An international research team led by scientists from the Technion Faculty of Physics presents a first-of-its-kind measurement of cosmic rays located at the core of the galactic nebula Barnard 68. The measurement was based on observations by the James Webb Space Telescope and will enable researchers to map the properties of cosmic rays in space and shed light on the process of star formation in the galaxy. The findings were published recently in Nature Astronomy , with companion analysis published in the Astrophysical Journal in collaboration with Johns Hopkins University.
What Are Cosmic Rays?
Despite their name, cosmic rays are not related to electromagnetic radiation (light). They are actually particles of matter – protons, electrons, and atomic nuclei – that fill galactic space and travel at speeds close to the speed of light.
Cosmic rays have a decisive impact on the process of star formation. Stars like our Sun are formed through the gravitational collapse of clouds of gas and dust in the galaxy. Thanks to their high energy, cosmic-ray particles can penetrate deep into a nebula and heat its gas, thereby delaying its collapse and the formation of a star. In addition to heating, cosmic-ray-driven ionization plays a key role in nebular chemistry and is involved in the creation of molecules such as water, ammonia, methanol, and more.
Cosmic rays were first discovered more than a century ago in Victor Hess’s famous balloon experiment. Today, measurements from the International Space Station and from the Voyager 1 and 2 spacecraft allow us to study cosmic rays in the vicinity of the Solar System. However, the question of what the properties of cosmic rays are throughout the galaxy—and particularly inside star-forming nebulae – remains open, and is considered one of the most important unresolved questions in modern astrophysics.
The Discovery
This year, an international team led by Dr. Shmuel Bialy of the Technion achieved a long-sought breakthrough: a direct measurement of cosmic-ray activity inside a galactic nebula. “When cosmic rays penetrate a nebula,” explained Dr. Bialy, “they cause hydrogen molecules to vibrate, emitting infrared radiation at a characteristic frequency of about 100 terahertz. This infrared radiation serves as a unique fingerprint of the interaction between cosmic rays and hydrogen in the nebula.”
The research team designed and conducted an observation using the James Webb Space Telescope (JWST) to measure this radiation from Barnard 68 – a cold, dense nebula (with temperatures around 10-20 Kelvin, barely above absolute zero) 400 light-years from Earth, located in the constellation Ophiuchus. The nebula has a diameter of roughly one-third of a light-year and a mass twice that of the Sun. According to predictions, it will collapse in about 200,000 years, forming a new star.
“The signals detected by the space telescope matched perfectly with the predictions of the theoretical model we developed,” said Amit Chemke, a master’s student in Dr. Bialy’s group and a co-author of the study. “We also examined alternative models, but none fit the observed signals. Our measurement provides unequivocal evidence that we are seeing cosmic rays.”
“These are the first photons ever detected from cosmic-ray–excited H₂,” said David Neufeld, professor of physics and astronomy at Johns Hopkins, who was also part of this study. “JWST has opened a completely new window on cosmic-ray astrophysics.”
What’s Next?
"Years ago, when I first proposed this approach, many experts were skeptical that we could detect such faint signals," said Dr. Bialy. "The James Webb Space Telescope's unprecedented capabilities changed everything. NASA has now allocated an additional 50 hours of telescope time to expand our cosmic-ray mapping across different galactic environments. Nebulae may now serve as enormous natural particle detectors – tens of thousands of solar systems in size – opening the door to the first systematic study of how cosmic rays propagate through galaxies and regulate star formation."
The Israeli team’s research was supported by the Technion, the Israel Science Foundation, and the German-Israeli Foundation for Scientific Research and Development.
Nature Astronomy
Observational study
Not applicable
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