BHR 71

Lore & Background

BHR 71 was discovered in 1977 by A. Sandqvist using the ESO B Atlas. In 1995 it was included in a catalogue by T. L. Bourke, A. R. Hyland and G. Robinson, which listed small molecular clouds called globules; these objects later received the acronym BHR. In 1997 a study discovered a highly collimated bipolar outflow in the center of the Bok globule, originating from a class 0 protostar called IRAS 11590-6452. In 2001 new near-infrared observations with the Anglo-Australian Telescope and carbon monoxide observations with the Swedish-ESO Submillimetre Telescope found that the source was actually two individual protostars, IRS 1 and IRS 2, separated by about 17 arcseconds (or 3400 AU). Each protostar drives its own molecular outflow, with IRS 1 driving the larger outflow and being more massive. The binary's formation was initially attributed to rotational fragmentation of a single collapsing protostellar core, but a later study using ALMA found it formed via turbulent fragmentation of the core. Dust observations with ALMA found compact objects with no clear Keplerian motion, meaning potential disks are not detected, likely deeply embedded in an envelope; upper mass limits were set at 0.46 M☉ for IRS 1 and 0.26 M☉ for IRS 2.

Reader's Guide

BHR 71's significance lies in its binary protostar system and the associated outflows, which offer a natural laboratory for studying star formation and fragmentation. The discovery of two protostars driving separate outflows, with one outflow partially colliding with another, provides direct evidence of interactions in a forming multiple-star system. The double-helical structure of IRS 1's jet indicates removal of angular momentum, while the highly collimated, knotty jet of IRS 2 suggests episodic accretion. The uncertainty over whether the binary formed via rotational or turbulent fragmentation highlights ongoing debates in star formation theory. The upper mass limits for the protostars constrain models of early stellar evolution. The globule's low kinetic temperature of 11 Kelvin and mass of 40 M☉ characterize it as a typical Bok globule, a site of low-mass star formation. The correction of the positions of Herbig-Haro objects 320 and 321 underscores the iterative nature of astronomical discovery.

Did You Know?

• The globule has a kinetic temperature of 11 Kelvin and a mass of 40 M☉.
• The binary protostars IRS 1 and IRS 2 are separated by about 3400 AU.
• The jet of IRS 1 shows a double-helical structure, evidence of angular momentum removal.

Origins & the Long Road to a Name

Musca traces its formal existence to the early Dutch maritime age. The constellation was established by Petrus Plancius, drawing on observations made by Pieter Dirkszoon Keyser and Frederick de Houtman during the Eerste Schipvaart, the first Dutch trading voyage to the East Indies. De Houtman listed it under the Dutch name De Vlieghe in his 1598 southern star catalogue, assigning four stars: Beta as the head, Gamma as the body, and Alpha and Delta as the left and right wings. The constellation first appeared, though unnamed, on a 35-centimeter celestial globe published in Amsterdam in 1598 by Plancius and Jodocus Hondius. Johann Bayer's 1603 Uranometria provided the first atlas depiction, but he called it Apis, the Bee, a name that stuck for roughly two centuries. Nicolas Louis de Lacaille later Latinized the French la Mouche into Musca Australis in 1763 to distinguish it from the now-obsolete Musca Borealis and to avoid confusion with Apus. Today it simply bears the name Musca and stands as the only official constellation depicting an insect.

Stellar Content & Astrophysical Significance

A striking number of Musca's brighter stars belong to the Scorpius–Centaurus association, a loose gathering of hot blue-white stars that appear to share a common birthplace and drift together across the Milky Way. Members include Alpha, Beta, Gamma, Zeta2, and likely Eta Muscae. The constellation also hosts HD 100546, a blue-white Herbig Ae/Be star encircled by a complex debris disk that harbors a large planet or brown dwarf and possibly a protoplanet. Two additional star systems within Musca have confirmed planets. For variable-star enthusiasts, two cepheid variables are visible to the unaided eye, while Theta Muscae is a triple system whose brightest component is a Wolf–Rayet star. Alpha Muscae itself, the constellation's brightest member at magnitude 2.7, is a B2IV-V star roughly 310 light-years distant, about eight times the Sun's mass and 4,520 times its luminosity, pulsating as a Beta Cephei variable with a 2.2-hour period. Gamma Muscae, marking the fly's tail, is a slowly pulsating B star varying between magnitudes 3.84 and 3.86 over 2.7 days.

Indigenous Sky Traditions

Long before European star charts, Aboriginal and Indigenous peoples of the southern hemisphere wove Musca's stars into rich cultural narratives. The Kalapalo people of Mato Grosso state in Brazil recognized Alpha and Beta Muscae, together with Beta and Kappa Crucis, as Kutsu anangagï, the Ornate Hawk-Eagle's double flutes. Among the Wardaman of Australia's Northern Territory, the main stars of Musca formed a ceremonial boomerang within the Central Arena, a sacred region surrounding Crux that depicts lightning creation beings teaching Wardaman customs. Alpha and Beta also signified a ceremonial headband, while Gamma and Delta represented two armbands. In central Australia, the Arrernte and Luritja peoples of the Hermannsburg mission divided the sky between them, with the eastern side of the Milky Way representing Arrernte camps and the western side Luritja camps. The stars of Musca, along with Fomalhaut, Alpha Pavonis, and Alpha and Beta Gruis, were all claimed by the Arrernte as belonging to their portion of the celestial landscape.

Physical Profile & Observability

Musca occupies a compact patch of the deep southern sky, spanning 138 square degrees and just 0.335 percent of the total night sky, placing it 77th among the 88 official constellations in area. Its borders, fixed by Belgian astronomer Eugène Delporte in 1930, are defined by a six-segment polygon. To the north it meets Crux, Carina lies to the west, Chamaeleon to the south, Apus and Circinus to the east, and Centaurus to the northeast. In equatorial coordinates, its right ascension stretches from 11 hours 19.3 minutes to 13 hours 51.1 minutes, while declination ranges from −64.64° to −75.68°. The entire constellation is visible only to observers south of 14° north latitude, meaning most Northern Hemisphere stargazers will never see it rise above the horizon. The International Astronomical Union adopted the three-letter abbreviation Mus in 1922. The pattern of its brightest stars loosely echoes the bowl-and-handle shape of Ursa Minor, a curious resemblance between a tiny southern insect and a much larger northern bear.

Gallery