The interstellar medium and the birth of stars

Reference: the astronomical image and movie page for Physics 1060, Introduction to Stars & Galaxies by Kirk Korista (University of Western Michigan).

• Our Galaxy, the Milky Way
• A dark cloud toward the center of our Galaxy
• Another dark, cold (10 K), molecular cloud, some 520 light years away and about 0.65 light year across, is partially transparent at infrared wavelengths. This is demonstrated in a dramatic way in this image, which shows the same image through each of the 6 broad-band filters separately - from 440 nm (blue visible light), to 550 nm (green visible light), and then 900 nm, 1250 nm, 1650 nm and 2160 nm in the infrared (the filter central wavelengths are given in units of microns = 1000 nm in the figure). This is a map measuring the extinction of light through the cloud. The first and outermost contour represents a loss of visible light at 550 nm by a factor of 40. Each contour inside is a step up in visible light extinction by a factor of 6.3. The maximum extinction represents a factor of 10¹⁴ loss of visible light!
• a tiny grain of cosmic dust, just 10 microns across (size of a human white blood vessel)
• lots of molecules are found in the cosmos, and many of these are the organic building blocks of life
• The constellation of Orion.

• The Orion Nebula, nearest stellar nursery, at visual wavelengths, and also here. The Orion star forming complex is just ~1 million years old, and 1500 light years away.
  
• Hubble Space Telescope visible and near-IR image of the Orion Nebula. This view is 13 light years across.
  
• The central Trapezium region of the Orion Nebula at infrared wavelengths, and a broader view at infrared wavelengths; here's another infrared  image of the Orion starforming complex.
• The Orion Nebula's Trapezium, visual vs. infrared, as observed by the Hubble Space Telescope. Note the large numbers of stars that come into view at infrared wavelengths - infrared light is not as easily blocked by dusty gas as is visible light. The dimmest points of light in the infrared image are "Brown Dwarfs", not massive enough to become stars.
• Two image galleries (1, 2) of solar systems forming around new stars in the Orion Nebula, and a cartoon. The dark, dusty disks might be forming planets.
• The Horsehead dark nebula in Orion; the bright star on the left is the leftmost star of Orion's belt - seen here in a spectacular style. The three bright stars of the "belt of Orion" are Alnitak, Alnilam, Mintaka.
• Short wavelength (blue) light emitted by stars scatters easily from dust grains within surrounding gas clouds - these dusty clouds reflect starlight, especially blue light, and are known as reflection nebulae.
  

• The Eagle Nebula, as imaged at visible wavelengths by the Hubble Space Telescope, and a close-up of one of the "pillars" showing the photo-evaporating gaseous globules, and a broad view of the surrounding region, including the main star cluster, at near-infrared wavelengths - note the near transparency of the Eagle Nebula at these wavelengths. Here is an unbelievably beautiful visible light, 20 light year wide, view of the molecular cloud complex surrounding the Eagle Nebula. Narrow band green, blue and red filters were used to sort out emission from hydrogen atoms, twice-ionized oxygen atoms, and singly-ionized sulphur atoms, respectively. This star forming region is 6500 light years away.
• Here is the Cone Nebula star forming complex, 2500 light years away. Note the newly formed stars emerging from the cone-shaped molecular gas near the bottom of the diagram. A close-up from the Hubble Space Telescope is here; the "cone" is about 1 light year across.
• Just 2 light years across and perhaps just a few hundred thousand  years old, a brand new stellar nursery lying in the constellation Cygnus, as seen in near-infrared light
• 50 light years across and extremely young, a newly emerging cluster of very young, massive stars in the nearby dwarf galaxy, the Large Magellanic Cloud
• A gargantuan star formation region & star cluster (some 1500 light years across) in a nearby spiral galaxy called M33. An even better view is here.
• Perhaps the largest star forming complex in the local universe, in the nearby dwarf galaxy the Large Magellanic Cloud 160,000 light years away, the Tarantula Nebula Star forming complex.  Shown is just the central region; images of the whole complex lie in the "Star Clusters" section, below. If it were at the distance of the Orion Nebula (1500 light years), it would be visible in the day time and span about 1/4 of the sky!
• The Trifid Nebula, an emission (red part) and reflection (blue part) nebula
• The Rosette Nebula; here's another view
• The Keyhole Nebula in Carina
• A young stellar cluster in a star forming region (NGC 3603): VLT near-infrared view
• Young stars with dusty gas disks around them: 1,2,3,4,5. When the disks are observed from the side, they are dark when viewed at visible wavelengths and bright when viewed at infrared wavelengths. Why might that be?