The Black River: Dark Silhouette of the Milky Way

The Black River: Galactic Eclipse

The Black River is a dense region of the Milky Way, observable as a dark silhouette crossing the galactic plane. This apparent phenomenon results from the absorption and scattering of starlight by interstellar clouds composed mainly of molecular gas and dust.

Silhouettes on the Milky Way

The dark clouds that make up the Black River are primarily composed of hydrogen molecules \( \mathrm{H_2} \), as well as dust consisting of silicate grains, amorphous carbons, ices, and other complex compounds. These microscopic grains cause selective extinction of light, more pronounced in the visible than in the infrared, explaining the appearance of a black silhouette against the more distant stars.

Location of the Black River in the Milky Way

The Black River, observable to the naked eye as a dark band interrupting the brightness of the Milky Way, extends over approximately 80 degrees of arc along the galactic plane. It begins in the constellation of Sagittarius, near the very dense galactic center, and extends northward through the constellations of Serpens, Aquila, and then Cygnus.

This dark silhouette results from the presence of molecular complexes and interstellar dust clouds concentrated in these directions, masking the light of background stars. The Black River is particularly visible during the summer in the northern hemisphere, when the galactic plane is high in the night sky.

In galactic coordinates, the Black River corresponds to a region around the galactic plane, between approximate galactic longitudes of 20° to 100°, where the density of interstellar matter is maximal.

Role in Star Formation

Dark regions like the Black River are privileged zones for star formation. The high density and low temperature favor the gravitational collapse of dense cores, initiating the creation of proto-stars.

Multi-Wavelength Observation

While the Black River is visible as an obscuration in the visible domain, its study is enriched by observations in radio waves, infrared (partially avoiding extinction), and X-rays (detecting very dense and hot regions). These techniques allow mapping the three-dimensional structure and internal dynamics of these clouds.

Comparative Table of Typical Properties of Dark Clouds in the Black River

• Source: Bergin & Tafalla (2007), Annual Review of Astronomy and Astrophysics (new window), NASA/IPAC Extragalactic Database (new window).