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X-ray astronomy chief George W. Clark dies at 94 » MIT Physics

Clark led investigations in cosmic-ray physics, and gamma-ray and X-ray astronomy.

Professor emeritus of physics George Whipple Clark PhD ’52, an astrophysicist who was a pioneer in X-ray and gamma-ray astronomy, died on April 6, 2023, in Boston. He was 94.

Clark employed buckets, balloons, rockets, and satellites in his practically lifelong pursuit to know the character and origins of cosmic rays, gamma rays, and X-rays.

Clark found the polarization of cosmic-ray muons, collaborated with the late Physics professor Bruno Rossi on a number of giant ground-based cosmic-ray air bathe experiments, and used balloon-borne and satellite tv for pc instrumentation to find X-ray sources. 

He was a principal scientist for satellite tv for pc experiments that resulted within the discovery of high-energy gamma rays from the Milky Manner galaxy, and produced proof for an isotropic part that’s now recognized to come up from different extra distant galaxies. His pioneering work in the usage of balloon-borne instrumentation for observing celestial X-ray sources led to his discovery of high-energy X-rays from the Crab Nebula. A main contributor to the NASA OSO-7 and Einstein satellite tv for pc X-ray astronomy missions, Clark initiated the usage of Bragg reflection for high-resolution X-ray spectroscopy with Professor Claude R. Canizares for the latter. He was the principal investigator for the MIT X-ray devices on the Third Small Astronomy Satellite tv for pc (SAS-3).

“He helped chart the way forward for X-ray astronomy by prioritizing the Chandra X-ray Observatory,” says MIT Kavli Institute director Robert Simcoe. “He performed a serious position within the discovery of celestial gamma-ray sources.” 

On the MIT Physics college for 44 years, Clark recruited and mentored a number of generations of main astrophysicists. George was a founding member of MIT’s Middle for Area Analysis, now the MIT Kavli Institute.

Early Curiosity in Science

Clark was born on August 31, 1928, one in all 4 youngsters raised by the late Robert Hold Clark, an MIT alum who was the overall supervisor of a range manufacturing unit, and Margaret Whipple Clark, a pianist and graduate of Oberlin Faculty. Rising up in Harvey, In poor health., his curiosity in science bloomed when, as a 7th grader, he was fascinated by his father’s 1895 faculty chemistry textbook. Collectively they arrange a basement lab. “I made all types of experiments and chemical substances, a few of which give me the willies after I take into consideration them now,” Clark had recalled.

Nevertheless it was his father’s copy of  Novice Telescope Making that taught George learn how to floor and polish a six-inch parabolic mirror, which he positioned right into a four-foot telescope that he mounted in a subject close to his household’s summer season dwelling. He would later use that 6-inch mirror when he taught Junior Lab at MIT.

In highschool, he took superior junior faculty programs in chemistry and calculus, and in 1945, he completed within the high 10 within the Westinghouse Science Expertise Search with an essay about his chemical work with rare-earth components. He earned a visit to Washington, the place he had his image taken with Vice-President Truman and had tea with First Girl Eleanor Roosevelt.

MIT Launch

After graduating from Harvard in 1949 with a B.A. in physics, he pursued his doctorate at MIT, becoming a member of Bruno Rossi’s Cosmic Ray Group within the Laboratory for Nuclear Science and Engineering. After receiving his PhD in 1952, he joined MIT as an teacher. 

“Professor Rossi invited me on a journey of exploration that might be guided by his unerring sense of scientific alternative,” Clark mentioned. He added that it was a time when “public assist of curiosity-driven analysis was at its peak, primarily based on the popularity that it was the inspiration of the spectacular successes of goal-oriented warfare analysis.”

Rossi and his group had been attempting to determine learn how to uncover the origins of cosmic rays, that are high-energy particles, principally protons, touring from outer house and getting into our ambiance. Interplay with atmospheric nuclei within the higher ambiance leads to a “bathe” of different particles, principally pions, which swiftly decay to emit muons that journey at practically the velocity of sunshine to the earth’s floor.  

Clark and different Cosmic Ray Group members labored on a number of giant cosmic-ray air bathe experiments (EAS) to measure the power spectrum of the first cosmic rays, in addition to to find out their arrival instructions. 

He partnered with Peter Bassi, a visiting scientist from Italy, to arrange scintillation detectors — 5-gallon cans stuffed with toluene — on the roof of the physics constructing. Electrical pulses had been displayed on an oscilloscope considered by an computerized movie digital camera, and the ensuing measurements proved that utilizing the novel strategies of density sampling and quick timing might yield arrival instructions inside a couple of levels and bathe sizes inside a couple of %. This led to a bigger such experiment on the grounds of the Agassiz Station of the Harvard Faculty Observatory, and different MIT-led air bathe experiments in India, Bolivia, and New Mexico.

two men lowering cover onto balloon gondola
Professors William Kraushaar (at left) and George Clark shut the air-tight cowl on the balloon gondola that carried the second of their two (unsuccessful) balloon experiments in seek for high-energy cosmic gamma rays. Credit score: MIT Museum

Clark and his colleague William Kraushaar created balloon-borne experiments to detect a really uncommon part of the first cosmic radiation however had been thwarted by the excessive fee of background occasions attributable to radiation greater up. That’s when the newly created NASA provided house on its Explorer 11 satellite tv for pc for Kraushaar and Clark’s high-energy gamma-ray telescope. 

Gamma and X-rays are high-energy photons that journey principally in straight traces by the galaxy like seen gentle. These alerts from outer house present details about the galactic and extragalactic media by which they journey in addition to the cosmic objects from which they emanate akin to stars white dwarfs, neutron stars, black holes, supernova remnants, galaxies, and diffuse fuel in galaxy clusters. 

The pair designed the 82-pound satellite tv for pc within the form of a potato masher, designed to tumble in orbit to scan all the sky; from April to September 1961 it registered 31 occasions of potential cosmic gamma rays till it powered down. Gordon Garmire joined them in creating an improved gamma-ray telescope that flew in 1967 on Orbiting Photo voltaic Observer 3 (OSO-3). It demonstrated convincingly that gammas of energies above 70 MeV had been emanating from the Milky Manner and in addition provided the primary proof for what’s now recognized to be gamma rays from distant galaxies. 

X-ray Imaginative and prescient

The Solar was the one recognized supply of cosmic X-rays, and Rossi wished to seek out different sources however was too busy with different initiatives, so he requested his former scholar Martin Annis for assist. Annis was president of American Science and Engineering (AS&E), a small analysis agency positioned on Carleton Avenue, the place the MIT Medical Middle is now. It had been based a couple of years earlier by Annis and Clark, his former Rossi Group scholar colleague and pal.

Annis referred Rossi to a latest rent, Riccardo Giacconi, who instantly took to Rossi’s suggestion {that a} seek for cosmic X-ray sources be carried out. The AS&E scientists and  Rossi carried out a rocket experiment in 1962 that found a brilliant celestial X-ray supply, which they known as Sco X-1, as a result of it was positioned within the constellation of Scorpius. This launched the sector of extra-solar X-ray astronomy.

AS&E started with contracts with the Air Drive Cambridge Analysis Laboratory to analysis weapons’ results, together with radiation, at excessive altitudes. However AS&E continued to make use of rockets to discover the X-ray sky with the participation of MIT scientists, one in all whom was a visiting scientist from Japan, Minoru Oda, who quickly grew to become the daddy of a thriving program of X-ray astronomy in Japan. In 1967, MIT started its personal X-ray astronomy rocket program beneath the path of Professor Hale Bradt.

Throughout all this exercise,  Clark centered his analysis on this new subject. Cosmic X-ray photons with energies higher than 15 keV might penetrate to altitudes accessible by a helium-filled balloon, so he loaded an X-ray telescope with a scintillation detector onto a large “skyhook” balloon in Texas. It scanned the Crab Nebula, which grew to become the primary recognized cosmic X-ray supply emitting X-ray energies higher than 15 kilovolts. The balloon program continued with productive outcomes beneath Clark’s graduate scholar James Overbeck after which beneath Professor Walter Lewin. Notable had been measurements of a change within the X-ray flux from the supply Cygnus X-1 and a flare within the flux from Sco X-1.

“X-ray astronomy was form of a shock,” says Bradt. “No one actually predicted that there must be detectable sources of X-rays on the market.”  

group of six men stand by desk
Within the SAS-3 management room is (left to proper) Invoice Mayer, Jeff McClintock, David Hearn, Saul Rappaport, George Clark, and Ben Laufer. Credit score: MIT Physics

Within the Sixties and Seventies, Clark’s analysis additionally used NASA satellites to hold out X-ray astronomy observations, notably OSO-7 (1971–1974), SAS-3 (1975-1979), and Einstein (1978-1981).

Clark pushed for an AS&E/NASA satellite tv for pc X-ray observatory, to be launched in 1970 from Kenya because the First Small Astronomy Satellite tv for pc (SAS-1), named Uhuru (Swahili for “freedom”) beneath the management of Giacconi. Scanning the entire sky, it found a whole bunch of beforehand unknown cosmic X-ray sources and supplied the primary observational proof that X-ray sources had been usually in binary star methods and that supernova remnants had been sometimes X-ray emitters, as had been Seyfert galaxies and clusters of galaxies. It additionally confirmed an earlier statement of an isotropic X-ray background. These outcomes, principally by the AS&E group,  established X-ray astronomy firmly as a serious department of astronomy alongside optical (visible-light) and radio astronomy. Giacconi was awarded a Nobel Prize for his efforts.  

Clark was a principal investigator on the Seventh Orbiting Photo voltaic Observatory, or OSO-7 Satellite tv for pc, for MIT’s first X-ray satellite tv for pc experiment which yielded, in collaboration with MIT analysis scientist Thomas Markert, an all-sky survey of X-ray sources. 

He adopted this as principal investigator on SAS-3, a NASA satellite tv for pc carrying the primary X-ray observatory that might level at a given supply constantly for sustained intervals. SAS-3 carried devices proposed and utilized by himself with David Hearn and by professors Bradt, Herbert Schnopper, and Lewin. Graduate scholar Saul Rappaport, who later joined the MIT college, quickly grew to become a serious person.  The SAS-3 satellite tv for pc may very well be “pushed” by a group of professors, postdocs, and college students taking turns across the clock to direct the observatory’s operation from MIT. It produced a plethora of wealthy outcomes and discoveries elucidating the character of  X-ray emitting binaries, “bursters,” novae,  pulsars, globular clusters, a gentle diffuse background, and magnetic white dwarfs. 

two men pose beside satellite prior to its launch
George Clark, at left, with Dick Taylor by the SAS-3 previous to its 1975 launch. Credit score: MIT Physics

“Inside a few hours of an statement we obtained ‘quick-look’ information by a devoted line from the NASA management middle, and some days later the entire statement and engineering information on magnetic tape,” recalled Clark. 

In the future Lewin observed a sequence of a number of quick X-ray bursts separated by about 20 seconds and positioned the view subject of the detector on a exceptional X-ray supply he nicknamed “The Speedy Burster,” an accretion-powered X-ray binary at a distance of greater than ten thousand gentle years.  

Clark obtained the NASA Distinctive Scientific Achievement Award for his work as PI of the Einstein Observatory Focal Aircraft Crystal Spectrometer, which used the strategy of Bragg spectroscopy to carry out high-resolution spectroscopic research of cosmic X-ray sources within the 0.2-3 keV power vary, on the Einstein X-Ray Observatory (HEAO-2, 1978-1981). The second of NASA’s three Excessive Power Astrophysical Observatories, Einstein was a Giant Orbiting X-Ray Telescope (LOXT) — the primary totally imaging X-ray telescope put into house.  

The X-ray sky is far more variable on human time scales than a lot of the seen sky. Sources range in depth on time scales from milliseconds to years. Clark strongly advocated for a NASA mission that might develop into the Rossi X-ray Timing Explorer (RXTE), which might carry an MIT experiment, an All-Sky Monitor, an effort led by Bradt. RXTE observers studied sources exhibiting depth variations starting from milliseconds to years over a interval of 16 years (1995-2012).  

“When George obtained in his head one thing that he thought was the correct factor to do, he charged forward, rattling the torpedoes and the political fallout,” says Bradt.

Clark and different X-ray astronomers within the U.S. took benefit of “visitor observer” alternatives with Japanese and European orbiting X-ray observatories throughout a hiatus of NASA X-ray astronomy missions within the Eighties.

As a member of the Nationwide Academy of Sciences decadal research (the “Area Report”) Clark helped chart the way forward for X-ray astronomy by prioritizing the event of Einstein’s successor, the Superior X-Ray Astrophysics Facility (AXAF), later renamed the Chandra X-ray Observatory. Chandra contains a high-resolution giant amassing space, and sensitivity to greater power X-rays to check extraordinarily faint sources in crowded fields. Clark used Chandra information to check the grain-scattered X-ray halos of accretion-powered binaries, and from the form and dimension of a halo he tried to determine the situation and traits of the mud and the space of the star.

Crew Coach

In the future, Clark mentioned to Canizares, “Did you ever assume what we’d be doing if we weren’t being paid to have enjoyable?” 

When Clark employed Canizares in 1971, it was a interval the place most astrophysicists within the division had been physicists studying astronomy as they went. Clark “took Bruno Rossi’s authentic concepts and actually was capable of transfer them ahead,” says Canizares. “He actually helped me all through my profession and did so much to additional the careers of his college students and colleagues.”

He propelled his colleagues’ careers by evolving the MIT X-ray astronomy effort into a number of distinct teams that he trusted to work independently.  

“We had been all freed to make our marks, and that led to lengthy careers at MIT for every of us,” recollects Bradt. “MIT grew to become one of many premier X-ray astronomy analysis teams on the earth largely due to this decentralized, non-hierarchical strategy initiated by Rossi and Clark.”

Added Bradt, “George was a gentleman by and thru. After one contentious encounter, he known as me and mentioned ‘It will be significant we keep buddies.’ I cherished him for that. He was instinctively empathetic towards people in tough conditions, typically extra so than others of us.”

Earth-bound Professor

Clark was a member of the MIT Physics college for 44 years, from his appointment as Teacher in 1952, Assistant Professor in 1954, Professor in 1965, and 1985 as the primary Breene Kerr Professor of Physics. He served as Astro division chair from 1983-1988 and took sabbaticals in 1985 and 1994 to carry out analysis on the Institute of Area and Astronautical Science in Tokyo, Japan.   

In 1996, he grew to become a professor post-tenure (retired). He continued to show 8.13/8.14 (Junior Lab) till 1998, and mentored college students till he formally retired and have become an Emeritus Professor in 2001. He continued to attend division colloquia, and he printed a serious single-author paper primarily based on Chandra information in 2018.

Clark was a member of the American Bodily Society, American Astronomical Society, American Academy of Arts and Sciences, and the Nationwide Academy of Sciences (NAS). He served on the Research Committee for Institutional Preparations for the Area Telescope, and on boards and committees with the Related Universities for Analysis in Astronomy, American Science and Engineering, and NASA. Clark left MIT for a semester in 1963 to affix the house analysis group beneath Prof. Giuseppe Ochiallini on the College of Milan, supported by a grant from the Guggenheim Basis and the Fulbright Program. 

At MIT, he was revered by colleagues and college students for his contributions to the sector and dedication to educating.

“My best satisfaction from sixty years of labor in science is having participated within the begin of a number of new areas of analysis in cosmic physics,” Clark mentioned. “I’m astonished and delighted to see how these areas have developed and awed on the scale and complexity of the initiatives developed to assist them.”

Clark was often known as the professor who provided clear explanations to his college students, stayed after his lectures to reply questions, and would usually be seen dashing by the halls to make it to the subsequent classroom. However Bradt recalled that as his advisor, Clark is also fairly hands-off. 

“Once I took my thesis experiment as much as New York State, three trailers with detectors, electronics, and a generator, I didn’t see George on the market however as soon as. We had been on the cellphone at crucial instances. He was not in your hair on a regular basis however was out there when wanted. He was the proper thesis supervisor.”

However Clark was additionally “the type of man who likes to roll up his sleeves and do some actual work,” Mark Schattenburg, now a senior analysis scientist on the MIT Kavli Institute, mentioned in a letter offered at Clark’s retirement fete. “Give him a ladder and a few roofing shingles, or an oscilloscope and a chunk of laboratory equipment, and it doesn’t matter, he’s pleased.”

Bradt was getting ready for a check run within the Constructing 26 Penthouse and was continuing very slowly, checking every digital circuit. When Clark stopped in, he did some “George Clarking” — turned on all the tools and watched it begin counting. “Rather a lot was improper, however we discovered about all of it straight away,” Bradt recollects. “He mentioned, ‘Attempt all of it, and that’s once you discover the place the issues are. Don’t spend ceaselessly fussing over every half, as a result of that’s your approach of claiming you’ll by no means end.’”

G.W. Clark additionally earned one other nickname: “Gee Whiz Clark,” due to his behavior of declaring, after an indication in electromagnetic principle, “Gee whiz, isn’t that attention-grabbing.”

One scholar recalled fastidiously eradicating wing nuts on one in all his liquid scintillators to avoid wasting them — when Clark dashed up, eliminated the nuts rapidly with two fingers, and flung them over his shoulder. He sought fast options. 

Whereas some professors had instructed MIT scholar Peter Yesley go away academia, Clark as a substitute put him to work within the Junior Lab to construct a muon parity violation experiment. “I felt as if I used to be getting the MIT schooling I had missed earlier than,” says Yesley. “Professor Clark made me assured about my work…it put my profession again on monitor.”

In 1991, Clark obtained the MIT College of Science Educating Prize for his a few years in command of the Junior Physics Laboratory. It was his regular work ethic that earned him this prize, recollects his stepson, Blair Reischer.

“My household was visiting my mom and George for a couple of days. After drinks and a dinner that ran sometimes late, everybody was retiring for the evening. Besides George, who went upstairs to his research to work. I popped my head in his door and requested him what he was doing. He mentioned he was getting ready a lecture for freshman physics. I mentioned, ‘George, you’ve been doing this for over thirty years. You must be capable of cellphone this in!’ He mentioned, ‘The youngsters get smarter yearly.’ “


man stands looking at his wife
George Clark together with his spouse Charlotte. Credit score: Clark Household

Lately, he was a well-recognized face at division occasions and astrophysics colloquia. At a latest occasion, Canizares discovered about his sickness, “however he was nonetheless filled with power and speaking about how he cherished his new Tesla.” 

Sickness didn’t gradual him down. Even every week earlier than he died, Clark was nonetheless driving that Tesla from his Chestnut Hill dwelling to his pleased place, Martha’s Winery, the place he had purchased a big parcel of land on the sting of Meshacket Cove close to Edgartown in 1969. 

“He was the everlasting younger man, the Jack Kennedy with a full head of hair, filled with power,” recollects Bradt.

On weekends, with buddies and college students, he constructed a cushty hexagonal home from a design printed in Widespread Mechanics. “He designed it as we went alongside,” says Claude. “He mentioned, ‘How onerous might it’s?’ We used to drag oysters from the pond as our form of reward.” He later constructed an addition, and put in a clay chip tennis court docket that “was his pleasure and pleasure,” recalled his stepson Blair Reischer. “He strictly enforced guidelines as to what sort of sneakers had been allowed to the touch its floor.” He and his spouse Charlotte loved enjoying tennis nicely into their 80s. 

His retirement retreat was not a spot of idleness. There have been croquet video games, giant gatherings of family and friends, and foraging journeys for oysters and mushrooms.  He tended the close by forest and stored the poison ivy at bay and the grass quick. 

An avid reader, earlier this yr the professor in him marked up his copy of Chip Wars by  Chris Miller with notes in regards to the writer’s errors and what he knew the Soviets had been as much as relating to early chip expertise throughout the Chilly Battle.

As a baby, he raced yachts alongside Inexperienced Bay, and at Martha’s Winery he remained a eager sailor. He was an avid windsurfer on Edgartown Nice Pond, and he and his spouse loved multi-day tenting and canoeing journeys alongside the lakes within the Boundary Waters Canoe Space Wilderness. He would take alongside a thick paperback novel, which he would share with Charlotte by ripping off 50 pages; when she was completed, they used the pages for kindling. 

George was a pianist like his mom, and in addition performed cello; he would be a part of division quartets and play together with his daughters Jacqueline and Kasia, who performed flute and violin. He and Charlotte attended artwork reveals by family members and pricey buddies, and he was very supportive of his youngsters’s and grandchildren’s careers in civil engineering, drugs, US-China relations, and classical music.

man windsurfing
George Clark windsurfing on Edgartown Nice Pond at Martha’s Winery in 1978. Credit score: Clark Household

Clark is survived by his daughter Jacqueline, his stepchildren Bridget Reischer, Blair Reischer, Sybil Reischer Ecroyd, and Electa Reischer, and 4 grandchildren, Otto Ecroyd, Rosalind Reischer, Peter Reischer, and Geneva Reischer Harburger. His daughter Katherine (Kasia) Whipple Clark died in October of 2022, and his beloved spouse Charlotte Huston Reischer died in 2019.

A celebration of his life might be held in Brookline at midday on Sunday, Might 21. All attendees are invited to talk. For extra data, e-mail

Memorial contributions could be made to the Dana-Farber Most cancers Institute or the Nationwide Academies’ Committee on Human Rights, the latter to which Clark had left a bequest to assist proceed their work supporting scientists and researchers in danger. 

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