A Hubble Space Telescope image of the dwarf galaxy NGC 4449 is drawing attention to a question about small galaxies: how much they shape the chemical makeup of the wider universe. NGC 4449 and similar dwarfs appear to be missing more oxygen than current models predict. That suggests the stellar winds and supernova explosions inside them expel heavy elements far more effectively than expected.
Small galaxies, large numbers
The Milky Way spans about 100,000 light-years and holds hundreds of billions of stars. Dwarf galaxies are far more modest. They measure roughly one-tenth the Milky Way’s diameter and contain only a few billion stars. Despite their size, they are the most common type of galaxy in the universe, so their combined influence could be considerable.
NGC 4449 is one such system, and Hubble’s image shows it as a representative of the class.
Where the oxygen goes
Astronomers use the abundance of elements such as oxygen to test how galaxies form and evolve. Oxygen and other heavy elements are produced inside stars and released when massive stars shed material in winds or end their lives as supernovae. In NGC 4449 and comparable dwarfs, the measured oxygen content falls short of what models predict.
The implication is that these processes are surprisingly efficient at driving heavy elements out of their host galaxies. Dwarf galaxies are small, and the material they eject may escape into the space around them rather than remain available for future star formation.
If that interpretation holds, dwarf galaxies may be significant contributors to the spread of heavy elements through the universe. Those elements are the raw materials for stars, planets and life. The finding is framed as a suggestion rather than a settled conclusion, and it points to stellar winds and supernovae in low-mass galaxies as an area where models may need refinement.
Source: science.nasa.gov
