| NGC 5728 | |
|---|---|
 Hubble Space Telescope image of the central region of NGC 5728 | |
| Observation data (J2000epoch) | |
| Constellation | Libra |
| Right ascension | 14h 42m 23.897s[1] |
| Declination | −17° 15′ 11.09″[1] |
| Redshift | 0.00935±0.00007[2] |
| Heliocentric radial velocity | 2,803±20 km/s[2] |
| Distance | 145.8 ± 10.3 Mly (44.70 ± 3.15 Mpc)[2] |
| Apparent magnitude (V) | 13.40[3] |
| Apparent magnitude (B) | 14.34[3] |
| Absolute magnitude (V) | −18.3[3] |
| Characteristics | |
| Type | SAB(r)a?[4] Sy 1.9[5] |
| Mass | 7.2×1010[5] M☉ |
| Size | 97.4 kly (29.86 kpc)[4] |
| Apparent size (V) | 203.3″ |
| Other designations | |
| GC 3977, GSC 06158-01021, h 1866, H 1–184, LEDA 52521, MCG -03-37-005, PBC J1442.4-1714, PGC 52424[6][7] | |
NGC 5728 is an activebarred spiral galaxy located 146[2] millionlight years away in the southernconstellation ofLibra. It was discovered on May 7, 1787 byWilliam Herschel. The designation comes from theNew General Catalogue ofJ. L. E. Dreyer, published in 1888.[7] It has anapparent visual magnitude of 13.40[3] and spans an angle of3.4 arcminutes. The galaxy shows ared shift of 0.00935 and has a heliocentricradial velocity of 2,803 km/s.[2] It has an estimated mass of 72[5] billion times themass of the Sun and stretches around30 kpc across.[4]
Themorphological classification of this galaxy is SAB(r)a?,[4] which indicates a weakly barred spiral galaxy (SAB) with a ring-like structure (r) and possible tightly wound arms (a?). TheSpitzer galactic survey lists a morphology code of (R1)SB(r′l,bl,nr,nb)0/a, meaning a barred spiral having a closer outer ring and an inner pseudo-ring/lens, plus a nuclear ring and bar/bar-lens.[5]Vera Rubin described it as having a "distinct elliptical structure intermediate between a spheroid and a disk".[8] Asymmetrical gas distribution in the galaxy suggests it has undergone a minormerger event that did not producetidal tails.[9]
In addition to the main bar, there is what appears to be a counter-rotating nuclear bar in the inner~10″, which is at an angle of 60° from the main bar.[10] There is evidence of star formation, but that has nearly ceased in the nuclear region due to the molecular gas being all but exhausted. The nuclear bar, if it exists, now consists of stars with little surrounding gas.[9]
This is a Seyfert galaxy of type 2, indicating it has an obscuredactive galactic nucleus (AGN) powered by asupermassive black hole at the center. The estimated mass of this object is3.4×107 M☉ and it is accreting mass at the rate of2.7×10−2 M☉·yr−1.[11] Energy released by the AGN is visible in the form of ionized cones that extend outward from the nucleus to a distance of more than2.5 kpc, and lie across the line of sight from the Earth.X-ray andradiojets have been detected. The nucleus is being fed by spiraling filaments and dust lanes from the surrounding galaxy. The AGN itself is hidden behind a bar of dust approximately 64 pc in length.[5] The outflow from the core is encountering the galactic ring at a distance of1 kpc and is significantly enhancing star formation in that region compared to other parts of the ring.[12]
Thetype Ia supernova SN 2009Y was reported in February 2009, before it reached maximum.[13] It was magnitude 16.0 at discovery and located24.7″ north and9.3″ east of the center of NGC 5728.[14]
Media related toNGC 5728 at Wikimedia Commons