Horsehead Nebula

The Horsehead Nebula is a dark molecular cloud (Barnard 33) silhouetted against the bright emission nebula IC 434, which forms the glowing red curtain behind it. The iconic horse-head shape is a dense pillar of gas and dust that protrudes from a larger molecular cloud, resisting the ionizing radiation that is destroying the surrounding material.

The nebula lies near the leftmost star in Orion’s belt (Alnitak), which provides part of the illuminating ultraviolet radiation. The bright spot at the top of the horsehead’s “nose” is a young stellar object embedded within the dark cloud, beginning to carve out its own cavity.

The Hubble infrared image from 2013, taken for Hubble’s 23rd anniversary, penetrates the dusty outer layers to reveal a wealth of detail invisible in visible light: filaments of gas, young stars forming within the dark cloud, and the complex three-dimensional structure of the interface between the molecular cloud and the ionized region.

The Horsehead is estimated to survive for only a few million more years before the radiation from Sigma Orionis and other nearby hot stars erodes it away completely.