Double and Double-Double

Today we have one case of seeing double, and another of seeing double-double, all from the efforts of “citizen scientists” who have volunteered their own time to assist professional astronomers. In the first case, a press release from Keck Observatory in Hawaii describes the new detection of a binary of brown dwarfs with the largest yet seen separation. Brown dwarfs are “also-ran” stars, ones with too low mass to have (hydrogen) nuclear fusion occur in their cores. How they form has been a matter of some debate in the past, with some suggesting they form in particularly massive disks of stars instead of “in situ” like other stars. In this case, the binary is separated by about 4 times the equivalent distance between Pluto and the Sun. Since the objects are relatively low mass, their ability to stay as a gravitationally connected object is relatively weak and could be disrupted relatively easily by a passing star. Nevertheless, this kind of binary suggests a more “in situ” formation route. The object was spotted first in a citizen science project called “Backyard Worlds: Planet Nine” which using all-sky data from NASA Widefield Infrared Survey Explorer (WISE) satellite observatory to look for signs of good ol’ Planet Nine. Here are links to the press release and the paper, the latter of which was co-authored by Gordon Walker’s former student Evgenya Shkolnik, who spent some time with us at DAO when completing her dissertation over 15 years ago.

Meanwhile, other citizen scientists have been combing through the nearly all-sky data from NASA’s Transiting Exoplanet Survey Satellite (TESS) for planets that pass in front of their host stars but they’ve made another interesting discovery: almost 100 newly identified quadruple star systems. These objects are like binaries that consist of two stars revolving around each other while bound together by their own gravity, but instead of two stars there are four. Indeed, the majority of these systems appear to consist of a “binary of binaries,” where two pairs of stars that are orbiting each other are themselves orbiting around each other. This sample doubles the known number of multiply eclipsing quadruple systems, and the team has also identified the first sextuply-eclipsing sextuple system, which could be a system of three pairs of binaries all gravitationally stuck together. I imagine planets around such systems, though not impossible, might be quite different than those in our solar system, with the effects of the multiple Suns on their surfaces of these planets of course depending on their respective distances. Here’s a link to the arXiv preprint about this result, for those who’d like more information. Well done citizen scientists for making contributions to astronomical discovery! (Thanks to Dennis Crabtree who gave me the heads-up yesterday about the brown dwarf binary story.)