team of researchers, Swiss astrophysicist Philippe Jetzer from the University of Zurich has now detected the first low-mass star in the globular cluster M22 indirectly. As their recent article accepted for publication in Astrophysical Journal Letters reveals, it involves a dwarf star that has less than a fifth of the mass of our sun and is 3.2 kiloparsecs from it (one kiloparsec corresponding to 3,210 light years).

The evidence, which enables the mass to be determined highly accurately, is based upon so-called gravitational microlensing and requires the highest technical standards available. The measurements were carried out on the ESO VLT 8-meter telescope with adaptive optics at the Paranal Observatory in Chile.

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NASA’s Hubble Finds Stellar Life and Death in a Globular Cluster

November 23, 2011 Leave a comment

Credit: P. Goudfrooij, STScI)

Credit: P. Goudfrooij, STScI)

A new NASA Hubble Space Telescope image shows globular cluster NGC 1846, a spherical collection of hundreds of thousands of stars in the outer halo of the Large Magellanic Cloud, a neighboring dwarf galaxy of the Milky Way that can be seen from the southern hemisphere.

Aging bright stars in the cluster glow in intense shades of red and blue. The majority of middle-aged stars, several billions of years old, are whitish in color. A myriad of far distant background galaxies of varying shapes and structure are scattered around the image.

The most intriguing object, however, doesn’t seem to belong in the cluster. It is a faint green bubble near the bottom center of the image. This so-called ‘planetary nebula’ is the aftermath of the death of a star. The burned-out central star can be seen inside the bubble. It is uncertain whether the planetary nebula is a member of NGC 1846, or simply lies along the line of sight to the cluster. Measurements of the motion of the cluster stars and the planetary nebula’s central star suggest it might be a cluster member.

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VISTA Finds New Globular Star Clusters

October 19, 2011 Leave a comment

Credit: ESO/D. Minniti/VVV Team

Credit: ESO/D. Minniti/VVV Team

Two newly discovered globular clusters have been added to the total of just 158 known globular clusters in our Milky Way. They were found in new images from ESO’s VISTA survey telescope as part of the Via Lactea (VVV) survey. This survey has also turned up the first star cluster that is far beyond the centre of the Milky Way and whose light has had to travel right through the dust and gas in the heart of our galaxy to get to us.

The dazzling globular cluster called UKS 1 dominates the right-hand side of the first of the new infrared images from ESO’s VISTA survey telescope at the Paranal Observatory in Chile. But if you can drag your gaze away, there is a surprise lurking in this very rich star field — a fainter globular cluster that was discovered in the data from one of VISTA’s surveys. You will have to look closely to see the other star cluster, which is called VVV CL001: it is a small collection of stars in the left half of the image.

But VVV CL001 is just the first of VISTA’s globular discoveries. The same team has found a second object, dubbed VVV CL002, which appears in image b [1]. This small and faint grouping may also be the globular cluster that is the closest known to the centre of the Milky Way. The discovery of a new globular cluster in our Milky Way is very rare. The last one was discovered in 2010, and only 158 globular clusters were known in our galaxy before the new discoveries.

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