Supernova (SN) Refsdal — Key Points Astronomers have been trying to understand space for thousands of years. Supernova Refsdal was the first known multiply-imaged supernova. Multiple images of the supernova are produced by strong gravitational lensing. Astronomers predicted the reappearance of the supernova before it was observed. The multiple images of the supernova exhibit measurable…
Big Bang: Key Points Hubble’s law (redshift of galaxies) and the Doppler effect provide direct evidence that the universe is expanding away from our reference point. Expansion has cooled the universe from the initial high temperatures at the Big Bang; radio astronomy detects signals from stars, galaxies, radio galaxies, quasars, and pulsars that trace this…
Introduction The universe was not perfectly uniform at the beginning; some regions had higher density than others. Over time these higher-density regions attracted most of the matter and began forming galaxies where matter concentration was greatest. The resulting large-scale structure—the “cosmic web”—connects observed galaxy clusters with a network of filaments. Figure 1 shows a model…
Overview Gravitational waves (GWs) are disturbances in spacetime produced by massive objects moving asymmetrically. Only the most massive and most relativistic systems produce GWs large enough to be detectable. The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors use laser interferometry to detect tiny ripples in the fabric of spacetime; they have already detected dozens…
Uranus’ Peculiar Tilt Uranus spins on its side. It has an obliquity (tilt) of 98° — its rotation axis lies closer to the ecliptic plane than any other planet — and astronomers still debate how it got that peculiar tilt. Uranus Key Points Uranus has an obliquity (tilt) of 98° — its rotation axis is…
Researchers simulating the accretion flow around Sagittarius A*, the supermassive black hole at the Milky Way’s center, have found that magnetic reconnection can accelerate cosmic rays enough to produce the very-high-energy (VHE) gamma rays already detected by the H.E.S.S. telescope array. Their models suggest the Cherenkov Telescope Array (CTA) could confirm and localize this emission…
Mary Somerville and Caroline Herschel were jointly honored by Google’s 2 February 2020 Doodle as the first two women elected honorary members of the Royal Astronomical Society (RAS). Somerville, a Scottish polymath born in 1780, became known for her 1831 work “The Mechanism of the Heavens,” and her scientific standing helped open the RAS to…