# Avi Loeb

Abraham "Avi" Loeb (Hebrew: אברהם (אבי) לייב; born February 26, 1962) is an Israeli and American theoretical physicist who works on astrophysics and cosmology. Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University, where since 2007 he has been Director of the Institute for Theory and Computation at the Center for Astrophysics. He chaired the Department of Astronomy from 2011 to 2020, and founded the Black Hole Initiative in 2016.
Loeb is a fellow of the American Academy of Arts and Sciences, the American Physical Society, and the International Academy of Astronautics. In 2015, he was appointed as the science theory director for the Breakthrough Initiatives of the Breakthrough Prize Foundation.
Loeb has published popular science books including Extraterrestrial: The First Sign of Intelligent Life Beyond Earth (2021) and Interstellar: The Search for Extraterrestrial Life and Our Future in the Stars (2023).
In 2018, he suggested that alien space craft may be in the Solar System, using ʻOumuamua as an example. In 2023, he claimed to have recovered material from an interstellar meteor that could be evidence of an alien starship, which some experts criticized as hasty and sensational, and for which other experts found more Earth-related explanations instead, demonstrating that the accuracy of one of the seismic sensors used by Loeb to locate the alleged interstellar meteor was compromised by interference from ordinary truck traffic.

## Life and career

Loeb was born in Beit Hanan, Israel, in 1962. He took part in the national Talpiot program of the Israeli Defense Forces at age 18. While in Talpiot, he obtained a BSc degree in physics and mathematics in 1983, an MSc degree in physics in 1985, and a PhD in physics in 1986, all from the Hebrew University of Jerusalem (HUJI). From 1983 to 1988, he led the first international project supported by the U.S. Strategic Defense Initiative. Between 1988 and 1993, Loeb was a long-term member at the Institute for Advanced Study at Princeton, where he started to work in theoretical astrophysics.
In 1993, he moved to Harvard University as an assistant professor in the department of astronomy, and was tenured three years later.
Loeb has written eight books, including textbooks How Did the First Stars and Galaxies Form? and The First Galaxies in the Universe. He has co-authored many papers on topics in astrophysics and cosmology, 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, the future collision between the Milky Way and Andromeda galaxies, the future state of extragalactic astronomy, astrophysical implications of black hole recoil in galaxy mergers, tidal disruption of stars, and imaging black hole silhouettes.
In 1992, Loeb and Andy Gould suggested that exoplanets could be detected through gravitational microlensing. In 1993, he proposed the use of the C+ fine-structure line to discover galaxies at high redshifts. In 2005, he predicted, in a series of papers with his postdoc Avery Broderick, how a hot spot in orbit around a black hole would appear; their predictions were confirmed in 2018 by the GRAVITY instrument on the Very Large Telescope which observed a circular motion of the centroid of light of the black hole at the center of the Milky Way, Sagittarius A*. 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, 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. In addition, a pulsar was discovered around the supermassive black hole Sagittarius A*, following a prediction by Pfahl and Loeb in 2004. Also, a hypervelocity star candidate from the Andromeda galaxy was discovered, as predicted by Sherwin, Loeb, and O'Leary in 2008. Together with his postdoc James Guillochon, Loeb predicted the existence of a new population of stars moving near the speed of light throughout the universe. 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*.
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. Loeb led a team that reported tentative evidence for the birth of a black hole in the young nearby supernova SN 1979C. In collaboration with Dan Maoz, Loeb demonstrated in 2013 that biomarkers, such as molecular oxygen (O $_2$), can be detected by the James Webb Space Telescope (JWST) in the atmosphere of Earth-mass planets in the habitable zone of white dwarfs.
In 2018, he served a term as chair of the Board on Physics and Astronomy (BPA) of the National Academies.

### Life in the universe

In a series of papers with his students and postdocs, Loeb addressed how and when the first stars and black holes formed and what effects they had on the young universe. In 2013, Loeb wrote about the "Habitable Epoch of the Early Universe". In April 2021, he presented an updated summary of his ideas of life in the early universe.
In 2020, Loeb published a paper about the possibility that life can propagate from one planet to another, followed by the opinion piece "Noah's Spaceship" about directed panspermia.
In 2024, Loeb delivered a speech in which he declared his view that the Messiah will be an alien who arrives from outer space.

### 'Oumuamua

In December 2017, Loeb cited ʻOumuamua's unusually elongated shape as one of the reasons the Green Bank Telescope in West Virginia should listen for radio emissions from it to see if there were any unexpected signs that it might be of artificial origin, although earlier limited observations by other radio telescopes such as the SETI Institute's Allen Telescope Array had produced no such results. The Green Bank Telescope observed the asteroid for six hours, detecting no radio signals.
On October 26, 2018, Loeb and his postdoctoral student Shmuel Bialy submitted a paper exploring the possibility that ʻOumuamua is an artificial thin solar sail accelerated by solar radiation pressure in an effort to help explain the object's non-gravitational acceleration. The consensus among other astrophysicists was that the available evidence is insufficient to consider such a premise, and that a tumbling solar sail would not be able to accelerate. In response, Loeb wrote an article detailing six anomalous properties of ʻOumuamua that make it unusual, unlike any comets or asteroids seen before.
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. They identified four candidates (2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6) for trapped interstellar objects that dedicated missions could visit. The authors pointed out that future sky surveys, such as with Large Synoptic Survey Telescope, could find many more.
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. On April 16, 2019, Loeb and Siraj reported the discovery of a meteor of interstellar origin. Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, a popular science account of ʻOumuamua by Loeb, was published in 2021. A followup book, Interstellar: The Search for Extraterrestrial Life and Our Future in the Stars, was published on August 29, 2023.

### The Galileo Project

In July 2021, Loeb founded The Galileo Project for the Systematic Scientific Search for Evidence of Extraterrestrial Technological Artifacts. 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. We now must 'dare to look through new telescopes', both literally and figuratively.
The three main avenues of research are:
* Obtaining high-resolution images of UAPs and discovering their nature
* Searching for and research of ʻOumuamua-like interstellar objects
* Searching for potential ETC satellites
Unlike other similar projects, the goal of the Galileo Project is to search for physical objects, and not electromagnetic signals, associated with extraterrestrial technological equipment. The project was covered by many independent publishers, among them Nature, Science, New York Post, Scientific American, The Guardian, etc. To allegations that studies of UFOs is pseudoscience, Loeb answers that the project aims not to study UFOs based on previous data, but to study Unidentified Aerial Phenomena "using the standard scientific method based on a transparent analysis of open scientific data to be collected using optimized instruments".

#### Interstellar Meteor IM1

In 2014 the US Department of Defense observed a fireball entering the atmosphere. Loeb made a series of claims about this event, from the meteor being from outside the solar system to its likely area of impact based on, among other things, a seismic signal that occurred around the same time, all culminating in 2023, when Loeb announced that he had found interstellar material on the ocean floor that he asserted came from the meteor and could be remnants of an extraterrestrial starship. These claims were criticized by other scientists as hasty, sensational, and part of a pattern of improper behavior. 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. Brown further said he was disturbed by Loeb's lack of engagement with relevant experts. In March 2022, the U.S. Space Force affirmed that their 2014 data indicated an interstellar origin, while the following month NASA stated the evidence for this was inconclusive.
Astrophysicist Steve Desch, at Arizona State University, commented "[Loeb's claims are] polluting good science—conflating the good science we do with this ridiculous sensationalism and sucking all the oxygen out of the room", and said several of his colleagues are consequently refusing to engage with Loeb in the peer review process. Monica Grady from the Open University argued that the evidence for Loeb's claims is "rather shaky" and pointed more plausibly to terrestrial pollution. Patricio A. Gallardo in an American Astronomical Society paper similarly concluded the samples were consistent with coal ash contamination. Loeb and collaborators subsequently published two papers saying chemical analysis ruled out coal ash contamination and indicated extrasolar origins. Loeb and Morgan MacLeod proposed a tidal disruption mechanism that could cause meteors to be ejected into trajectories leading to the described observations. In 2024 planetary seismologist Benjamin Fernando led a team that analyzed the seismic signals that lead Loeb to search that specific region of the ocean, and they concluded that the seismic signals from one of the sensors used was in fact caused not by a meteor, but by a truck driving near the sensor, and that this may have increased the uncertainty about the location of the meteor site.

## Media appearances

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. In 2008, he was featured in a Smithsonian magazine cover story on black holes, and in two Astronomy magazine cover stories, one on the collision between the Milky Way and the Andromeda Galaxy and the second on the future state of our universe. In 2009, Loeb reviewed in a Scientific American article a new technique for imaging black hole silhouettes. Loeb received considerable media attention after proposing in 2011 (with E.L. Turner) a new technique for detecting artificially-illuminated objects in the Solar System and beyond, 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.
He has been profiled a number of times, including in Science magazine, Discover, and The New York Times. He has been interviewed by Astronomy magazine, by Lex Fridman, Joe Rogan, and Mick West, and by the H3 Podcast. On August 24, 2023, The New York Times published an article about Loeb and his search for signs of extraterrestrial life.
Loeb also regularly writes opinion essays on science and policy.

## Honors and awards

Loeb has received many honors, including:
* 1987 – The Kennedy Prize of the Hebrew University of Jerusalem
* 2002 – Guggenheim Fellowship
* 2004 – Distinguished Visiting Professorship at the Faculty of Physics & Einstein Center for Theoretical Physics of the Weizmann Institute of Science
* 2006/7 – John Bahcall Lecturer at the Tel Aviv University
* 2006 – Salpeter Lectureship at Cornell University
* 2012 – Time magazine's 25 most influential people in space.
* 2012 – Elected member of the American Academy of Arts and Sciences
* 2012 – Galileo Galilei Chair (Cattedra Galileiana) Award of the Scuola Normale Superiore, Pisa, Italy
* 2013 – Chambliss Astronomical Writing Award from the American Astronomical Society, for the book How Did the First Stars and Galaxies Form? (2010)
* 2014 – Member of the Board on Physics and Astronomy (BPA) of the National Academies of Sciences, Engineering, and Medicine
* 2015 – Elected Fellow of the International Academy of Astronautics (IAA) SETI Permanent Committee
* 2015 – Elected Member of the American Physical Society (APS)
* 2020 – Appointed to the President's Council of Advisors on Science and Technology