With the satellite Transiting Exoplanet Survey Satellite, a team of astronomers discovered a mysterious object orbiting a binary star, TIC 400799224. This object blocks the light of a host star in a very volatile way: light drops are detected in about one third or five transits, suggesting that the body is still an uncertain nature that occasionally emits dust.
The TESS satellite was launched in April 2018. Since its launch, the satellite has detected 172 confirmed exoplanets and compiled a list of 4,703 exoplanet candidates, and the TESS entry catalogue contains more than a billion objects.
The mystery object can block up to 37% or 75% of the light from the host star.
Given the unusual variation of light, scientists suggest that an unknown object occasionally emits dense dust. At least this has already been observed in other star systems, such as Kepler 1520.
Astronomers consider TIC 400799224, although very unusual, to be the equivalent of these systems, since the orbital body has signs of decay, the resulting transit changes in depth, form and duration, and finally transit is relatively accidental — the eclipse is optically measurable in only one of the three or five transits. However, there are several features in TIC 400799224 that classify it as a separate category.
The analysis of the data first showed that it was a double system, one of whose stars pulsates with a period of 19.77 days. In addition, the amount of dust emitted by a shadowing object is relatively large, equivalent to the amount of dust emitted by an asteroid within a radius of 10 km. However, if it were an asteroid, given the speed at which the dust must be formed to produce the observed eclipse, it would only exist for about 8,000 years before it disappears, the Harvard-Smixon Astrophysics Centre press release specifies that the frequency remains the same within six years of subsequent observation of the object, and the shadowing object seems to remain intact at each passage.
The result of multiple collisions?
What is the nature of this object and how can such amounts of dust be generated in the TIC 400799224 system? In the case of decaying planets, the formation of dust is due to the heat wind generated by surface exposure and evaporative effects such that the pressure of silicates vapours is too small to cause the expected mass loss rate.
Dust could also occur as a result of collisions with small bodies that create sporadic dust clouds, or as a result of the transfer of dust from a planet buried in a star drive. Given the mass limitations, the constant frequency of the object for six years and the highly variable depths of the eclipse, the team believes that the collision scenario is the most likely. The same explanation was offered for the white dwarf ZTF J0328-1219, which is also periodically eclipsed by the clots of crashed debris.
The object studied here is subject to collisions with small bodies too small to damage it or alter its orbital period. These collisions are likely to be regular enough and occur in the same orbital phase of the object; each impact produces a cloud of dust and small particles that eclipses the star for a while and then scatters... until a new impact forms a new cloud.
To eliminate uncertainty, astronomers plan to continue to observe this mysterious object and to include historical observations of the sky in their analysis to try to determine changes over several decades. They note that the object is sufficiently bright to be observed by small telescopes that can detect future transits.