Posts Tagged ‘formation’

Lives And Deaths Of Sibling Stars

Credit: ESO/G. Beccari

Credit: ESO/G. Beccari

In this striking new image from ESO’s La Silla Observatory in Chile young stars huddle together against a backdrop of clouds of glowing gas and lanes of dust. The star cluster, known as NGC 3293, would have been just a cloud of gas and dust itself about ten million years ago, but as stars began to form it became the bright group of stars we see here. Clusters like this are celestial laboratories that allow astronomers to learn more about how stars evolve.

This beautiful star cluster, NGC 3293, is found 8000 light-years from Earth in the constellation of Carina (The Keel). This cluster was first spotted by the French astronomer Nicolas-Louis de Lacaille in 1751, during his stay in what is now South Africa, using a tiny telescope with an aperture of just 12 millimetres. It is one of the brightest clusters in the southern sky and can be easily seen with the naked eye on a dark clear night.

Star clusters like NGC 3293 contain stars that all formed at the same time, at the same distance from Earth and out of the same cloud of gas and dust, giving them the same chemical composition. As a result clusters like this are ideal objects for testing stellar evolution theory.

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Hidden Nurseries In The Milky Way

APEX, the Atacama Pathfinder Experiment, is a telescope of 12 m diameter at an exceptional site on Earth: the Chajnantor plateau is located 5100 m above sea level in the Atacama desert in Chile. It was used to map the whole inner part of the plane of our Milky Way, ranging from the Southern constellations of Vela and Carina all the way to the Northern constellations of Aquila and the great Cygnus rift. The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) mapped the Galactic Plane at a wavelength of 0.87 mm. Cold interstellar dust emits strongly in this part of the electromagnetic spectrum, called the sub-millimeter range, while it is blocking visible and infrared wavelengths. The survey has revealed an unprecedented number of cold dense clumps of gas and dust as the cradles of massive stars, thus providing a complete view of their birthplaces in the Milky Way. Based on this census, an international team of scientists led by Timea Csengeri from the Max Planck Institute for Radio Astronomy in Bonn has estimated the time scale for these nurseries to grow stars. This has been found to be a very fast process: with only 75,000 years on average it is much shorter than the corresponding time scales typically found for nurseries of lower mass stars.

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A Turbulent Birth for Stars In Merging Galaxies

Using state of the art computer simulations, a team of French astrophysicists have for the first time explained a long standing mystery: why surges of star formation (so called ‘starbursts’) take place when galaxies collide. The scientists, led by Florent Renaud of the AIM institute near Paris in France, publish their results in a letter to the journal Monthly Notices of the Royal Astronomical Society.

Stars form when the gas inside galaxies becomes dense enough to collapse, usually under the effect of gravitation. When galaxies merge however, this increases the random motions of their gas generating whirls of turbulence which should hinder the collapse of the gas. Intuitively this turbulence should then slow down or even shut down the formation of stars, but in reality astronomers observe the opposite.

The new simulations were made using two of the most powerful supercomputers in Europe. The team modelled a galaxy like our own Milky Way and the two colliding Antennae galaxies.

For the Milky Way type galaxy, the astrophysicists used 12 million hours of time on the supercomputer Curie, running over a period of 12 months to simulate conditions across 300,000 light years. For the Antennae type system, the scientists used the supercomputer SuperMUC to cover 600,000 light years. This time they needed 8 million hours of computational time over a period of 8 months. With these enormous computing resources the team were able to model the systems in great detail, investigating details that were only a fraction of a light year across.

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Astrophysicists Launch Ambitious Assessment Of Galaxy Formation Simulations

December 11, 2013 Leave a comment

One of the most powerful tools for understanding the formation and evolution of galaxies has been the use of computer simulations–numerical models of astrophysical processes run on supercomputers and compared with astronomical observations. Getting computer simulations to produce realistic-looking galaxies has been a challenge, however, and different codes (simulation programs) produce inconsistent results.

Now, an international collaboration led by astrophysicists at the University of California, Santa Cruz, aims to resolve these issues through an ambitious multi-year project named AGORA (Assembling Galaxies of Resolved Anatomy). AGORA will run direct comparisons of different codes using a common set of initial conditions and astrophysical assumptions. Each code treats some aspects of the physics differently, especially the way that energy from stars and supernovas is fed back into the simulated galaxies. The simulations are being run at the best resolutions currently possible, and they are using the same input physics as much as possible. The simulation results will be systematically compared with each other and against a variety of observations using a common analysis and visualization tool.

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A Rare Snapshot Of A Planetary Construction Site

October 25, 2013 Leave a comment

Credit: Á. Kóspál (ESA) and A. Moór (Konkoly Observatory)

Credit: Á. Kóspál (ESA) and A. Moór (Konkoly Observatory)

When a star similar to our Sun is born, it is surrounded by a disk of dust and gas. Within that disk, the star’s planetary system begins to form: The dust grains stick together to build larger, solid, kilometer-sized bodies known as planetesimals. Those either survive in the form of asteroids and comets, or clump together further to form solid planets like our Earth, or the cores of giant gas planets.

Current models of planet formation predict that, as a star reaches the planetesimal stage, the original gas should quickly be depleted. Some of the gas falls into the star, some is caught up by what will later become giant gas planets like Jupiter, and the rest is dispersed into space, driven by the young star’s intense radiation. After 10 million years or so, all the original gas should be gone.

But now a team of astronomers from the Netherlands, Hungary, Germany, and the US has found what appears to be a rare hybrid disk, which contains plenty of original gas, but also dust produced much later in the collision of planetesimals. As such, it qualifies as a link between an early and a late phase of disk evolution: the primordial disk and a later debris phase.

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Astronomers Witness Birth Of Milky Way’s Most Massive Star

The team used the new ALMA (Atacama Large Millimetre/submillimetre Array) telescope in Chile – the most powerful radio telescope in the world – to view the stellar womb which, at 500 times the mass of the Sun and many times more luminous, is the largest ever seen in our galaxy.

The researchers say their observations – to be published in the journal Astronomy and Astrophysics – reveal how matter is being dragged into the centre of the huge gaseous cloud by the gravitational pull of the forming star – or stars – along a number of dense threads or filaments.

“The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud,” said lead author Dr Nicolas Peretto, from Cardiff University. “We wanted to see how monster stars form and grow, and we certainly achieved our aim. One of the sources we have found is an absolute giant — the largest protostellar core ever spotted in the Milky Way!

“Even though we already believed that the region was a good candidate for being a massive star-forming cloud, we were not expecting to find such a massive embryonic star at its centre. This cloud is expected to form at least one star 100 times more massive than the Sun and up to a million times brighter. Only about one in 10,000 of all the stars in the Milky Way reach that kind of mass.”

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Cosmic Dust Belts Without Dust

Planets and asteroids, red giants and brown dwarfs – there are all kinds of objects in our Universe. Debris disks are among them. These are belts consisting of countless dust particles and planetesimals, circling around one central star. “At least one fifth of stars are surrounded by dust belts like these,” Prof. Dr. Alexander Krivov from the Friedrich-Schiller-University Jena explains. “They are the remains of the formation of planets, in which the unused, building materials are collected,” the astrophysicist points out. Therefore debris disks are an important piece in the puzzle to be able to better understand the variety of planetary systems.

For astronomers like Alexander Krivov debris disks are actually nothing new. Our sun is also orbited by such dust belts: the Asteroid Belt and the Kuiper Belt with Pluto being perhaps the most well-known object in it. However, the Jena astrophysicist, accompanied by an international team of scientists, has observed six stars similar to the sun with extraordinary dust belts: The newly discovered debris disks are not only bigger than the Kuiper Belt. Above all they are extremely cold. With a temperature of about minus 250 °C they are the coldest debris disks known so far. The scientists report on it in the science journal ‘The Astrophysical Journal’, which is already online and will be available in a print version from 20 July. “We were surprised that such cold debris disks exist at all,” Alexander Krivov, the lead author of the new study, says. By way of comparison: The Kuiper Belt is about 70 °C degree warmer, some of the dust disks even reach room temperature.

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Astronomers Spy On Galaxies In The Raw

A CSIRO radio telescope has detected the raw material for making the first stars in galaxies that formed when the Universe was just three billion years old — less than a quarter of its current age. This opens the way to studying how these early galaxies make their first stars.

The telescope is CSIRO’s Australia Telescope Compact Array telescope near Narrabri, NSW. “It one of very few telescopes in the world that can do such difficult work, because it is both extremely sensitive and can receive radio waves of the right wavelengths,” says CSIRO astronomer Professor Ron Ekers.

The raw material for making stars is cold molecular hydrogen gas, H2. It can’t be detected directly but its presence is revealed by a ‘tracer’ gas, carbon monoxide (CO), which emits radio waves.

In one project, astronomer Dr Bjorn Emonts (CSIRO Astronomy and Space Science) and his colleagues used the Compact Array to study a massive, distant conglomerate of star-forming ‘clumps’ or ‘proto-galaxies’ that are in the process of coming together as a single massive galaxy. This structure, called the Spiderweb, lies more than ten thousand million light-years away [at a redshift of 2.16].

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Hubble Movies of Supersonic Jets from Young Stars

August 31, 2011 Leave a comment

Stellar jets HH 47, HH 34 and HH 2. Image credit: NASA, ESA, and P. Hartigan (Rice University)

Stellar jets HH 47, HH 34 and HH 2. Image credit: NASA, ESA, and P. Hartigan (Rice University)

Stars  aren’t shy about sending out birth announcements. They fire off  energetic jets of glowing gas travelling at supersonic speeds in  opposite directions through space.

Although  astronomers have looked at still pictures of stellar jets for decades,  now they can watch movies, thanks to the NASA/ESA Hubble Space  Telescope.




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Discovery Sheds Light on Ecosystem of Young Galaxies

August 30, 2011 Leave a comment

A team of scientists, led by Michael Rauch from the Carnegie Observatories, has discovered a distant galaxy that may help elucidate two fundamental questions of galaxy formation: How galaxies take in matter and how they give off energetic radiation. Their work will be published in the Monthly Notices of the Royal Astronomical Society.

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