The Hubble Picture of the Week this week reveals the subtle glow of the galaxy named IC 3430, located 45 million light-years from Earth in the constellation Virgo. It is part of the Virgo cluster, a rich collection of galaxies both large and small, many of which are very similar in type to this diminutive galaxy.
IC 3430 is a dwarf galaxy, a fact well reflected by this view from Hubble, but it is more precisely known as a dwarf elliptical or dE galaxy. Like its larger cousins, this galaxy has a smooth, oval shape lacking any recognisable features like arms or bars, and it is bereft of gas to form very many new stars. Interestingly, IC 3430 does feature a core of hot, massive blue stars, an uncommon sight in elliptical galaxies that indicates recent star-forming activity. It’s believed that ram pressure from the galaxy ploughing through gas within the Virgo cluster has ignited what gas does remain in IC 3430’s core to form some new stars.
Dwarf galaxies are really just galaxies with not many stars, usually fewer than a billion, but that is often enough for them to reproduce in miniature the same forms as larger galaxies. There are dwarf elliptical galaxies like IC 3430, dwarf irregular galaxies, dwarf spheroidal galaxies and even dwarf spiral galaxies! The so-called Magellanic spiral is a distinct type of dwarf galaxy, too, the best example being the well-known dwarf galaxies that are the Magellanic Clouds.
[Image Description: A relatively small, oval-shaped galaxy, tilted diagonally. It glows brightly at the centre and dims gradually to its edge. At the centre it is crossed by some wisps of dark dust, and a few small, blue, glowing spots are visible, where stars are forming. The galaxy is on a dark background in which many background galaxies and foreground stars can be seen.]