HZDR Research: Cosmic jets of young stars formed by magnetic fields

This is an artist's rendering showing the birth of a star: A dust and gas cloud is forming a spiraling disk around a massive baby star while jets of material shoot from its core. 

Credit: ESO/L. Calada

Astrophysical jets are counted among our Universe's most spectacular phenomena: From the centers of black holes, quasars, or protostars, these rays of matter sometimes protrude several light years into space.

Now, for the first time ever, an international team of researchers has successfully tested a new model that explains how magnetic fields form these emissions in young stars.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were part of this research.

Their findings have been published in the journal Science. The insights gleaned from this research may even apply to cancer therapy.

Whenever an object in space forms a rotating disc of matter, chances are that it gives rise to a "jet" – a thin, straight emission of matter which emanates from the disc's center and that looks like a spintop.

These structures can be observed especially during the formation of new stars, but understanding how such thin beams are able to form within the disc is something that continues to elude scientists.

Now, HZDR researchers, along with their European, American, and Asian colleagues, have investigated this process in the lab.

At the Laboratoire pour l'Utilisation des Lasers Intenses (LULI), in France, scientists hit a plastic sample with laser light which set the electrons at the target's core in motion, transforming the solid plastic object into conductive plasma.

"Think of it as a sort of rapidly expanding hot cloud of electrons and ions. On a small scale, the plasma represents a young star's accumulation of matter," explains Professor Thomas Cowan, the study's co-author and Director of the HZDR Institute of Radiation Physics.

Miniature versions of young stars for the lab
What made the experiment special was the fact that the plasma was exposed to a very powerful pulsed magnetic field.

The idea behind it: under a magnetic field's influence, the normally widely scattered plasma begins to focus, forming a hollow center.

This ultimately produces a shockwave, from which a very thin beam starts to project, a jet.

The experiment was set up in such a way as to allow for extrapolation to conditions as they would be encountered in the Universe: within as little as 20 nanoseconds, over 100,000 times faster than a fly flapping its wings, the lab plasma forms structures similar to a young star's jet in approximately six years.

This allowed the researchers to test their model with astronomical observations, which were made possible through space telescopes, in the last two decades.

The data were in good agreement. In a jet, for instance, a crossing over of particle streams can occur, which in turn results in the formation of very hot spots.

"X-ray measurements of actual jets show these features at the exact same points as our true-to-scale plasma model in the lab," says Cowan.

With its help, the researchers were able to offer a model that, for the first time ever, is capable of explaining the formation of jets solely by way of magnetic fields.

Previous approaches had considered the rotation of matter about the young star another influencing factor.

The realisation that plasma can be focused in this way may prove a real practical boon in the field of medical engineering.

According to Cowan, it's conceivable that with the help of pulsed magnetic fields, a particularly thin proton beam could be produced for use in radiation therapy.

It's what Florian Kroll, Ph.D. student at the HZDR and one of the study's co-authors, is investigating.

Special pulse generator designed at the Dresden High Magnetic Field Lab

To produce strong pulsed magnetic fields for the experiment, the researchers drew on the expertise at the HZDR's Dresden High Magnetic Field Lab: "We developed a special pulse generator which allowed our French colleagues to set up powerful magnetic fields within a small, enclosed lab space," says Dr. Thomas Herrmannsdörfer, head of division at the High Magnetic Field Lab.

The generator, just about the size of a wardrobe, is capable of generating currents of up to 300 kiloampere.

According to Herrmannsdörfer, building such a compact facility was a real technical challenge: "Our electrical engineers came up with some very innovative solutions."

"This is also helping us now with developing these types of generators for application in industry and medical technology."

Currently, the pulse generator is still located at the French laser lab at Palaiseau near Paris, because beginning in December the Dresden scientists are planning on once again working together with their LULI colleagues.

More information: Science DOI: 10.1126/science.1259694

UWISH-2 Survey: Numerous unknown jets from young stars and planetary nebulae

The area shown here was part of the very first image taken for the UWISH2 survey. 

It shows on the top a region of massive star formation (called G35.2N) with two spectacular jets. 

On the bottom an intermediate mass young stellar cluster (Mercer14) can be seen. 

Several jets are visible in its vicinity, as well as a region of photo-ionized material surrounding a young massive star. 

Credit: University of Kent

For many years astronomers have known that young 'protostars' drive supersonic jets of gas from their north and south poles. However, this is the first time that so many of them have been detected at once.

The results come from a five year survey undertaken with the UK Infra-Red Telescope (UKIRT) and are expected to prompt significant changes in the understanding of the planetary nebulae population in the Galaxy, as well as the properties of jets ejected from young forming stars.

By examining images of excited hydrogen molecules at infrared wavelengths, scientists have been able to see through the gas and dust in the Milky Way to observe more distant targets.

These targets are normally hidden from view and many of them have never been seen before.

The entire survey area covers approximately 1450 times the size of the full moon, or the equivalent of a 95 GigaPixel image.

The survey reveals jets from protostars and planetary nebulae, as well as supernova remnants, the illuminated edges of vast clouds of gas and dust, and the warm regions that envelope massive stars and their associated clusters of smaller stars.

Based on current estimates using these data, the project expects to identify about 1000 unique jets from young stars, at least 90% of these are new discoveries, as well as 300 planetary nebulae, with almost half of them unknown.

This is a text-book example of triggered star formation. 

There is the outline of a molecular cloud, which is illuminated by ionizing radiation of massive stars situated off the bottom of the image. 

The radiation pressure has compressed the cloud and started the process of star formation.

The forming stars can be identified by reflection nebulae surrounding them, or by their jets. 

Models of the process of triggered star formation predict an age gradient of the forming stars with younger objects further inside, away from the source of the ionizing radiation.

The object shown here is a prime example that confirms this scenario with reflection nebulae ranging in colours from blue, near the tip of the molecular cloud, to green and yellow further inside.

The colour change towards red indicates the objects are further embedded in their parental cloud core and thus younger. 

The youngest object is completely invisible even at these infrared wavelengths, and can only by identified by the jet it is launching (top of image). 

Credit: University of Kent

Dr Dirk Froebrich of the University of Kent's Centre for Planetary Science said: "These discoveries are very exciting."

"We will ultimately have much better statistics, meaning we will be able to investigate the physical mechanisms that determine the jet lengths, as well as their power."

"This will bring us much closer to answering some of the fundamental questions of star formation: How are these jets launched and how much energy, mass and momentum do they feed back into the surrounding interstellar medium."

To mark the 5th anniversary of the start of the observations of the survey on 27 August, the project has released a number of images taken with the UK Infra-Red Telescope (UKIRT), based in Hawaii and used for the research.

This image shows a field that contains a newly discovered photogenic planetary nebulae. 

Internally dubbed by the research team as the "Jelly-Fish PN" it shows an almost circular ring of emission from molecular hydrogen with a variety of structure in the ring itself and inside. 

The central ionizing source responsible for the radiation is a white dwarf, which is too faint at the near infrared wavelengths to be visible in the image. 

Credit: University of Kent

The project has been led by Dr Dirk Froebrich from the Centre for Planetary Sciences at the University of Kent, in collaboration with Dr Chris J. Davis from the Astrophysics Research Institute at Liverpool John Moores University.

ESO Wide Field Imager Image: Young stars paint spectacular stellar landscape

The Wide Field Imager on the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile has captured the best image so far of the star cluster NGC 3572, a gathering of young stars, and its spectacular surroundings. 

This new image shows how the clouds of gas and dust around the cluster have been sculpted into whimsical bubbles, arcs and the odd features known as elephant trunks by the stellar winds flowing from the bright stars. 

The brightest of these cluster stars are heavier than the Sun and will end their short lives as supernova explosions. 

Credit: ESO/G. Beccari

Astronomers at ESO have captured the best image so far of the clouds around the star cluster NGC 3572.

This image shows how these clouds of gas and dust have been sculpted into bubbles, arcs and the odd features known as elephant trunks by the stellar winds flowing from this gathering of hot stars.

The brightest of these cluster stars are much heavier than the Sun and will end their short lives as supernova explosions.

Most stars do not form alone, but with many siblings that are created at about the same time from a single cloud of gas and dust. NGC 3572, in the southern constellation of Carina (The Keel), is one of these clusters.

It contains many hot young blue-white stars that shine brightly and generate powerful stellar winds that tend to gradually disperse the remaining gas and dust from their surroundings.

The glowing gas clouds and accompanying cluster of stars are the subjects of a new picture from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile.

In the lower part of the image a big chunk of the molecular cloud that gave birth to these stellar youngsters still can be seen.

It has been dramatically affected by the powerful radiation coming from its smoldering offspring.

The radiation not only makes it glow with a characteristic hue, but also sculpts the clouds into amazingly convoluted shapes, including bubbles, arcs and the dark columns that astronomers call elephant trunks.

A strange feature captured in this image is the tiny ring-like nebula located slightly above the centre of the image.

Astronomers still are a little uncertain about the origin of this curious feature. It is probably a dense leftover from the molecular cloud that formed the cluster, perhaps a bubble created around a very bright hot star.

But some authors have considered that it may be some kind of oddly shaped planetary nebula—the remnants of a dying star.

Spitzer discovers young stars with a 'hula hoop'

In this artist's impression, a disk of dusty material leftover from star formation girds two young stars like a hula hoop. 

As the two stars whirl around each other, they periodically peek out from the disk, making the system appear to "blink" every 93 days. 

Image credit: NASA/JPL-Caltech

Astronomers using NASA's Spitzer Space Telescope have spotted a young stellar system that "blinks" every 93 days.

Called YLW 16A, the system likely consists of three developing stars, two of which are surrounded by a disk of material left over from the star-formation process.

As the two inner stars whirl around each other, they periodically peek out from the disk that girds them like a hula hoop.

The hoop itself appears to be misaligned from the central star pair, probably due to the disrupting gravitational presence of the third star orbiting at the periphery of the system.

The whole system cycles through bright and faint phases, with the central stars playing a sort of cosmic peek-a-boo as the tilted disk twirls around them.

It is believed that this disk should go on to spawn planets and the other celestial bodies that make up a solar system.

Spitzer observed infrared light from YLW 16A, emitted by the warmed gas and dust in the disk that still swathes the young stars.

Other observations came from the ground-based 2MASS survey, as well as from the NACO instrument at the European Southern Observatory's Very Large Telescope in Chile.

NB: NACO is an Adaptive Optics facility producing images as sharp as if taken in space. It is also equipped with a spectrometer, polarimeter, coronographs, etc

YLW 16A is the fourth example of a star system known to blink in such a manner, and the second in the same star-forming region Rho Ophiuchus.

The finding suggests that these systems might be more common than once thought.

Blinking star systems with warped disks offer scientists a way to study how planets form in these environments.

The planets can orbit one or both of the stars in the binary star system. The famous science fictional planet Tatooine in "Star Wars" orbits two stars, hence its double sunsets.

Such worlds are referred to as circumbinary planets. Astronomers can record how light is absorbed by planet-forming disks during the bright and faint phases of blinking stellar systems, which in turn reveals information about the materials that comprise the disk.

"These blinking systems offer natural probes of the binary and circumbinary planet formation process," said Peter Plavchan, a scientist at the NASA Exoplanet Science Institute and Infrared Processing and Analysis Center at the California Institute of Technology, Pasadena, Calif., and lead author of a new paper accepted for publication in Astronomy & Astrophysics.

More information: arxiv.org/abs/1304.2398