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physical object > natural object > celestial body > collection of stars > galaxy > active galaxy > blazar > BL Lacertae

BL Lacertae (BL Lac)
subject			fact

BL Lacertae	has synonym BL Lac
	has definition A highly variable object (the most rapid radio variable known, also an optically violent variable - mv = 12 to 15 mag - and an infrared source). Probably an exceedingly compact nonthermal object, and undoubtedly extragalactic. Its optical spectrum is characterized by an absence of lines, so its redshift cannot be measured. (In 1974 Oke and Gunn infer z = 0.07 from an Hβ absorption line in the surrounding halo and conclude that it lies at the center of a bright (Mv = - 23) elliptical. If true, this would make BL Lac the nearest known quasar.)
	has definition A member of a class of astronomical objects with the following characteristics: (1) rapid variations in intensity at radio, infrared, and optical wavelengths; (2) energy distributions such that most of the energy is emitted at infrared wavelengths; (3) absence of discrete features in low-dispersion spectra; and (4) strong and rapidly varying polarization at visual and radio wavelengths.
	is a kind of blazar
active galaxy	has luminosity 1043 to 1046 ergs s-1
galaxy	has number of stars 106 to 1012
	has catalog galaxy catalog
radio source	has wavelength radio
	is a part of celestial sphere
	has catalog radio source catalog
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has mass
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

Kinds of BL Lacertae :

• High energy peaked BL Lac object (2 facts) (HBL)
• X-ray selected BL Lac object (2 facts) (SBL)

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