Abraham "Avi" Loeb (Hebrew: אברהם (אבי) לייב) is an Israeli American theoretical physicist who works on astrophysics and cosmology. Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University. He serves as Chair of the Harvard Astronomy department (since 2011), Chair of the Advisory Committee for the Breakthrough Starshot project – which aims to launch lightweight spacecraft towards the nearest stars using a powerful laser (since 2016), founding director of Harvard's Black Hole Initiative – the first interdisciplinary center worldwide dedicated to the study of black holes  (since 2016), and director of the Institute for Theory and Computation (ITC) (since 2007) within the Harvard-Smithsonian Center for Astrophysics.
Loeb is an elected fellow of the American Academy of Arts and Sciences, the American Physical Society, and the International Academy of Astronautics. As of July 2018, he was appointed as chair of the Board on Physics and Astronomy (BPA) of the National Academies, which is the Academies' principal forum for issues connected with the fields of Physics and Astronomy including oversight of their decadal surveys. In December 2012, TIME magazine selected Loeb as one of the 25 most influential people in space. In 2015, Loeb was appointed as the Science Theory Director for the Breakthrough Initiatives of the Breakthrough Prize Foundation. In 2018, he attracted media attention for suggesting that alien space craft may be in our solar system, using the anomalous behavior of 'Oumuamua as an example. In 2019, Loeb reported together with his Harvard undergraduate student, Amir Siraj, the first discovery of a meteor that originated outside the Solar System.
Loeb was born in Beit Hanan, Israel in 1962 and took part in the national Talpiot program before receiving a graduate degree in plasma physics at age 24 from the Hebrew University in Jerusalem. Between 1988 and 1993, Loeb was a long-term member at the Institute for Advanced Study in 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, where he was tenured three years later.
Loeb has published nearly seven hundred papers on a broad range of research areas 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 (GRBs) at high redshifts, 21-cm cosmology, the use of the Lyman-alpha forest to measure the acceleration/deceleration of the universe in real time (the so-called "Sandage–Loeb test"), 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. Some of his papers (e.g., on planet microlensing, and 21-cm cosmology) are considered as pioneering in areas that have become by now the focus of established communities of astrophysicists.
Several of Loeb's early predictions were confirmed in recent years. In 1992, he suggested with Andy Gould that exoplanets could be detected through gravitational microlensing, a technique that is routinely used these days. In 1993, he proposed the use of the C+ fine-structure line to discover galaxies at high redshifts, as done routinely now. In 2005, he predicted in a series of papers with his postdoc at the time, 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 VLT which observed a circular motion of the centroid of light of the black hole at the center of the Milky Way, SgrA*. In 2009, Broderick and Loeb predicted the shadow of the black hole in the giant elliptical galaxy M87, 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 through the detection of relativistic beaming of its parent star, based on a technique proposed by Loeb and Gaudi in 2003. In addition, a pulsar was discovered around the supermassive black hole, SgrA*, 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 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 the dark matter, another result reported in TIME magazine.
He led a team that discovered tentative evidence for the birth of a black hole in the young nearby supernova SN1979C.
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) over the next decade in the atmosphere of Earth-mass planets in the habitable zone of white dwarfs.
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 Milky Way's central supermassive black-hole Sagittarius A*.
Loeb was among the very first theorists to trigger the research frontier on the "cosmic dawn" of the first stars and galaxies. In a series of papers with his students and postdocs, he addressed how and when the first stars and black holes formed and what effects they had on the young universe.
Together with his former student Steve Furlanetto (currently a professor at UCLA), Loeb published in December 2012 an extensive textbook entitled "The First Galaxies in the Universe".. He is currently writing a textbook on "Extraterrestrial Life: From Bio-Signatures to Techno-Signatures" with his postdoc, Manasvi Lingam, to be published by Harvard University Press.
In 2013, Loeb introduced the new concept of "The Habitable Epoch of the Early Universe", and mentored Harvard undergraduate, Henry Lin, in the study of industrial pollution on exoplanets as a new method to search for extraterrestrial civilizations.
In December 2017, Loeb cited ʻOumuamua's unusually elongated shape as one of the reasons why the Green Bank Telescope in West Virginia would 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. On 13 December 2017, the Green Bank Telescope observed the asteroid for six hours across four bands of radio frequency. No radio signals from ʻOumuamua were detected in this very limited scanning range, but observations are ongoing.
On 26 October 2018, Loeb and his postdoc Shmuel Bialy submitted a paper exploring the possibility of the interstellar object ʻOumuamua being an artificial thin solar sail accelerated by solar radiation pressure in an effort to help explain the object's non-gravitational acceleration. Other scientists have stated 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 `Oumuamua that make it unusual, unlike any comets or asteroids seen before.
On 27 November 2018, Loeb and his undergraduate student at Harvard College, Amir Siraj, proposed a search for `Oumuamua-like objects which are trapped in the Solar System as a result of losing orbital energy through a close encounter with Jupiter. They identified 4 candidates for trapped interstellar objects that could be visited by dedicated missions (2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6). The authors pointed out that future sky surveys, such as with LSST, should find many more.
In public interviews and private communications with reporters and academic colleagues, Loeb has become increasingly vocal regarding the prospects of proving the existence of alien life.
On April 16, 2019, Loeb and his undergraduate student, Amir Siraj, reported the discovery of the first meteor of interstellar origin.  This discovery pioneers a new path for studying the composition and nature of interstellar objects.
In 2006, Loeb was featured in a cover story of TIME magazine on the first stars and in a Scientific American article on the Dark Ages of the universe. In 2008, he was featured in a cover story of Smithsonian magazine on black holes and in two cover stories of Astronomy Magazine, 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. In 2010 he wrote a textbook entitled "How Did the First Stars and Galaxies Form?", published by Princeton University Press. In the same year, Loeb wrote an article encouraging young researchers to be creative. 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.
Science magazine published a detailed article about Loeb's career in April 2013, and Discover magazine reviewed his pioneering research on the first stars in April 2014. The New York Times published a science profile of Loeb in December 2014. In May 2015, Astronomy magazine posted a podcast of an hour-long interview with Loeb in its series entitled "Superstars of Astronomy". In April 2016, Stephen Hawking visited Loeb's home and attended the inaugurations of the Starshot and Black Hole Initiatives that Loeb leads.
Loeb's latest eBook on Kindle details his career path from childhood on a farm with interests in philosophy to chairing the Harvard Astronomy department and directing the ITC, and includes opinion essays on the importance of taking risks in research and promoting diversity. Loeb regularly writes timely opinion essays on science and policy.
Honors and awards
Loeb has received many honors, including the Kennedy Prize in 1987, the Guggenheim Fellowship in 2002, the Salpeter Lectureship at Cornell University in 2006, the Bahcall Lectureship at Tel Aviv University in 2006, the Merle Kingsley Lectureship at Caltech in 2007, the Australian Institute of Physics Lectureship at the University of Melbourne in 2007, the Distinguished Visiting Lectureship at the Carnegie Observatories in 2009, the Las Cumbres Observatory Lectureship at Santa Barbara in 2011, the Sackler Lectureship at Leiden Observatory in 2011, the Galileo Galilei Chair ("Cattedra Galileiana") for 2011–12 from Scuola Normale Superiore in Pisa, Italy, and the Miegunyah Distinguished Visiting Fellowship for 2013 at the University of Melbourne in Australia.
For over two decades he held a visiting professorship at the Weizmann Institute of Science, and since 2011 he was awarded a Sackler Professorship by special appointment in the School of Physics and Astronomy at Tel Aviv University. In 2012 Loeb was elected as a member of the American Academy of Arts and Sciences. In 2013, he was awarded the Chambliss Astronomical Writing Award by the American Astronomical Society for the book he published in 2010.
- "Department of Astronomy". Astronomy.fas.harvard.edu. Retrieved 2016-02-19.
- "Breakthrough Starshot". breakthroughinitiatives.org/Leaders/3/. Retrieved 2016-04-12.
- "Black Hole Initiative". bhi.fas.harvard.edu/. Retrieved 2016-04-21.
- "Institute for Theory and Computation - Harvard-Smithsonian Center for Astrophysics". cfa.harvard.edu. Retrieved 2016-02-19.
- "BPA". nationalacademies.org. Retrieved 2016-09-07.
- David Bjerklie. "The 25 Most Influential People in Space" (PDF). cfa.harvard.edu. Retrieved 2016-02-19.
- Groll, Johan (7 January 2019). "Thinking About Distant Civilizations Isn't Speculative". derSpiegel. Retrieved 7 January 2019.
- Siraj, A. and, Loeb, A. (16 April 2019). "Discovery of a Meteor of Interstellar Origin" (PDF). ApJL. Retrieved 16 April 2019.
- Abraham Loeb (1998). "DIRECT MEASUREMENT OF COSMOLOGICAL PARAMETERS FROM THE COSMIC DECELERATION OF EXTRAGALACTIC OBJECTS" (PDF). The Astrophysical Journal. 499: L111/L114. arXiv:astro-ph/9802122. Bibcode:1998ApJ...499L.111L. doi:10.1086/311375. Retrieved 2016-02-19.
- "The collision between the Milky Way and Andromeda". Monthly Notices of the Royal Astronomical Society. 386: 461–474. 2008. arXiv:0705.1170. Bibcode:2008MNRAS.386..461C. doi:10.1111/j.1365-2966.2008.13048.x.
- "Long-term future of extragalactic astronomy". Physical Review D. 65: 47301. 2002. arXiv:astro-ph/0107568. Bibcode:2002PhRvD..65d7301L. doi:10.1103/PhysRevD.65.047301.
- "Recoiled star clusters in the Milky Way halo: N-body simulations and a candidate search through the SDSS". Monthly Notices of the Royal Astronomical Society. 421: 2737–2750. 2012. arXiv:1102.3695. Bibcode:2012MNRAS.421.2737O. doi:10.1111/j.1365-2966.2011.20078.x.
- Stone, N; Loeb, A (2012). "Observing Lense-Thirring Precession in Tidal Disruption Flares". Physical Review Letters. 108: 61302. arXiv:1109.6660. Bibcode:2012PhRvL.108f1302S. doi:10.1103/PhysRevLett.108.061302. PMID 22401052.
- "Testing General Relativity with High-Resolution Imaging of Sgr A*". Journal of Physics: Conference Series. 54: 448–455. 2006. arXiv:astro-ph/0607279. Bibcode:2006JPhCS..54..448B. doi:10.1088/1742-6596/54/1/070.
- "Discovering planetary systems through gravitational microlenses". The Astrophysical Journal. 396: 104. 1992. Bibcode:1992ApJ...396..104G. doi:10.1086/171700.
- "Expected Number and Flux Distribution of Gamma‐Ray Burst Afterglows with High Redshifts". The Astrophysical Journal. 540: 687–696. arXiv:astro-ph/0002412. Bibcode:2000ApJ...540..687C. doi:10.1086/309384.
- Loeb, Abraham; Zaldarriaga, Matias (25 May 2004). "Measuring the Small-Scale Power Spectrum of Cosmic Density Fluctuations through 21 cm Tomography Prior to the Epoch of Structure Formation". Physical Review Letters. 92 (21): 211301. arXiv:astro-ph/0312134. Bibcode:2004PhRvL..92u1301L. doi:10.1103/PhysRevLett.92.211301. PMID 15245272.
- Faigler, S.; Tal-Or, L.; Mazeh, T.; Latham, D. W.; Buchhave, L. A. (1 July 2013). "BEER Analysis of Kepler and CoRoT Light Curves. I. Discovery of Kepler-76b: A Hot Jupiter with Evidence for Superrotation". The Astrophysical Journal. 771 (1): 26. arXiv:1304.6841. Bibcode:2013ApJ...771...26F. doi:10.1088/0004-637X/771/1/26.
- Abraham Loeb; B. Scott Gaudi (2003). "PERIODIC FLUX VARIABILITY OF STARS DUE TO THE REFLEX DOPPLER EFFECT INDUCED BY PLANETRY COMPANIONS" (PDF). The Astrophysical Journal. 588: L117–L120. arXiv:astro-ph/0303212. Bibcode:2003ApJ...588L.117L. doi:10.1086/375551. Retrieved 2016-02-19.
- "A Strongly Magnetized Pulsar within the Grasp of the Milky Way's Supermassive Black Hole". The Astrophysical Journal. 775: L34. 2013. arXiv:1307.6331. Bibcode:2013ApJ...775L..34R. doi:10.1088/2041-8205/775/2/L34.
- Eric Pfahl; Abraham Loeb (2004). "PROBING THE SPACETIME AROUND SAGITTARIUS A* WITH RADIO PULSARS" (PDF). The Astrophysical Journal. 615: 253–258. arXiv:astro-ph/0309744. Bibcode:2004ApJ...615..253P. doi:10.1086/423975. Retrieved 2016-02-19.
- "Hypervelocity Star Candidates in the SEGUE G and K Dwarf Sample". The Astrophysical Journal. 780: 7. 2014. arXiv:1308.3495. Bibcode:2014ApJ...780....7P. doi:10.1088/0004-637X/780/1/7.
- Blake D. Sherwin; Abraham Loeb; Ryan M. O'Leary (2008). "Hypervelocity stars from the Andromeda galaxy". Monthly Notices of the Royal Astronomical Society. 386: 1179–1191. arXiv:0709.1156. Bibcode:2008MNRAS.386.1179S. doi:10.111/j.1365-2966.2008.13097.x.
- "The Mystery of Dark Matter Clarified—a Little". Time. 5 September 2013.
- "Supernova Shines Light On Black Hole Formation". NPR.org. Retrieved 2016-02-19.
- "Could Tiny Stars Be Home to Mirror Earths?". Time. 6 March 2013.
- Lemonick, Michael D. (26 November 2014). "You've Heard of Shooting Stars, But This is Ridiculous". Time.
- Howard Chen; John C. Forbes; Abraham Loeb (2018). "Habitable Evaporated Cores and the Occurrence of Panspermia Near the Galactic Center" (PDF). The Astrophysical Journal Letters. 855: L1. arXiv:1711.06692. Bibcode:2018ApJ...855L...1C. doi:10.3847/2041-8213/aaab46. Retrieved 2018-03-01.
- ""The First Galaxies in the Universe" by Loeb and Furlanetto". Cfa.harvard.edu. Retrieved 2016-02-19.
- Loeb, Abraham (9 September 2014). "The habitable epoch of the early Universe". International Journal of Astrobiology. 13 (04): 337–339. arXiv:1312.0613. Bibcode:2014IJAsB..13..337L. doi:10.1017/S1473550414000196.
- Adam Frank. "First Life In The Universe : 13.7: Cosmos And Culture". NPR.org. Retrieved 2016-02-19.
- Lemonick, Michael D. (24 July 2014). "The Search for Extraterrestrial Air Pollution". Time.
- Ian Sample (11 December 2017). "Astronomers to check interstellar body for signs of alien technology". The Guardian. Retrieved 12 December 2017.
Green Bank telescope in West Virginia will listen for radio signals from ʻOumuamua, an object from another solar system ... "Most likely it is of natural origin, but because it is so peculiar, we would like to check if it has any sign of artificial origin, such as radio emissions," said Avi Loeb, professor of astronomy at Harvard University and an adviser to the Breakthrough Listen project. "If we do detect a signal that appears artificial in origin, we’ll know immediately." ... While many astronomers believe the object is an interstellar asteroid, its elongated shape is unlike anything seen in the asteroid belt in our own solar system. Early observations of ʻOumuamua show that it is about 400m long but only one tenth as wide. "It's curious that the first object we see from outside the solar system looks like that," said Loeb.
- Billings, Lee (11 December 2017). "Alien Probe or Galactic Driftwood? SETI Tunes In to ʻOumuamua". Scientific American. Retrieved 12 December 2017.
So far limited observations of ‘Oumuamua, using facilities such as the SETI Institute’s Allen Telescope Array, have turned up nothing.
- "Breakthrough Listen Releases Initial Results and Data from Observations of 'Oumuamua". Breakthrough Listen. 13 December 2017. Retrieved 15 December 2017.
No evidence of artificial signals emanating from the object so far detected by the Green Bank Telescope, but monitoring and analysis continue. Initial data are available for public inspection in the Breakthrough Listen archive
- Ian Sample (15 December 2017). "Is 'Oumuamua an alien spacecraft? Initial scans show no signs of technology". The Guardian. Retrieved 15 December 2017.
- Williams, Matt (2 November 2018). "Could Oumuamua Be an Extra-Terrestrial Solar Sail?". Universe Today. Retrieved 2 November 2018.
- Bialy, Shmuel; Loeb, Abraham (26 October 2018). "Could Solar Radiation Explain ʻOumuamua's Peculiar Acceleration?". arXiv:1810.11490v4 [astro-ph.EP].
- Loeb, Abraham (26 September 2018). "How to Search for Dead Cosmic Civilizations". Scientific American. Retrieved 26 September 2018.
- Scientists push back against Harvard 'alien spacecraft' theory. Kerry Sheridan, PhysOrg. 7 November 2018.
- Boyle, Alan (2018-11-06). "'Oumuamua, oh my! Was interstellar object actually an alien solar sail? Not so fast". Yahoo!. Retrieved 2018-11-08.
- Schadwinkel, Alina (2018-11-08). "Glaubt dieser Harvard-Professor selbst, was er sagt?". Zeit Online. Retrieved 2018-11-08.
- Cigar-shaped interstellar object may have been an alien probe, Harvard paper claims. CNN News. 6 November 2018.
- Koren, Marina (23 January 2019). "When a Harvard Professor Talks About Aliens - News about extraterrestrial life sounds better coming from an expert at a high-prestige institution". The Atlantic. Retrieved 23 January 2019.
- Loeb, Abraham (20 November 2018). "6 Strange Facts about the Interstellar Visitor 'Oumuamua". Scientific American. Retrieved 20 November 2018.
- Chotiner, Isaac (16 January 2019). "Have Aliens Found Us? A Harvard Astronomer on the Mysterious Interstellar Object 'Oumuamua". The New Yorker. Retrieved 16 January 2019.
- Siraj, Amir; Loeb, Abraham (27 November 2018). "Identifying Interstellar Objects Trapped in the Solar System through Their Orbital Paramteters". arXiv:1811.09632v2 [astro-ph.EP].
- Siraj, Amir; Loeb, Abraham (29 November 2018). "Identifying Interstellar Objects Trapped in the Solar System through Their Orbital Parameters" (PDF). Monthly Notices of the Royal Astronomical Society. 000: 1–5. Retrieved 1 December 2018.
- Post, The Washington. "Harvard's top astronomer says an alien ship may be among us". nola.com. Retrieved 2019-02-05.
- "How Did the First Stars and Galaxies Form?" book jacket (pdf)
- "Loeb, A.: How Did the First Stars and Galaxies Form? (eBook and Paperback)". Press.princeton.edu. 2016-02-08. Retrieved 2016-02-19.
- Abraham Loeb (2010-08-09). "Taking "The Road Not Taken": On the Benefits of Diversifying Your Academic Portfolio". arXiv:1008.1586 [astro-ph.IM].
- "Breaking News, Analysis, Politics, Blogs, News Photos, Video, Tech Reviews - TIME.com". Time. 10 November 2011.
- Loeb, Abraham; Turner, Edwin L. (April 2012). "Detection Technique for Artificially Illuminated Objects in the Outer Solar System and Beyond". Astrobiology. 12 (4): 290–294. arXiv:1110.6181. Bibcode:2012AsBio..12..290L. doi:10.1089/ast.2011.0758.
- Ginsburg, Idan; Loeb, Abraham; Wegner, Gary A. (11 June 2012). "Hypervelocity planets and transits around hypervelocity stars". Monthly Notices of the Royal Astronomical Society. 423 (1): 948–954. arXiv:1201.1446. Bibcode:2012MNRAS.423..948G. doi:10.1111/j.1365-2966.2012.20930.x.
- Avi Loeb. "NewsFocus : From Cosmic Dawn to Milkomedia, and beyond" (PDF). Cfa.harvard.edu. Retrieved 2016-02-19.
- Steve Nadis. "First" (PDF). Cfa.harvard.edu. Retrieved 2016-02-19.
- Dreifus, Claudia (2 December 2014). "Much-Discussed Views That Go Way Back - Avi Loeb Ponders the Early Universe, Nature and Life". The New York Times. Retrieved 3 December 2014.
- "Abraham Loeb: From cosmic origins to our galaxy's fate". Astronomy.com. 2015-05-06. Retrieved 2016-02-19.
- "Last Visit of Stephen Hawking to the US in April 2016". cfa.harvard.edu/~loeb/SI.html. 2018-03-16. Retrieved 2018-03-16.
- "From the First Star to Milkomeda, Abraham Loeb, Dror Burstein, Todd Hasak-Lowy, Noa Moav". Amazon.com. Retrieved 2016-02-19.
- "Opinion Essays by Abraham Loeb". cfa.harvard.edu~/loeb/Opinion.html. 2018-03-18. Retrieved 2018-03-18.
- Avi Loeb's home page
- Loeb's recent preprints
- Loeb's published papers
- "Scientific American article on "Portrait of a Black Hole"" (PDF). (393 KB)
- "Scientific American article on "The Dark Ages of the Universe"" (PDF). (393 KB)
- "ASTRONOMY magazine article on "The State of the Universe"" (PDF). (5.72 MB)
- "Smithsonian Magazine cover story on "Homing In on Black Holes"" (PDF). (2.65 MB)
- "ASTRONOMY Magazine cover story on "Milkomeda"" (PDF). (853 KB)
- "TIME Magazine cover story, entitled: "Let There Be Light"" (PDF). (51.5 MB)
- Future Collision of the Milky Way and Andromeda
- An introductory movie to Loeb's book