clusters by gravity could not be explained by the visible matter within those clusters, which provided further evidence for studies of dark matter. Observations by Einstein also helped to determine the frequency of irregularly-shaped clusters compared to round, uniform clusters. Galactic jets Einstein detected jets of x-rays emanating from Centaurus A and M87 that were aligned with previously-observed jets in the radio spectrum. See also Timeline of artificial satellites and space probes List of things named after Albert Einstein Sources References External links Einstein Observatory (HEAO-2) Space telescopes X-ray telescopes 1978 in spaceflight Spacecraft launched in 1978 TRW Inc.