Hercules A

Hercules A is a bright astronomical radio source in the constellation Hercules corresponding to the galaxy 3C 348.^[1][2]

Hercules A
Visible light image obtained by Hubble superposed with a radio image taken by the VLA.
Observation data (J2000 epoch)
Constellation	Hercules
Right ascension	16h 51m 08.15s
Declination	+04° 59′ 33.32″
Redshift	0.155000
Heliocentric radial velocity	46,468 km/s
Distance	2.1 Gly (643.9 Mpc)
Apparent magnitude (V)	0.261
Apparent magnitude (B)	0.345
Characteristics
Type	cD; E3
Other designations
Herc A, 3C 348, PGC 59117, 4C +05.66, MCG +01-43-006, NRAO 0518

Observation

During a survey of bright radio sources in the mid-20th century, astronomers found a very bright radio source in the constellation Hercules. The radio source is strongest in the middle range frequency and emits synchrotron radiation, suggesting the source of radio emission may be gravitational interaction. In 1959, astronomers from the Radio Astronomy Group (later the Cavendish Astrophysics Group) detected the radio source using the Cambridge Interferometer of the Cavendish Observatory in Cambridge University in the United Kingdom, including it in the Third Cambridge Catalogue of Radio Sources (3C) as 3C 348, the 348th object detected by the survey.

Characteristics

Galaxy

The galaxy, 3C 348, is a supergiant elliptical galaxy.^[3][4] It is located inside a poor galaxy cluster with an X-ray luminosity of L_bol = 4.8 × 10³⁷ W.^[5] 3C 348 is classified as type E3 to E4 of the updated Hubble–de Vaucouleurs extended galaxy morphological classification scheme. It has a companion galaxy, shown appearing as a secondary nucleus, indicating it is merging.^[6][7]

3C 348, the galaxy located in the center of the image, appears to be a relatively normal elliptical galaxy in visible light. When imaged in radio waves, however, plasma jets over one million light years long appear. Detailed analyses indicate that the galaxy is actually over 1,000 times more massive (approx. 10¹⁵ solar masses) than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive (approx. 4 billion solar masses) than the black hole at our Milky Way's center, one of the largest known. The physics that creates the jets is poorly understood, with a likely energy source being matter ejected perpendicular to the accretion disc of the central black hole^[8] which has grown more times than 1.7×10⁸ M_solar, enough to produce a shock front in the cluster's interstellar medium.^[9][10]

Radio source

The radio source in 3C 348 is considered powerful.^[11] It is double-lobed with striking bizarre features such as a double optical core and radio intensity rings clustered together inside one of the host galaxy's two radio lobes. Despite not being a Fanaroff-Riley Class II neither an FR I source, it instead shows similarities to both types.^[12][13]

See also

• List of largest galaxies

References

1. "A Multi-Wavelength View of Radio Galaxy Hercules A". NASA.
2. Baum, Stefi A.; O'Dea, Christopher P.; de Koff, Sigrid; Sparks, William; Hayes, Jeffrey J. E.; Livio, Mario; Golombek, Daniel (1996-07-01). "Hubble Space Telescope Observations of Obscuration Rings in Hercules A: Implications for Energy Transport in Powerful Radio Galaxies". The Astrophysical Journal. 465: L5. Bibcode:1996ApJ...465L...5B. doi:10.1086/310131. ISSN 0004-637X.
3. Zirbel, Esther L. (1996-12-01). "Properties of Host Galaxies of Powerful Radio Sources". The Astrophysical Journal. 473 (2): 713–732. Bibcode:1996ApJ...473..713Z. doi:10.1086/178184. ISSN 0004-637X.
4. Sadun, A. C.; Hayes, J. J. E. (1993-04-01). "The Optical Structure of the Radio Galaxy Hercules A". Publications of the Astronomical Society of the Pacific. 105: 379. Bibcode:1993PASP..105..379S. doi:10.1086/133165. ISSN 0004-6280.
5. Gizani, Nectaria A. B.; Leahy, J. P. (2004-05-01). "A multiband study of Hercules A - I. ROSAT observations of the intracluster medium". Monthly Notices of the Royal Astronomical Society. 350 (3): 865–878. arXiv:astro-ph/0402072. Bibcode:2004MNRAS.350..865G. doi:10.1111/j.1365-2966.2004.07685.x. ISSN 0035-8711.
6. O'Dea, C. P.; Baum, S. A.; Tremblay, G. R.; Kharb, P.; Cotton, W.; Perley, R. (2013-07-01). "Hubble Space Telescope Observations of Dusty Filaments in Hercules A: Evidence for Entrainment". The Astrophysical Journal. 771 (1): 38. arXiv:1305.4935. Bibcode:2013ApJ...771...38O. doi:10.1088/0004-637X/771/1/38. ISSN 0004-637X.
7. West, M. J. (1994-05-01). "Anisotropic mergers at high redshifts: the formation of cD galaxies and powerful radio sources". Monthly Notices of the Royal Astronomical Society. 268: 79–102. Bibcode:1994MNRAS.268...79W. doi:10.1093/mnras/268.1.79. ISSN 0035-8711.
8. Nemiroff, R.; Bonnell, J., eds. (5 December 2012). "Plasma Jets from Radio Galaxy Hercules A". Astronomy Picture of the Day. NASA.Portions of this public domain text are used here.
9. Nulsen, P. E. J.; Hambrick, D. C.; McNamara, B. R.; Rafferty, D.; Birzan, L.; Wise, M. W.; David, L. P. (2005-05-01). "The Powerful Outburst in Hercules A". The Astrophysical Journal. 625 (1): L9–L12. arXiv:astro-ph/0504350. Bibcode:2005ApJ...625L...9N. doi:10.1086/430945. ISSN 0004-637X.
10. Hambrick, D. C.; Nulsen, P. E. J.; MacNamara, B. R.; Rafferty, D. A.; Birzan, L. (2004). "Cooling Flows and Heating Shocks in Hercules A". American Astronomical Society Meeting Abstracts. 205. Bibcode:2004AAS...20514508H.
11. Dreher, J. W.; Feigelson, E. D. (1984-03-01). "Rings and wiggles in Hercules A." Nature. 308 (5954): 43–45. Bibcode:1984Natur.308...43D. doi:10.1038/308043a0. ISSN 0028-0836.
12. Sadun, Alberto C.; Morrison, Philip (2002-05-01). "Hercules A (3C 348): Phenomenology of an Unusual Active Galactic Nucleus". The Astronomical Journal. 123 (5): 2312–2320. Bibcode:2002AJ....123.2312S. doi:10.1086/339829. ISSN 0004-6256.
13. Mason, Andrea; Morrison, Philip; Sadun, Alberto C. (1988-06-01). "The radio rings of Hercules A". Nature. 333 (6174): 640–642. Bibcode:1988Natur.333..640M. doi:10.1038/333640a0. ISSN 0028-0836.