Massive Stars Make Their Mark in Hubble Image

• The Hubble Space Telescope has captured an image of Markarian 178 (Mrk 178), a blue dwarf galaxy located 13 million light-years away, featuring a unique blend of young stars and rare massive Wolf-Rayet stars.
• Mrk 178 is one of over 1,500 Markarian galaxies, named after Armenian astrophysicist Benjamin Markarian, who identified them as unusually bright in ultraviolet light due to their abundance of young, hot stars.
• The galaxy’s red hue is caused by the presence of rare massive Wolf-Rayet stars, which are concentrated near the galaxy’s edge and cast off their atmospheres through powerful winds, leaving behind a trail of ionized hydrogen and oxygen lines.
• Researchers believe that a recent burst of star formation in Mrk 178 was triggered by either a gas cloud crashing into the galaxy or the intergalactic medium disturbing its gas as it moved through space.

This NASA/ESA Hubble Space Telescope image features a glittering blue dwarf galaxy called Markarian 178 (Mrk 178). The galaxy, which is 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, who compiled a list of galaxies that were surprisingly bright in ultraviolet light.

While the bulk of the galaxy is blue due to an abundance of young, hot stars with little dust shrouding them, Mrk 178 gets a red hue from a collection of rare massive Wolf–Rayet stars. These stars are concentrated in the brightest, reddish region near the galaxy’s edge. Wolf–Rayet stars cast off their atmospheres through powerful winds, and the bright emission lines from their hot stellar winds are etched upon the galaxy’s spectrum. Both ionized hydrogen and oxygen lines are particularly strong and appear as a red color in this photo.

Massive stars enter the Wolf–Rayet phase of their evolution 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’s not clear what could be the cause — Mrk 178 doesn’t seem to have any close galactic neighbors that may have stirred up its gas to form new stars. Instead, researchers suspect that a gas cloud crashed into Mrk 178, or that the intergalactic medium disturbed its gas as the galaxy moved through space. Either disturbance could light up this tiny galaxy with a ripple of bright new stars.

Media Contact:

Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, MD

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