I Zwicky 18 is a blue compact dwarf galaxy located about 59 million light years away[2] in the constellation Ursa Major.

[7] Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is almost exclusively composed of hydrogen and helium, the main ingredients created in the Big Bang.

The Cepheid distance also was validated through the observed brightness of the brightest red stars older than one billion years.

[14] I Zwicky 18 may still be creating Population III stars—spectroscopy shows that its stars are composed almost entirely of hydrogen and helium, with heavier elements almost completely absent.

[15] The concentrated bluish-white knots embedded in the heart of the galaxy are two major starburst regions where stars are forming at a furious rate.

The wispy blue filaments surrounding the central starburst regions are bubbles of gas that have been blown away by stellar winds and supernovae explosions from a previous generation of hot, young stars.