The universe in the visible wavelength range remains largely unexplored at sub-second time scales and sub-milliarcsecond angular resolutions due to instrumental limitations. Overcoming these impediments would bring a breakthrough in our knowledge of stellar physics, evolution and modelling by imaging the stars and their surroundings and unravel the history of the Solar System.
Imaging Atmospheric Cherenkov Telescopes (IACTs), originally designed to detect very-high-energy gamma rays by observing Cherenkov light from air showers, possess unique capabilities that can be repurposed for optical astronomy. Their large apertures, fast time resolution (~1 ns), and sensitivity to UV/blue light make them ideal for high-time-resolution photometry and stellar intensity interferometry (SII). The revival of SII, a technique pioneered in the 1960s, offers a cost-effective way to achieve microarcsecond (μas) resolution by correlating photon arrival times across multiple telescopes, bypassing the need for optical path stability required by traditional amplitude interferometry.
The Cherenkov Telescope Array Observatory (CTAO), a next-generation IACT project, presents an unprecedented opportunity to leverage these capabilities. With its extensive array of telescopes and long baselines, CTAO could become the first observatory to achieve μas resolution in the visible regime. However, realizing this potential requires significant upgrades to existing and future IACTs, including advanced readout electronics, high-speed correlators, and innovative calibration and imaging techniques.
The MicroStars project, led by its Principal Investigator Tarek Hassan at CIEMAT, aims to transform current and next-generation IACTs into powerful tools for ultra-fast optical astronomy. The project has two primary scientific goals:
1) Unprecedented Imaging of Stars and Their Surroundings: By upgrading IACTs into SII arrays, MicroStars will demonstrate CTAO could achieve μas resolution, enabling direct imaging of stellar surfaces, limb darkening, and starspots. This would provide new insights into stellar physics, magnetic activity, and the properties of massive stars like OB and Wolf-Rayet stars. This will be only possible if we demonstrate the feasibility of a correlator capable of handling a large number of input signals as well as a high-level analysis capable of employing this information. MicroStars will develop a scalable GPU-based correlator to handle the high data rates of SII and validate imaging techniques to reconstruct model-independent images from interferometric data.
2) Unraveling the Collisional History of the Solar System: MicroStars will use IACTs as high-time-resolution photometers to detect occultations of stars by sub-kilometer Kuiper Belt Objects. These observations will constrain the size distribution of primordial planetesimals, shedding light on the formation processes of the Solar System. The project will implement fast readout electronics and template-matching algorithms to identify occultation events with millisecond precision, significantly improving sensitivity to small KBOs.
