AP Librae is a

BL Lacertae object A BL Lacertae object or BL Lac object is a type of active galactic nucleus (AGN) or a galaxy with such an AGN, named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and ...

located at a distance of 700 million

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s in the southern constellation of

Libra Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...

. In the visual

band Band or BAND may refer to: Places *Bánd, a village in Hungary * Band, Iran, a village in Urmia County, West Azerbaijan Province, Iran * Band, Mureș, a commune in Romania * Band-e Majid Khan, a village in Bukan County, West Azerbaijan Province, ...

it is one of the most active

blazar A blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from t ...

s known. AP Lib is surrounded by an extended source with a

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of color ...

characteristic of a red-shifted

giant elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Rea ...

. The derived

visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of this region is 15.0, and it follows a radially decreasing brightness that is characteristic of an elliptical. Seven fainter galaxies are visible within an angular radius of , suggesting it is the brightest member of a

galactic cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

. This object was first identified as an optical variable by Martha D. Ashbrook in 1942, who noted the brightness changed irregularly from magnitude 15.0 down to 16.0. The source was found to vary chaotically on time scales of days and even hours. Howard E. Bond and Francois Biraud in 1971 noted the coincidence of this object with the position of the radio source PKS 1514–24. In 1965,

John G. Bolton John Gatenby Bolton (5 June 1922 – 6 July 1993) was a British-Australian astronomer who was fundamental to the development of radio astronomy. In particular, Bolton was integral in establishing that discrete radio sources were either gala ...

and associates identified the latter as a sixteenth magnitude

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Rea ...

. Glenn M. Frye and associates in 1971 suggested that it may be a

gamma-ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically sh ...

source. The similarity of this object to

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, but was originally thought to be an irregular variable star in the Milky Way gal ...

was noted, leading to it being designated as a BL Lac object. AP Librae emits a

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...

component to its

spectral energy distribution A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a 'spectrum' of flux density vs frequency or wavelength). It is used in many branches of astronomy to characterize astron ...

(SED). The peak component of this radiation lies in the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...

band, making this a low-frequency peaked BL Lac (LBL). It is one of the few LBLs known to emit gamma rays. The width of the high energy component of the SED is considered extremely broad for objects of this class, ranging in energy from around up to the TeV level. In 1998–99, extended radio emission was detected from a one-sided

jet Jet, Jets, or The Jet(s) may refer to: Aerospace * Jet aircraft, an aircraft propelled by jet engines ** Jet airliner ** Jet engine ** Jet fuel * Jet Airways, an Indian airline * Wind Jet (ICAO: JET), an Italian airline * Journey to Enceladus a ...

that starts in a south-easterly direction from the source before bending to the northeast. This non-thermal jet extends from AP Lib (equivalent to ~), and in 2013 was found to emit

X-rays X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

. The jet may be the source for the gamma-ray emission in the TeV range.

References

Further reading