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 was on MIT Cable TV, with every week a different 1-hour program. They were aired 24 hours per day helping freshmen with their weekly homework assignments (they were called help sessions). Walter Lewin's 1992 lectures on Newtonian mechanics (co-lectured with Bob Ledoux) and Lewin's help sessions have been shown for over six years (starting in 1995) on UWTV in Seattle, WA, reaching an audience of about four million people. Years later, Bill Gates wrote to Lewin that he watched him very frequently on UWTV. Lewin personally responded to thousands of e-mail requests that he received per year from UWTV viewers. Videos of Lewin's 94 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] The videos can also be viewed on YouTube, iTunes and Earth Academic.
Since February 2015, Lewin has been running and managing his own YouTube channel called "Lectures by Walter Lewin. They will make you ♥ Physics".[24] All of his lectures can be viewed online on this channel. Here Lewin vlogs about his everyday life and also host quizzes on physics and art. In April 2021, this channel crossed a million subscribers. In year 2021, his channel gathered over 52 million views, and gathered over 96 million views in total. Several of Lewin's lectures have been viewed more than a million times. His 2011 farewell lecture "For the Love of Physics" is one of his most popular lectures. As of January 2022, this lecture 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 massive influence on online education.[27]
Two of Lewin's courses were converted into edX courses, 8.01x (classical mechanics) and 8.02x (electricity and magnetism). People who pass "x" courses receive a certificate from MIT. Lewin's course on electricity and magnetism went online in February 2013, Newtonian mechanics is online as of September 2013. As of May 2014, there were yet no plans to convert 8.03 "vibrations and waves" into an edX course.[28]
Videos of Lewin's lectures on Videos on Teaching Excellence at MIT, YouTube and iTunes U have been viewed more than 12 million times by people all over the world – including Bill Gates, who has confessed to repeated viewings.[29][30]
In the summer of 2012, Lewin returned from his retirement to deliver a lecture series[31] initiated and funded by the Japanese Broadcasting Corporation (NHK). Each lecture features a selection of physics demonstrations that Lewin has used in his more than 43 years of teaching physics at MIT. The lectures consist of 8 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.[32]
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.[33] 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.[33] 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.[34]
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 explosions that have been observed in distant galaxies, described by NASA as "the most powerful class of explosions in the universe". They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten milliseconds to several hours. After an initial flash of gamma rays, a longer-lived "afterglow" is usually emitted at longer wavelengths.
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 1971 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.
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 Krzeminski's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray emission.
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 currently a professor of astronomy and planetary science at California Institute of Technology, and he served as director of Caltech Optical Observatory (COO) at California Institute of Technology, in which capacity he oversaw the Palomar and Keck among other telescopes. He is the recipient of a number of awards and honours.
Vela X-1 is a pulsing, eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru source 4U 0900-40 and the supergiant star HD 77581. The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion. Vela X-1 is the prototypical detached HMXB.
GRS 1915+105 or V1487 Aquilae is an X-ray binary star system which features a regular star and a black hole. It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat. "GRS" stands for "GRANAT source", "1915" is the right ascension and "105" reflects the approximate declination. The near-infrared counterpart was confirmed by spectroscopic observations. The binary system lies 11,000 parsecs away in Aquila. GRS 1915+105 is the heaviest of the stellar black holes so far known in the Milky Way Galaxy, with 10 to 18 times the mass of the Sun. It is also a microquasar, and it appears that the black hole rotates at least 950 times per second, close to the maximum of 1,150 times per second, with a spin parameter value between 0.82 and 1.00.
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.
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↑ 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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