The images show the star dimming, dropping to 20% of its peak brightness in just a few hours before recovering slightly, dimming again, and ending up back where it started two days later.<\/p>\n
Since astronomers started monitoring large numbers of stars with the precision required to catch the transit of tiny exoplanets<\/a> across the face of their parent stars, there have been a steadily increasing number of \u2018dipping stars\u2019.<\/span><\/p>\n More from Chris Lintott:<\/strong><\/em><\/p>\n Kepler<\/a>, the predecessor of TESS, was particularly useful in spotting them, and was responsible for the identification of the most famous example, Boyajian\u2019s <\/span>Star.<\/p>\n This object, first identified by participants in the Planet Hunters citizen science<\/a> project, showed such dramatic brightness variations that for a while the most plausible explanation was the presence of an \u2018alien megastructure\u2019 around the star.<\/p>\n Follow-up observations soon revealed that intervening dust \u2013 not aliens with grand plans \u2013 were responsible for the behaviour of Boyajian\u2019s Star.<\/span><\/p>\n In the case of TIC 400799224, there were observations already on hand, thanks to the Evryscope project, which has been scanning the sky nightly since 2017, and ASAS-SN, a survey built to hunt supernovae<\/a>.<\/span><\/p>\n These archive observations, plus a targeted follow-up with the global network of telescopes belonging to the Las Cumbres Observatory, also reveal shallower dips that happen frequently, each accounting for a drop of a few per cent in the system\u2019s total brightness, as well as a regular cycle of brightening and fading with a period of about 20 days.<\/span><\/p>\n So what\u2019s going on? So-called \u2018speckle\u2019 imaging, which uses short exposures to capture ultra-sharp images in moments where the air above the observatory is suddenly still, reveals that the system is a binary, with two probably young stars in orbit around each other.<\/span><\/p>\n The system does shine more brightly than <\/span>expected in longer-wavelength light, which suggests the presence of dust in the system, and this turns out to be key to the mystery: something is producing substantial amounts of dust, which is blocking light from at least one of the two stars.<\/p>\n The researchers have worked out that, given the size of the dips that we see, if an object the size of the largest asteroid in our Solar System, Ceres<\/a>, was reduced to rubble it would produce enough dust to keep TIC 400799224<\/span> dipping for 8,000 years.<\/p>\n Rather than invoke such a catastrophic event, however, the team think the most likely scenario involves a large orbiting asteroid that is colliding repeatedly with smaller objects that lie in its way, which produces dust with each collision.<\/p>\n Is that the right explanation? Right now I\u2019ve no idea \u2013 that\u2019s why studying these unusual objects is such fun.<\/p>\n At a normal magnitude of +12.6, the star is bright enough for back-garden observers to keep an eye on it; whatever is going on around TIC 400799224, more observations from all sorts of telescopes are key to understanding it.<\/p>\n![\""Illustration\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2021\/11\/tabbys-star-e1637241310548.jpeg?quality=90&resize=620%2C349"\" "\\"\"tabbys\\"")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>\n![\""Dwarf\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2019\/04\/CeresAtmosMAIN-a3c3d62.jpg?quality=90&resize=620%2C350"\" "\\"\"Dwarf\\"\/")
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