Fabio Pacucci

Fabio Pacucci (born 1988) is an Italian-American astrophysicist and science communicator. He is currently a Staff Astrophysicist at the Center for Astrophysics Harvard & Smithsonian, a collaboration between Harvard University and the Smithsonian Astrophysical Observatory. also known as black hole seeds. Pacucci led the discovery of the first candidate direct collapse black holes and contributed to identifying the farthest gravitationally-lensed quasar and galaxy known prior to the launch of the James Webb Space Telescope. More recently, he has been a leading contributor to the study of "Little Red Dots", a population of compact, high-redshift sources potentially hosting overmassive black holes.

Pacucci is also active in science communication. He has collaborated with TED-Ed since 2018, creating a series of animated educational videos viewed by millions and translated into over 25 languages. In addition to numerous public talks, he has written for media outlets such as Scientific American, Sky & Telescope, and The Conversation.

Early life and education Pacucci was born in 1988 in Taranto, in the Apulia region of southern Italy. He attended the "Battaglini" Scientific High School and later enrolled at the Sapienza University of Rome, where he earned both his Bachelor of Science degree in Physics and his Master of Science degree in Astronomy and Astrophysics, graduating cum laude. He completed his Ph.D. in Physics in 2016 at the Scuola Normale Superiore in Pisa, Italy, under the supervision of Professor Andrea Ferrara. and Black Hole Initiative Fellowship at the Center for Astrophysics Harvard & Smithsonian.

In 2025, Pacucci was appointed Staff Astrophysicist at the CfA and became a Senior Member of the Institute for Theory and Computation at Harvard University.

Pacucci is also active in the international astronomical community. Using this model, Pacucci led the discovery of the first two candidate direct collapse black holes, collapsed objects thought to have formed without passing through a stellar phase, based on multi-wavelength observations from the Hubble Space Telescope, Chandra X-ray Observatory, and Spitzer Space Telescope. led by Xiaohui Fan. suggesting that a significant population of similar objects may have been missed by existing surveys.

Little red dots

With the launch of the James Webb Space Telescope, Pacucci led several studies on "Little Red Dots" a population of compact, red, high-redshift galaxies thought to host overmassive black holes. He also proposed, in a study with Avi Loeb, that the properties of little red dots may be explained by their origin in low-spin dark matter halos, linking their morphology to cosmological structure formation models. More recently, he authored the first study that identified the population of little red dots with accreting direct collapse black holes, intermediate-mass black holes, and planetary dynamics. He has co-authored more than 200 scientific publications and has directly supervised tens of students, both graduate and undergraduate. 2019: Clay Fellowship at the Smithsonian Astrophysical Observatory 2017: Livio Gratton Prize – Prize for the best Ph.D. thesis in astronomy in Italy (period 2014-2016) 2012: Enrico Persico Prize – from the Accademia Nazionale dei Lincei These animations have been viewed by millions of people worldwide and translated into over 25 languages, as noted in a feature by the Harvard Gazette. Sky & Telescope, and The Conversation. His articles explore topics ranging from JWST discoveries to the philosophical dimensions of astrophysics. He has advised cultural projects like "The Black Hole Symphony" at the Boston Museum of Science. Pacucci has also delivered over 100 public outreach talks internationally.

Selected publications Pacucci et al. (2014), The X-ray Spectra of the First Galaxies: 21 cm Signatures, MNRAS, Volume 443, Issue 1, p.678-686. Pacucci et al. (2016), First Identification of Direct Collapse Black Hole Candidates in the Early Universe in CANDELS/GOODS-S, MNRAS, Volume 459, Issue 2, p. 1432-1439. Pacucci et al. (2023), JWST CEERS and JADES Active Galaxies at z = 4-7 Violate the Local M_BH-M_star Relation at >3sigma: Implications for Low-mass Black Holes and Seeding Models, ApJ Letters, Volume 957, Issue 1, id.L3, 10 pp. Pacucci & Loeb (2024), The Redshift Evolution of the M_BH–M_star Relation for JWST's Supermassive Black Holes at z > 4, ApJ, Volume 964, Issue 2, id.154, 7 pp. Pacucci & Narayan (2024), Mildly Super-Eddington Accretion onto Slowly Spinning Black Holes Explains the X-Ray Weakness of the Little Red Dots, ApJ, Volume 976, Issue 1, id.96, 14 pp. Pacucci, Ferrara & Kocevski, The Little Red Dots Are Direct Collapse Black Holes, submitted.