Messier 109 (also known as NGC 3992) is a barred spiral galaxy some 137,000 light years across, with an estimated mass of 250 billion solar masses. It is about 67.5 million light-years away, and running away from us at an approximate speed of 1142 kilometers per second.
It is the brightest galaxy in the M109 Group, a large group of galaxies in the constellation Ursa Major where 79 galaxies have been identified. Messier 109 has three satellite galaxies (UGC 6923, UGC 6940 and UGC 6969) and possibly even more.
Detailed hydrogen observations have been obtained from M109 and its satellites. M109’s neutral atomic hydrogen (H I) distribution is regular with a low level radial extension outside the stellar disk, while at exactly the region of the bar, there is a central H I hole in the gas distribution. Possibly the gas has been transported inwards by the bar; because of the emptiness of the hole no large accretion events can have happened in the recent past.
In March 1956, type Ia supernova 1956A was observed in the southeast part of the galaxy and that is also the only supernova observed in M109 since its discovery.