Original title: Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31
David Rubin, Istvan Szapudi · September 2026
Tiny primordial black holes formed in the early universe might make up dark matter, an unseen substance filling space. If one passes in front of a distant star, its gravity acts like a lens, briefly brightening the starlight for just minutes or seconds. Spotting these quick flashes requires rapid, precise measurements in packed fields of stars. To do this, researchers built FLASH, a software pipeline that processes images from the James Webb Space Telescope. It preserves fast timing data and carefully measures light from crowded stars while correcting camera detector quirks. The team tested FLASH on public telescope data of the Andromeda galaxy, taken every 21.5 s. They established that JWST can capture these fast events and placed constraints on asteroid-mass black holes, showing future dedicated telescope monitoring could search deeper.
Imagine trying to spot a single firefly in a stadium full of flashing cell phones during a concert. The firefly flashes for only a second, and you have to catch it among thousands of other lights. Here, the firefly is a tiny black hole magnifying a star for a few seconds, the stadium is the crowded disk of the Andromeda galaxy, and the cell phones are all the other stars. The FLASH pipeline is like a camera that takes pictures every second and a computer that looks for the one brief flash that stands out.
Dark matter makes up most of the universe's mass, but we don't know what it is. This work shows that JWST can search for black holes as light as asteroids, a mass range ground telescopes cannot reach. If such black holes exist, they could explain all dark matter; if not, we rule out another possibility.
The observations used were not designed for microlensing, so the constraints are weak (less than 100% of dark matter at one mass). A dedicated monitoring program would be needed to improve them. The pipeline has only been tested on M31 data, and its performance on other fields is not established.
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Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31 — David Rubin, Istvan Szapudi
Abstract licence: CC0
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