Astronomers have discovered the closest black hole on record, located 1,100 light-years away from our solar system. This black hole is part of the star system HR 6819, which consists of two bright, bluish stars. On a clear, dark night, these stars can be seen with the naked eye in the constellation Telescopium from the Southern Hemisphere. See also: Black hole; Constellation; Light pollution; Light-year; Star

According to extensive geophysical evidence, approximately 66 million years ago, a massive asteroid collided with Earth and triggered the Cretaceous-Paleogene mass extinction—a cataclysmic event that eliminated 75% of all plant and animal species on the planet. With the broad acceptance of this asteroid impact theory for a few decades now, attention has turned to how such a dire event could potentially be stopped. To further this goal, a Planetary Defense Coordination Office was established within the U.S. National Aeronautics and Space Administration (NASA) in 2016. This office funded the first-ever mission of its kind, the Double Asteroid Redirection Test (DART), to crash a spacecraft into an asteroid to see if such a kinetic impact could alter the asteroid's course. On September 26, 2022, DART successfully impacted an asteroid’s surface, and mission investigators subsequently confirmed that the impact affected the asteroid as intended. The results suggest that humans do possess the means to redirect dangerous asteroids that may come hurtling toward Earth in the future. See also: Asteroid; Chicxulub impact crater; Mass extinctions; Space probe

Black holes pack an extraordinary amount of mass into a small spatial volume, resulting in gravitational fields so powerful that not even light can escape. These extreme objects occur as two distinct populations in the universe. The first, called stellar black holes, form from the collapse of massive stars and can possess anywhere from a few to dozens of times the Sun's mass. The second population, supermassive black holes, are found usually as single (although occasionally as double) objects in the cores of most galaxies. As their name suggests, supermassive black holes contain millions to even billions of times the Sun's mass. Astrophysicists expect that a third population of black holes exists, bridging the substantial mass gap between the two well-documented black hole populations. This third population, known as intermediate-mass black holes (IMBHs), would have on the order of hundreds to thousands to even tens of thousands of solar masses. If confirmed, IMBHs would help solve the mystery of the formation of supermassive black holes. Depending on their mass and cosmic environments, IMBH origins could be “bottom-up,” involving the merging of many stellar black holes, or the merging of numerous massive stars within dense star clusters into a colossal object that quickly collapses into an IMBH. Alternatively, IMBHs could have a top-down genesis, arising from the collapse of huge amounts of available mass in the early universe. That top-down scenario is the favored—albeit unsubstantiated—formation model for supermassive black holes as well. Whichever way IMBHs appear to form would accordingly hone formation and evolution theories for supermassive black holes by potentially showing the lower-end mass levels that can arise from the top-down scenario or placing supermassive black holes alone in that origin scenario. See also: Black hole; Mass; Universe

The supermassive black hole at the center of the Milky Way serves as a unique laboratory for testing predictions of general relativity. In a new study, researchers report that a long-studied star—called S2 or sometimes S-02—moves in a rosette-shaped orbit around this black hole, just as general relativity mandates a star should. Nearly three decades’ worth of observations have borne out this observation that S2's orbit is not a simple ellipse. Instead, the orbit precesses, meaning that each time the star completes a loop around the black hole, the closest point of the orbit rotates away from the previous orbit's closest point, resulting in a rosette pattern. These findings are the first to measure precession by a star around a supermassive black hole. See also: Ellipse; Orbital motion; Precession; Star

After a 40-year search, astronomers have identified the first star shown to pulsate on only one side. Many kinds of stars, called variables, undergo natural pulsations, or periodic changes in brightness that are visible across the whole star. The newly observed star's pulsations, however, are largely confined to a single hemisphere. The reason for this one-sided pulsing: a small companion star, whose gravity pulls the pulsing star into a teardrop shape. This distortion alters the distribution of pulsations that would typically ripple evenly across a spherical star. See also: Gravity; Star; Variable star