NASA's Webb Captures Celestial Fireworks Around Forming Star

L1527 and Protostar (MIRI Image)
Credits: Image: NASA, ESA, CSA, STScI

L1527 and Protostar (MIRI Compass Image)
Credits: Image: NASA, ESA, CSA, STScI

Images

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The cosmos seems to come alive with a crackling explosion of pyrotechnics in this new image from NASA’s James Webb Space Telescope. Taken with Webb’s MIRI (Mid-Infrared Instrument), this fiery hourglass marks the scene of a very young object in the process of becoming a star. A central protostar grows in the neck of the hourglass, accumulating material from a thin protoplanetary disk, seen edge-on as a dark line. )

The protostar, a relatively young object of about 100,000 years, is still surrounded by its parent molecular cloud, or large region of gas and dust. Webb’s previous observation of L1527, with NIRCam (Near-Infrared Camera), allowed us to peer into this region and revealed this molecular cloud and protostar in opaque, vibrant colors.

Both NIRCam and MIRI show the effects of outflows, which are emitted in opposite directions along the protostar’s rotation axis as the object consumes gas and dust from the surrounding cloud. These outflows take the form of bow shocks to the surrounding molecular cloud, which appear as filamentary structures throughout. They are also responsible for carving the bright hourglass structure within the molecular cloud as they energize, or excite, the surrounding matter and cause the regions above and below it to glow. This creates an effect reminiscent of fireworks brightening a cloudy night sky. Unlike NIRCam, however, which mostly shows the light that is reflected off dust, MIRI provides a look into how these outflows affect the region’s thickest dust and gases.

The areas colored here in blue, which encompass most of the hourglass, show mostly carbonaceous molecules known as polycyclic aromatic hydrocarbons. The protostar itself and the dense blanket of dust and a mixture of gases that surround it are represented in red. (The sparkler-like red extensions are an artifact of the telescope’s optics). In between, MIRI reveals a white region directly above and below the protostar, which doesn’t show as strongly in the NIRCam view. This region is a mixture of hydrocarbons, ionized neon, and thick dust, which shows that the protostar propels this matter quite far away from it as it messily consumes material from its disk.

As the protostar continues to age and release energetic jets, it’ll consume, destroy, and push away much of this molecular cloud, and many of the structures we see here will begin to fade. Eventually, once it finishes gathering mass, this impressive display will end, and the star itself will become more apparent, even to our visible-light telescopes.

The combination of analyses from both the near-infrared and mid-infrared views reveal the overall behavior of this system, including how the central protostar is affecting the surrounding region. Other stars in Taurus, the star-forming region where L1527 resides, are forming just like this, which could lead to other molecular clouds being disrupted and either preventing new stars from forming or catalyzing their development.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

Source: NASA's James Webb Space Telescope/News

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Protostar displays a strange geometry

Figure 1: Integrated intensity distribution of CCH, superposed on the 0.8 mm dust continuum map. The infalling rotating envelope traced by CCH is broadened inward of the radius of about 150 au.Credit: Sakai et al. (RIKEN) .  Click to enlarge

One of the big puzzles in astrophysics is how stars like the sun manage to form from collapsing molecular clouds in star-forming regions of the universe. The puzzle is known technically as the angular momentum problem in stellar formation. The problem essentially is that the gas in the star-forming cloud have some rotation, which gives each element of the gas an amount of angular momentum. As they collapse inward, eventually they reach a state where the gravitational pull of the nascent star is balanced by the centrifugal force, so that they will no longer collapse inward of a certain radius unless they can shed some of the angular momentum. This point is known as the centrifugal barrier.

Now, using measurements taken by radio antennas, a group led by Nami Sakai of the RIKEN Star and Planet Formation Laboratory has found clues as to how the gas in the cloud can find their way to the forming star. To gain a better understanding of the process, Sakai and her group turned to the ALMA observatory, a network of 66 radio dishes located high in the Atacama Desert of northern Chile. The dishes are connected together in a carefully choreographed configuration so that they can provide images on radio emissions from protostellar regions around the sky. 

The group chose to observe a protostar designated as L1527, located in a nearby star-forming region known as the Taurus Molecular Cloud. The protostar, located about 450 light years away, has a spinning protoplanetary disk, almost edge-on to our view, embedded in a large envelope of molecules and dust. 

Previously, Sakai had discovered, from observations of molecules around the same protostar, that unlike the commonly held hypothesis, the transition from envelope to the inner disk--which later forms into planets--was not smooth but very complex. "As we looked at the observational data," says Sakai, "we realized that the region near the centrifugal barrier--where particles can no longer infall--is quite complex, and we realized that analyzing the movements in this transition zone could be crucial for understanding how the envelope collapses. Our observations showed that there is a broadening of the envelope at that place, indicating something like a 'traffic jam' in the region just outside the centrifugal barrier, where the gas heats up as the result of a shock wave. It became clear from the observations that a significant part of the angular momentum is lost by gas being cast in the vertical direction from the flattened protoplanetary disk that formed around the protostar."

Figure 2: Artist's impression of L1527
Credit: RIKEN 

Click to enlarge

This behavior accorded well with calculations the group had done using a purely ballistic model, where the particles behave like simple projectiles that do not need to be influenced by magnetic or other forces. 

According to Sakai, "We plan to continue to use observations from the powerful ALMA array to further refine our understanding of the dynamics of stellar formation and fully explain how matter collapses onto the forming star. This work could also help us to better understand the evolution of our own solar system."

Paper and Research team

These observation results were published as Sakai et al. "Vertical Structure of the Transition Zone from Infalling Rotating Envelope to Disk in the Class 0 Protostar, IRAS04368+2557" in the Monthly Notices of the Royal Astronomical Society in February 2017.

The research team members are:

Nami Sakai (The Institute of Physical and Chemical Research (RIKEN)), Yoko Oya (The University of Tokyo), Aya E. Higuchi (RIKEN), Yuri Aikawa (University of Tsukuba), Tomoyuki Hanawa (Chiba University), Cecilia Ceccarelli (Laboratoire d'Astrophysique de Grenoble), B. Lefloch (Laboratoire d'Astrophysique de Grenoble), Ana López-Sepulcre (The University of Tokyo / Institut de Radioastronomie Millimétrique), Yoshimasa Watanabe (The University of Tokyo), Takeshi Sakai (The University of Electro-Communications), Tomoya Hirota (National Astronomical Observatory of Japan), Emmanuel Caux (Universite de Toulouse), Charlotte Vastel (Universite de Toulouse), Claudine Kahane (Laboratoire d'Astrophysique de Grenoble), Satoshi Yamamoto (The University of Tokyo)

This research was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science and the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 25400223, 25108005, 16H03964).

ALMA array from the air

Credit: Clem & Adri Bacri-Normier (wingsforscience.com)/ESO

Click to Enlarge

ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation 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 National Science Council of Taiwan (NSC) 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.

Source: Atacama Large Millimeter/submillimeter Array (ALMA)

A Very Young Circumstellar Disk in Scattered Light

Figure 1: Gemini NIRI image of L1527 taken in L'-band (3.8 microns). The bright yellow areas are the disk surfaces separated by the narrow dark lane of the disk mid-plane. The fainter, diffuse red features are scattered light from the inner outflow cavities of the protostar.

Figure 2: Left is the Gemini NIRI image from Figure 1 and the right is the Spitzer Space Telescope image taken at a similar wavelength 3.6 micron. The dashed boxes mark the region that the Gemini NIRI image covers encompassing the point-like feature in the Spitzer Space telescope image.

Figure 3: Top row: Observations of L1527 from Spitzer and Gemini. Middle row: First model of L1527 that was constructed without the Gemini data. Bottom row: Refined model using new Gemini imaging of the disk.

Recent observations with the Near-Infrared Imager (NIRI) on the Gemini North telescope have revealed the presence of a large circumstellar disk around the young embedded protostar L1527. The discovery team, led by University of Michigan astronomer John Tobin and including Lee Hartmann also of the University of Michigan and Laurent Loinard of the Centro de Radioastronomía y Astrofísica - Universidad Nacional Autonoma de Mexico, detected the disk in scattered mid-infrared light, as shown in Figure 1. The upper layers of the disk appear as two bright bowl-shaped features. The mid-plane of the disk hides the central protostar from direct view, resulting in the dark band between the disk surfaces.

The object, located in a star-forming region in the constellation of Taurus, is at a distance of about 450 light-years (140 parsecs) making it one of the nearest and youngest protostars known. Although L1527 is otherwise a fairly typical protostar and will probably result in a star with a final mass about that of the Sun, L1527 is set apart from other young stars with disks because it is very early in the star formation process, even compared to its contemporaries within its host star-forming region. This stage of evolution is called the Class 0 phase, where the protostar is surrounded by a dense infalling envelope composed of gas and dust. The protostar is emitting ultraviolet and visible light, but at this early stage, radiation at these wavelengths remains directly undetectable, being absorbed by the dense envelope and disk and then re-radiated mainly in the far-infrared.

No optical or near-infrared radiation has ever been detected toward the center of the L1527 protostar, but the Spitzer Space Telescope detected a small, faint point of light coming from the center in the mid-infrared (Figure 2). The light’s source was unknown because the central protostar was expected to be completely obscured. Tobin’s team hypothesized that there must be some structure that obscures the protostar but bright and compact enough to appear unresolved in the Spitzer Space Telescope images. Tobin et al. constructed a model that resembled a large disk and proposed Gemini observations to test the hypothesis. The initial model is shown in Figure 3.

According to Tobin, “We utilized Gemini's unique ability to take images in the mid-infrared from the ground at high resolution. Under natural seeing conditions Gemini was able to give exquisite image quality; the seeing for the observations was 0.3 arcseconds, the equivalent angular size of a penny 8 miles away.”

While Tobin states that the team was “astounded” by how similar their model, based on only the Spitzer images was to the observations, the team refined the model (shown in Figure 3) to better fit the new detailed Gemini images. They found that the disk must be 190 AU in radius or 5 times the size of Pluto's orbit to reproduce the images. This disk size is typical for young stars without envelopes; however, it was expected that L1527 would have a smaller disk because it is at such an early stage of evolution, before the disk has grown. This result implies that disks can grow quite fast, which requires a rapid collapse of the natal cloud. The team also noticed that the disk extends vertically from it equator about twice as far as other disks; this may be due to material from the surrounding envelope falling onto the disk. Finally, the team concludes that these images from Gemini have captured a protoplanetary disk-in-formation around this young star implying that the ingredients for planet formation are already in-place at a very early time in protostellar evolution. The complete work will appear in The Astrophysical Journal Letters and is currently available on astro-ph.

Source: Gemini Observatory