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Name: Swan or Omega  Nebula - M17 / NGC6618

M17, is much like M42, an active star forming region.  In a small area west of of the swan's neck, a young cluster hardly one million years old with more than 8,000 to 10,000 member stars lies mostly hidden inside the nebula.  The core alone contains 750 stars.  These very young objects have between 5 and 20 solar masses each and nine very luminous cluster members of spectral type 0 ( > 30,000K very hot, blue stars, lines of ionized helium ) must weigh about 60 solar masses.   However their light has been extinguished by 30 magnitudes of absorption by the dust within the nebula, in addition to the 1.8 magnitudes of interstellar extinction.  Only five of these stars are visible.  They are brighter than magnitude 14.2, two of them even brighter than 10th magnitude in visible light.  The rest of this cluster can only be studied in infrared light, where the absorption by dust is less severe.

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