JWST confirms: The tiniest galaxies made the cosmos visible

JWST has puzzled astronomers by revealing large, bright, massive early galaxies. But the littlest ones pack the greatest cosmic punch.


JWST reveals the mystery of cosmic reionization

Shortly after the hot Big Bang, the Universe was opaque to starlight due to neutral atoms blocking and absorbing emitted starlight.

It took hundreds of millions of years for enough stars to form and release ultraviolet photons to make the Universe transparent to starlight.

Contrary to expectations, the tiniest dwarf galaxies, rather than the largest and most luminous galaxies, played a key role in the reionization process.

JWST's discovery in a patch of sky

The JWST UNCOVER Treasury Survey revealed about 50,000 objects, predominantly background galaxies, in a small patch of sky.

Gravitational lensing was used to study the surrounding cluster and uncover even more distant galaxies.

This discovery shed light on the early stages of galaxy evolution and the transition from an opaque to transparent Universe.

The role of ultraviolet photons in reionization

Before the formation of stars, neutral atoms absorbed visible light, making space opaque.

Only the ionizing ultraviolet photons emitted by stars could render the neutral atoms transparent to visible light.

Energetic ultraviolet photons were crucial in reionizing the Universe and making it transparent.