Two massive, icy worlds collided in a distant star system, obliterating each other and forming a red hot, donut-shaped cloud.
It turned out this wasn't the star's first fluctuation, either, as scouring previous observations revealed that in the three years preceding the dimming, ASASSN-21qj had actually doubled in brightness in the infrared spectrum. Upon colliding, the two worlds essentially vaporized each other, billowing out a donut-shaped cloud of extremely hot debris. The heat of that cloud, estimated to be around 1,300 degrees Fahrenheit, would explain the infrared brightening.
And though a planetary collision seems the most likely possibility based on the evidence, it's still, overall, rare. At an estimated 300 million years old, the star system should be too mature for planetary collisions to still happen.