Discovery of Interaction between Jet and Disk Wind from a Star-Forming Accretion Disk

Figure 1: (Left) ALMA composite image of dust emission (gray image), SO emission (orange), and SiO emission (green) towards the center of the HH 212 star-forming system. Accretion disk is seen in dust emission, jet is seen in SiO and SO emission along the symmetric axis, bow shocks are seen in SiO emission at large distances from the protostar. Faint wind is seen in SO emission, fanning out from the disk. The shells produced by the jet-wind interaction is also seen in SO emission, connecting to the bow shocks at large distances. Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.  (Right) An artistic conception showing the disk, jet, wind (greenish), and shells in the system. Credit: Ya-Ling Huang /ASIAA. Hi-res image

Figure 2. Schematic diagram showing the launching of the jet and disk wind from an accretion disk, driving the accretion process for star formation. Credit: Ya-Ling Huang/ASIAA

An international research team, led by Chin-Fei Lee at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan), has spatially resolved a magnetic wind launched from a star-forming accretion disk and discovered the first jet and disk wind interaction in star formation, using the Atacama Large Millimeter/submillimeter Array (ALMA). The finding supports that disk wind and jet can both be present, extracting angular momentum from different parts of the disk, allowing material to transport within the disk from the outer to the inner part and then fall onto the central protostar (baby star), providing a combined solution to the long-standing angular momentum problem in the accretion process for star formation.

 Excitements:

“Thanks to the powerful ALMA, we spatially resolve a previously detected disk wind in the HH 212 star-forming system and confirm it to be a magnetic wind launched from an accretion disk”, says Chin-Fei Lee at ASIAA with excitement. “In addition, we also detect its interaction with the jet, providing the first evidence of jet and disk wind interaction in star formation. A thin shell produced by the interaction can be clearly seen, forming an inner boundary of the disk wind and connecting to the large bow shocks driven by the jet at large distance.”

Benoit Tabone at Leiden Observatory, who provided the theoretical model to this study, said “It is amazing to see how well our magnetic disk wind models can match the observed morphology and kinematics of the HH 212 wind. Our model initially reproduced low spatial resolution ALMA observations, but with these new high angular resolution observations we are able to robustly test the magnetic disk wind models and infer the angular momentum carried away by the wind.”

“The observations and modeling of the jet-wind interaction open an entirely new and promising avenue to constrain the large-scale magnetic field in accretion disks, which can have fundamental impact on the early process of planet formation”, commented also Sylvie Cabrit at Observatoire de Paris.

Properties of the Target:

HH 212 is a nearby star-forming system in Orion at a distance of about 1300 ly. The central protostar (baby star) is very young with an age of only ~ 40,000 yrs (which is about 10 millionth of the age of Our Sun) and a mass of ~ 0.25 Msun. It accretes material actively through an accretion disk. A powerful bipolar jet is ejected from the center of the disk, allowing disk material there to be accreted to the central protostar.

New ALMA observations of the Target:

Previous search in SO molecular emission at a resolution of 60 au detected a disk wind around the jet. Now with a resolution of 13 au (i.e. about 5 times higher resolution) and an unprecedented high sensitivity, ALMA resolved the disk wind and detected its interaction with the jet (see Figure 1). Quantitative modeling indicates (see Figure 2): 

(1) the wind is consistent with an extended magnetic disk wind launched from ≃ 4 to 40 au, extracting angular momentum to drive disk accretion; 

(2) the jet is launched from the dust-free zone of the disk, allowing material there to fall onto the baby star; and 

(3) the jet drives large bow shocks interacting with the disk wind and producing a cavity, with a thin SO shell forming its boundary. This interaction provides unique first clues to the unknown magnetic field strength and distribution in young accretion disks.

More Information

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organization for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

This research was presented in a paper “First Detection of Interaction between a Magnetic Disk Wind and an Episodic Jet in a Protostellar System,” by Lee et al. appeared in the Astrophysical Journal Letters on Feb 2nd, 2021.

The team is composed of Chin-Fei Lee (ASIAA, Taiwan; National Taiwan University, Taiwan), Benoit Tabone (Leiden Observatory, Leiden University, Netherlands; Observatoire de Paris, France), Sylvie Cabrit (Observatoire de Paris, France), Claudio Codella, Linda Podio (INAF, Osservatorio Astrofisico di Arcetri, Italy), Jonathan Ferreira, and Jonatan Jacquemin-Ide (Univ. Grenoble Alpes, CNRS, France)

Media Contact

 

Dr. Chin-Fei Lee

Email: cflee@asiaa.sinica.edu.tw 

Tel: +886 2 2366 5445 

 

Source:  Academia Sinica, Institute of Astronomy & Astrophysics (ASIAA)

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NASA’s Webb Telescope Will Investigate Cosmic Jets From Young Stars

A pair of jets protrude outwards in this infrared image of Herbig-Haro 212 (HH 212), taken by the European Southern Observatory’s Very Large Telescope. Webb’s high resolution and sensitivity will allow astronomers to examine objects like this in greater detail than ever before. Credits: ESO/M. McCaughrean

The formation of a star sounds like a simple process: a cloud of gas collapses in on itself, growing denser and hotter until nuclear fusion ignites and a star begins to shine. The reality is more complex and dramatic.

Swirling gas spins faster and faster, threatening to rip the still-forming star into pieces. Clumps of matter are captured within a tangle of magnetic fields and squirt outward at supersonic speeds. All of it happens within a dusty shroud that blocks visible light. NASA’s James Webb Space Telescope will penetrate that dusty veil and reveal new secrets of star birth.

As an interstellar gas cloud contracts, it spins more rapidly, just as a twirling ice skater does when she draws in her arms. The only way for the gas to continue moving inward is for some of the spin (known as angular momentum) to be removed.

In a process that’s still not fully understood, magnetic fields funnel some of the swirling material into twin jets that shoot outward in opposite directions. These jets travel at speeds of hundreds of miles per second and spread across light-years of space.

“Jets are signposts of star formation,” said Tom Ray, an astronomer at the Dublin Institute for Advanced Studies. Ray and many other scientists are planning to use Webb to study these jets and stellar outflows. Their goals include learning more about how stars form, and how their jets interact with the surrounding interstellar medium of gas and dust.

Over the span of 14 years, the Hubble Space Telescope looked at a bright, clumpy jet known as HH 34 ejected from a young star. Several bright regions in the clumps signify where material is slamming into each other, heating up, and glowing. Credits: NASA, ESA, P. Hartigan (Rice University), and G. Bacon (STScI)

Shock Waves in Space

They will study objects like Herbig-Haro (HH) 212, located about 1,400 light-years away in the constellation Orion. At the center of HH 212 resides a still-forming star or protostar that will eventually grow to become about the mass of our Sun. Jets from the protostar extend across about 5 light-years of space.

The material in those jets is traveling at supersonic speeds. When it slams into surrounding material, it creates a shock wave, much like the “sonic boom” of a supersonic aircraft. The shock heats the interstellar gas, causing it to glow at specific wavelengths of light that depend on the conditions within the shock wave itself.

“With Webb, we’ll be able to dissect the interactions of the protostar with its surroundings that were previously blurred into a single blob,” said Ewine van Dishoeck of Leiden University.

Webb’s exquisite angular resolution will allow it to pick up the tiniest details. This will allow it to see solar-system-scale features at the distance of objects like HH 212. And since the farther along a jet you go from the protostar, the longer the time since the material was ejected, astronomers can probe the history of the star’s matter-gathering or accretion process.

“Webb has higher sensitivity and higher angular resolution at long infrared wavelengths than anything we could do previously. Webb will answer questions we can’t answer from the ground,” said Alberto Noriega-Crespo of the Space Telescope Science Institute.

Webb also will precisely discern different wavelengths of infrared light. This will allow it to detect infrared light from a variety of chemical elements associated with the shock wave, including iron, neon and sulfur.

When a jet of material traveling at supersonic speeds slam into interstellar gas and dust, it creates a shock wave that compresses and heats matter.  Credits: NASA and J. Olmsted (STScI). Hi-res image

A New Star Emerges

HH 212 is about 100,000 years old. Over the course of the next million years, its protostar will gather a sun’s worth of gas. The remainder of the surrounding material will either condense into planets or get swept away by outflows and other processes. Eventually, a fully formed star will emerge.

“By studying HH 212, and objects like it, we want to learn how jets and outflows help the star escape from its cocoon,” said Mark McCaughrean of the European Space Agency.

The observations described here will be taken as part of Webb’s Guaranteed Time Observation (GTO) program. The GTO program provides dedicated time to the scientists who have worked with NASA to craft the science and instrument capabilities of Webb throughout its development.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency.

For more information about Webb, visit www.nasa.gov/webb

By Christine Pulliam
Space Telescope Science Institute, Baltimore, Md.

Editor: Lynn Jenner

Source: NASA/Solar System and Beyond

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Feeding a Baby Star with a Dusty Hamburger

HH 212

Credit: ALMA (ESO/NAOJ/NRAO)/ Lee et al.

This intriguing image may look like a collection of coloured blobs, but it is actually a high-resolution snapshot of a newborn star enshrouded in dust. Just 1300 light-years away in the Orion Nebula, the star, named HH 212, is remarkably young. The average lifespan of such a low-mass star is around 100 billion years, but this star is only 40 000 years old — truly an infant in stellar terms.

In the cores of the vast molecular clouds in star formation regions, an ongoing battle rages; gravity versus the pressure of gas and dust. If gravity wins, it forces the gas and dust to collapse into a hot dense core that eventually ignites — forming a protostar. All the leftover gas and dust form a spinning disc around this baby star, and in many star systems they eventually coalesce to make planets. Such very young protostellar discs have been hard to image because of their relatively small size, but now the exceedingly high resolution of the Atacama Large Millimeter/submillimeter Array (ALMA) makes it possible to understand the intricate details of star and planet formation.

A closer look at HH 212 reveals a prominent, cool, dark dust lane running through the disc, sandwiched between two brighter regions that are heated by the protostar. The result resembles a cosmic “hamburger”. This is the very first time astronomers have spotted such a dust lane in the earliest phases of star formation, and so it may provide clues as to how planetary systems are born.

Source: ESO/Potw

The onset of an extra-solar system - feeding a baby star with a dusty hamburger

Figure 1: Jet and disk in the HH 212 protostellar system: (a) A composite image for the jet in different molecules, produced by combining the images from the Very Large Telescope (McCaughrean et al. 2002) and ALMA (Lee et al. 2015). Orange image around the center shows the dusty envelope+disk at submillimeter wavelength obtained with ALMA at 200 AU resolution. (b) A zoom-in to the very center for the dusty disk at 8 AU resolution. Asterisks mark the possible position of the central protostar. A dark lane is seen in the equator, causing the disk to appear as a "hamburger". A size scale of our solar system is shown in the lower right corner for size comparison. (c) An accretion disk model that can reproduce the observed dust emission in the disk.  Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.

An international research team, led by Chin-Fei Lee in Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan), has made a new high-fidelity image with the Atacama Large Millimeter/submillimeter Array (ALMA), catching a protostar (baby star) being fed with a dusty "Hamburger", which is a dusty accretion disk. This new image not only confirms the formation of an accretion disk around a very young protostar, but also reveals the vertical structure of the disk for the first time in the earliest phase of star formation. It not only poses a big challenge on some current theories of disk formation, but also potentially brings us key insights on the processes of grain growth and settling that are important to planet formation.

"It is so amazing to see such a detailed structure of a very young accretion disk. For many years, astronomers have been searching for accretion disks in the earliest phase of star formation, in order to determine their structure, how they are formed, and how the accretion process takes place. Now using the ALMA with its full power of resolution, we not only detect an accretion disk but also resolve it, especially its vertical structure, in great detail", says Chin-Fei Lee at ASIAA.

"In the earliest phase of star formation, there are theoretical difficulties in producing such a disk, because magnetic fields can slow down the rotation of collapsing material, preventing such a disk from forming around a very young protostar. This new finding implies that the retarding effect of magnetic fields in disk formation may not be as efficient as we thought before," says Zhi-Yun Li at University of Virginia.

HH 212 is a nearby protostellar system in Orion at a distance of about 1300 ly. The central protostar is very young with an age of only ~40,000 yrs (which is about 10 millionth of the age of Our Sun) and a mass of ~0.2 Msun. It drives a powerful bipolar jet and thus must accrete material efficiently. Previous search at a resolution of 200 AU only found a flattened envelope spiraling toward the center and a hint of a small dusty disk near the protostar. Now with ALMA at a resolution of 8 AU, which is 25 times higher, we not only detect but also spatially resolve the dusty disk at submillimeter wavelength.

The disk is nearly edge-on and has a radius of about 60 AU. Interestingly, it shows a prominent equatorial dark lane sandwiched between two brighter features, due to relatively low temperature and high optical depth near the disk midplane. For the first time, this dark lane is seen at submillimeter wavelength, producing a "hamburger"-shaped appearance that is reminiscent of the scattered-light image of an edge-on disk in optical and near infrared. The structure of the dark lane clearly implies that the disk is flared, as expected in an accretion disk model.

Our observations open up an exciting possibility of directly detecting and characterizing small disks around the youngest protostars through high-resolution imaging with ALMA, which provides strong constraints on theories of disk formation. Our observations of the vertical structure can also yield key insights on the processes of grain growth and settling that are important to planet formation in the earliest phase.

Paper and research team 

This research was presented in a paper "First Detection of Equatorial Dark Dust Lane in a Protostellar Disk at Submillimeter Wavelength," by Lee et al. to appear in the journal Science Advances.

The team is composed of Chin-Fei Lee (ASIAA, Taiwan; National Taiwan University, Taiwan), Zhi-Yun Li (University of Virginia, USA), Paul T.P. Ho (ASIAA, Taiwan; East Asia Observatory), Naomi Hirano (ASIAA, Taiwan), Qizhou Zhang (Harvard-Smithsonian Center for Astrophysics, USA), and Hsien Shang (ASIAA, Taiwan).

The figure above shows an artist's impression of an accretion disk feeding the central protostar and a jet coming out from the protostar. Credit: Yin-Chih Tsai/ASIAA  

Source: Atacama Large Millimeter/submillimeter Array (ALMA)

Outbursts from a newborn star

HH 212

Credit: ESO/M. McCaughrean

A pair of jets protrude outwards in near-perfect symmetry in this image of Herbig-Haro object (HH) 212, taken by ESO’s already decommissioned Infrared Spectrometer And Array Camera (ISAAC).

The object lies in the constellation of Orion (The Hunter) in a dense molecular star-forming region, not far from the famous Horsehead Nebula. In regions like this, clouds of dust and gas collapse under the force of gravity, spinning faster and faster and becoming hotter and hotter until a young star ignites at the cloud’s centre. Any leftover material swirling around the newborn protostar comes together to form an accretion disc that will, under the right circumstances, eventually evolve to form the base material for the creation of planets, asteroids and comets.

Although this process is still not fully understood, it is common that a protostar and its accretion disc, as seen here edge-on, are the cause of the jets in this image. The star at the centre of HH 212 is indeed a very young star, at only a few thousand years old. Its jets are remarkably symmetric, with several knots appearing at relatively stable intervals. This stability suggests that the jet pulses vary quite regularly, and over a short timescale — maybe even as short as 30 years! Further out from the centre, large bow shocks spread out into interstellar space, caused by ejected gas colliding with dust and gas at speeds of several hundred kilometres per second.

Source: ESO