BL Lacertae

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BL Lacertae (short BL Lac ) is the prototype of the BL Lacertae objects , a class of variable active galaxy nuclei that are now known as blazars .

BL Lacertae was classified as a variable star by Cuno Hoffmeister in 1929 because of its variable brightness and its star-like appearance and later named as usual with a letter code and the name of the constellation.

In 1968 this object was identified by J. L. Schmitt with a radio source and a faint nebulous surrounding object was found. In a spectrum of this surrounding object recorded in 1973, Oke and Gunn were able to determine absorption lines that identified it as a galaxy at a redshift  z = 0.07 and thus a distance of about 900 million light years . So BL Lacertae is not a star, but an active galactic core.

In the case of BL Lacertae objects, the core appears particularly bright due to a jet of matter directed at us and outshines the surrounding galaxy so strongly that it is difficult or impossible to investigate even with today's methods.

The brightness of BL Lacertae fluctuates between around 14th and 17th  magnitude in quiet phases, while the sporadic outbreaks (2013, 2015, 2018 and most recently in August 2020) reached the 12th magnitude within hours to days. The phases of activity can also be detected with gamma telescopes. The position in the sky is RA  22h02m43.3s, DEC  + 42 ° 16'40 "( J2000.0 ).

literature

  • C. Hoffmeister. In: Astronomical News . 236, 1929, p. 233.
  • JL Schmitt. In: Nature . Volume 218, 1968, p. 663.
  • JB Oke, J. Gunn. In: Astrophysical Journal . 189, 1974, L5.
  • Alan Marscher et al .: The inner jet of an active galactic nucleus as revealed by a radio-to-γ-ray outburst . In: Nature . Volume 452, 2008, p. 966. ( Abstract )

Individual evidence

  1. ↑ Remco Steineke, Lukas Waller, David Reinhart, Felix Hemrich, Kilian Schoch, Johannes Knoett, Nils Zottmann, Martin Feige, Christian Lorey (all Friedrich-Koenig-Gymnasium / Hans-Haffner-Sternwarte), Karl Mannheim (Universitaet Wuerzburg), Dominik Elsaesser (TU Dortmund): Decadal optical outbreak of BL Lac as observed at the Hans-Haffner-Sternwarte. Accessed August 30, 2020 (English).
  2. ↑ Oscar Blanch (IFAE-BIST, Barcelona), on behalf of the MAGIC collaboration: MAGIC detection of very-high-energy gamma-ray flaring activity from BL Lacertae during the current historical optical and high-energy gamma-ray flare. Accessed August 30, 2020 (English).