Abraham "Avi" Loeb (Hebrew: אברהם (אבי) לייב; born February 26, 1962) is an Israeli and American theoretical physicist who works on astrophysics and cosmology.

[16] He has co-authored many papers on topics in astrophysics and cosmology,[2][5] including the first stars, the epoch of reionization, the formation and evolution of massive black holes, the search for extraterrestrial life, gravitational lensing by planets, gamma-ray bursts at high redshifts, the use of the Lyman-alpha forest to measure the acceleration/deceleration of the universe in real time,[17] the future collision between the Milky Way and Andromeda galaxies,[18] the future state of extragalactic astronomy,[19] astrophysical implications of black hole recoil in galaxy mergers,[20] tidal disruption of stars,[21] and imaging black hole silhouettes.

In 2009, Broderick and Loeb predicted the shadow of the black hole in the giant elliptical galaxy Messier 87, which was imaged in 2019 by the Event Horizon Telescope.

In 2013, a report was published on the discovery of the "Einstein Planet" Kepler-76b,[23] the first Jupiter-size exoplanet identified by detecting the relativistic beaming of its parent star, based on a technique Loeb and Gaudi proposed in 2003.

[29] Together with his postdoc John Forbes and Howard Chen of Northwestern University, Loeb made another prediction that sub-Neptune-sized exoplanets have been transformed into rocky super-Earths by the activity of Sagittarius A*.

[30] Together with Paolo Pani, Loeb showed in 2013 that primordial black holes in the range between the masses of the Moon and the Sun cannot make up dark matter.

[32] In collaboration with Dan Maoz, Loeb demonstrated in 2013 that biomarkers, such as molecular oxygen (O2), can be detected by the James Webb Space Telescope (JWST) in the atmosphere of Earth-mass planets in the habitable zone of white dwarfs.

[53][54] On November 27, 2018, Loeb and Amir Siraj, a Harvard undergraduate, proposed a search for ʻOumuamua-like objects that might be trapped in the Solar System as a result of losing orbital energy through a close encounter with Jupiter.

[56] In public interviews and private communications with reporters and academic colleagues, Loeb has become more vocal about the prospects of proving the existence of alien life.

[66][67] The project was inspired by the detection of ʻOumuamua and by release of the Office of the Director of National Intelligence report on Unidentified Aerial Phenomena (UAP).

As stated on the project's website, the aim is: Given the recently discovered abundance of Earth-Sun systems, the Galileo Project is dedicated to the proposition that humans can no longer ignore the possible existence of Extraterrestrial Technological Civilizations (ETCs), and that science should not dogmatically reject potential extraterrestrial explanations because of social stigma or cultural preferences, factors which are not conducive to the scientific method of unbiased, empirical inquiry.

Peter Brown, a meteor physicist at the University of Western Ontario, argued the material can be explained as non-interstellar, noting that measurements from Defense Department data are opaque and error-prone.

[72] Patricio A. Gallardo in an American Astronomical Society paper similarly concluded the samples were consistent with coal ash contamination.

[80] In 2006, Loeb was featured in a Time magazine cover story on the first stars, and in a Scientific American article on the Dark Ages of the universe.

Loeb received considerable media attention[81] after proposing in 2011 (with E.L. Turner) a new technique for detecting artificially-illuminated objects in the Solar System and beyond,[82] and showing in 2012 (with I. Ginsburg) that planets may transit hypervelocity stars or get kicked to a fraction of the speed of light near the black hole at the center of the Milky Way.