| Leo A | |
|---|---|
 Leo A byHubble Space Telescope | |
| Observation data (J2000epoch) | |
| Constellation | Leo |
| Right ascension | 09h 59m 26.4s[1] |
| Declination | +30° 44′ 47″[1] |
| Redshift | 0.000067[1] |
| Distance | 2.6 ± 0.1Mly (790 ± 40kpc)[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] | |
Leo A (also known as Leo III) is anirregulargalaxy that is part of theLocal Group. It lies2.6 millionlight-years fromEarth, and was discovered byFritz Zwicky in 1942.[4] The estimated mass of this galaxy is(8.0 ± 2.7) × 107solar masses, with at least 80% consisting ofdark 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 ofRR Lyrae variables shows that the galaxy has an old stellar population that is up to 10 billion years in age.[7]
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 higheratomic 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 theMilky 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 fourH II regions powered by short-lived,O-class stars.[8]
Media related toLeo A at Wikimedia Commons
