The NASA Hubble Space Telescope has conducted observations that contribute to the understanding of star formation, capturing images of both Herbig-Haro (HH) objects and protoplanetary disks. These observations detail processes by which young stars develop, including the ejection of high-speed gas jets and the formation of material disks that may lead to planetary systems.
Herbig-Haro Objects
Hubble has captured an image featuring the bright pink and green patches of HH 80/81, a pair of Herbig-Haro objects. HH objects are luminous regions formed when jets of ionized gas, ejected by a protostar, collide with slower gas outflows previously emitted by the same star.
HH 80/81 Specifics:
- Location: Situated 5,500 light-years away within the Sagittarius constellation.
- Scale: The outflow from HH 80/81 spans over 32 light-years, making it the largest known protostellar outflow.
- Brightness: These objects are recognized as the brightest known Herbig-Haro objects.
- Energy Source: The protostar IRAS 18162-2048, which has approximately 20 times the mass of the Sun, is the energy source for HH 80/81 and is located in the L291 molecular cloud.
- Speed: Astronomers have measured parts of HH 80/81 to move at speeds exceeding 1,000 km/s. This makes it the fastest recorded outflow in both radio and visual wavelengths observed from a young stellar object.
- Driving Star: Unusually, this is the only identified HH jet driven by a young, very massive star, contrasting with the more common young, low-mass stars that drive most HH jets.
- Instrumentation: Hubble's Wide Field Camera 3 provided the sensitivity and resolution necessary to study the intricate details, movements, and structural changes of these objects.
Protoplanetary Disks and Star Formation
The Hubble Space Telescope has also captured new images of protoplanetary disks, which are swirling masses of gas and dust around forming stars. These observations were made in both visible and infrared wavelengths.
General Star Formation Process:
Stars develop from collapsing clouds of gas and dust. As material falls toward a protostar, it forms a rotating disk that feeds the central star. Planets can later form from the remaining material within these disks. Jets originating from a protostar's magnetic poles dissipate angular momentum, which enables the protostar to accrete material by slowing its rotation.
Visible-Light Observations:
- Visible-light images reveal protoplanetary disks and jets of gas emanating from protostars.
- Observed protostars are located in the Taurus Molecular Cloud (450 light-years away) and the Chameleon I star-forming region (500 light-years away).
- Key observations include:
- HH 390: Displays a one-sided nebula, indicating the disk is not viewed edge-on.
- Tau 042021: A large, symmetrical, edge-on disk showing advanced dust evolution with clumped particles.
- HH 48: A binary protostar system where gravitational tidal forces from the primary star may influence the secondary object's disk.
- ESO Hα574: A compact disk with a collimated outflow, identified as one of the faintest edge-on disks.
- These images show dark, planet-forming dust disks surrounding developing protostars, accompanied by bipolar jets of gas generally traveling at approximately 150 km/s.
- Bright yellow areas observed above and below disks are reflection nebulae, illuminated by starlight.
Infrared-Light Observations:
- Infrared images show bright central protostars and the shadows cast by their dusty disks.
- Edge-on views in infrared reveal thick, dusty protoplanetary disks, with dark regions representing wide shadows from the central disks within the surrounding envelope. Bright haze indicates light scattering from dust grains in the cloud.
- Observed protostars are located in the Orion Molecular Cloud complex (1,300 light-years away) and the Perseus Molecular Cloud (1,500 light-years away).
- Infrared light can penetrate the 'protostellar envelope,' which visible light cannot. This allows for the observation of earlier-stage disks still shrouded in dust, unlike the more evolved protostars seen in visible light where much of the envelope has dissipated.
- While bipolar jets are present in these earlier stages, their hot gas emission was insufficient for Hubble's infrared detection.
Jet Dynamics
Jets are formed when ionized material in accretion disks interacts with the protostars' strong magnetic fields. These fields direct particles towards the poles and outward as high-speed jets. The glow observed in HH objects and broadening jets is a result of shock emission, where fast jets collide with surrounding gas, heating the gas clouds and exciting atoms.
Binary Star Systems
Hubble observations have also focused on binary systems. HOPS 150 is identified as part of a binary system with another young protostar, HOPS 153. A broader Hubble survey of Orion protostars, including HOPS 150 and HOPS 367, indicated a correlation between regions of higher stellar density and an increased number of companion stars. The survey also noted a comparable number of companions between main-sequence stars and their younger counterparts.