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.

NASA Spitzer Image: Star-forming region ON2

Massive stars are born in tumultuous clouds of gas and dust.

They lead a brief but intense life, blowing powerful winds of particles and radiation that strike their surroundings, before their explosive demise as supernovas.

The interplay between massive stars and their environment is revealed in this image of the star-forming region ON2.

It combines X-ray coverage from ESA’s XMM-Newton X-ray observatory with an infrared view from NASA’s Spitzer Space Telescope.

This stellar cradle is associated with the open cluster of stars named Berkeley 87, some 4000 light-years from Earth.

The cluster is home to over 2000 stars, most of which are low-mass stars like our Sun or smaller, but some, a few dozen, are stellar monsters weighing 10–80 times more.

Two glowing clouds of gas and dust, the raw material from which stars form, dominate the centre of the image and are shown in red.

Scattered across the image are a multitude of protostars, seeds of future stellar generations; these are shown in green.

The bright yellow star in the upper part of the image is BC Cygni, a massive star that has puffed up enormously and will eventually explode as a supernova.

Shown in blue is XMM-Newton X-ray view of ON2: it reveals individual sources, young, massive stars as well as protostars, and more diffuse regions of X-rays.

Two ‘bubbles’ of X-rays can be seen in the upper and lower clouds, respectively, pink against the red background.

These two bubbles conceal the cumulative emissions from many protostars, but also light radiated by very energetic particles, a signature of shockwaves triggered by massive stars and their winds.

The image combines observations performed in the X-ray energy range of 0.25–12 keV (blue) and at infrared wavelengths of 3.6 microns (green) and 8 microns (red).

It spans about 15 arcminutes on each side; north is up and east is to the left.

More Information:  paper “Hard X-Ray Emission in the Star-Forming Region ON 2: Discovery with XMM-Newton” by Oskinova et al. in April 2010.

ALMA: 'Death stars' in Orion blast planets before they even form - Video

This artist's concept shows two proplyds, or protostars, around a massive O-type star. 

The nearer proplyd is having its planet-forming dust and gas blasted away by the radiation from the star. 

The farther proplyd is able to retain its planet-making potential. 

Credit: NRAO /AUI /NSF, B. Saxton

The Orion Nebula is home to hundreds of young stars and even younger protostars known as proplyds.

Many of these nascent systems will go on to develop planets, while others will have their planet-forming dust and gas blasted away by the fierce ultraviolet radiation emitted by massive O-type stars that lurk nearby.

A team of astronomers from Canada and the United States has used the Atacama Large Millimeter/submillimeter Array (ALMA) to study the often deadly relationship between highly luminous O-type stars and nearby protostars in the Orion Nebula.

Their data reveal that protostars within 0.1 light-years (about 600 billion miles) of an O-type star are doomed to have their cocoons of dust and gas stripped away in just a few millions years, much faster than planets are able to form.

Rita Mann

"O-type stars, which are really monsters compared to our Sun, emit tremendous amounts of ultraviolet radiation and this can play havoc during the development of young planetary systems," remarked Rita Mann, an astronomer with the National Research Council of Canada in Victoria, and lead author on a paper in the Astrophysical Journal.

"Using ALMA, we looked at dozens of embryonic stars with planet-forming potential and, for the first time, found clear indications where protoplanetary disks simply vanished under the intense glow of a neighbouring massive star."

Many, if not all, Sun-like stars are born in crowded stellar nurseries similar to the Orion Nebula.

Over the course of just a few million years, grains of dust and reservoirs of gas combine into larger, denser bodies.

Left relatively undisturbed, these systems will eventually evolve into fully fledged star systems, with planets, large and small and ultimately drift away to become part of the galactic stellar population.

Astronomers believe that massive yet short-lived stars in and around large interstellar clouds are essential for this ongoing process of star formation.

At the end of their lives, massive stars explode as supernovas, seeding the surrounding area with dust and heavy elements that will get taken up in the next generation of stars.

These explosions also provide the kick necessary to initiate a new round of star and planet formation, but while they still shine bright, these larger stars can be downright deadly to planets if an embryonic solar systems strays too close.



"Massive stars are hot and hundreds of times more luminous than our Sun," said James Di Francesco, also with the National Research Council of Canada.

"Their energetic photons can quickly deplete a nearby protoplanetary disks by heating up its gas, breaking it up, and sweeping it away."

James Di Francesco

Earlier observations with the Hubble Space Telescope revealed striking images of proplyds in Orion.

Many had taken on tear-drop shapes, with their dust and gas trailing away from a nearby massive star.

These optical images, however, couldn't reveal anything about the amount of dust that was present or how the dust and gas concentrations changed in relation to massive stars.

The new ALMA observations detected these and other never-before-imaged proplyds, essentially doubling the number of protoplanetary disks discovered in that region.

"Taken together, our investigations with ALMA suggest that extreme UV regions are not just inhospitable, but they're downright hazardous for planet formation. With enough distance, however, it's possible to find a much more congenial environment," said Mann.

"This work is really the tip of the iceberg of what will come out of ALMA; we hope to eventually learn how common solar systems like our own are."

Journal Reference: Rita K. Mann, James Di Francesco, Doug Johnstone, Sean M. Andrews, Jonathan P. Williams, John Bally, Luca Ricci, A. Meredith Hughes, Brenda C. Matthews. ALMA OBSERVATIONS OF THE ORION PROPLYDS. The Astrophysical Journal, 2014; 784 (1): 82 DOI: 10.1088/0004-637X/784/1/82