Alcyoneus (galaxy)

SDSS J081421.68+522410.0
Composite image of Alcyoneus in LOFAR radio data at 144 MHz (orange) and WISE infrared data at 3.4 micron (blue)
Observation data (J2000.0 epoch)
Constellation	Lynx
Right ascension	08h 14m 21.68s
Declination	+52° 24′ 10.08″
Redshift	0.24674±0.00006
Heliocentric radial velocity	73,969.90±17.69 km/s
Galactocentric velocity	74,013±18 km/s
Distance	3.5 billion light-years (1.1 Gpc)
Apparent magnitude (V)	17.16
Characteristics
Type	E (purported with 89% chance)[1]
Mass	2.4×1011 M☉
Size	242,700 ly (74.40 kpc) (diameter; 25.0 r-mag/arcsec2)
Notable features	Giant radio galaxy
Other designations
Alcyoneus, 2MASS J08142169+5224103, WISEA J081421.70+522410.0
References: [2]

Alcyoneus is a low-excitation, Fanaroff–Riley class II radio galaxy located 3.5 billion light-years (1.1 gigaparsecs) from Earth, corresponding to the galaxy SDSS J081421.68+522410.0.^[2] It is located in the constellation Lynx and it was discovered in Low-Frequency Array (LOFAR) data by a team of astronomers led by Martijn Oei. It has the largest extent of any radio galaxy identified, with lobed structures spanning 5 megaparsecs (16 million light-years) across, described by its discoverers as the "largest known structure of galactic origin."^[1][a] For comparison, another similarly sized giant radio galaxy is 3C 236, with lobes 15 million light-years across.

Aside from the size of its radio emissions, the central galaxy is otherwise of ordinary radio luminosity, stellar mass, and supermassive black hole mass. It is a standalone galaxy with an isophotal diameter at 25.0 r-mag/arcsec² of about 242,700 light-years (74.40 kpc), with the nearest cluster located 11 million light years away from it.^[1] The galaxy was named after the giant Alcyoneus from Greek mythology.^[1]

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