Definition of BL Lac object in English:

BL Lac object

noun

Astronomy
  • A type of remote elliptical galaxy with a very compact starlike nucleus, remarkable for its considerable short-term variations in brightness and radio emissions.

    • ‘However, BL Lac objects are the active cores of elliptical galaxies.’
    • ‘Active elliptical galaxies are called BL Lac objects if their jets are viewed end-on; they look very different, having giant radio lobes, if their jets are viewed from the side.’
    • ‘The bright reddish object to the lower left of the center is a BL Lac object at the center of a cluster of galaxies.’
    • ‘A number of BL Lac objects are known in the vicinity of clusters of galaxies so this provides indirect evidence in support of their extragalactic nature.’
    • ‘This result supports the interpretation of H2155 304 as a highly luminous BL Lac object.’

Origin

BL Lac, short for BL Lacertae, the designation of the first such object discovered (originally thought to be a variable star).