Free Astronomy Magazine September-October 2021

6 SEPTEMBER-OCTOBER 2021 ASTRO PUBLISHING do companion stars affect the forma- tion of planets?” The first concrete answers to these questions came in 2014 from a team of researchers led by Elliott Horch (Southern Con- necticut State Uni- versity). The team acquired images of over 600 stars with transits already observed by the Kepler Space Telescope, reveal- ing 49 stellar com- panions within 1 arc second of the primary stars. To accomplish this feat, Horch and col- leagues used a technique known as “speckle imaging” (devised in the 1960s and developed over the fol- lowing decades) with the 3.5-meter WIYN and 8.1-meter Gemini North telescopes. Speckle imaging consists of obtain- ing images of a small portion of the sky around a star with exposure times so short (a few hundredths of a second) that they freeze out the deleterious effects of atmospheric turbulence and reach the diffrac- tion limit of the instrument used. The individual exposures are then combined and treated through software employing complex algo- rithms to provide a final image of the star and its possible companion with a better resolution than that achievable by the Hubble Space Tel- escope. Thanks to this technique, Horch’s team was able to reveal companion stars up to 125 times fainter than the primaries, sepa- rated by just 0.05 arcseconds, equiv- alent in most cases to about 100 astronomical units (AU). Although based on a rather limited dataset and an only approximate character- ization of the binary systems, this T his chart, updated as of August 20, 2021, tracks the current number of known planet discoveries beyond our solar system, sorted by type. Confirmed exoplanets have been validated by multiple observations. [NASA] that at least half of all stars are in binary systems, containing a com- panion star to which a primary star is gravitationally linked. If the pair is far enough away from us as to be inseparable through the instrument ob- serving them, then the combined light of the two stars could make imperceptible the transit of a planet otherwise visible if its host star were single. It is, therefore, likely that the number of Earth-sized planets is much higher than that estimated so far from the number of recorded transits. For several years, as- tronomers have asked themselves two cru- cial questions: “How many host stars are binary?” and “Are stars with planets equally likely to have a companion star or T his graph shows the exoplanets so far confirmed, divided accord- ing to the type of discovery method. As expected, the planets dis- covered thanks to transits in front of stellar disks have pe- riods of revolu- tion that are shorter on av- erage, while most of those discovered through radial velocities have very signifi- cant masses. [NASA]