Dark Nebula Barnard 68

Dark Nebula Barnard 68
Name	Barnard 68
Type	Dark nebula
Epoch	J2000
Ra	17h22m38s
Dec	-23°49′54″
Constellation	Ophiuchus
Distance	~125 pc
Size	~0.5 ly
Mass	~2 M☉

Dark Nebula Barnard 68 is a compact, opaque dark nebula situated against the star fields of the Milky Way. It appears as a silhouette because it blocks light from background stars in the region of Ophiuchus, and it has been the subject of studies by astronomers using facilities such as the European Southern Observatory and the Hubble Space Telescope. The cloud's isolation and relatively simple morphology make it a benchmark object in studies by institutions like the Max Planck Institute for Astronomy and observatories such as Cerro Paranal.

Introduction

Barnard 68 is cataloged within compilations by Edward Emerson Barnard and is noted in surveys conducted by the Royal Astronomical Society and the Astronomical Society of the Pacific. It lies in proximity on the sky to catalogued objects including the Pipe Nebula and the Rho Ophiuchi cloud complex, and has been imaged by missions like the Hubble Space Telescope and instruments operated by the National Aeronautics and Space Administration. Researchers affiliated with Harvard–Smithsonian Center for Astrophysics and the European Southern Observatory have used Barnard 68 as a case study for dense molecular cores, linking analyses to theoretical frameworks developed at institutions such as the California Institute of Technology and the University of Cambridge.

Physical Characteristics

The nebula's angular extent corresponds to a physical diameter of order 0.1–0.3 parsecs given its measured distance; its extinction profile produces near-total obscuration of background stars in optical bands, a property measured by teams from the Space Telescope Science Institute and the Max Planck Society. Spectral line studies using facilities like the Atacama Large Millimeter/submillimeter Array and the James Clerk Maxwell Telescope have detected molecules studied in programs at the Smithsonian Astrophysical Observatory, while photometric work referenced by researchers at the University of Arizona and the University of Leiden has constrained temperature and density gradients. Observers from institutions such as the European Southern Observatory and the National Radio Astronomy Observatory have reported a cold kinetic temperature consistent with dense prestellar cores cataloged in surveys by the Institut d’Astrophysique de Paris.

Distance and Location

Parallax and extinction mapping by teams at the European Space Agency and the Gaia mission, combined with photometric studies from the Two Micron All Sky Survey conducted by the University of Massachusetts Amherst and the Infrared Processing and Analysis Center, place the cloud at approximately 125 parsecs from the Sun in the star field of Ophiuchus. Its projected neighborhood on the sky includes objects surveyed by the Palomar Observatory and the Cerro Tololo Inter-American Observatory, and its location relative to star-forming complexes has been discussed in papers from the University of Tokyo and the University of Colorado.

Observational History

First noted in Barnard’s catalog compiled at the Lick Observatory and referenced in works from the Royal Astronomical Society, the object has since appeared in imaging programs led by teams at the Space Telescope Science Institute and the European Southern Observatory. Photographic atlases produced by the Lowell Observatory and the Harvard College Observatory recorded its silhouette early in the 20th century, and later high-resolution studies by researchers at the Institute for Astronomy, University of Hawaii, and the Max Planck Institute for Astronomy used infrared campaigns by the Spitzer Space Telescope and radio campaigns by the National Radio Astronomy Observatory to probe its interior. Conferences such as those organized by the International Astronomical Union and the American Astronomical Society have featured results on its properties.

Star Formation Potential

Analyses by theorists at the University of Cambridge, Princeton University, and the California Institute of Technology have applied Bonnor–Ebert sphere models and Jeans instability criteria developed in classical studies to determine whether collapse will occur, with observational constraints provided by teams from the Max Planck Institute and the Harvard–Smithsonian Center for Astrophysics. Molecular depletion signatures reported by researchers at the University of Stockholm and the University of Bonn, together with dust continuum measurements from the James Clerk Maxwell Telescope and the Atacama Pathfinder Experiment, inform assessments of core stability. Comparisons with protostellar cores cataloged by the Spitzer Gould Belt Survey and the Herschel Space Observatory place Barnard 68 on the threshold between stable and collapsing states according to models refined at the Kavli Institute for Theoretical Physics and the University of Leiden.

Structure and Composition

The cloud is primarily composed of molecular hydrogen traced via CO isotopologues observed by the Institut de Radioastronomie Millimétrique and the Nobeyama Radio Observatory, with dust grains containing silicates and carbonaceous material inferred from extinction laws characterized by teams at the University of Arizona and the University of Paris. Observations by the Submillimeter Array and ALMA, and chemical models developed at the Max Planck Institute for Extraterrestrial Physics and the University of Illinois, show depletion of volatile species onto grains in the densest regions. Magnetic field estimates derived from polarimetric studies by groups at the University of Chicago and the Institut d’Astrophysique Spatiale contribute to models of support against gravity used by theorists at Princeton University and the University of California, Berkeley.

Scientific Studies and Significance

Barnard 68 has served as a pedagogical and research reference in work by investigators at institutions such as the European Southern Observatory, the Space Telescope Science Institute, and the Max Planck Society, informing theoretical developments at universities including Harvard, Cambridge, and Princeton. It features in surveys by the Herschel Space Observatory and the Spitzer Space Telescope and figures in comparative studies with regions like Taurus and Perseus cataloged by the Gould Belt surveys and the James Clerk Maxwell Telescope. Its apparent isolation makes it a test case in papers presented to the International Astronomical Union and at meetings of the American Astronomical Society, influencing models produced at the Kavli Institute and motivating follow-up observations by ALMA, ESO, and national observatories worldwide.

Category:Dark nebulae