Alcyoneus (galaxy)

Source: Wikipedia, the free encyclopedia.
For other uses, see Alcyoneus (disambiguation).
SDSS J081421.68+522410.0
billion light-years (1.1 Gpc)
Apparent magnitude (V)17.16
Characteristics
TypeE (purported with 89% chance)[1]
Mass2.4×1011 M☉
Size242,700 ly (74.40 kpc)
(diameter; 25.0 r-mag/arcsec2)
Notable featuresGiant radio galaxy
Other designations
Alcyoneus, 2MASS J08142169+5224103, WISEA J081421.70+522410.0
References: [2]

Alcyoneus is a low-excitation,

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]

Discovery

Alcyoneus had been first reported in a paper published in February 2022 by Martijn Oei and colleagues after obtaining results from the

Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS), an interferometric radio survey of the Northern Sky. The object was first observed as a bright, three component radio structure visible on at least four spatial resolutions of the LoTSS (6, 20, 60, and 90 arcsecond resolutions).[1] The two outer components of the radio structure are separated by a similar distance to the smaller, elongated radio structure, signifying their nature as possible radio lobes.[1] Further confirmations using radio-optical overlays dismiss the possibility of the two being separate radio lobes from different galaxies, and confirm that they have been produced by the same source.[1]

Characteristics

Alcyoneus has been described as a giant

a). This classifies it as a low excitation radio source, with Alcyoneus obtaining most of its energy due to relativistic process of the central galaxy's jet rather than radiation from its active galactic nucleus.[1]

The central host galaxy of Alcyoneus has a stellar mass of 240 billion solar masses (2.4×1011 M☉), with its central supermassive black hole estimated to have a mass of 390±170 million solar masses ((3.9±1.7)×108 M☉); both typical for elliptical galaxies, but substantially lower than for similar galaxies generating giant radio sources.[1]

It is currently unknown how Alcyoneus's radio emissions grew so large. One explanation proposes that the radio galaxy’s cosmic web environment might be less dense than that of other giant radio galaxies, leading to a lower resistance to growth. In comparison to other known giant radio galaxies, Alcyoneus does not appear to have a particularly massive stellar population or central black hole, or particularly powerful jet streams.[3]

See also

Notes

  1. ^ Various media outlets at the time of Alcyoneus's announcement described it as "the largest galaxy known", however this is misleading. It has the largest radio ejecta of any radio galaxy, which are not often taken into consideration in determining galaxy sizes. For details about how physical diameters of galaxies are measured, see Galaxy#Physical diameters.

References

  1. ^
    S2CID 246823634
    .
  2. ^ a b c "Results for WISEA J081421.70+522410.0". NASA/IPAC Extragalactic Database.
  3. ^ a b "Astronomers find largest radio galaxy ever". Universiteit Leiden. 16 February 2022. Retrieved 18 February 2022.
  4. ^ Turner, Ben (17 February 2022). "Largest galaxy ever discovered baffles scientists". Live Science. Retrieved 18 February 2022.
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