Protoplanetary disc replenishment by late-stage infall
Protoplanetary disc replenishment by late-stage infall
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Protoplanetary discs have long been understood to be isolated systems after the approx. 100 000 years they take to form from collapsing gas from the interstellar medium (ISM). Much of our theory about planet formation is based on the assumption that after this period, the star-disc system is isolated from its environment. However, recent theory and observations are challenging this assumption...
This figure on the left is adapted from Speedie et al. 2025, and shows CO emission surrounding AB Aurigae, a disc with infall and gravitational instability.
A new model for discs fed by the ISM
A new model for discs fed by the ISM
In this work, we developed a novel theoretical approach for calculating how much mass is added to discs from the interstellar medium over their lifetime. We found the surprising result that a model that only includes infall from the ISM can reproduce the masses of discs and the rate r which material falls onto the host star (stellar accretion rate). The figure on the right shows observed properties (red points) compared to our (yellow background). This strongly suggests that late stage infall is a vital aspect of understanding planet formation processes. This has many consequences for how understand the assembly of planets, and the physics of the protoplanetary discs from which they form.
Statistical evidence that late-stage infall influences stellar accretion
Statistical evidence that late-stage infall influences stellar accretion
Does late-stage infall really affect the whole process of planet formation, particularly for 'terrestrial' planets like the Earth born close to their host star? To test this, we explored whether stellar accretion rates, which are the rate at which material falls onto the star, depends on the environment in the ~2 Myr old Lupus star forming region. We particularly focused on the clustered Lupus 3 region, as pictured below. We found that this accretion rate is more rapid in regions where the ISM is more dense (see right figure), suggesting that environmental infall affects planet formation right down to the scale of the stellar radius. If this interpretation is correct, this would have wide-reaching consequences for planet formation.
The figure above shows the core of the Lupus 3 region, with background showing a Spitzer 24 micron map. The measured accretion rates of young stellar objects (YSOs) are shown as coloured points (Alcala et al. 2017).
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