Image credit: Markus Eisenstöck of flickr, via... [+]
Named "nebulae" because of their structure on the sky, these bright objects are actually nothing more than neutral gas.
The reason they appear illuminated at all are because they either reflect/disperse starlight or emit light themselves, as
Image credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space... [+]
This emission occurs when electrons recombine with nuclei post-ionization, where ionization is caused by the intense ultraviolet light from hot, blue stars.
Image credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space... [+]
The hottest, most massive stars ionize the gas fastest, with the least gas-dense regions becoming completely ionized first.
Image credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space... [+]
When ionization is complete, not only are even the faintest stars revealed, but light from all the stars and galaxies beyond streams through.
The finals stages of this evaporation are visible through the tadpole-like tendrils known as evaporating gaseous globules (EGGs): the last gasps of the neutral gas.
Principal Investigator(s): John Bally and Adam Ginsberg, University of Colorado and the GeMS/GSAOI... [+]
Until the gas is completely ionized, visible light can be reflected or absorbed, depending on the orientation of the stars and gas with respect to us.
The only way to see through neutral gas is by looking in the infrared, which is sensitive to other features.
Once the gas is 100% ionized, it's 100% transparent, and the entire Universe is revealed.
Image credit: Infrared (R): NASA; K.L. Luhman (Harvard-Smithsonian Center for Astrophysics,... [+]
Mostly Mute Monday tells the story of a single astronomical phenomenon or object in visuals, images and video in no more than 200 words.
