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Investigating the Nested Structure of the Outflow from the Low Luminosity Protostar IRAS 16253-2429 using JWST and ALMA

Using JWST and ALMA observations of the Class 0 protostar IRAS 16253-2429, this study reveals a nested structure of collimated jets and wide-angle molecular outflows, suggesting a magnetohydrodynamic wind as the likely launching mechanism.

Original authors: Mayank Narang, Himanshu Tyagi, Nagayoshi Ohashi, P. Manoj, S. Thomas Megeath, John J. Tobin, Ewine F. van Dishoeck, Neal J. Evans, Dan M. Watson, Alessio Caratti o Garatti, Jes K. Jørgensen, Robert Gu

Published 2026-02-12

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CC BY 4.0

Original authors: Mayank Narang, Himanshu Tyagi, Nagayoshi Ohashi, P. Manoj, S. Thomas Megeath, John J. Tobin, Ewine F. van Dishoeck, Neal J. Evans, Dan M. Watson, Alessio Caratti o Garatti, Jes K. Jørgensen, Robert Gutermuth, Yusuke Aso, Henrik Beuther, Leslie W. Looney, David A. Neufeld, Guillem Anglada, Mayra Osorio, Adam E. Rubinstein, Samuel Federman, Lee W. Hartmann, Pooneh Nazari, Nicole Karnath, Hendrik Linz, Thomas Stanke, Tyler L. Bourke, Yao-Lun Yang, Rolf Kuiper, Joel Green, Pamela Klaassen, Wafa Zakri, Nolan Habel, Nashanty Brunken, James Muzerolle, Katerina Slavicinska, Amelia M. Stutz, Lukasz Tychoniec, Scott Wolk, Will R. M. Rocha, William J. Fischer

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Tale of the Cosmic Wasp: Unmasking a Baby Star’s Secret Exhaust System

Imagine you are watching a construction site for a massive skyscraper, but instead of cranes and trucks, everything is happening in the pitch-black vacuum of space. At the center of this site is a "baby star" named IRAS 16253-2429.

This star is tiny—much smaller and dimmer than our Sun—but it is incredibly busy. It is currently in its "infancy" (a stage astronomers call Class 0), meaning it is still frantically eating up the gas and dust around it to grow.

Scientists used two of the most powerful "microscopes" ever built—the James Webb Space Telescope (JWST) and the ALMA radio telescope—to zoom in on this baby star. What they found wasn't just a single object, but a complex, multi-layered "exhaust system" that tells us exactly how stars are born.

1. The "Wasp Waist" Nebula (The Shape)

The first thing astronomers noticed is the shape. Because of the way light bounces off the dust around the star, it looks like a tiny, glowing wasp. It has a very thin "waist" (the disk where the star lives) and two wide, flared-out wings (the outflow cavities).

Think of it like a spinning top sitting in a pile of flour. As the top spins, it clears out two funnel-shaped holes in the flour, creating a "waist" in the middle.

2. The Nested Exhaust System (The "Matryoshka Doll" Effect)

This is the most exciting part of the discovery. Usually, we think of a star's "exhaust" (the gas it blows away) as one single wind. But this star has nested layers, much like a Russian Matryoshka doll.

The Inner Jet (The High-Speed Needle): Right at the center, there is a super-fast, skinny "needle" of hot, ionized gas. This is like the high-pressure jet of water coming out of a power washer. It’s incredibly fast and very narrow.
The Middle Wind (The Warm Breeze): Surrounding that needle is a layer of warm molecular hydrogen gas. This layer is faster than the outer layer but slower than the jet.
The Outer Shell (The Slow Fog): Finally, there is a wide, slow-moving cloud of cold gas (detected by ALMA) that forms the outer boundary. This is like a gentle breeze carrying the dust and debris away.

Why does this matter? This "nested" structure is a smoking gun. It suggests that the star isn't just blowing bubbles; it is using magnetic fields like invisible, spinning slingshots to launch different layers of gas at different speeds and angles. This is called a "Magnetohydrodynamic (MHD) wind."

3. The "Speed vs. Heat" Rule

The researchers found a fascinating pattern: The hotter the gas, the faster it moves and the narrower it is.

Imagine a group of people running out of a building.

The people in the very center are sprinters (the hot, fast jet).
The people slightly further out are joggers (the warm, medium-speed wind).
The people on the very edge are just walking (the cold, slow gas).

By measuring the "temperature" of the gas using JWST, the scientists could actually see this hierarchy of speed.

The Big Picture: Why should we care?

Every star, including our own Sun, went through this chaotic "infancy." By studying how this tiny baby star manages its "exhaust," we are learning the rules of the universe's construction manual.

We are seeing how a star regulates its own growth—using these magnetic winds to blow away excess material so it doesn't grow too big, while simultaneously clearing out the space where future planets might one day form. We aren't just looking at a star; we are looking at the birth of a solar system in real-time.

Technical Summary: Investigating the Nested Structure of the Outflow from the Low Luminosity Protostar IRAS 16253-2429 using JWST and ALMA

1. Problem Statement

A fundamental challenge in star and planet formation is understanding the complex interplay between mass accretion, disk evolution, and feedback mechanisms (outflows and jets). Specifically, the mechanism that launches these outflows—whether they are magnetohydrodynamic (MHD) disk winds, X-winds (launched from the co-rotation radius), or jet-driven bow shocks—remains a subject of intense debate. While disk wind models predict a "nested" velocity and morphology structure (where more collimated flows move faster), observing this in the earliest, most embedded stages of star formation (Class 0 protostars) is difficult due to high extinction and the need for high spatial and spectral resolution across multiple wavelengths.

2. Methodology

The study utilizes a multi-wavelength, multi-instrument approach to probe different physical components of the protostellar system:

JWST (NIRSpec & MIRI): Provides high-resolution infrared spectroscopy and imaging (2.87–28 $\mu$ m). This allows for the detection of pure rotational $\text{H}_2$ transitions (tracing warm molecular gas), atomic/fine-structure lines like $[\text{Fe II}]$ and $[\text{Ne II}]$ (tracing fast, collimated jets), and scattered light continuum (tracing the outflow cavity walls).
ALMA: Provides high-resolution millimeter observations (1.3 mm continuum and $^{12}\text{CO}$ $J=2-1$ line) to trace the cold dust disk, the Keplerian gas disk, and the large-scale, slow-moving molecular outflow.
Comparative Analysis: The researchers employed Gaussian fitting to determine outflow widths, second-order derivatives to delineate cavity edges, and Position-Velocity (PV) diagrams to analyze the kinematics of different gas excitation states.

3. Key Contributions

Multi-Scale Mapping: The paper successfully maps the transition from the highly collimated atomic jet to the wide-angle molecular wind and finally to the large-scale entrained envelope.
Excitation-Dependent Morphology: It quantifies how the outflow's appearance changes based on the excitation energy ( $E_{up}$ ) of the molecular tracer used.
Kinematic Differentiation: It provides empirical evidence of a velocity gradient within the molecular component of the outflow, linking higher excitation to higher velocities.

4. Results

Nested Structure: The study confirms a nested morphology. The outflow opening angle narrows significantly as the excitation energy increases: from $\sim 40^\circ$ – $35^\circ$ for low- $J$ $\text{H}_2$ and cold $^{12}\text{CO}$ to $\sim 28^\circ$ – $19^\circ$ for high- $J$ $\text{H}_2$ transitions.
Velocity Gradient: PV diagrams reveal that the "hotter" gas (high $E_{up}$ ) moves significantly faster ( $\sim 28.5 \text{ km s}^{-1}$ inclination-corrected) than the "cooler" gas ( $\sim 12.5 \text{ km s}^{-1}$ ).
Spatial Scales: At the protostellar base, the $\text{H}_2$ outflow width is $\leq 35 \text{ au}$ , which is comparable to the $\sim 30 \text{ au}$ diameter of the dust and Keplerian gas disks, but wider than the $20 $–$ 23 \text{ au}$ atomic jet.
Cavity Interaction: The $^{12}\text{CO}$ emission from ALMA is slower and colder than the $\text{H}_2$ wind, suggesting the CO traces gas from the infalling envelope that has been entrained and accelerated along the cavity walls by the wide-angle $\text{H}_2$ wind.
Positional Offset: A $\sim 38 \text{ au}$ offset was detected between the JWST $14 \mu\text{m}$ continuum peak and the ALMA $1.3 \text{ mm}$ disk, likely due to scattered light from illuminated cavity walls rather than a physical separation of the protostar.

5. Significance

The findings strongly support the MHD disk wind model over X-wind or photoevaporative models. The observed nested velocity and collimation structure—where the fastest, most collimated material is found closest to the axis—is a hallmark prediction of MHD disk winds.

By demonstrating this in a Class 0 protostar (the earliest stage of star formation), the study proves that these organized, disk-driven feedback mechanisms are already firmly established during the primary accretion phase. This has profound implications for how stars regulate their final mass and how the initial conditions for planet formation are set in the presence of powerful, multi-component outflows.