https://phys.org/news/2018-11-production-evolved-exoplanetary.html

A white dwarf star is the evolutionary end product of stars like our sun which, in another seven billion years or so, will no longer be able to sustain burning its nuclear fuel. With only about half of its mass then remaining, it will shrink to a fraction of its radius and become a white dwarf. White dwarf stars are common, the most famous one being the companion to the brightest star in the sky, Sirius. CfA astronomer Scott Kenyon was part of a team that has been studying the white dwarf star GD56 for 11.2 years, and has seen its light rise and fall by about 20% consistent with dust production or depletion from its disk.

The team used the IRAC camera on Spitzer, the WISE mission, and ground-based observations from the UKIRT and Keck telescopes to characterize these fluctuations. They found that there was no change to the color of the light, implying that all the dust being destroyed or created was at about the same temperature, and hence was probably located at about the same distance from the star. The scientists hypothesize that gravitational attraction or collisional grinding between particles in the disk are responsible for the decreases or increases, respectively, in the disk's dusty area and hence in the varying obscuration.