The Transiting Exoplanet Survey, TESS, satellite was launched in 2018 with the aim of discovering small planets around neighboring stars closest to the Sun. TESS has so far discovered 172 confirmed exoplanets and compiled a list of 4,703 candidate exoplanets. Its sensitive camera takes images that cover a huge field of view, more than double the area of the constellation Orion, and TESS has also assembled a TESS Entry Catalog (TIC) with over a billion objects. . Tracking studies of TIC objects have shown that they result from stellar pulses, supernova shocks, decaying planets, self-lensing gravitational binary stars, eclipsing triple star systems, disk occultations, etc.
CfA astronomer Karen Collins was a member of a large team that discovered the mysterious variable object TIC 400799224. They searched the catalog using machine learning-based computational tools developed from the observed behaviors of hundreds of thousands of known variable objects; the method has already found decaying planets and bodies that emit dust, for example. The unusual TIC 400799224 source was spotted by chance due to its rapid drop in brightness, nearly 25% in just four hours, followed by several sharp variations in brightness that could each be interpreted as an eclipse.
Astronomers have studied TIC 400799224 with various rigs, some of which have been mapping the sky for longer than TESS has been operating. They discovered that the object is probably a binary star system, and that one of the stars pulses with a period of 19.77 days, possibly from an orbiting body that periodically emits clouds of dust that obscure the star. But while the periodicity is strict, the star’s dust occultations are erratic in their shapes, depths, and duration, and are only detectable (at least from the ground) about a third of the time or less. The nature of the orbiting body itself is confusing because the amount of dust emitted is large; if it were produced by the decay of an object like the asteroid Ceres in our solar system, it would only survive about eight thousand years before disappearing. Yet, remarkably, during the six years of observing this object, the periodicity has remained strict and the dust-emitting object has apparently remained intact. The team plans to continue monitoring the object and incorporate historical observations of the sky in an attempt to determine its variations over several decades.
Reference: “Mysterious Dust-emiting Object Orbiting TIC 400799224”, Brian P. Powell, Veselin B. Kostov, Saul A. Rappaport, Andrei Tokovinin, Avi Shporer, Karen A. Collins, Hank Corbett, Tamás Borkovits, Bruce L. Gary, Eugene Chiang, Joseph E. Rodriguez, Nicholas M. Law, Thomas Barclay, Robert Gagliano, Andrew Vanderburg, Greg Olmschenk, Ethan Kruse, Joshua E. Schlieder, Alan Vasquez Soto, Erin Goeke, Thomas L. Jacobs, Martti H. Kristiansen, Daryll M. LaCourse, Mark Omohundro, Hans M. Schwengeler, Ivan A. Terentev and Allan R. Schmitt, The astronomical journal 162, 299, 2021.