DDO 190 (or UGC 9240) is a

dwarf Dwarf or dwarves may refer to: Common uses *Dwarf (folklore), a being from Germanic mythology and folklore * Dwarf, a person or animal with dwarfism Arts, entertainment, and media Fictional entities * Dwarf (''Dungeons & Dragons''), a humanoid ...

irregular galaxy in the vicinity of the Milky Way, as it is relatively small and lacks clear structure. It is away from Earth and lies out of the Local Group, determined by the

tip of the red giant branch Tip of the red-giant branch (TRGB) is a primary distance indicator used in astronomy. It uses the luminosity of the brightest red-giant-branch stars in a galaxy as a standard candle to gauge the distance to that galaxy. It has been used in conj ...

method. The outskirts of the galaxy are harbouring older (reddish) stars, while the centre is crowded with younger (bluish) stars. Heated gas is observed at several places. DDO 190 still experiences some active star formation. The galaxy is categorised as a Magellanic dwarf galaxy of morphological type Im. Its

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

is e/H= −1.55 ± 0.12. DDO 190 is small, but not tiny: about 15,000 light years across—about 1/6 the size of our galaxy. It is also well outside the Local Group, which contains nearby galaxies (the Andromeda galaxy is less than 3 million light years distant from Earth, for comparison), and is instead thought to be part of the M94 galaxy group. But if true it is fairly isolated even from the others on its team; the nearest neighbor appears to be another dwarf galaxy, DDO 187, at a distance of .

History

The galaxy was discovered by the Canadian astronomer

Sidney van den Bergh Sidney Van den Bergh, OC, FRS (born 20 May 1929 in Wassenaar) is a retired Dutch-Canadian astronomer. He showed an interest in science from an early age, learning to read with books on astronomy. In addition to being interested in astronomy. ...

in 1959 and put in the DDO catalogue.

References

{{Boötes, state=collapsed 9240 Dwarf galaxies Boötes Astronomical objects discovered in 1959