Herbig–Haro objects

Herbig–Haro objects
ESA/Hubble & NASA, D. Padgett (GSFC), T. Megeath (University of Toledo), and B. · Public domain · source
Name	Herbig–Haro objects

Herbig–Haro objects are compact emission nebulae associated with newborn stellar objects and protostellar outflows. They appear as bright knots and bow shocks within bipolar jets emanating from accreting young stellar sources, and are observed across nearby star-forming regions. Their study links observations from major observatories and space telescopes to theoretical work by astronomers and institutions developing models of stellar birth.

Introduction

Herbig–Haro objects were first identified in optical surveys of star-forming regions by astronomers such as George Herbig and Gustav Haro, and remain key targets for facilities including the Hubble Space Telescope, the Very Large Array, the Atacama Large Millimeter/submillimeter Array and the European Southern Observatory. They are found in molecular clouds catalogued in surveys by teams at institutions like the Smithsonian Astrophysical Observatory, the Max Planck Institute for Astronomy and the National Aeronautics and Space Administration. Observations often reference regions such as the Orion Nebula, the Taurus Molecular Cloud, the Rho Ophiuchi cloud complex and the Perseus molecular cloud. Studies of these nebulae involve spectroscopic work from instruments aboard missions by European Space Agency, Japan Aerospace Exploration Agency collaborations and ground campaigns led by observatories on Mauna Kea and the Cerro Paranal Observatory.

Formation and Physical Properties

Herbig–Haro phenomena originate from collimated jets launched by accreting protostars, particularly those in evolutionary stages identified in classification schemes by researchers at the Harvard College Observatory and the Cavendish Laboratory. The jets interact with ambient material in molecular clouds such as Barnard 68 and regions mapped by the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer, producing shocks that heat gas to emit in lines identified in spectra by teams at the Royal Observatory Edinburgh and the California Institute of Technology. Magnetohydrodynamic mechanisms proposed by groups at the Princeton University and the Max Planck Institute for Radio Astronomy invoke magnetic fields anchored in circumstellar disks first modeled in studies associated with Cambridge University and the University of Chicago. Characteristic shock velocities, densities and excitation conditions are constrained using diagnostics developed at the Space Telescope Science Institute and laboratories collaborating with observatories such as Kitt Peak National Observatory.

Observational Characteristics

Herbig–Haro knots display emission lines such as forbidden transitions whose analysis has been advanced by spectroscopists at the Royal Society-affiliated observatories and the Los Alamos National Laboratory. Imaging campaigns with the Hubble Space Telescope’s instruments and with adaptive optics systems on telescopes operated by the Keck Observatory reveal proper motions and morphological evolution comparable to studies by the European Southern Observatory and the Subaru Telescope. Multiwavelength data from the Chandra X-ray Observatory, the XMM-Newton mission and the James Webb Space Telescope probe high-energy shocks and infrared-excited regions in protostellar environments catalogued in surveys curated by the National Radio Astronomy Observatory and the Royal Astronomical Society. Time-resolved monitoring programs led by the Carnegie Institution for Science and the Leiden Observatory track knot velocities and variability linked to accretion bursts studied by teams at the University of Cambridge.

Classification and Examples

Herbig–Haro objects are catalogued with nomenclature systems and examples documented in atlases assembled by the Harvard College Observatory and the Steward Observatory. Well-studied examples are associated with objects in the Orion Nebula like those near the Becklin–Neugebauer Object, the jets from sources in the HH 1/2 region (historically observed by George Herbig and Gustav Haro), and flows in regions such as HH 46/47 discovered in southern surveys by the European Southern Observatory. Other notable flows are found in the Taurus Molecular Cloud and in associations mapped by the Palomar Observatory and the Mount Wilson Observatory. Comparative studies reference protostellar sources catalogued by the Two Micron All Sky Survey teams and by missions coordinated by the Jet Propulsion Laboratory.

Role in Star Formation and Evolution

Herbig–Haro flows trace angular momentum removal and feedback processes central to models developed at research centers including the Institute of Astronomy, Cambridge and the Max Planck Institute for Astrophysics. The interaction of jets with parent molecular clouds such as Lynds Dark Nebula 1551 influences cloud structure studied in surveys by the National Science Foundation-funded projects and by international collaborations involving the Canadian Astronomy Data Centre. Observational links to episodic accretion events described in work at the University of Exeter and the University of California, Berkeley connect HH phenomena to evolutionary sequences classified in schemes from the Royal Observatory Greenwich archives.

Theoretical Models and Simulations

Theoretical frameworks for jet launching and shock propagation have been developed by groups at the Princeton University Observatory, the University of Oxford and the Max Planck Institute for Plasma Physics, employing magnetohydrodynamic simulations on computing facilities such as those at the Lawrence Berkeley National Laboratory and the National Center for Supercomputing Applications. Numerical models calibrated against datasets from the Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array explore magnetic launching scenarios first proposed in work associated with the University of Cambridge and the California Institute of Technology. Cross-disciplinary collaborations with plasma physics groups at the MIT and with instrumentation teams at the European Southern Observatory continue to refine predictions for emission-line ratios, shock microphysics and jet collimation observable in planned surveys by the Square Kilometre Array and next-generation space missions.

Category:Star formation