Malin 1

Malin 1 is a giant low surface brightness (LSB) spiral galaxy, the prototype of LSB galaxies. It is located 1.19 billion light-years (366 Mpc) away in the constellation Coma Berenices, near the North Galactic Pole. As of February 2015 it is the largest known spiral galaxy so far discovered, with an approximate diameter of 650,000 light-years (200,000 pc), six and a half times the diameter of our Milky Way. It was discovered by astronomer David Malin in 1986 and is the first LSB galaxy verified to exist. As such, it is also the first giant LSB galaxy discovered. Its high surface brightness central spiral is 30,000 light-years (9,200 pc) across, with a bulge of 10,000 light-years (3,100 pc). The central spiral is a SB0a type barred-spiral.

Malin 1 is peculiar in several ways: its diameter alone would make it the largest barred spiral galaxy ever to have been observed.

Malin 1 was found later to be interacting with two other galaxies, namely Malin 1B and SDSS J123708.91+142253.2. Malin 1B is located 46,000 light-years (14,000 pc) away from the high surface brightness central spiral of Malin 1, which may be responsible for the formation of the galaxy's central bar. Meanwhile, SDSS J123708.91+142253.2 is located within the huge, faint halo of Malin 1 and might have caused the formation of the extended low surface brightness disc through tidal stripping.

Malin 1 was once thought to be over 1,000 times the diameter of the Milky Way which would have made it the largest known galaxy. Due to more detailed study, its low surface brightness disk was measured with higher precision bringing the galaxy down to smaller size that is still exceptionally large.

Observations by Galaz, et al., in April 2014 revealed a detailed view of the spiral structure of Malin 1 in optical bands. The galaxy exhibits giant and very faint spiral arms, with a thickness of up to one-third the diameter of the Milky Way. Other details, such as possible stellar streams and formation regions, are revealed as well.