Leo A

Leo A (also known as Leo III) is an irregular galaxy that is part of the Local Group. It lies 2.6 million light-years from Earth, and was discovered by Fritz Zwicky in 1942.^[4] The estimated mass of this galaxy is (8.0 ± 2.7) × 10⁷ solar masses, with at least 80% consisting of dark matter.^[5] It is one of the most isolated galaxies in the Local Group and shows no indications of an interaction or merger for several billion years. However, Leo A is nearly unique among irregular galaxies in that more than 90% of its stars formed more recently than 8 billion years ago, suggesting a rather unusual evolutionary history.^[6] The presence of RR Lyrae variables shows that the galaxy has an old stellar population that is up to 10 billion years in age.^[7]

Leo A
Leo A by Hubble Space Telescope
Observation data (J2000 epoch)
Constellation	Leo
Right ascension	09h 59m 26.4s[1]
Declination	+30° 44′ 47″[1]
Redshift	0.000067[1]
Distance	2.6 ± 0.1 Mly (790 ± 40 kpc)[2][3]
Apparent magnitude (V)	12.9[1]
Characteristics
Type	IBm[1]
Apparent size (V)	5.1′ × 3.1′[1]
Other designations
Leo III, UGC 5364, DDO 69, PGC 28868[1]

The neutral hydrogen in this galaxy occupies in a volume similar to its optical extent, and is distributed in a squashed, uneven ring. The galaxy is not rotating and the hydrogen is moving about in random clumps. The proportion of elements with higher atomic numbers than helium is only about 1–2% of the ratio in the Sun. This indicates a much less complete conversion of gas into stars than in the Milky Way galaxy. The Leo A galaxy shows sign of increased star formation some time within the last 1–4 billion years, although the current level is low. There are four H II regions powered by short-lived, O-class stars.^[8]