Lewin's contributions in astrophysics include the first discovery of a rotating neutron star through all-sky balloon surveys and research in X-ray detection in investigations through satellites and observatories. Lewin has received awards for teaching and is known for his lectures on physics and their publication online via YouTube, MIT OpenCourseWare and edX.
In December 2014, MIT revoked Lewin's Professor Emeritus title after an MIT investigation determined that Lewin had violated university policy by sexually harassing an online student in a MITx course he taught in fall 2013.[1][2][3]
Early life and education
Lewin was born to Walter Simon Lewin and Pieternella Johanna van der Tang in 1936 in The Hague, Netherlands. He was a child when Nazi Germany occupied The Netherlands during World War II.[4] His paternal grandparents Gustav and Emma Lewin, who were Jewish, died in Auschwitz in 1942.[5][6] To protect the family, Lewin’s father — who was Jewish, unlike his mother — decided one day to simply leave without telling anyone. His mother was left to raise the children and run a small school she and her husband had started together. After the war ended, his father resurfaced; Lewin describes having a “more or less normal childhood.” His parents continued running the school, which he says strongly influenced his love of teaching.[4][7]
At MIT, Lewin joined the X-ray astronomy group and conducted all-sky balloon surveys with George W. Clark. Through the late seventies, there were about twenty successful balloon flights. These balloon surveys led to the discovery of five new X-ray sources, whose spectra were very different from the X-ray sources discovered during rocket observations. The X-ray flux of these sources was variable. Among them was GX 1+4 whose X-ray flux appeared to be periodic with a period of about 2.4 minutes. This was the first discovery of a slowly rotating neutron star.[9]
In October 1967 when Scorpius X-1 was observed, an X-ray flare was detected. The flux went up by a factor of about 4 in ten minutes after which it declined again. This was the first detection of X-ray variability observed during the observations. The rockets used by other researchers could not have discovered that the X-ray sources varied on such short time scales because they were only up for several minutes, whereas the balloons could be in the air for many hours.[10]
Lewin was co-investigator on the Small Astronomy Satellite 3 (SAS-3) project. He directed the burst observations and discovered several X-ray bursters, among them was the rapid burster[11] which can produce thousands of X-ray bursts in one day. His group also discovered that the rapid burster produces two types of bursts and established a classification of bursts as type I (thermonuclear flashes) and type II (accretion flow instabilities).[12]
Lewin was co-principal investigator on High Energy Astronomy Observatory 1 HEAO-1 (A4), which has yielded the first all sky catalog at high-energy X rays. With H. Pedersen and J. van Paradijs, Lewin made extensive studies of optical bursts which are associated with X-ray bursts; for X-ray detections they used SAS-3 and the Japanese observatory "Hakucho". Their combined burst observations demonstrated that the optical bursts are a few seconds delayed relative to the X-ray bursts. This established the size of the accretion disc surrounding the accreting neutron stars.
In his search for millisecond X-ray pulsations from low-mass X-ray binaries, in 1984–85 Lewin made guest observations with the European observatory EXOSAT in collaboration with colleagues from Amsterdam and Garching, Germany. This led to the unexpected discovery of intensity-dependent quasi-periodic oscillations (QPO) in the X-ray flux of GX 5-1. During 1989 to 1992, using the Japanese observatory "Ginga", Lewin and his co-workers studied the relation between the X-ray spectral state and the radio brightness of several bright low-mass X-ray binaries.[13]
Lewin was closely involved in ROSAT observations of the nearby galaxies M31 and Messier 81. Lewin and his graduate student Eugene Magnier have made deep optical charge-coupled device observations of M31 in four colors; they have published a catalogue of 500,000 objects. Lewin and his graduate student David Pooley initiated the successful X-ray observations within six days of the appearance of supernova SN 1993J in M81.
Lewin and graduate student Jeffrey Kommers have worked on data from the Compton Gamma Ray Observatory (GRO). This was a collaboration with the BATSE Group[17] in Huntsville, AL. In early December 1995, with co-workers Chryssa Kouveliotou and Van Paradijs, they discovered a new type of X-ray burst source: (GRO J1744-28) the Bursting Pulsar, and received a NASA Achievement Award for this discovery.
In 1996–1998, Lewin's collaboration with Michiel van der Klis in Amsterdam led to the discovery of kHz oscillations in many X-ray binaries.
2003 – MIT Everett Moore Baker Memorial Award for Excellence in Undergraduate Teaching[20]
2011 – first recipient of the Educator Award for OpenCourseWare Excellence (ACE)[21]
On April 3, 2012, Lewin was ranked by the Princeton Review among "The Best 300". He was the only MIT faculty member (albeit, retired) to make it to that list.[22][23]
Lectures
Lewin with a blackboard
For about 15 years (starting in 1982) Lewin presented a one-hour program weekly on MIT Cable TV. The shows were aired 24 hours per day helping freshmen with their weekly homework assignments. Videos of Lewin's lectures on Newtonian mechanics (1999), electricity and magnetism (2002) and the physics of vibrations and waves (2004), among others, could be viewed on the MIT OpenCourseWare web site until MIT removed them after finding that Lewin had sexually harassed a student in the online course.[3]
Since February 2015, Lewin has been running and managing his own YouTube channel called "Lectures by Walter Lewin. They will make you ♥ Physics".[24] Several of his lectures have been viewed more than a million times. His 2011 farewell lecture "For the Love of Physics" has been viewed around 15 million times - 1 million times on MIT's OCW, 6.9 million times on the channel "For the Allure of Physics" [25] and 6.9 million times on his personal channel.[26] In 2007, The New York Times featured Lewin on the front page, talking about his influence on online education.[27]
In the summer of 2012, Lewin returned from his retirement to deliver a lecture series initiated and funded by the Japanese Broadcasting Corporation (NHK).[28] Each lecture features a selection of physics demonstrations that Lewin has used in his lectures at MIT. The lectures consist of eight TV programs that were broadcast in Japanese on NHK in Japan in 2013. As of 2015, a region 2 DVD box set of this series is available in Japanese, with an optional partial English audio track and English subtitles.[29]
Sexual harassment
In early December 2014, MIT determined that Lewin had sexually harassed an online MITx learner, in violation of MIT's policies.[1]Inside Higher Ed reported that this learner was one of at least 10 female students to whom Lewin had sent inappropriate messages, which MIT confirmed.[30] The victim, a 32-year-old woman living in France, said that she came forward to ensure that the case was not forgotten, stating that Lewin pushed her to participate in sexual role-playing and send naked pictures of herself.[30] As a consequence of its internal investigation, MIT revoked Lewin's professor emeritus title,[2] and removed his lectures from the institute's online learning platforms.[31]
Lewin, Walter; van der Klis, Michiel, eds. (2006). Compact stellar X-ray sources. Cambridge University Press. ISBN978-0-521-82659-4.
Lewin, Walter H.G.; van Paradijs, Jan; van den Heuvel, Edward P.J., eds. (1995). X-ray binaries. Cambridge University Press. ISBN978-0-521-41684-9.
Truemper, J.; Lewin, W.H.G.; Brinkmann, W., eds. (1986). The evolution of galactic X-ray binaries. D. Reidel Pub. Co.; Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers. ISBN978-90-277-2184-6.
Lewin, Walter H.G.; van den Heuvel, Edward, eds. (1983). Accretion-driven stellar X-ray sources. Cambridge University Press. ISBN0-521-24521-4.
Selected publications
Lewin has published about 450 scientific articles,[16] below are a selected[how?] few.
J. Miller; A. Fabian; R. Wijnands; R. Remillard; P. Wojdowski; N. Schulz; etal. (2002). "Resolving the Composite Fe K-alpha Emission Line in the Galactic Black Hole Cygnus X-1 with Chandra". Astrophysical Journal. 578 (1): 348–356. arXiv:astro-ph/0202083. Bibcode:2002ApJ...578..348M. doi:10.1086/342466. S2CID119393282.
D. Pooley; W. Lewin; L. Homer; S. Anderson; B. Gaensler; B. Margon; etal. (2002). "Optical Identifications of Multiple Faint X-ray Sources in the Globular Cluster NGC~6752: Evidence for Numerous Cataclysmic Variables". Astrophysical Journal. 569 (1): 405. arXiv:astro-ph/0110192. Bibcode:2002ApJ...569..405P. doi:10.1086/339210. S2CID12626024.
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic events occurring in distant galaxies which represent the brightest and "most powerful class of explosion in the universe." These extreme electromagnetic events are second only to the Big Bang as the most energetic and luminous phenomenon ever known. Gamma-ray bursts can last from a few milliseconds to several hours. After the initial flash of gamma rays, a longer-lived §afterglow is emitted, usually in the longer wavelengths of X-ray, ultraviolet, optical, infrared, microwave or radio frequencies.
Cygnus X-1 (abbreviated Cyg X-1) is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole. It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources detectable from Earth, producing a peak X-ray flux density of 2.3×10−23 W/(m2⋅Hz) (2.3×103 jansky). It remains among the most studied astronomical objects in its class. The compact object is now estimated to have a mass about 21.2 times the mass of the Sun and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole. If so, the radius of its event horizon has 300 km "as upper bound to the linear dimension of the source region" of occasional X-ray bursts lasting only for about 1 ms.
X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the donor, to the other component, called the accretor, which is either a neutron star or black hole. The infalling matter releases gravitational potential energy, up to 30 percent of its rest mass, as X-rays. The lifetime and the mass-transfer rate in an X-ray binary depends on the evolutionary status of the donor star, the mass ratio between the stellar components, and their orbital separation.
X-ray bursters are one class of X-ray binary stars exhibiting X-ray bursts, periodic and rapid increases in luminosity that peak in the X-ray region of the electromagnetic spectrum. These astrophysical systems are composed of an accreting neutron star and a main sequence companion 'donor' star. There are two types of X-ray bursts, designated I and II. Type I bursts are caused by thermonuclear runaway, while type II arise from the release of gravitational (potential) energy liberated through accretion. For type I (thermonuclear) bursts, the mass transferred from the donor star accumulates on the surface of the neutron star until it ignites and fuses in a burst, producing X-rays. The behaviour of X-ray bursters is similar to the behaviour of recurrent novae. In the latter case the compact object is a white dwarf that accretes hydrogen that finally undergoes explosive burning.
The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the Space ShuttleColumbia during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2024.
Centaurus X-3 is an X-ray pulsar with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation Centaurus. The system consists of a neutron star orbiting a massive, O-type supergiant star dubbed Krzemiński's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray emission.
GRB 970228 was the first gamma-ray burst (GRB) for which an afterglow was observed. It was detected on 28 February 1997 at 02:58 UTC. Since 1993, physicists had predicted GRBs to be followed by a lower-energy afterglow, but until this event, GRBs had only been observed in highly luminous bursts of high-energy gamma rays ; this resulted in large positional uncertainties which left their nature very unclear.
Claude R. Canizares is an American physicist who stepped down June 30, 2015 from his post as Vice President of MIT. He remains the Bruno Rossi Professor of Physics at MIT and associate director for MIT of the Chandra X-Ray Observatory Center.
Shrinivas Ramchandra Kulkarni is a US-based astronomer born and raised in India. He is a professor of astronomy and planetary science at California Institute of Technology, and was director of Caltech Optical Observatory (COO) at California Institute of Technology, overseeing the Palomar and Keck among other telescopes. He is the recipient of a number of awards and honours.
GRS 1915+105 or V1487 Aquilae is an X-ray binary star system containing a main sequence star and a black hole. Transfer of material from the star to the black hole generates a relativistic jet, making this a microquasar system. The jet exhibits apparent superluminal motion.
The Small Astronomy Satellite 3 was a NASA X-ray astronomy space telescope. It functioned from 7 May 1975 to 9 April 1979. It covered the X-ray range with four experiments on board. The satellite, built by the Johns Hopkins University Applied Physics Laboratory (APL), was proposed and operated by MIT's Center for Space Research (CSR). It was launched on a Scout vehicle from the Italian San Marco platform near Malindi, Kenya, into a low-Earth, nearly equatorial orbit. It was also known as Explorer 53, as part of NASA's Explorer program.
GX 339-4 is a moderately strong variable galactic low-mass X-ray binary (LMXB) source and black hole candidate that flares from time to time. From spectroscopic measurements, the mass of the black-hole was found to be at least of 5.8 solar masses.
Circinus X-1 is an X-ray binary star system that includes a neutron star. Observation of Circinus X-1 in July 2007 revealed the presence of X-ray jets normally found in black hole systems; it is the first of the sort to be discovered that displays this similarity to black holes. Circinus X-1 may be among the youngest X-ray binaries observed.
GRB 970508 was a gamma-ray burst (GRB) detected on May 8, 1997, at 21:42 UTC; it is historically important as the second GRB with a detected afterglow at other wavelengths, the first to have a direct redshift measurement of the afterglow, and the first to be detected at radio wavelengths.
The history of gamma-ray began with the serendipitous detection of a gamma-ray burst (GRB) on July 2, 1967, by the U.S. Vela satellites. After these satellites detected fifteen other GRBs, Ray Klebesadel of the Los Alamos National Laboratory published the first paper on the subject, Observations of Gamma-Ray Bursts of Cosmic Origin. As more and more research was done on these mysterious events, hundreds of models were developed in an attempt to explain their origins.
X-ray emission occurs from many celestial objects. These emissions can have a pattern, occur intermittently, or as a transient astronomical event. In X-ray astronomy many sources have been discovered by placing an X-ray detector above the Earth's atmosphere. Often, the first X-ray source discovered in many constellations is an X-ray transient. These objects show changing levels of X-ray emission. NRL astronomer Dr. Joseph Lazio stated: " ... the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths, ...". There are a growing number of recurrent X-ray transients. In the sense of traveling as a transient, the only stellar X-ray source that does not belong to a constellation is the Sun. As seen from Earth, the Sun moves from west to east along the ecliptic, passing over the course of one year through the twelve constellations of the Zodiac, and Ophiuchus.
OSO 3, or Third Orbiting Solar Observatory was launched on March 8, 1967, into a nearly circular orbit of mean altitude 550 km, inclined at 33° to the equatorial plane. Its on-board tape recorder failed on June 28, 1968, allowing only the acquisition of sparse real-time data during station passes thereafter; the last data were received on November 10, 1969. OSO 3 reentered the Earth's atmosphere and burned up on April 4, 1982.
David Louis Band or David L. Band was an astronomer who studied the theory of gamma-ray bursts.
Johannes A. van Paradijs was a Dutch high-energy astrophysicist. He is best known for discovering the first optical afterglow of a gamma-ray burst, GRB 970228, in February 1997, together with two of his students, and for establishing that gamma-ray bursts are extragalactic events. He was married to the astrophysicist Chryssa Kouveliotou.
Filippo Frontera is an Italian astrophysicist and professor, who deals with astronomical investigations on celestial gamma-rays.
↑ Lewin, Walter H. G.; Ricker, George R.; McClintock, Jeffrey E. (October 1971). "X-Rays from a New Variable Source GX 1+4". Astrophysical Journal. 169: L17. Bibcode:1971ApJ...169L..17L. doi:10.1086/180805.
↑ Lewin, Walter H. G.; McClintock, Jeffrey E.; Ryckman, Stanley G.; Glass, Ian S.; Smith, William B. (November 1970). "Continual Variations in the High-Energy Flux of X-Rays from Scorpius X-1". Astrophysical Journal. 162: L109. Bibcode:1970ApJ...162L.109L. doi:10.1086/180635.
↑ Lewin, Walter H. G.; Van Paradijs, J.; Van Der Klis, M. (1991). "Quasi-periodic oscillations in low-mass X ray binaries". NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives: 251. Bibcode:1991heaa.conf..251L.
↑ Walter H. G. Lewin (2003). Edward P. van den Heuvel; Lex Kaper; Evert Rol; Ralph A.M.J. Wijers (eds.). My Quarter Century with Jan. ASP Conference Proceedings. Vol.308. p.27. arXiv:astro-ph/0105344. Bibcode:2003ASPC..308...27L.
↑ "Walter Lewin". Royal Netherlands Academy of Arts and Sciences. Archived from the original on 20 July 2015. Retrieved 17 July 2015.
↑ Pooley, David; Lewin, Walter H. G.; Verbunt, Frank; Homer, Lee; Margon, Bruce; Gaensler, Bryan M.; Kaspi, Victoria M.; Miller, Jon M.; Fox, Derek W. (28 March 2002). "Chandra Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X-ray Luminosity Functions". The Astrophysical Journal. 573 (1): 184–190. arXiv:astro-ph/0111212. Bibcode:2002ApJ...573..184P. doi:10.1086/340498. ISSN0004-637X. S2CID119401055.
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