By staring at the sky for over 200 hours, the Spitzer Space Telescope collected light that finally reached Earth after a 13-billion-year voyage through space.

This light left its origin so long ago that researchers studying this imagery are essentially peering back — way back — in time, to the ancient cosmic past.

Using Spitzer data, a research team observed 135 distant galaxies and found that these celestial bodies, which formed over 13 billion years ago and just 1 billion years after the Big Bang, were brighter than expected.

Researchers coupled their Spitzer findings with archival data from the Hubble Space Telescope in a recent paper published in the Monthly Notices of the Royal Astronomical Society.

Related: This 13.5-Billion-Year-Old Star Is a Tiny Relic from Just After the Big Bang

These 135 galaxies were particularly bright in two wavelengths of infrared light, which was created by radiation mingling with galactic gases like hydrogen and oxygen, according to a statement released May 9 — showing that the galaxies were releasing a high level of so-called ionizing radiation.

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