Original title: Stellar age is not disk age
M. Kuffmeier, A. Winter, A. Kuznetsova, M. Vioque +1 · September 2026
Astronomers often look at the percentage of stars that still have planet-forming disks of gas and dust to figure out how long these disks survive. They usually assume older stars just have older leftover disks. The authors show this assumption might be wrong. Later material falling in from space can refill or even rebuild a disk around a star after its original disk fades. The researchers created a model where disks are a mix of original material and this newly added material. They found that a single long-lived disk looks the exact same in disk count data as a short-lived disk that gets replenished multiple times. This means a star's age does not necessarily match its disk's age.
Imagine a teacher counting how many students still have their textbooks each month, assuming the count reveals how long a textbook lasts before wearing out. Some students lose books and grab replacements from the lost-and-found box, so their book is not old — it is repeatedly renewed, and counting cannot tell a single long-lived book from several short-lived ones. In this paper, the textbooks are the gas-and-dust structures around young stars, and the lost-and-found box is extra material falling in from the surrounding cloud; counting how many stars still have these structures cannot tell a long-lived one from a short-lived one that keeps being replenished.
Astronomers use the fraction of stars with disks to estimate how long planet-forming disks survive. If that estimate is wrong, models of planet formation and disk evolution rest on a false clock. The result also suggests a single star can host several disks over its life, each with different material — which changes what kinds of planets might form.
The abstract does not prove that late infall actually replenishes disks; it argues the data cannot rule it out. It also does not establish whether regions of the same stellar age actually show a spread in disk fractions — that is posed as a key test. No quantitative predictions for the supply rate or disk lifetimes are given.
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Stellar age is not disk age — M. Kuffmeier, A. Winter, A. Kuznetsova et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.