Researchers estimate that the mass of the companion star that passed between our star and us is over three times that of Jupiter. Therefore, it could be a brown dwarf, meaning a body larger than a planet but smaller than a regular star.
In late 2024, an unusual phenomenon was detected in one of the automated sky surveys. A star that had seemed stable for years began to gradually fade, then dropped in brightness dramatically. At the peak of the event, about 97% of its light was blocked. This was not a short eclipse of days, nor weeks. The fading lasted an unusually long time, and the star remained dim for months. Such events are very rare, because they require almost perfect alignment between the light source and the “occluder.”
The researchers quickly ruled out an explanation of internal activity in the star itself. The more appropriate picture is an eclipse, that is, a body that passed in the line of sight and blocked the light. But here comes the surprising detail. To block light almost completely for such a long period of time, an ordinary planet is not enough. A much larger structure is needed, one that can continue the eclipse over time. The model that best explains this is a giant ring system around a companion body that is not directly visible.
Sealed rings, gradual entry and long bottom
According to the analysis, there is a particularly wide and dense ring system around the companion. The rings are not uniform. The outer parts are thinner, so the onset of the dimming was gradual. As denser regions passed in front of the star, the dimming became very profound. The combination of “thin” rings on the outside and “thick” rings on the inside explains the shape of the light curve, and the fact that the event lasted so long.
The circumference of the ring system has been estimated to be about 0.17 astronomical units in radius. This is equivalent to about 25 million kilometers. In other words, it is a structure that is about half the distance between the Sun and Mercury. Such a scale makes the event a rare window into a ring system outside our solar system, without being able to “photograph” it directly.
The researchers estimate that the companion's mass is over three times that of Jupiter. It could therefore be a brown dwarf, a body larger than a planet but smaller than a regular star, or alternatively a "super-Jupiter," an extremely massive gaseous planet. At this stage, the data allow us to constrain a minimum mass, but not to determine unequivocally which type it belongs to.
Why is this important for understanding the formation of rings and planets?
Ring systems are familiar to us mainly from our immediate neighborhood, like Saturn. But here we are talking about rings around a much more massive body and on a gigantic scale. This raises new questions. How does such a ring system form? Is it stable over time or does it break apart? Does it have lumps that start to turn into moons? And what is its connection to the formation processes of distant planets?
The event also demonstrates the power of modern sky surveys. They are not just “supernova hunters.” They provide continuous monitoring of millions of stars, and can therefore monitor rare events that would previously have slipped under the radar. In this case, the eclipse makes it possible to learn about the structure, density, and extent of rings, just from the way the light curve changes.
The researchers also note an important prediction for the future. If this is a stable trajectory, a similar event may occur again in about 42–43 years. While this is far away, this is exactly why it is important to document the current event well. The more complete the data, the easier it will be to compare in the future, and to see if the ring system remains the same, changes, or even disappears.
More of the topic in Hayadan:
