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Dr Zacharias Roupas

Astrophysicist

Marie Curie Fellow
Physics department, University of Milano-Bicocca, Italy
zacharias.roupas@unimib.it

Active Project: Horizon Europe 2020 - Marie Skłodowska Curie grant agreement No. 101149270—ProtoBH

Gravitational-wave astronomy offers a unique glimpse into the universe from its infancy to the present by detecting gravitational radiation emitted by black holes paired in binaries. Star clusters at their birth and early stages of evolution, when a significant amount of residual gas is still present, offer an ideal environment for these objects to form and grow in mass by accretion. The black holes' spins also increase as accretion disks form, generated by transverse velocity shears induced by the black holes' own motions. The ProtoBH project aims to provide coherent models for the formation and growth of black holes in gaseous environments, and methods for identifying the astrophysical origin of the signals detected by present and future gravitational-wave experiments.

Publications

  1. Zacharias Roupas
    "Black hole spin-mass correlation and vector resonant relaxation in gaseous star clusters: the origin of GW231123?"
    arXiv:2607.17869 (2026)
  2. Zacharias Roupas
    "Accretion-disk formation around orbiting stellar black holes in gaseous star clusters"
    arXiv:2607.12465 (2026)
  3. Zacharias Roupas
    "Spin-up and spin distribution of stellar black holes grown by gas accretion in proto-stellar clusters"
    Astronomy & Astrophysics, 709, A5 (2026)
  4. Zacharias Roupas
    "Massive Black hole formation in proto-stellar clusters via early gas accretion"
    Particles, 9, 18 (2026)
  5. Zacharias Roupas
    "Black hole mass function shift in proto-stellar-clusters driven by gas accretion"
    Astronomy & Astrophysics, 702, Α208 (2025)
  6. Zacharias Roupas
    "Radical reform is needed to combat power abuses in academia"
    Nature Human Behaviour, 9, 424 (2025)
  7. Zacharias Roupas
    "Self-gravitating isothermal sphere in an expanding background"
    Physical Review D, 110, 123020 (2024)
  8. Zacharias Roupas
    "Thermodynamic instability of dark energy equation of state"
    Physics of the Dark Universe, 101181 (2023)
  9. Zacharias Roupas
    "The Cosmological Black Hole"
    AIP Conf. Proc. 2872, 060012 (2023)
  10. Zacharias Roupas
    "Detectable universes inside regular black holes"
    European Physical Journal C, 82:255 (2022)
  11. Zacharias Roupas
    "Thermodynamic origin of quantum time-energy uncertainty relation"
    Journal of Statistical Mechanics: Theory and Experiment, 093207 (2021)
  12. Zacharias Roupas
    "Gravitational Brownian motion as inhomogeneous diffusion: Black hole populations in globular clusters"
    Astronomy & Astrophysics, 646, A20 (2021)
  13. Zacharias Roupas, Grigoris Panatopoulos and Ilidio Lopes
    "QCD color superconductivity in compact stars: color-flavor locked quark star candidate for GW190814"
    Physical Review D, 103, 083015 (2021)
  14. Zacharias Roupas
    "Secondary component of gravitational-wave signal GW190814 as an anisotropic neutron star"
    Astrophysics and Space Science, 366, 9 (2021)
  15. Zacharias Roupas
    "Relativistic Gravitational Collapse by Thermal Mass"
    Communications in Theoretical Physics, 73, 015401, (2021)
  16. Amr El-Zant, Zacharias Roupas and Joseph Silk
    "Ejection of supermassive black holes and implications for merger rates in fuzzy dark matter haloes"
    Monthly Notices of the Royal Astronomical Society, 499(2), 2575 (2020)
  17. Zacharias Roupas and Gamal L. Nashed
    "Anisotropic Neutron Stars Modelling: Constraints in Krori-Barua Spacetime"
    European Physical Journal C, 80, 905, (2020)
  18. Zacharias Roupas
    "Gravitational Potential from Maximum Entropy Principle"
    Classical and Quantum Gravity, 37, 097001, (2020)
  19. Zacharias Roupas
    "Statistical Mechanics of Gravitational Systems with Regular Orbits: Rigid Body Model of Vector Resonant Relaxation"
    Journal of Physics A: Mathematical and Theoretical, 53, 045002 (2020)
  20. Zacharias Roupas and Demosthenes Kazanas
    "Generation of massive stellar black holes by rapid gas accretion in primordial dense clusters"
    Astronomy & Astrophysics, 632, L8 (2019)
  21. Zacharias Roupas
    "Gravitational Instability Caused by the Weight of Heat"
    Symmetry, 11(12), 1435 (2019)
  22. Zacharias Roupas and Demosthenes Kazanas
    "Binary Black Hole Growth by Gas Accretion in Stellar Clusters"
    Astronomy & Astrophysics, 621, L1 (2019)
  23. Zacharias Roupas and Pierre-Henri Chavanis
    "Relativistic Gravitational Phase Transitions and Instabilities of the Fermi Gas"
    Classical and Quantum Gravity, 36, 065001 (2019)
  24. Zacharias Roupas
    "The Gravothermal Instability at all scales: from Turnaround Radius to Supernovae"
    Universe, 5(1), 12 (2019)
  25. Zacharias Roupas, Bence Kocsis and Scott Tremaine
    "Isotropic--Nematic Phase Transitions in Gravitational Systems"
    The Astrophysical Journal, 842, 90 (2017)
  26. Zacharias Roupas
    "Thermal Mass Limit of Neutron Cores"
    Physical Review D, 91, 023001 (2015)
  27. Zacharias Roupas
    "Relativistic Gravothermal Instabilities"
    Classical and Quantum Gravity, 32, 135023 (2015)
  28. Zacharias Roupas, Minos Axenides, George Georgiou, and Emmanuel N. Saridakis
    "Galaxy clusters and structure formation in quintessence versus phantom dark energy Universe"
    Physical Review D, 89, 083002 (2014)
  29. Zacharias Roupas
    "Thermodynamical instabilities of perfect fluid spheres in General Relativity"
    Classical and Quantum Gravity, 30, 115018 (2013)
  30. Zacharias Roupas
    "Corrigendum: Thermodynamical instabilities of perfect fluid spheres in General Relativity"
    Classical and Quantum Gravity, 32, 119501 (2015)
  31. Minos Axenides, George Georgiou, and Zacharias Roupas
    "Gravitational instabilities of isothermal spheres in the presence of a cosmological constant"
    Nuclear Physics B, 871, 21 (2013)
  32. Minos Axenides, George Georgiou, and Zacharias Roupas
    "Gravothermal instability with a cosmological constant in the canonical ensemble"
    J. Phys.: Conf. Ser., 410, 012130 (2013)
  33. Minos Axenides, George Georgiou, and Zacharias Roupas
    "Gravothermal Catastrophe with a Cosmological Constant"
    Physical Review D, 86, 104005 (2012)
  34. Zacharias Roupas
    "Phase space geometry and chaotic attractors in dissipative Nambu mechanics"
    Journal of Physics A: Mathematical and Theoretical, 45, 195101 (2012)
  35. F. del Aguila, et al.
    "Collider aspects of flavour physics at high Q"
    The European Physical Journal C, 57, 183 (2008)