Massive Stars Make Their Mark in Hubble Image

This NASA/ESA Hubble Space Telescope image shows a shimmering blue dwarf galaxy called Markarian 178 (Mrk 178). The galaxy, which is significantly smaller than our own Milky Way, lies 13 million light years away in the constellation Ursa Major (Ursa Major).

Mrk 178 is one of more than 1,500 Markarian galaxies. These galaxies get their name from Armenian astrophysicist Benjamin Markarian, who compiled a list of galaxies that are surprisingly bright in ultraviolet light.

While most of the galaxy is blue due to an abundance of young, hot stars surrounded by little dust, Mrk 178 takes on a red hue thanks to a collection of rare massive Wolf-Rayet stars. These stars are concentrated in the brightest reddish region, near the edge of the galaxy. Wolf-Rayet stars shed their atmospheres with powerful winds, and the bright emission lines from their hot stellar winds are etched on the galaxy spectrum. The ionized lines of hydrogen and oxygen are particularly strong and appear red in this photo.

Massive stars enter the Wolf-Rayet phase of their evolution just before collapsing into black holes or neutron stars. Since Wolf-Rayet stars only last a few million years, researchers know that something must have triggered a recent burst of star formation in Mrk 178. At first glance, the cause is unclear – Mrk 178 does not appear 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 that the intergalactic medium disrupted its gas as the galaxy moved through space. Either disturbance could light up this small galaxy with a ripple of bright new stars.

Media contact:

Claire Andreoli (claire.andreoli@nasa.gov)
from NASA Goddard Space Flight Center, Greenbelt, Maryland