Discover the cosmos!Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2012 June 21
WR 134 Ring Nebula Image
Credit & Copyright: Don Goldman
Explanation: Made with narrow and broad band filters, this colorful cosmic snap shot covers a field of view about the size of the full Moon within the boundaries of the constellation Cygnus. It highlights the bright edge of a ring-like nebula traced by the glow of ionized hydrogen and oxygen gas. Embedded in the region’s interstellar clouds of gas and dust, the complex, glowing arcs are sections of bubbles or shells of material swept up by the wind from Wolf-Rayet star WR 134, brightest star near the center of the frame. Distance estimates put WR 134 about 6,000 light-years away, making the frame over 50 light-years across. Shedding their outer envelopes in powerful stellar winds, massive Wolf-Rayet stars have burned through their nuclear fuel at a prodigious rate and end this final phase of massive star evolution in a spectacular supernova explosion. The stellar winds and final supernovae enrich the interstellar material with heavy elements to be incorporated in future generations of stars.
Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
The Milky Way in Infrared
Credit: E. L. Wright (UCLA), The COBE Project, DIRBE, NASA
Explanation: At night, from a dark location, part of the clear sky looks milky. This unusual swath of dim light is generally visible during any month and from any location. Until the invention of the telescope, nobody really knew what the “Milky Way” was. About 300 years ago telescopes caused a startling revelation: the Milky Way was made of stars. Only 70 years ago, more powerful telescopes brought the further revelation that the Milky Way is only one galaxy among many. Now telescopes in space allow yet deeper understanding. The above picture was taken by the COBE satellite and shows the plane of our Galaxy in infrared light. The thin disk of our home spiral galaxy is clearly apparent, with stars appearing white and interstellar dust appearing red.
Trigger-Happy Star Formation
This composite image, created using data from the Chandra X-ray Observatory and the Spitzer Space Telescope, shows the molecular cloud Cepheus B, located in our galaxy about 2,400 light years from the Earth. A molecular cloud is a region containing cool interstellar gas and dust left over from the formation of the galaxy and mostly contains molecular hydrogen. The Spitzer data, in red, green and blue shows the molecular cloud (in the bottom part of the image) plus young stars in and around Cepheus B, and the Chandra data in violet shows the young stars in the field.
The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission. The Spitzer data showed whether the young stars have a so-called “protoplanetary” disk around them. Such disks only exist in very young systems where planets are still forming, so their presence is an indication of the age of a star system.
These data provide an excellent opportunity to test a model for how stars form. The new study suggests that star formation in Cepheus B is mainly triggered by radiation from one bright, massive star (HD 217086) outside the molecular cloud. According to the particular model of triggered star formation that was tested — called the radiation- driven implosion (RDI) model — radiation from this massive star drives a compression wave into the cloud triggering star formation in the interior, while evaporating the cloud’s outer layers.
Different types of triggered star formation have been observed in other environments. For example, the formation of our solar system was thought to have been triggered by a supernova explosion, In the star-forming region W5, a “collect-and-collapse” mechanism is thought to apply, where shock fronts generated by massive stars sweep up material as they progress outwards. Eventually the accumulated gas becomes dense enough to collapse and form hundreds of stars. The RDI mechanism is also thought to be responsible for the formation of dozens of stars in W5. The main cause of star formation that does not involve triggering is where a cloud of gas cools, gravity gets the upper hand, and the cloud falls in on itself.
Image Credit: X-ray: NASA/CXC/PSU/K. Getman et al.; IRL NASA/JPL-Caltech/CfA/J. Wang et al.