Aquila X-1 (frequently abbreviated to Aql X-1) is a

low-mass x-ray binary X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively common main sequence star), to the other component, called the ''acc ...

(LMXB) and the most luminous X-Ray source in the constellation

Aquila Aquila may refer to: Arts, entertainment, and media * ''Aquila'', a series of books by S.P. Somtow * ''Aquila'', a 1997 book by Andrew Norriss * ''Aquila'' (children's magazine), a UK-based children's magazine * ''Aquila'' (journal), an orni ...

. It was first observed by the satellite

Vela 5B Vela was the name of a group of reconnaissance satellites developed as the Vela Hotel element of Project Vela by the United States to detect nuclear detonations and monitor Soviet Union compliance with the 1963 Partial Test Ban Treaty. Vela ...

which detected several outbursts from this source between 1969 and 1976. Its optical counterpart is variable, so it was named V1333 Aql according to the

IAU The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

standards. The system hosts a

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

that accretes matter from a

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

star of

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

K4. The binary's orbital period is 18.9479 hours. The neutron star radiation flux is slightly variable due to the nuclear burning of the accreted helium on the surface.

References

K-type main-sequence stars Neutron stars X-ray binaries Aquila (constellation) Aquilae, V1333 J19111604+0035058 {{var-star-stub