This Tiny Blue Galaxy Is Glowing With Rare and Violent Stars

A tiny blue galaxy packed with doomed giant stars hints at a recent, mysterious cosmic collision.

The sparkling blue object featured as this ESA Hubble Picture of the Week is a compact dwarf galaxy known as Markarian 178 (Mrk 178). Much smaller than the Milky Way, this galaxy sits about 13 million light-years from Earth in the constellation Ursa Major (The Great Bear).

Markarian 178 belongs to a larger family of more than 1500 Markarian galaxies. These systems were cataloged by Armenian astrophysicist Benjamin Markarian, who identified galaxies that stood out for their unusually strong ultraviolet light.

Why Markarian 178 Shines Blue and Red

Most of Markarian 178 glows blue because it is filled with young, extremely hot stars that are not heavily obscured by dust. However, parts of the galaxy also appear red due to a dense concentration of massive stars clustered near its brightest outer region. This vivid cloud hosts a remarkable number of rare Wolf–Rayet stars.

Wolf–Rayet stars are massive stars that are rapidly shedding their outer layers through intense stellar winds. In Markarian 178, these winds produce strong emission signatures that are clearly visible in the galaxy’s spectrum. When viewed through specialized Hubble filters, glowing ionized hydrogen and oxygen show up as red tones, adding contrast to the galaxy’s dominant blue color.

Clues to a Recent Burst of Star Formation

Stars enter the Wolf–Rayet stage shortly before collapsing into black holes or neutron stars. Since this phase lasts only a few million years, the abundance of Wolf–Rayet stars in Markarian 178 indicates that the galaxy experienced a recent surge in star formation.

The cause of this activity is not immediately obvious. Markarian 178 appears relatively isolated, with no large nearby galaxies that could have easily disturbed its gas. Astronomers think the trigger was an encounter with a much smaller companion galaxy. Deep observations from the Large Binocular Telescope revealed faint tidal structures surrounding Mrk178, suggesting a past interaction. Upcoming high-resolution Hubble observations will be key to uncovering the full star formation history of this energetic dwarf galaxy.

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