Newborn Star Found Growing Inside Magnetic Nest of Chaos

ProtoStarMagFieldLines
NRAO/AUI/NSF; D. Berry

Conventional wisdom would have us believe that stars form in extremely powerful and ordered magnetic fields. But “conventional,” our universe is not (as Yoda might say).

In a new and fascinating study published in Astrophysical Journal Letters and carried out by astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, a star some 1,400 light-years away in the Serpens star-forming region had its magnetic field gauged.

The star, called Ser-emb 8, is embedded inside the magnetic field passing through the molecular cloud it was born in. As the surrounding dust aligns itself with the direction of these magnetic field lines, ALMA is able to make precise measurements of the polarization of the emissions produced by this dust. From these incredibly sensitive measurements, a map of the polarization of light could be created, providing a view of the magnetic nest the star was born in.

newborn-star
Texture represents the magnetic field orientation in the region surrounding the Ser-emb 8 protostar, as measured by ALMA. The gray region is the millimeter wavelength dust emission. Credit: ALMA (ESO/NAOJ/NRAO); P. Mocz, C. Hull, CfA

And this nest is an unexpected one; it’s a turbulent region lacking the strong and ordered magnetism that would normally be predicted to be in the immediate vicinity of Ser-emb 8. Previous studies have shown newborn stars to possess powerful magnetic fields that take on an “hourglass” shape, extending from the protostar and reaching light-years into space. Ser-emb 8, however, is different.

“Before now, we didn’t know if all stars formed in regions that were controlled by strong magnetic fields. Using ALMA, we found our answer,” said astronomer Charles L. H. “Chat” Hull, at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. “We can now study magnetic fields in star-forming clouds from the broadest of scales all the way down to the forming star itself. This is exciting because it may mean stars can emerge from a wider range of conditions than we once thought.”

By comparing these observations with computer simulations, an insightful view of the earliest magnetic environment surrounding a young star has been created.

“Our observations show that the importance of the magnetic field in star formation can vary widely from star to star,” added Hull in a statement. “This protostar seems to have formed in a weakly magnetized environment dominated by turbulence, while previous observations show sources that clearly formed in strongly magnetized environments. Future studies will reveal how common each scenario is.”

Hull and his team think that ALMA has witnessed a phase of star formation before powerful magnetic fields are generated by the young star, wiping out any trace of this pristine magnetic environment passing through the star forming region.

Two Exoplanets Are Whipping-Up a Pretty Protoplanetary Gas Spiral

alma-spirals
ALMA (ESO/NAOJ/NRAO)/Tang et al.

Using the awesome power of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers have probed the protoplanetary disk of a young star system — with a twist.

ALMA is no stranger to protoplanetary disks; the array of 66 radio antennae in the Atacama desert is extremely sensitive to the emissions from the gas and dust surrounding stars. But this observation has revealed something more — there are two obvious dusty rings (orange) that are being sculpted by the presence of massive worlds, but between them (in blue) is a spiral gas structure. If there’s one thing I love it’s space spirals!

When comparing these observations with theoretical modeling of the system — called AB Aurigae, located about 470 light-years away — for that gas spiral to exist, there must be some interplanetary interplay between two exoplanets orbiting the star at 30 and 80 AU (astronomical units, where 1 AU is the average distance that Earth orbits the sun). The spiral is following the direction of rotation of the disk.

Besides looking really pretty, studies of these spiral structures help astronomers identify the presence of exoplanets and build a better understanding of the nature of protoplanetary disks.

ALMA Reveals the True Nature of Hubble’s Enigmatic Ghost Spiral

Appearing as a ghostly apparition in deep space, the LL Pegasi spiral nebula signals the death of a star — and the world’s most powerful radio observatory has delved into its deeper meaning.

170302-graphics3
Left: HST image of LL Pegasi publicized in 2010. Credit: ESA/NASA & R. Sahai. Right: ALMA image of LL Pegasi. Credit: ALMA (ESO/NAOJ/NRAO) / Hyosun Kim et al.

When the Hubble Space Telescope revealed the stunning LL Pegasi spiral for the first time, its ghostly appearance captivated the world.

Known to be an ancient, massive star, LL Pegasi is dying and shedding huge quantities of gas and dust into space. But this is no ordinary dying star, this is a binary system that is going out in style.

The concentric rings in the star system’s nebula are spiraling outwards, like the streams of water being ejected from a lawn sprinkler’s head. On initial inspection of the Hubble observation, it was assumed that the spiral must be caused by the near-circular orbit of two stars, one of which is generating the flood of gas. Judging by the symmetry of the rings, this system must be pointing roughly face-on, from our perspective.

Though these assumptions generally hold true, new follow-up observations by the Atacama Large Millimeter/submillimeter Array (ALMA) on the 5,000 meter-high Chajnantor plateau in Chile has added extra depth to the initial Hubble observations. Astronomers have used the incredible power of ALMA to see a pattern in the rings, revealing the complex orbital dynamics at play deep in the center of the spiral.

“It is exciting to see such a beautiful spiral-shell pattern in the sky. Our observations have revealed the exquisitely ordered three-dimensional geometry of this spiral-shell pattern, and we have produced a very satisfying theory to account for its details,” said Hyosun Kim, of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan and lead researcher of this work.

Just as we read tree rings to understand the history of seasonal tree growth and climatic conditions, Kim’s team used the rings of LL Pegasi to learn about the nature of the binary star’s 800 year orbit. One of the key findings was the ALMA imaging of bifurcation in the rings; after comparing with theoretical models, they found that these features are an indicator that the central stars’ orbit is not circular — it’s in fact highly elliptical.

ALMA observation of the molecular gas around LL Pegasi. By comparing this gas distribution with theoretical simulations, the team concluded that the bifurcation of the spiral-shell pattern (indicated by a white box) is resulted from a highly elliptical binary system. Credit: ALMA (ESO/NAOJ/NRAO) / Hyosun Kim et al.

Probably most striking, however, was that Hubble was only able to image the 2D projection of what is in fact a 3D object, something that ALMA could investigate. By measuring the line-of-sight velocities of gas being ejected from the central star, ALMA was able to create a three-dimensional view of the nebula, with the help of numerical modeling. Watch the animation below:

“While the [Hubble Space Telescope] image shows us the beautiful spiral structure, it is a 2D projection of a 3D shape, which becomes fully revealed in the ALMA data,” added co-author Raghvendra Sahai, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., in a statement.

This research is a showcase of the power of combining observations from different telescopes. Hubble was able to produce a dazzling (2D) picture of the side-on structure of LL Pegasi’s spirals, but ALMA’s precision measurements of gas outflow speed added (3D) depth, helping us “see” an otherwise hidden structure, while revealing the orbital dynamics of two distant stars.

A special thanks to Hyosun Kim for sending me the video of the LL Pegasi visualization!