The Dark River to Antares . ... Credit Copyright: Mюximo Ruiz Explanation: Connecting the Pipe Nebula to the bright star Antares is a flowing dark cloud nicknamed the Dark River . The murkiness of the Dark River is caused by absorption of background starlight by dust , although the nebula contains mostly hydrogen and molecular gas. Antares , the bright star that appears yellow just below the center of the frame, is embedded in the colorful Rho Ophiuchi nebula clouds. ...