BL Lacertae

BL Lacertae or BL Lac is a highly variable, extragalactic active galactic nucleus (AGN or active galaxy). It was first discovered by Cuno Hoffmeister in 1929,[1] but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation. In 1968, the "star" was identified by John Schmitt at the David Dunlap Observatory as a bright, variable radio source. A faint trace of a host galaxy was also found.[2] In 1974, Oke and Gunn measured the redshift of BL Lacertae as z = 0.07, corresponding to a recession velocity of 21,000 km/s with respect to the Milky Way.[3] The redshift figure implies that the object lies at a distance of 900 million light years.

Due to its early discovery, BL Lacertae became the prototype and namesake of the class of active galactic nuclei known as "BL Lacertae objects" or "BL Lac objects". This class is distinguished by rapid and high-amplitude brightness variations and by optical spectra devoid (or nearly devoid) of the broad emission lines characteristic of quasars. These characteristics are understood to result from relativistic beaming of emission from a jet of plasma ejected from the vicinity of a supermassive black hole. BL Lac objects are also categorized as a type of blazar.

BL Lacertae changes in apparent magnitude over fairly small time periods, typically between values of 14 and 17. In January 2021, it exhibited extreme flaring behavior and was reported to reach magnitude 11.45 in the R filter band.[4]

References

Hoffmeister, Cuno (1929). "354 neue Veränderliche". Astronomische Nachrichten. 236 (15): 233–244. Bibcode:1929AN....236..233H. doi:10.1002/asna.19292361502.
Schmitt, John L. (May 1968). "BL Lac identified as a Radio Source". Nature. 218 (5142): 663. Bibcode:1968Natur.218..663S. doi:10.1038/218663a0. S2CID 4213061. Archived from the original on September 19, 2008.
Oke, J. B.; Gunn, J. E. (1974). "The Distance of BL Lacertae". Astrophysical Journal Letters. 189: 5. Bibcode:1974ApJ...189L...5O. doi:10.1086/181450.

Bonnoli, Giacomo. "ATel #14329". The Astronomer's Telegram. Retrieved 20 January 2021.

External links

"BL Lacertae". aavso.org. 13 April 2010.
"NAME BL Lac". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 3 April 2018.

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Constellation of Lacerta

List of stars in Lacerta Lacerta in Chinese astronomy

Stars
Bayer

α β

Flamsteed

1 2 4 5 6 8 9 10 11 12 13 14 15 16

Variable

S U V X Y Z RR RT RW SS SW VX VY AR AW BG CM CO CP CZ DE DI DK EV EW GL HK HT PP V345 V350 V362 V364 V365 V377 V399 V405 V416 V424

8422 8424 8429 8445 8463 8485 8487 8489 8510 8519 8536 8549 8553 8588 8589 8594 8606 8607 8609 8617 8626 8633 8643 8648 8651 8652 8654 8661 8666 8678 8682 8688 8692 8705 8708 8712 8718 8723 8733

211660 212334 215473

Other

ADS 16402 HAT-P-40 IRAS 22223+4327 IRAS 22272+5435 PSR B2217+47 SAO 51891

Exoplanets

HAT-P-1b

Star clusters

NGC 7209 NGC 7243 NGC 7245 NGC 7295

Nebulae

IC 5217

Galaxies
NGC

7197 7223 7227 7228 7231 7240 7242 7248 7250 7263 7264 7265 7273 7274 7276 7282 7330 7379 7395 7426

Other