A galaxy is like a house with drawn curtains: bright ultraviolet light is born inside, but from outside you only see what manages to sneak through dust and gas. Astronomers need to know how much of this light escapes into intergalactic space, because it ionizes hydrogen in the early Universe and makes it transparent. But directly measuring this escaping flux from distant galaxies is nearly impossible — dust hides it from telescopes.
In the new study, scientists found a workaround. They used the SPHINX20 cosmological simulation, which models 1380 galaxies, and computed spectra with silicon absorption lines (SiII 1260 and 1526 angstroms) for each. These lines form when starlight passes through cold gas, and silicon atoms absorb some of the photons. They then compared how the residual flux of the silicon line, after correcting for dust, relates to the fraction of escaping ultraviolet light.
Tests on real data from the LzLCS and CLASSY surveys confirmed the method works, though accuracy drops due to errors in dust estimates. Dust is especially tricky: standard tools often underestimate its effect when it is strongest. But even with these caveats, the silicon line remains a reliable "escape detector" for ultraviolet radiation.
The SiII 1526 angstrom line is one of the brightest in galaxy ultraviolet spectra, visible even in very distant objects.
In Stanisław Lem's novel "Solaris," the ocean studies humans using radiation — astronomers similarly read a galaxy's "character" from its spectral lines.