Stars Reveal the Secrets of Looking Young

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Some people are in great shape at the age of 90, while others are decrepit before they’re 50. We know that how fast people age is only loosely linked to how old they actually are — and may have more to do with their lifestyle. A new study using both the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory and the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.

Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity. Relics of the early years of the Universe, with ages of typically 12–13 billion years (the Big Bang took place 13.7 billion years ago), there are roughly 150 globular clusters in the Milky Way and they contain many of our galaxy’s oldest stars.

But while the stars are old and the clusters formed in the distant past, astronomers using the MPG/ESO 2.2-metre telescope and the NASA/ESA Hubble Space Telescope have found that some of these clusters are still young at heart. The research is presented in the 20 December 2012 issue of the journal Nature.

“Although these clusters all formed billions of years ago,” says Francesco Ferraro (University of Bologna, Italy), the leader of the team that made the discovery, “we wondered whether some might be aging faster or slower than others. By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging.”

Star clusters form in a short period of time, meaning that all the stars within them tend to have roughly the same age. Because bright, high-mass stars burn up their fuel quite quickly, and globular clusters are very old, there should only be low-mass stars still shining within them.

This, however, turns out not to be the case: in certain circumstances, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a close neighbour, or if they collide. The re-invigorated stars are called blue stragglers [1], and their high mass and brightness are properties that lie at the heart of this study.

Heavier stars sink towards the centre of a cluster as the cluster ages, in a process similar to sedimentation. Blue stragglers’ high masses mean they are strongly affected by this process, while their brightness makes them relatively easy to observe [2].

To better understand cluster aging, the team mapped the location of blue straggler stars in 21 globular clusters, as seen in images from the MPG/ESO 2.2-metre telescope and Hubble, among other observatories [3]. Hubble provided high resolution imagery of the crowded centres of 20 of the clusters, while the ground-based imagery gave a wider view of their less busy outer regions.

Analysing the observational data, the team found that a few clusters appeared young, with blue straggler stars distributed throughout, while a larger group appeared old, with the blue stragglers clumped in the centre. A third group was in the process of aging, with the stars closest to the core migrating inwards first, then stars ever further out progressively sinking towards the centre.

“Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster,” said Barbara Lanzoni (University of Bologna, Italy), a co-author of the study. “In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the Universe.”

As a cluster’s heaviest stars sink towards the centre, the cluster eventually experiences a phenomenon called core collapse, where the centre of the cluster bunches together extremely densely. The processes leading towards core collapse are quite well understood, and revolve around the number, density and speed of movement of the stars. However, the rate at which they happened was not known until now [4]. This study provides the first empirical evidence of how quickly different globular clusters age.

Notes

[1] Blue stragglers are so called because of their blue colour, and the fact that their evolution lags behind that of their neighbours.

[2] Blue stragglers combine being relatively bright and high mass by the standards of globular cluster stars, but they are not the only stars within these clusters that are either bright or massive.

Red giant stars are brighter, but they have a much lower mass, and therefore are not affected by the sedimentation process in the same way. (It is easy to distinguish these from blue stragglers because their colour is very different.)

Neutron stars, the extremely dense cores of stars much bigger than the Sun that exploded billions of years ago in the early history of globular clusters, have a similar mass to blue stragglers, and are affected by the sedimentation process, but they are incredibly difficult to observe and therefore do not make a useful subject for this study.

Blue stragglers are the only stars within clusters that combine high mass and high brightness.

[3] Of the 21 clusters covered by this research, 20 were studied with Hubble, 12 with the MPG/ESO 2.2-metre telescope, eight with the Canada-France-Hawaii telescope and one with NAOJ’s Subaru Telescope.

[4] Such a rate depends in a complex manner on the number of stars, their density and their velocity within a cluster. While the first two quantities are relatively easy to measure, velocity is not. For these reasons, previous estimates of the rate of globular cluster dynamical aging were based only on theoretical arguments, while the new method allows a totally empirical measurement.

More information

This research was presented in a paper, “Dynamical age differences amongst coeval star clusters as revealed by blue stragglers“, by F. R. Ferraro et al., to appear in the journal Nature on 20 December 2012.

The team is composed of F. R. Ferraro (University of Bologna, Italy), B. Lanzoni (University of Bologna), E. Dalessandro (University of Bologna), G. Beccari (ESO, Garching, Germany), M. Pasquato (University of Bologna), P. Miocchi (University of Bologna), R. T. Rood (University of Virginia, Charlottesville, USA), S. Sigurdsson (Pennsylvania State University, USA), A. Sills (McMaster University, Hamilton, Canada), E. Vesperini (Indiana University, Bloomington, USA), M. Mapelli (INAF-Osservatorio Astronomico di Padova, Italy), R. Contreras (University of Bologna), N. Sanna (University of Bologna), A. Mucciarelli (University of Bologna).

This research is part of the Cosmic-Lab project (www.cosmic-lab.eu) funded by the ERC (European Research Council) for a total amount of € 1.8 million for 5 years. Set up in 2007 by the European Union, the ERC aims to stimulate scientific excellence in Europe by encouraging competition for funding between the very best, creative researchers of any nationality and age. Since its launch, the ERC has funded over 2 500 researchers and their frontier research projects across Europe. The ERC operates according to an “investigator-driven”, or “bottom-up”, approach, allowing researchers to identify new opportunities in all fields of research (Physical Sciences and Engineering, Life Sciences, and Social Sciences and Humanities). It has also become a benchmark of the competitiveness of national research systems and complements existing funding schemes at national and European levels. The ERC, which is the newest component of the EU’s Seventh Research Framework Programme, has a total budget of €7.5 billion from 2007 to 2013. Last year, the European Commission proposed a substantial increase in the ERC’s budget for 2014 to 2020 under the new framework programme (‘Horizon 2020’). The ERC is composed of an Executive Agency and a Scientific Council. The Scientific Council is made up of 22 top researchers and sets the ERC’s scientific strategy. The ERC is led by President Prof. Helga Nowotny and the Scientific Council is represented in Brussels by Secretary General Prof. Donald Dingwell. The ERC Executive Agency implements the “Ideas” Specific Programme and is led by Director (ad int.) Pablo Amor.

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Contacts

Francesco Ferraro
University of Bologna
Italy
Tel: +39 051 209 5774
Email: francesco.ferraro3@unibo.it

Barbara Lanzoni
University of Bologna
Italy
Tel: +39 051 209 5792
Email: barbara.lanzoni3@unibo.it

Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Oli Usher
Hubble/ESA
Garching bei München, Germany
Tel: +49 89 3200 6855
Email: ousher@eso.org

Source: eso.org

The Stars Streak Overhead

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Although this image might at first look like abstract modern art, it is in fact the result of a long camera exposure of the night sky over the Chajnantor Plateau in the Chilean Andes. As the Earth rotates towards another day, the stars of the Milky Way above the desert stretch into colourful streaks. The high-tech telescope in the foreground, meanwhile, takes on a dreamlike quality.

This mesmerising photo was taken 5000 metres above sea level on the Chajnantor Plateau, home of the Atacama Pathfinder Experiment (APEX) telescope, which is seen here. APEX is a 12-metre-diameter telescope which collects light with wavelengths in the millimetre and submillimetre range. Astronomers use APEX to study objects ranging from the cold clouds of gas and cosmic dust where new stars are being born, to some of the earliest and most distant galaxies in the Universe.

APEX is a pathfinder for the Atacama Large  Millimeter/submillimeter Array (ALMA), a revolutionary telescope that ESO, together with its international partners, is building and operating, also on the Chajnantor Plateau. When ALMA is completed in 2013, it will be an array of 54 antennas with 12-metre diameters, and an additional 12 antennas with 7-metre diameters. The two telescopes are complementary: thanks to its larger field of view, APEX can find many targets across wide areas of sky, which ALMA will study in great detail due to its far higher angular resolution. APEX and ALMA are both important tools to help astronomers find out more about the workings of our Universe, such as the formation of the stars seen wheeling overhead in this image.

ESO Photo Ambassador Babak Tafreshi took this picture. He is also founder of The World At Night, a programme to create and exhibit a collection of stunning photographs and time-lapse videos of the world’s most beautiful and historic sites against a nighttime backdrop of stars, planets and celestial events.

APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. Operation of APEX at Chajnantor is entrusted to ESO. ALMA is an international astronomy facility, and a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ESO is the European partner in ALMA.

Links

Credit:

ESO/B. Tafreshi (twanight.org)

Source: eso.org

An unexpected population of young-looking stars

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The NASA/ESA Hubble Space Telescope offers an impressive view of the centre of globular cluster NGC 6362. The image of this spherical collection of stars takes a deeper look at the core of the globular cluster, which contains a high concentration of stars with different colours.

Tightly bound by gravity, globular clusters are composed of old stars, which, at around 10 billion years old, are much older than the Sun. These clusters are fairly common, with more than 150 currently known in our galaxy, the Milky Way, and more which have been spotted in other galaxies.

Globular clusters are among the oldest structures in the Universe that are accessible to direct observational investigation, making them living fossils from the early years of the cosmos.

Astronomers infer important properties of globular clusters by looking at the light from their constituent stars. For many years, they were regarded as ideal laboratories for testing the standard stellar evolution theory. Among other things, this theory suggests that most of the stars within a globular cluster should be of a similar age.

Recently, however, high precision measurements performed in numerous globular clusters, primarily with the Hubble Space Telescope, has led some to question this widely accepted theory. In particular, certain stars appear younger and bluer than their companions, and they have been dubbed blue stragglers. NGC 6362 contains many of these stars.

Since they are usually found in the core regions of clusters, where the concentration of stars is large, the most likely explanation for this unexpected population of objects seems to be that they could be either the result of stellar collisions or transfer of material between stars in binary systems. This influx of new material would heat up the star and make it appear younger than its neighbours.

NGC 6362 is located about 25 000 light-years from Earth in the constellation of Ara (The Altar). British astronomer James Dunlop first observed this globular cluster on 30 June 1826.

This image was created combining ultraviolet, visual and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys and the Wide Field Camera 3. An image image of NGC 6362 taken by the MPG/ESO 2.2-metre telescope will be published by the European Southern Observatory on Wednesday. See it on www.eso.org from 12:00 on 31 October.

Credit:

ESA/Hubble & NASA 

Source: spacetelescope.org

ESOcast 46: Catching Light — Special 50th anniversary episode #6 (by ESOobservatory)

ESOcast 46 is the sixth special episode of this series. It describes how state-of-the-art cameras and spectrographs help ESO’s powerful telescopes collect and analyse the faint light from the distant Universe. Without these instruments, ESO’s eyes on the sky would be blind.

Today’s astronomical images are very different from those from the 1960s. Back then, astronomers used large photographic glass plates, which were not very sensitive and hard to handle. Nowadays, ESO’s telescopes use some of the largest and most sensitive electronic detectors in the world. They catch almost every cosmic photon and recover almost every possible bit of information. For instance, the VLT Survey Telescope’s camera — OmegaCAM — has 32 detectors, which team up to produce spectacular images of the Universe, each with an impressive 268 million pixels.

But astronomy is not only about taking breathtaking images. Astronomers are always after as much information as possible so they need to dissect the starlight into its component colours to study its composition. Spectroscopy is one of the most powerful tools in astronomy and ESO’s telescopes also have some of the world’s most powerful spectrographs, such as the powerful X-shooter at the Very Large Telescope. Spectroscopy allows astronomers to infer important properties of the stars, such as the chemical elements they contain, their temperatures, motions, and even their ages. Moreover, they can study the atmospheres of exoplanets orbiting distant stars or newborn galaxies at the edge of observable Universe.

Watch this episode to discover more about ESO’s state-of-the-art astronomical instruments.

More information and download-options: http://www.eso.org/public/videos/esocast46a/

Credit:
An ESO production

Source: youtube.com

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