NGC 2403

Spiral galaxy NGC 2403 is located in the constellation Camellia and has an apparent magnitude of 8.2m. The galaxy is located at a distance of about 10 million light-years from the Sun. It contains blue open star clusters, dark dust lanes, and a relatively small nucleus at the center. Older yellow stars are located closer to the center, and younger blue star-forming regions are located in the spiral arms.

In 2004, one of the brightest supernovae exploded in this galaxy. The galaxy was discovered by William Herschel in 1788. Edwin Hubble discovered Cepheids in NGC 2403 using the Hale telescope, making it the first galaxy outside the Local Group in which a Cepheid was discovered.

Supernovae and Imposters

Four astronomical transients have been detected in the galaxy:

• SN 1954J — initially observed as a bright blue variable star, later classified as an imposter supernova, i.e. a highly luminous, massive star surrounded by a dusty nebula.
• SN 2002kg — discovered in 2002 and classified as a type IIn supernova. In 2021, it was reclassified as a Gap transient.
• SN 2004dj (a type II-P supernova, mag. 11.2) was discovered by Koichi Itagaka in 2004.
• AT 2016ccd — a luminous blue variable star discovered in 2013, with outbursts observed until 2021.

History

The galaxy was discovered by William Herschel in 1788. Edwin Hubble discovered Cepheids in NGC 2403 using the Hale Telescope, making it the first galaxy outside the Local Group to have a Cepheid detected.

Satellites

NGC 2403 has two known satellites:

• DDO 44 is a relatively massive dwarf galaxy that is now being disrupted by NGC 2403.
• MADCASH J074238+652501-dw (MADCASH-1) is a dwarf galaxy similar to typical dwarf spheroidal galaxies in the Local Group.

Bright Blue Variables in NGC 2403

There are four known bright blue variables in the galaxy:

• AT 2016ccd
• NGC 2403 V14
• NGC 2403 V37
• NGC 2403 V12

The galaxy NGC 2403 is the second largest object in the M81 group, after M81 itself. In a broader context, NGC 2403 and the M81 group are part of the Coma-Sculpture Cloud, which includes our Local Group.

Supernovae

• The galaxy has hosted three supernovae in the past 70 years, including one of the brightest in 2004. In 1954, Zwicky noted an event that later turned out to be not a true supernova, but an eruption similar to Eta Carinae in the 19th century.