Mysterious dusty object spotted orbiting a distant star

There are a lot of unexplained things in the universe, and scientists have just added something new to the list – a strange, dusty object that may be causing its host star to dim by up to 75%. Often, when something is blocking out the light of a star, it’s an exoplanet or an asteroid, but in this case, it’s more erratic and more persistent. According to a study published in The Astronomical Journal, although scientists have a theory for what the object may be, they are baffled by the quantity of dust it is emitting.

We’ve discovered this mysterious object, known as TIC 400799224, thanks to the Transiting Exoplanet Survey Satellite (TESS). TESS was launched in 2018 with the goal of discovering small planets around the Sun’s nearest neighbour stars – thus far, it has discovered 172 confirmed exoplanets and has a list of 4703 further candidates. It has a camera taking images that span a huge field of view, and it has assembled a TESS Input Catalogue (TIC) with over one billion objects. Follow-up studies of TIC objects have found some interesting things, from stellar pulsations and shocks from supernovae to disintegrating planets.

The object has since been seen to block up to 75% of its host’s light

TIC 400799224 was discovered by a large team, spotted because of its rapid drop in brightness, by nearly 25% in just a few four hours, followed by several sharp brightness variations that could each be interpreted as an eclipse (the object has since been seen to block up to 75% of its host’s light). This would usually signal a disintegrating planet or orbiting body that’s being broken down and releasing dust – something scientists are keen to learn more about. But after looking back through six years of data on the mysterious object, the team found that something strange is going on.

The first observation is that TIC 400799224 isn’t orbiting a single star system. Further examination shows it’s orbiting a binary star system, in which one of the stars pulsates with a 19.77-day period. While that periodicity seems pretty reliable, the object that dims the light is erratic in its shape, depth, and duration – which is why the astronomers assume it’s most likely caused by some kind of orbiting body that periodically emits clouds of dust. But it’s not clear what exactly that object is, and that’s what scientists want to find out.

It is gathering mass from its surrounding envelope of dust and gas, often in the form of a disk around the star

According to a press release from the Harvard-Smithsonian Centre for Astrophysics: “The nature of the orbiting body itself is puzzling because the quantity of dust emitted is large; if it were produced by the disintegration of an object like the asteroid Ceres in our Solar System, it would survive only about eight thousand years before disappearing. Yet remarkably, over the six years that this object has been observed, the periodicity has remained strict and the object emitting the dust apparently has remained intact.”

After analysing the data, the researchers have a few potential leads. They think the most likely outcome is that one of the stars is still pre-main-sequence, meaning its gathering mass from its surrounding envelope of dust and gas, often in the form of a disk around the star. They also have a few possible explanations for the dust in their study, from the disintegration of an object as it passes directly from a solid into a gas state to dust being shepherded by a planet embedded in the star’s disk. The favourite explanation at the moment is a possible collision with a minor planet-like object, blasting off dust and explaining both the regular periodicity and the variations in depths.

The astronomers intend to continue monitoring the object, incorporating historical observations of the sky to try and determine its variations over many decades. They’re also hoping to determine which of the two stars the object is actually orbiting, which could influence their findings. Similar discoveries have ended up being disintegrating planets, but the team felt this data is different enough that it isn’t likely in this case – with an air of excitement, they suggest that it may end up being in a category of its own after further study.