Hubble Characterizes the High-Velocity Smith Cloud

The infalling Smith Cloud does not emit light at wavelengths that the NASA/ESA Hubble Space Telescope is sensitive to. The cloud can be seen in radio wavelengths. However, Hubble's Cosmic Origins Spectrograph can measure how the light from distant background objects is affected as it passes through the cloud. These measurements yield clues to the chemical composition of the cloud. By using these intergalactic forensics, astronomers trace the cloud's origin to the disc of our Milky Way. Combined ultraviolet and radio observations correlate to the cloud's infall velocities, providing solid evidence that the spectral features link to the cloud's dynamics.