Dwingeloo 2 is a small

irregular galaxy An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearan ...

discovered in 1996 and located about 10 million

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away from the Earth. Its discovery was a result of the Dwingeloo Obscured Galaxy Survey (DOGS) of the

Zone of Avoidance The Zone of Avoidance (ZOA, ZoA), or Zone of Galactic Obscuration (ZGO), is the area of the sky that is obscured by the Milky Way. The Zone of Avoidance was originally called the Zone of Few Nebulae in an 1878 paper by English astronomer Richard ...

using the

Dwingeloo Radio Observatory The Dwingeloo Radio Observatory is a single-dish radio telescope near the village of Dwingeloo () in the northeastern Netherlands. Construction started in 1954, and the telescope was completed in 1956. The radio telescope has a diameter of 25 ...

. Dwingeloo 2 is a companion galaxy of Dwingeloo 1. Dwingeloo 2 was first detected at

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

s from the 21 cm

emission line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

of neutral

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

(known to

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

s as HI) in the course of follow-up observations after the discovery of Dwingeloo 1. Dwingeloo 2 is thought to be a member of the IC 342/Maffei Group, a

galaxy group A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 1010 times the luminosity of the Sun); collections of galaxi ...

adjacent to the

Local Group The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...

. The galaxy recedes from the Milky Way at the speed of about 241 km/s. The visible radius of Dwingeloo 2 is approximately 2′, which at the distance of 3 Mpc corresponds to about 2 kpc. Dwingeloo 2 has a well defined rotating HI disk inclined at approximately 69° with respect to observer. The distribution of the neutral hydrogen in Dwingeloo 2 is quite irregular, and it is detected as far as 3.2 kpc from the center of the galaxy. The total mass of the galaxy within this radius is estimated at 2.3 billion Solar masses, while the mass of the neutral hydrogen is estimated at 100 million

Solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es. The total mass of the galaxy is about five times less than that of Dwingeloo 1. The irregular structure of Dwingeloo 2 is likely related to its interaction with the much larger nearby galaxy Dwingeloo 1, which lies at a distance of only 24 kpc from Dwingeloo 2.

References

External links

* {{Sky, 02, 54, 08.47, +, 59, 00, 19.1 Irregular galaxies IC 342/Maffei Group Astronomical objects discovered in 1996 101304 Cassiopeia (constellation)