Nebulae (but not Galaxies)

  • The Crab Nebula The remnant of SN 1054 in our Galaxy. The supernova was first recorded by Chinese astronomers 1054 July 4. The remnant was discovered in the 18th century and is M1 in the Messier Catalog. It is now about 3 parsecs across and is still expanding at about 1800 km/sec. It is broken up into filaments that are heated to the point of radiation by shock interaction with the ejecta. There is also synchroton radiation. The Crab Pulsar (on the right side of the star pair near the left lower center of the image, but not visible??) was discovered in 1968: it was the first pulsar. It has a 33 ms period and originally people wondered if it could be a signal from extraterrestrials.
  • The Whole Orion Nebula The Orion Nebula is an emission nebula powered by the UV light from hot young OB stars (no more that a million years old). It is about 1500 lyr away. Its diameter is about 30 lyr: about 1 degree on the sky or twice the diameter of the Moon. It is visible to the naked-eye and rewarding with a telescope. The nebula is comprised of M42 and M43 which here appear as the large left-hand pink cloud and a smaller right-hand reflection nebula. (M stands for Messier nebula.) Behind, invisible, and much broader is a dark, dusty nebula where more young stars are forming. This cloud extends over about half of Orion or 10 degrees. The Orion Nebula is appears middle star in Orion's sword. The left-hand side of the left bright region (M42) is centered on the Trapezium cluster of young stars four large stars: the four brightest stars are the Trapezium. (Frak399--400)
  • The Ring Nebula A planetary nebula of expanding gas ejected from a dying redgiant star. The nebula is probably a torus viewed pole on. There is a hot (100,000 K) white dwarf remnant: the central star???. The emission from the remnant exites the exanding nebula: the inner region emits in the UV and appears dark in visible, then a green region of forbidden oxygen and nitrogen emission, and red emission from hydrogen on the outside. The nebula will persist for only a few tens of thousands of years. The white dwarf remnant will cool off forever eventually becoming black dwarf.