dwarf galaxy

History

The first dwarf galaxies were discovered in the mid-20th century, but their ubiquity became clear thanks to telescopes like Hubble. Astronomer Vera Rubin, studying their rotation, found evidence of dark matter.

How it works

Stars in a dwarf galaxy move faster than they should if only visible mass is considered. This means there is invisible 'dark' matter inside, creating additional attraction.

History

The first dwarf galaxies were discovered in the mid-20th century, but their ubiquity became clear thanks to telescopes like Hubble. Astronomer Vera Rubin, studying their rotation, found evidence of dark matter.

How it works

Stars in a dwarf galaxy move faster than they should if only visible mass is considered. This means there is invisible 'dark' matter inside, creating additional attraction.

History

Dwarf satellites of the Milky Way began to be discovered in the 1930s–1940s (the Sculptor Dwarf Galaxy, 1937). In the 1970s, Vera Rubin used rotation curves to confirm the high fraction of dark matter in dwarf irregular galaxies. Fritz Zwicky had already hypothesized hidden mass in clusters in the 1930s, but it was in dwarfs that the connection became obvious. Since the 1990s, the Sloan Digital Sky Survey has revealed many ultra-faint dwarf satellites.

How it works

Dwarf galaxies form in mini-halos of dark matter, where primordial gas cools and forms stars. Their evolution is determined by star formation, suppressed by supernova outbursts and tidal interactions with massive neighbors. The rotation of stars and gas is described by Newtonian dynamics with the inclusion of hidden mass: the law of universal gravitation is used to estimate the gravitational potential. Dark matter dominates, and rotation curves remain flat far beyond the stellar disk. The virial theorem allows estimating the total mass from the velocity dispersion: M ≈ 5Rσ²/G.

Open problems & fun facts

The missing satellites problem (discrepancy between the predicted and observed numbers of dwarf galaxies); The nature of dark matter (WIMPs, axions, or modified gravity); How dwarf galaxies lose gas and cease star formation

💡 The ultra-faint dwarf galaxy Segue 1 contains only a few hundred stars, but in terms of dark matter mass it is comparable to a small globular cluster, and its dark matter density is one of the highest among known objects.