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The dark horsehead nebula isn’t dark at all, but only if you look at the invisible forms of light.
“If you are fearful, a horse will back off. If you are calm and confident, it will come forward. For those who are often flattered or feared, the horse can be a welcome mirror of the best in human nature.” –Clare Balding
The great Orion Nebula might be the easiest deep-sky object to spot, but to telescope-equipped skywatchers, the Horsehead Nebula is even more spectacular.
The Horsehead Nebula, as taken from a ground-based telescope at Kitt Peak. Alnitak (Zeta Orionis) is just off-screen to the left. Image credit: T.A.Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA).
Located along Orion’s Belt, just south of the easternmost belt star,Alnitak, the nebula is part of the great Orion molecular cloud complex.
The great Orion molecular cloud complex, with the Orion Nebula below the belt and the Horsehead Nebula between the belt’s first and second stars from the left. Image credit: Rogelio Bernal Andreo, under a c.c.a.-s.a.-3.0 license.
From behind the nebula, the brilliant but obscured quintuple star system, σ Orionis, emits intense ionizing, ultraviolet light.
The Horsehead Nebula and the neighboring Flame Nebula can be seen both flanking the bright star Alnitak in Orion, but it’s Sigma Orionis, to the right of the horse’s head, that lights up the Horsehead Nebula. Image credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin.
The ionized electrons meet up with free protons, creating the luminous pink glow seen in many emission nebulae.
The dark Horsehead Nebula, with the red emission nebula behind it and the blue reflection nebula where new stars live at its base. Image credit: Ken Crawford, under a c.c.a.-s.a.-3.0 license.
But the Horsehead itself is slightly closer, with heavily concentrated dust.
The silhouette of a horse’s head is unmistakeable in visible light. Image credit: Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT.
This efficiently and effectively blocks the light from both the emission nebula and the stars behind it.
The full gamut of visible-light data on the Horsehead Nebula reveals color and structure, but still shows a huge amount of darkness, as much remains invisible. Image credit: ESO, via https://www.eso.org/public/images/eso0202a/.
Viewing the nebula in infrared wavelengths, as Hubble did in 2013, reveals an intricate collection of star-forming material.
The pillar-like structures of gas and dust are present in the horse’s head, along with low-mass stars, as revealed by Hubble’s infrared capabilities. Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).
Low-mass stars are present inside the horse’s head itself, while the base of the nebula showcases bright spots: young stars that are in the process of forming.
A deep look inside the base of the Horsehead Nebula shows newly forming stars that will eventually dominate this region’s view once the dust has been burned off. Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).
With seven times the light-gathering power and the capability to see wavelengths more than 10 times as long as Hubble, NASA’s James Webb Space Telescope, launching in 2018, will peer inside these nebulae as never before.
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