Dwarf Galaxy Markarian 178: Where massive stars make their mark | Hubble

Dwarf Galaxy Markarian 178: Where massive stars make their mark | Hubble

The glittering blue galaxy in this Hubble Space Telescope picture is a blue compact dwarf galaxy called Markarian 178 (Mrk 178). This galaxy, substantially smaller than our own Milky Way, lies 13 million light-years away in the constellation Ursa Major (The Great Bear). Mrk 178 is one of more than 1,500 Markarian galaxies. These galaxies get their name from the Armenian astrophysicist Benjamin Markarian. He compiled a list of galaxies that were surprisingly bright in ultraviolet light.

While the bulk of the galaxy is blue owing to an abundance of young, hot stars with little dust shrouding them, Mrk 178 gets a red hue from a collection of massive stars that are especially concentrated in the brightest, reddish region near the galaxy’s edge. This azure cloud is home to a large number of rare objects called Wolf–Rayet stars. Wolf–Rayet stars are massive stars that are casting off their atmospheres through powerful winds. Because Mrk 178 contains so many Wolf–Rayet stars, the bright emission lines from these stars’ hot stellar winds are etched upon the galaxy’s spectrum. Particularly ionized hydrogen and oxygen appear as a red color to Mrk 178 in this photo, observed using Hubble’s specialized light filters.

Massive stars enter the Wolf–Rayet phase just before they collapse into black holes or neutron stars. Because Wolf–Rayet stars last for only a few million years, researchers know that something must have triggered a recent burst of star formation in Mrk 178. At first glance, it is not clear what could be the cause—Mrk 178 does not seem to have any close galactic neighbors that could have stirred up its gas to form new stars. Instead, researchers suspect that a gas cloud crashed into Mrk 178, or its gas may have been disturbed as the galaxy swims through the intergalactic medium, lighting up this tiny galaxy with a ripple of bright new stars.

Image Description: A pale blue dwarf galaxy seen on the black backdrop of space with faraway galaxies. The galaxy itself resembles a fuzzy cloud of tightly-packed stars with a broad halo of stars dispersed around it. Several small, glowing patches of gas are spread across the galaxy’s core, where very hot stars are concentrated.

Credit: ESA/Hubble & NASA, F. Annibali, S. Hong
Release Date: Dec. 8, 2025

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