X-ray astronomy chief George W. Clark dies at 94 » MIT Physics
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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 Method 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 significant function within the discovery of celestial gamma-ray sources.”
On the MIT Physics school 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 among 4 kids raised by the late Robert Preserve Clark, an MIT alum who was the final supervisor of a range manufacturing unit, and Margaret Whipple Clark, a pianist and graduate of Oberlin School. Rising up in Harvey, Unwell., his curiosity in science bloomed when, as a 7th grader, he was fascinated by his father’s 1895 school chemistry textbook. Collectively they arrange a basement lab. “I made all types of experiments and chemical compounds, a few of which give me the willies once I take into consideration them now,” Clark had recalled.
Nevertheless it was his father’s copy of Newbie Telescope Making that taught George floor and polish a six-inch parabolic mirror, which he positioned right into a four-foot telescope that he mounted in a discipline close to his household’s summer time dwelling. He would later use that 6-inch mirror when he taught Junior Lab at MIT.
In highschool, he took superior junior school 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 parts. 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 stated. He added that it was a time when “public help of curiosity-driven analysis was at its peak, based mostly on the popularity that it was the inspiration of the spectacular successes of goal-oriented struggle analysis.”
Rossi and his staff had been making an attempt to determine uncover the origins of cosmic rays, that are high-energy particles, principally protons, touring from outer area and coming 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 vitality 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 seen by an computerized movie digicam, and the ensuing measurements proved that utilizing the novel strategies of density sampling and quick timing may yield arrival instructions inside a couple of levels and bathe sizes inside a couple of p.c. This led to a bigger such experiment on the grounds of the Agassiz Station of the Harvard School Observatory, and different MIT-led air bathe experiments in India, Bolivia, and New Mexico.
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 charge of background occasions brought on by radiation larger up. That’s when the newly created NASA supplied area 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 means of the galaxy like seen mild. These alerts from outer area present details about the galactic and extragalactic media by means of which they journey in addition to the cosmic objects from which they emanate corresponding to stars white dwarfs, neutron stars, black holes, supernova remnants, galaxies, and diffuse gasoline 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 your entire 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 Method and in addition supplied 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 search out different sources however was too busy with different tasks, so he requested his former pupil Martin Annis for assist. Annis was president of American Science and Engineering (AS&E), a small analysis agency situated on Carleton Road, 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 pupil colleague and buddy.
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 shiny celestial X-ray supply, which they referred to as Sco X-1, as a result of it was situated within the constellation of Scorpius. This launched the sphere 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 among 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 underneath the course of Professor Hale Bradt.
Throughout all this exercise, Clark centered his analysis on this new discipline. Cosmic X-ray photons with energies better than 15 keV may 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 better than 15 kilovolts. The balloon program continued with productive outcomes underneath Clark’s graduate pupil James Overbeck after which underneath 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 type of a shock,” says Bradt. “No person actually predicted that there needs to be detectable sources of X-rays on the market.”
Within the Nineteen 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”) underneath the management of Giacconi. Scanning the entire sky, it found lots of of beforehand unknown cosmic X-ray sources and offered the primary observational proof that X-ray sources had been usually in binary star methods and that supernova remnants had been usually X-ray emitters, as had been Seyfert galaxies and clusters of galaxies. It additionally confirmed an earlier remark of an isotropic X-ray background. These outcomes, principally by the AS&E staff, established X-ray astronomy firmly as a significant 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 would level at a given supply repeatedly for sustained intervals. SAS-3 carried devices proposed and utilized by himself with David Hearn and by professors Bradt, Herbert Schnopper, and Lewin. Graduate pupil Saul Rappaport, who later joined the MIT school, quickly grew to become a significant person. The SAS-3 satellite tv for pc might be “pushed” by a staff 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 delicate diffuse background, and magnetic white dwarfs.
“Inside a few hours of an remark we acquired ‘quick-look’ information by a devoted line from the NASA management heart, and some days later the whole remark and engineering information on magnetic tape,” recalled Clark.
Sooner or later Lewin observed a sequence of a number of brief X-ray bursts separated by about 20 seconds and positioned the view discipline of the detector on a exceptional X-ray supply he nicknamed “The Fast Burster,” an accretion-powered X-ray binary at a distance of greater than ten thousand mild years.
Clark acquired 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 vitality vary, on the Einstein X-Ray Observatory (HEAO-2, 1978-1981). The second of NASA’s three Excessive Power Astrophysical Observatories, Einstein was a Massive Orbiting X-Ray Telescope (LOXT) — the primary totally imaging X-ray telescope put into area.
The X-ray sky is far more variable on human time scales than a lot of the seen sky. Sources differ in depth on time scales from milliseconds to years. Clark strongly advocated for a NASA mission that might turn out to be 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 best 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 Nineteen Eighties.
As a member of the Nationwide Academy of Sciences decadal examine (the “Subject 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 accumulating space, and sensitivity to larger vitality 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 placement and traits of the mud and the gap of the star.
Workforce Coach
Sooner or later, Clark stated to Canizares, “Did you ever assume what we might 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 unique concepts and actually was in a position to transfer them ahead,” says Canizares. “He actually helped me all through my profession and did quite a bit 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 this planet largely due to this decentralized, non-hierarchical method initiated by Rossi and Clark.”
Added Bradt, “George was a gentleman by means of and thru. After one contentious encounter, he referred to as me and stated ‘It will be significant we keep mates.’ I cherished him for that. He was instinctively empathetic towards people in troublesome conditions, typically extra so than others of us.”
Earth-bound Professor
Clark was a member of the MIT Physics school 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 significant single-author paper based mostly 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 area analysis group underneath 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 sphere and dedication to educating.
“My biggest 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 stated. “I’m astonished and delighted to see how these areas have developed and awed on the scale and complexity of the tasks developed to help them.”
Clark was often called the professor who supplied clear explanations to his college students, stayed after his lectures to reply questions, and would usually be seen dashing by means of the halls to make it to the following classroom. However Bradt recalled that as his advisor, Clark may be fairly hands-off.
“After 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 telephone at essential occasions. He was not in your hair on a regular basis however was obtainable when wanted. He was the right thesis supervisor.”
However Clark was additionally “the form 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, stated in a letter introduced 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 making ready for a take a look at 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 the entire gear and watched it begin counting. “Loads was flawed, however we discovered about all of it instantly,” Bradt recollects. “He stated, ‘Attempt all of it, and that’s once you discover the place the issues are. Don’t spend eternally fussing over every half, as a result of that’s your means 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 illustration in electromagnetic principle, “Gee whiz, isn’t that attention-grabbing.”
One pupil recalled rigorously eradicating wing nuts on one among his liquid scintillators to save lots of them — when Clark dashed up, eliminated the nuts shortly with two arms, and flung them over his shoulder. He sought fast options.
Whereas some professors had prompt MIT pupil Peter Yesley go away academia, Clark as an alternative 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 observe.”
In 1991, Clark acquired the MIT College of Science Educating Prize for his a few years answerable for 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 usually late, everybody was retiring for the evening. Besides George, who went upstairs to his examine to work. I popped my head in his door and requested him what he was doing. He stated he was making ready a lecture for freshman physics. I stated, ‘George, you’ve been doing this for over thirty years. It’s best to have the ability to telephone this in!’ He stated, ‘The children get smarter yearly.’ “
Retirement
In recent times, he was a well-known face at division occasions and astrophysics colloquia. At a latest occasion, Canizares realized about his sickness, “however he was nonetheless filled with vitality and speaking about how he cherished his new Tesla.”
Sickness didn’t sluggish him down. Even per 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 vitality,” recollects Bradt.
On weekends, with mates and college students, he constructed a cushty hexagonal home from a design printed in Fashionable Mechanics. “He designed it as we went alongside,” says Claude. “He stated, ‘How laborious may or not it’s?’ We used to tug oysters from the pond as our type of reward.” He later constructed an addition, and put in a clay chip tennis courtroom that “was his pleasure and pleasure,” recalled his stepson Blair Reischer. “He strictly enforced guidelines as to what sort of footwear had been allowed to the touch its floor.” He and his spouse Charlotte loved enjoying tennis effectively 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 brief.
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 creator’s errors and what he knew the Soviets had been as much as concerning early chip expertise through the Chilly Conflict.
As a toddler, 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 accomplished, they used the pages for kindling.
George was a pianist like his mom, and in addition performed cello; he would be 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 kin and pricey mates, and he was very supportive of his kids’s and grandchildren’s careers in civil engineering, medication, US-China relations, and classical music.
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 shall be held in Brookline at midday on Sunday, Could 21. All attendees are invited to talk. For extra info, e mail georgeclarkmemorial1928@gmail.com.
Memorial contributions may 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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