IAU PhD prize awarded to Riccardo Arcodia

July 27, 2022

The IAU has awarded MPE junior scientist Riccardo Arcodia with a PhD prize for his thesis on “Accretion onto black holes across the mass scale”. Along with the other nine prizewinners, he will give a talk at the next IAU general assembly, taking place at the beginning of August in Busan, Republic of Korea.

Black holes are amongst the most fascinating concepts both for (astro-)physicists and the public. Many of the most luminous phenomena, both persistent and transient, that we know in the Universe are somehow related to accretion of matter onto black holes. Supermassive black holes with a million to several billion times the mass of our Sun can be found at the centers of galaxies. If there are rich gas reservoirs available for accretion, they can be very luminous and are then called active galactic nuclei (AGN). The others are generally quiescent, but reveal themselves, if they receive a sudden donation of matter in their vicinity. The accretion processes powering these systems can make them bright at all wavelengths, and may easily outshine the galaxies that host them. This contrast is particularly striking in X-rays, which trace the innermost regions around black holes.

Since the discovery of quasars in the 1960s, much observational effort has been devoted to their study, along with the development of accretion theory to understand them. An important observed feature is the correlation between optical/UV and X-ray luminosities seen in bright AGN. While the observed correlation is well established and quantified, a solid and conclusive theoretical explanation is still lacking. In his PhD thesis, Riccardo Arcodia uses a self-consistently coupled disk-corona model, adapted and improved from the literature, to tackle this open question. In his model, the inner accretion flows of brighter sources are dominated by radiation pressure through a much larger region compared to fainter sources. A further intriguing and long-standing question exists as to whether the accretion flow around black holes is similar for both stellar-mass black holes and AGN. Riccardo Arcodia compared the observational properties of disk-corona systems in both stellar and supermassive black holes, and found that the disk-corona systems in the two black holes classes compare quite nicely.

In addition to continuously accreting black holes, they are often exhibiting transient and variable phenomena. So-called quasi-periodic eruptions (QPEs) are extreme high-amplitude bursts of X-ray radiation of currently unknown nature, recurring every few hours and originating near the central supermassive black holes in galactic nuclei. With a blind and systematic search over half of the X-ray sky with the eROSITA X-ray telescope, Riccardo Arcodia found such sources in two new galaxies, doubling the number of known QPEs at that time. (Link to previous press release)

For his thesis, “Accretion onto Black Holes Across the Mass Scale”, the IAU awarded Riccardo Arcodia with the PhD prize in the Division D: High Energy Phenomena and Fundamental Physics. Each of the IAU’s nine divisions awards a prize to the candidate it feels has carried out the most remarkable work in the previous year, and the nine divisions together also agree on jointly awarding an extra prize, the PhD at-large Prize. In 2021, 120 PhD theses, defended between 16 December 2020 and 15 December 2021, were submitted. Riccardo Arcodia has been invited to the next IAU general assembly, taking place 2-11 August in Busan, Republic of Korea, where he will give a talk about his work.

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