An international team led by researchers at the Technion found the connection between cold nebulae, cosmic rays, and star formation.

First measurement of galactic nebula core using James Webb Space Telescope reveals how cosmic radiation heats and ionizes cold gas clouds, affecting the chemistry and rate of collapse that gives birth to stars

Cold nebulae are the “birth chambers” of stars: dense clouds of gas and dust, at temperatures of a few tens of Kelvin, where gravity tries to shrink matter until a star ignites. But it is precisely the cold and density that create a problem for measurement and understanding: ordinary ultraviolet radiation almost does not penetrate inside, so it is difficult to know what processes heat, ionize and chemically change the material in the core. This is where cosmic rays come into the picture: a stream of high-energy particles (mainly protons, but also electrons and atomic nuclei) that is able to penetrate deep into such clouds, becoming a “quiet” but decisive factor in the formation of stars.

An international team led by researchers from the Faculty of Physics at the Technion has for the first time directly measured the cosmic ray activity in the core of Barnard 68 – a dense, cold galactic nebula about 400 light-years (about 123 parsecs) from Earth. The measurement was based on observations from the James Webb Space Telescope, and was published on February 3, 2026 in Nature Astronomy, alongside a complementary analysis published the same day in The Astrophysical Journal in collaboration with Johns Hopkins University.

Why does cosmic radiation “dominate” in cold nebulae?

Star-forming nebulae have two main characteristics: high density and strong light obscuration. The dust inside the nebula absorbs and scatters ultraviolet and weak X-ray radiation, so that the inner core becomes a very dark place from an electromagnetic perspective. Without photons ionizing the gas, one would expect the material to be “neutral” and relatively quiet. In fact, ionization processes and active chemistry also occur in the heart of the cloud. The main source of this is cosmic radiation, which manages to penetrate even when light is blocked.

The connection between cold nebulae and cosmic rays is expressed in three main mechanisms:

1. Gentle heating slows gravitational collapse
   Gravitational collapse progresses more quickly when the gas is colder, because the gas pressure is lower. Cosmic rays add energy to the gas as they collide with particles and transfer energy to them. This heating doesn’t “burn” the cloud, but it can change delicate balances: how quickly the cloud loses energy, what the core temperature is, and what the conditions are for star formation to begin. Simply put: cosmic rays are like a weak thermostat, but one that works exactly where other thermostats don’t.
2. Ionization that activates the chemistry of molecules
   When a cosmic particle ionizes a molecule or atom, ions and free electrons are created. Even if the ionization rate is small, it is enough to set off a chain of chemical reactions. Within a cold cloud, more complex molecules are thus formed over time, and processes that also lead to the creation of common molecules such as water, ammonia, and methanol. In this sense, cosmic radiation does not just “heat”; it activates an entire chemical laboratory within a cloud that appears quiet and frozen from the outside.
3. Link between gas and magnetic fields
   In such clouds, the magnetic field can slow or delay collapse, but for a magnetic field to “affect” the gas, the gas needs to be slightly ionized, otherwise it slips through. The ionization created by cosmic rays provides this link. So cosmic rays help shape the big question: Will the cloud collapse quickly and form a star, or will it be delayed by a combination of pressure, magnetism, and internal motion?

What's new in measurement, and why is it considered "impossible"?

Until now, cosmic rays have been measured mainly in the vicinity of the solar system, using instruments in space (such as the Voyager spacecraft) and in orbiting stations. The problem is that star-forming clouds are far away, and the signals that directly link cosmic rays to what is happening inside the cloud have been considered too weak to detect.

The team led by Dr. Shmuel Bialy from the Technion used a focused physical principle: when cosmic radiation penetrates a cloud and collides with molecular hydrogen, it can cause the hydrogen molecules to vibrate. As a result, a Infrared radiation At a typical frequency around 100 terahertz, this radiation is a direct “stamp” of an interaction between cosmic rays and hydrogen in a cold cloud.

This is where the advantage of the James Webb Space Telescope comes in: unprecedented sensitivity in the infrared, which makes it possible to search for very weak signatures against a background of other radiation. The observations focused on a very dense and cold nebula, at a temperature of about 10–20 Kelvin. According to the description, the team built a theoretical model that predicts what signal should appear if it is indeed cosmic rays, and then checked whether the measured signal matches. Amit Chamka, a graduate student in the group, describes that the fit was excellent, and that alternative models were also tested that failed to reproduce the observation.

Professor David Neufeld of Johns Hopkins University, who participated in the study, noted that these are the first photons ever detected that originate from molecular hydrogen emitted as a result of a cosmic ray impact, and that the James Webb Space Telescope has thus opened a “new window” into the astrophysics of cosmic rays.

Why this matters for understanding star formation in the galaxy

Direct measurement in the core of a cold cloud does two important things at once:
One, it allows Calibrate modelsSecond, it opens the door to: Instead of assuming roughly what the cosmic ray flux is in such clouds, it can be measured precisely.Systematic mapping: If it is possible to measure in one cloud, it is possible to compare between different clouds, between different star formation regions, and perhaps even between different parts of the galaxy.

The group reports that following their success, they have been granted an additional 50 hours of observation time by NASA. The goal is to expand the measurements to additional galactic environments and build what the researchers describe as the first systematic study of the way cosmic radiation propagates through galaxies and regulates star formation. In a nice metaphor, nebulae could become “natural particle detectors” on a vast scale: not a room-sized device, but a cloud on the scale of many solar systems, which responds directly to the passage of high-energy particles.

The research also has practical value for understanding the future of the nebula itself. Barnard 68 is a cloud about a third of a light-year in diameter (about 0.1 parsec) and about twice the mass of the Sun. According to the estimates presented, it may collapse within about 200 years and give rise to a new star. To understand when and how this will happen, you need to understand the energy balance and chemistry inside, and cosmic radiation is a significant part of this equation.

To the article in NATURE ASTRONOMY

More of the topic in Hayadan:

• A new means of measuring cold collisions
• Hubble photographed four spectacular planetary nebulae
• Strange flames on the space station
• Spectacular images: the universe in X-rays
• What will happen when our sun dies?