NASA's Hubble Space Telescope (HST) has provided astronomers with their clearest look yet at a vast cloud of gas being heated by the birth of a new star.
Called Herbig-Haro object #2 (HH-2), the cloud is heated by shock waves from jets of high speed gas being ejected from a newborn star. Because the star itself is embedded in a dusty cocoon, HH-2 provides the only visible clues to physical processes occurring in the young star.
The Hubble observations made with the Wide Field/Planetary Camera (WF/PC) provide new insight into similar events that probably occurred when our Sun and Solar System formed 4.6 billion years ago. "The fine detail, never before seen in such objects, provides a challenge to astronomers who are attempting to model the physical processes associated with star formation," said Dr. Richard D. Schwartz, of the University of Missouri at St. Louis.
Dr. Schwartz and an international team of astronomers used Hubble to obtain detailed images which "reveal a rich array of structures with diameters of a few billion miles, comparable to the size of the Solar System," according to Schwartz. He explained, "The existence of such small features was unexpected based upon earlier images obtained with ground-based telescopes."
HH-2 is one of several peculiar nebulae first discovered by American astronomer George Herbig and Mexican astronomer Guillermo Haro in the early 1950s.
The nebula has been an enigma to astronomers because of its irregular, somewhat chaotic appearance. The nebula differs from the regular, symmetric bow-shock structures seen in other HH objects. Such bow-shock structures have the shape of a wave that leads a boat traveling through water. Schwartz said that the structures in HH-2 may result from the fragmentation of a bow-shock at the head of a gas jet coming from the young star.
HH-2 lies at a distance of about 1,500 light-years, in a star-forming region of the constellation Orion. The object is located at the leading edge of a supersonic gas flow that emanates from a young star located about 1/2 light-year from the object. The star is detectable only with infrared and radio telescopes.
The high-speed jets that create HH-2 form as a young star contracts under its own gravitational pull. The star reaches a stage where it releases a strong outflow of gas. A thick disk of cool gas and dust around the star, perhaps coupled with a strong magnetic field, forces the hot gas to squirt outward along the system's rotational axis. This forms a pair of narrow jets that plow through the gas of the parent cloud in the star formation region. Gas shoots away from the star at velocities of up to 500,000 miles per hour (fast enough to span the distance between Earth and the Moon in 1/2 hour!)
The supersonic flow forms strong shock waves, heating gas in the parent cloud to temperatures more than 200,000 degrees Fahrenheit (93,000 degrees Celsius). Though a cocoon of dust obscures the star from view, the effects of the jets can be see across great distances.
The hot gas radiates energy in visible light associated with atoms of hydrogen, oxygen, nitrogen, sulfur, and other common elements, forming the structure of a Herbig-Haro object.
HH objects offer clues into the nature of young stellar objects. "The energetics, degree of collimation, and evolutionary time scales of HH objects all serve to constrain models of the environment and physical properties of the young stellar object at the center of the outflow," said Schwartz.
Co-investigators: Martin Cohen (Univ. of California-Berkeley), Burton Jones Univ. of California-Santa Cruz), Karl-Heinz Bohm (Univ. of Washington), John Raymond and Lee Hartmann (Harvard-Smithsonian Center for Astrophysics), Reinhard Mundt (Max- Planck-lnstitut fur Astronomie, Heidelberg, Germany), Michael Dopita (Mt. Stromlo and Siding Spring Observatories, Australia), and Angie Schultz (graduate student at Washington Univ., St. Louis, conducting Ph.D. thesis work at Univ. of Missouri-St. Louis).