2 December 2016 | HH 555

HH 555

Image credit & copyright: Nik Szymanek | Click image to enlarge

Image Data

  • Location: Spain
  • Camera: QSI 683wsg
  • Optics: Ikharos 10″ (254mm) Ritchey-Chretien
  • Mount: Paramount MX
  • Filters: Astrodon 5nm
  • Exposure: Ha: 95 x 10m, OIII: 90 x 10m, SII: 56 x 10m

This image shows a very interesting part of the star-forming Pelican Nebula (IC5067), which lies about 1,800 light-years away from Earth, northeast of the bright star Deneb in the constellation of Cygnus (the Swan). At the top of the pillar above and to the right of the middle you see two small outflows (going left and right). These are known as HH 555, a Herbig-Haro object.

A star forms from a collapsing cloud of cold hydrogen gas. As the star grows, it gravitationally attracts more matter, creating a large spinning disk of gas and dust around it. The disk material gradually spirals onto the star and escapes as narrow, high-speed jets along the star’s axis of spin.

These narrow jets of gas and matter, ejected by newly born stars at speeds of several hundred kilometers per second are called Herbig–Haro objects (HH) – named after astronomers George Herbig and Guillermo Haro who studied the outflows in the 1950s. They collide with nearby gas and dust in the interstellar medium, producing bright shock fronts that glow as the gas is heated by friction while the surrounding gas is excited by the high-energy radiation of nearby hot stars.

The jet phase stops when the disk runs out of material. After at most a few tens to a few hundreds of thousands of years after the star’s birth, the jets disperse in the interstellar medium under the action the wind produced by the newly formed star. The jets can evolve visibly over quite short timescales as they move rapidly away from their parent star into the gas clouds in interstellar space. Herbig–Haro objects are ubiquitous in star-forming regions, and several are often seen around a single star.

HH 555 is the clearest example of a Herbig-Haro object in the Pelican Nebula. In this image detail you can easily see the jet shooting out of the tip of a long, dense pillar of dusty material, indicating the presence of an unseen protostar.

The pillar is formed by the ultraviolet radiation of several massive stars located off the image. The radiation is eroding the surrounding molecular cloud; only some dense clumps of gas and dust, parts of the dense and cold molecular cloud, survive to produce such long dusty pillars. Herbig-Haro object 555 squirts out of the tip of one of these pillars.


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