High-frequency radio astronomy and MISTRAL: Recent breakthroughs in observational astronomy, coupled with rapid advancements in spaceflight technology, are reshaping our understanding of the cosmos and laying the groundwork for an interplanetary future
A new era in high-frequency radio astronomy has dawned with the successful commissioning of MISTRAL, a groundbreaking multi-pixel receiver installed on the Sardinia Radio Telescope (SRT). This innovative instrument, a product of collaboration between Sapienza University of Rome and the National Institute for Astrophysics (INAF), is set to revolutionise our ability to image faint and extended cosmic sources, providing unprecedented detail into the Universe’s most enigmatic phenomena.
A leap in receiver technology: The power of multi-pixel imaging
Traditionally, radio astronomy receivers have been “mono-pixel,” requiring extensive scanning to build up images of the sky.
MISTRAL, standing for “MIllimetric Sardinia radio Telescope Receiver based on Array of Lumped elements kids,” shatters this limitation. It boasts an ultra-cold core containing a remarkable matrix of 415 Kinetic Inductance Detectors (KIDs), developed in partnership with CNR-IFN in Rome. Cooled to an astonishing 0.2 degrees above absolute zero (or -273.15 degrees Celsius), this high detector count, combined with a specialised optical system, makes MISTRAL an exceptionally fast and effective tool for wide-field imaging.
As Paolo de Bernardis, Scientific Coordinator for Sapienza University of Rome, emphasises, this combination is key to its ability to capture images of “weak and extended sources.”
Overcoming challenges: The journey to first light
Installed in May 2023 at the Gregorian focus of the 64-meter SRT dish, the commissioning of MISTRAL was no small feat. It demanded pushing the telescope’s performance to its absolute limits, particularly for a millimetre-wave receiver. “Commissioning… becomes a real challenge in the case of a millimetre-wave receiver like MISTRAL,” explains Matteo Murgia, Scientific Manager for INAF. Early hurdles included achieving the incredibly low temperatures required for the KIDs to activate. Elia Battistelli, Project Manager for Sapienza University of Rome, recounts overcoming “several obstacles related to the truly exceptional cryogenics of the receiver.”
By September 2024, improvements to the SRT’s active surface allowed for the necessary sensitivity calibration, followed by meticulous alignment of MISTRAL’s optics. The commissioning team, alongside INAF and Sapienza, tirelessly developed essential software and procedures for pointing, focusing, calibration, and imaging, paving the way for “first light” observations.
Unveiling cosmic wonders: MISTRAL’s inaugural images
MISTRAL’s initial observations of three iconic celestial objects have unequivocally demonstrated its remarkable capabilities and versatility.
In December 2024, MISTRAL turned its gaze to the famed Orion Nebula (M42). The resulting image, at an angular resolution of 12 arcseconds, vividly showcases the Orion Bar and emission peaks near the Trapezium stars and the Kleinmann–Low Nebula. This observation provides a detailed look at one of the closest active star-forming regions, revealing a mix of radiation from ionised hydrogen and cold dust.
February 2025 saw MISTRAL observe the radio galaxy M87, whose active nucleus famously hosts a supermassive black hole. The receiver successfully captured the internal radio lobes, structures powered by relativistic radio jets from the central black hole. Observing these at high frequencies offers valuable insights into the physical mechanisms driving the radio-emitting particles.
Finally, in April 2025, MISTRAL delivered stunning images of the supernova remnant Cassiopeia A (Cas-A), one of the sky’s most intense radio sources. The expanding gas shell is clearly visible, with the SRT’s angular resolution allowing for detailed appreciation of its filamentary structure and brightness variations.
A new chapter for SRT and radio astronomy
The “first light” observations mark a significant milestone for both MISTRAL and the SRT. “The milestone achieved… marks an important step in broadening the scientific horizons of this radio telescope,” stated Isabella Pagano, Scientific Director of INAF. With this initial phase of technical testing complete, MISTRAL is now entering a crucial scientific validation phase. It is poised to tackle a vast array of scientific questions, from cosmology and galaxy cluster physics to the study of active galactic nuclei, star formation within molecular clouds, and celestial bodies within our own Solar System.
The ongoing efforts of the commissioning team aim to verify MISTRAL’s performance across these diverse scientific cases, making this powerful new instrument available to the wider scientific community as soon as possible, truly ushering in a new era for high-frequency radio astronomy.
![Figure 1: Sketch of the evolution of the Universe over the last 13.77 billion years. It started with the Big Bang, followed by an extremely short period of rapid exponential expansion. The furthest we can see is the cosmic microwave background, when radiation decoupled from matter, approximately 380,000 years after the Big Bang. This is followed by the ‘dark ages,’ during which this radiation redshifted from the visible regime into infrared and sub-mm wavelengths. The occurrence of the first stars, about 400 million years after the Big Bang, ended this phase, spearheading the formation of galaxies as we see them today. [Credit: NASA/WMAP Science Team, public domain]](https://www.openaccessgovernment.org/wp-content/uploads/2025/05/Fig-1_1200-100x70.jpg "How did the first stars form in space?")
