In September 2020, researchers answered a longstanding question about why planetary nebulae display such a rich variety of shapes. Winds from aging stars produce planetary nebulae as the winds eject the stars' outer layers, shrouding the stars in stellar material. Views through early telescopes made this ejected material appear rounded and planet-like. As telescope technology improved, however, astronomers came to realize that planetary nebulae can look like flowers and butterflies, among other varied, asymmetrical shapes. Those shapes confounded astronomers, given their assumption that stellar winds are spherical in nature, similar to stars themselves, and should thus produce only rounded nebulae. The September 2020 study revealed, however, that these winds actually blow asymmetrically. Furthermore, as winds throw material off the star unevenly, stellar companions—such as other stars and planets—can scramble the material, rather like a spoon stirring creamer in hot coffee. Overall, these effects combine to produce the observed diversity of nebular forms. See also: Nebula; Planet; Planetary nebula; Star; Telescope; Wind

Among the most compelling exoplanets discovered to date is a "super-Earth" around Barnard's star, the closest single star to our solar system. This star, a cool red dwarf significantly smaller than the Sun, is located only six light-years away—just a bit farther than the nearest stars, the triple-star Alpha Centauri system. The proximity of its parent star makes the newfound world a potentially excellent candidate for detailed studies with future instruments. See also: Alpha Centauri; Earth; Exoplanet; Light-year; Planet; Solar system; Star; Sun

Highly energetic light emitted by aged stars causes asteroids to keep spinning faster and faster to the point of disintegration, a new study finds. The findings help explain why white dwarf stars—remnants of Sunlike stars—often have metallic asteroid signatures in their light. As an aging star's powerful light pulverizes asteroids in the star's vicinity, a debris field is created, the study suggests. The aging star then transitions into a white dwarf, with the debris field coalescing into a disk around the new stellar remnant. Asteroidal material then rains down onto the white dwarf, polluting its surface and generating an observable metallic signature (Fig. 1). See also: Asteroid; Stellar evolution; White dwarf star

The Kepler space telescope—the most prolific discoverer of exoplanets, or worlds outside our solar system, to date—has run out of fuel and ceased science operations, NASA announced on October 30, 2018. Kepler leaves a legacy for first revealing that exoplanets are ubiquitous, actually outnumbering stars. Within the Milky Way Galaxy alone, home to some 300 billion stars, Kepler's findings have statistically suggested that there are on the order of a trillion planets. See also: Exoplanet; Galaxy; Kepler mission; Milky Way Galaxy; Planet; Solar system; Star; Telescope; Universe

Astronomers have arrived at a new, precise measurement of the mass of the Milky Way. Historical estimates have varied widely, from 500 billion times the mass of the Sun—a quantity known as a solar mass—to as high as three trillion solar masses. The new figure, which combines observations from NASA's Hubble Space Telescope and the European Space Agency's Gaia spacecraft, winnows this estimate closer to 1.5 trillion solar masses. Accurately accounting for the amount of mass in the Milky Way is an important step in building ever-more powerful models of galaxy formation and evolution on vast cosmological scales. Literally closer to home, the improved measurement aids in tracing the history of the single galaxy we are uniquely positioned to study from the inside-out. See also: Cosmology; Galaxy; Gaia mission; Hubble Space Telescope; Mass; Milky Way Galaxy; Sun

Observing a neutron star in infrared light—a low-energy form of radiation seldom used for studying these cosmic objects—has revealed features that seem to have eluded astronomers' notice going back decades. The features could be a dusty disk encircling the neutron, or a wind of particles streaming off the star into nearby space. In either case, the features would present a newly complex picture of the immediate environment around neutron stars, as well as offer novel ways to investigate their characteristics. See also: Energy; Infrared astronomy; Infrared radiation; Light; Neutron star; Radiation; Star

After a decades-long search, the first evidence for a vast population of black holes inhabiting the core regions of the Milky Way Galaxy has emerged. Astronomers had theorized that in addition to a single supermassive black hole, the Galactic center likely harbors thousands of smaller black holes. Derived from the demise of colossal stars, these "stellar" black holes should readily develop due to the rich stores of star-forming material in the Milky Way's core. The migration of black holes originating from farther out in the galaxy, drawn by the supermassive black hole's gravity, should further boost this theorized population's numbers. See also: Astronomy; Black hole; Galaxy; Gravitation; Mass; Milky Way Galaxy; Star; Stellar evolution; Stellar population; Supergiant star; Supermassive black holes