External photoevaporation and planet formation

The majority of stars and planets from in massive groups of stars, called clusters or associations. These regions are luminous at ultraviolet violet wavelengths due to the massive, short-lived stars.

The figure below shows the distribution FUV luminosities of local star forming regions (SFRs) compared to the number of cluster members. Taurus is a typical region in which protoplanetary discs have been studied in detail - we also need to study the discs in higher UV regions to learn more about planet formation!

Click here for a review article on external photoevaporation.

"File:Proplyd 181-825 in the Orion Nebula (captured by the Hubble Space Telescope).jpg" by NASA/ESA and L. Ricci (ESO) is licensed under CC BY 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0?ref=openverse.

Proplyds

A 'proplyd' - originally a contraction of 'PROtoPLanetarY Disc' - is a term that now applies to strongly irradiated discs. These discs are heated externally by neighbouring massive stars and can undergo rapid mass-loss.

Planet formation in irradiated discs

Massive planets grow and migrate inwards in the protoplanetary disc. External disc depletion via photoevaporation leads to reduced time for this growth and migration, leading to lower mass, longer period planets. The plot below shows how higher FUV fluxes can result in an anti-correlation between orbital period and planet mass. This may lead to an apparent reduction in the number of detected planets with periods longer than ~ 1000 days, as seen in observed radial-velocity planets (red crosses). For more information, see the full paper here.

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