Edwin Hubble Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology and is regarded as one of the most important astronomers of all time. Hubble discovered that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way. He used the strong direct relationship between a classical Cepheid variable's luminosity and pulsation period (discovered in 1908 by Henrietta Swan Leavitt) for scaling galactic and extragalactic distances. Hubble provided evidence
Extragalactic cosmic ray many more possible sources scientists are considering. These include colliding galaxy systems, accretion flow shocks to clusters of galaxies, and more exotic processes from the very early universe, such as the decay of superheavy particles trapped in the galactic halo, or topological defects. Due to the very low flux of extragalactic cosmic particles received on Earth, little is known about their composition. Most estimates, based on theoretical and numerical models, predict that light atomic nuclei such as protons are the dominant particle type. Extragalactic cosmic ray Extragalactic cosmic rays are very-high-energy particles that flow into the Solar System from beyond