Blog #4 | February 28, 2026
The Quasars Pioneers
(disclaimer: the list emphasizes absorption line work)
Faced with the Cosmic Quandary of the Century
They Ushered in an Astronomy Revolution
by Christopher W. Churchill
Embedded Files
Honoring scientists of our past.
Acknowledging upon who's shoulders we stand.
For some of us shall become the pioneers of our future's past.
I was recently taken on a wonderful journey. As I researched the fields of quasar science and quasar absorption lines while writing my two-volume set of textbooks entitled Quasar Absorption Lines, I became deeply re-acquainted with the spectacular works of scores of dedicated scientists.
Over the 30 years that I have engaged in this science, I have come to personally know many of these amazing people. Others, I have only briefly met. Some I have never met (but may have met their colleagues and/or students). Collectively, these individuals built the field of quasar absorption lines. They may not be common household names, but they are the giants of our science; in the renown yet quiet halls of academia, they revolutionized our world view of the cosmos.
I was moved to dedicated my two books to the those individuals who were there from the very beginning and smashed scientific barriers. These individuals are the Quasar Pioneers,
They struggled with data that forced them to think outside the box. They were compelled to conclude they were witnessing an entirely new astronomically revolutionary phenomena. These individuals brilliantly proposed wholly new concepts and deduced previously unimagined astrophysics.
These pioneers carved a rough-and-ready path that we have since polished smooth with our slick modern cutting-edge science on cosmic chemical evolution, galaxy evolution, the baryon cycle, HI and HeII reionization, D/H ratios, and large-scale hierarchical structure growth.
The pioneers I have selected are: John Bahcall, Jaqueline Bergeron, John Bolton, Margaret Burbidge, Geoffrey Burbidge, Roger Lynds, Cyril Hazard, Marteen Schmidt, Alan Sandage, Wal Sargent, and Art Wolfe. I am sad to report that each has slipped the bonds of Earth.
The criteria I used to build this list were: The individual (a) was at ground zero in 1960-1963 and was directly involved in the discovery of quasi-stellar objects, (b) was directly involved in wrestling with identifying the true nature of these quasi-stellar objects, (c) provided a clarity of insight during the very first years that pointed the broader scientific community in the right direction, or (d) established new techniques, solved the most burning open questions, and/or was first to discover a class of absorber and open new windows on the universe.
I have also assembled a short list entitled Quasar Pioneers: Honorable Mentions. In addition, I present an incomplete list of Quasar Absorption Trailblazers to highlight the foundational works of second and third generation quasar researcher. There are no doubt many deserving individuals who earned entry onto such a listing, I apologize in advance to any who are omitted but feel they should be included. Suggestions welcome. This list of trailblazers is truncated in the late-1980s, and early-1990s as the mid- to late-1990s is a natural demarcation due to the advent of the "game changing" Keck 10-meter telescope that revolutionized absorption line studies and the explosion in computing power that fueled a rapid growth of theoretical works in the field.
--- I hope you will enjoy these brief biographies.
The Pioneers
#1 John Gatenby Bolton
John Bolton
John Bolton was considered one of the most talented and capable radio astronomer/engineers of his era. His enlistment in the Royal Navy circuitiously led to his working with radar during World War 2 and then, after the war, when hearing about Karl Jasnky's work, getting engaged in radio astronomy. Bolton had postulated radio-load stars and began to search for them in the 1940s, well before quasi-stellar objects were discovered. As it turns out, Bolton discovered the first such object. He was awarded the Gold Medal of the Royal Society and the Bruce Medal. During his career he served as Director of both the Owens Valley Radio Observatory and the Parks radio telescope. Bolton lived to be 71 years old.
Born: June 5, 1922
Died: July 6, 1993
PhD: Trinity College, Cambridge
Nationality: British-Australian
Built high resolution radio telescopes (Owens Valley, Parkes)
Found and reported first precise quasar positions (w/ Cyril Hazard, Tom Matthews)
Claims to have been the first to realize that the redshift of 3C 48 was z=0.37
John Bolton is Quasar Pioneer #1 because he was intrumental in finding the precise locations of the first optical counter parts of the radio sources. He collaborated with optical spectroscopists to obtain and interpret the first spectra of these objects.
John Bolton came to Caltech in 1955 with the expressed purpose of building a radio telescope that would yield precise positions of faint radio sources. It was believed that the discrete (small) radio sources at high latitudes (out of the plane of the Galaxy) were high-redshift galaxies, the so-called radio galaxies. The quest to find high-redshift galaxies was intense and competitive.
Famously, Bolton obtained the precise locations of the radio sources 3C 48 and 3C 273. He passed the coordinates to Allan Sandage and Marteen Schmidt, and these were among the first quasars with optical spectra. Their blue colors and optical emission lines presented a quandary. Though some toyed with the idea these point-like objects may be high-redshift galaxies, including Bolton, 3C 48 and the first published quasars were published as strange radio emitting stars inside our Galaxy. If extragalactic, the required energies were so high that they were too far outside the box for any astronomer to risk their career claiming they were extragalactic. That all changed when Marteen Schmidt showed that the redshift of 3C 273 was at z=0.15, following which 3C 48 was determined to be at z=0.37.
Selected Works:
Bolton, J.G., 1969, Extragalactic radio sources, AJ, 74, 13
Bolton, J.G., 1966, Identification of radio galaxies and quasi-stellar objects, Nature, 211, 917
Bolton, J.G., 1956, Radio telescopes and position finding, AJ 61, 168
Bolton's two 90-foot dishes were a tour de force of engineering that opened up the field of high-resolution radio precision astronomy.
A 20 year-old Bolton at the 1962 International Union Radio Science conference in Sydney.
#2 Cyril Hazard
Cyril Hazard
Cyril Hazard began his career at Jordell Bank, but ultimately worked on three continents. Although he spent the majority of his career at Cambridge University, he also worked at the Univ. of Sydney, the Univ. of Pittsburgh, and Cornell. In the mid-1980s, he discovered the then highest redshift quasar. Hazard is celebrated for his work that supported and inspired many astronomers and for perfecting a method that allowed many quasars to be located with precision. Hazard lived to be 97 years old.
Born: March 18, 1928
Died: June 14, 2025
PhD: University io Manchester
Nationality: British
Perfected lunar occultations to pinpoint quasar positions
Hunted down and pinpointed countless quasar positions
Cyril Hazard is Quasar Pioneer #2 because he was intrumental in finding the precise locations of the optical counter parts of the radio sources. Hazard used a novel method to locate quasars; he used lunar occultations. Hazard collaborated closely with Jon Bolton, though Hazard (at the ripe age of 24) was working at the Parks Radio Observatory in Australia while Bolton was at Caltech.
The typical error box for a 3C radio source was 2 arcmin by 2-10 armin. So, finding the precise poistion of their optical counterparts was not trivial. The radio source 3C 273 experienced five lunar occultations in 1962 and Hazard observed two of them. Hazard perfected methods to obtain precise positions by marking the sky location where the radio flux was occulted by the Moon. It was tricky business due to Fresnel diffraction patterns during the occultations and because 3C 273 is an extended radio source with a bright knot and an extended jet (though it was thought to be an edge-on disk galaxy before Maarten Schmidt unveiled its true nature). Ultimately, Hazard obtained good coordinates for both components and passed them up to Schmidt in fall 1963. Schmidt had to wait until December for 3C 273 to become observable. Schmidt and Hazard each published their findings in Nature in March 1963, (Hazard p. 1037; Schmidt p. 1040). These two articles are the birth announcements of quasar astronomy.
Hazard had a long and productive career finding quasars. Before SDSS and other larger surveys came on line, many quasar absorption line scientists working at the forefront of the field personally requested the coordinates of these objects directly from Hazard faster than he was able to publish them. If you knew Hazard, you got to observe them first! He was a very "popular" collaborator!
Selected Works:
Hazard, C. McMahon, R.G., Webb, J.K, & Morton, D.C. 1987, The remarkable broad absorption line QSO 0059-2735 with extensive FeII absorption, ApJ, 323, 263
Hazard, C. Arp, H.C., & Morton, D.C. 1979, A compact group of four QSOs with two appearing physically associated, Nature, 282, 271
Hazard, C., Mackey, M.B., & Shimmeris, A.J. 1963, Investigation of the radio source 3C 273 by the method of lunar occultations, Nature, 197, 1037
Young Hazard at the Parkes console observing radio waves.
A mid-career Cyrll Hazard lecturing at University of Cambridge.
Hazard in 1981 at University of Cambridge.
#3 Allan Rex Sandage
Allan Sandage
Allan Sandage was the student of the late great Edwin Hubble. He was a prolific scientist across a range of sub-fields in astronomy. He was co-author on the first real paper on galaxy evolution theory (known as "ELS") and spent countless hours working to refine the value of the Hubble-Lemaitre constant. Sandage was a member of the National Academy of Science and a Fellow of the Royal Society. He was honored with an array of awards, including Gold Medal of the Royal Astronomical Scoiety, the National Medal of Science, the Bruce Medal, and the coveted Gruber Prize in Cosmology. Sandage spent the majority of his career at Carnegie Observatories. He lived to be 84 years old.
Born: June 18, 1926
Died: November 13, 2010
PhD: Caltech, 1953
Nationality: American
First optical spectra of quasars (w/ Thomas Matthews)
Discovered first absorption line in a quasar spectrum
Established radio-quiet population of quasars
Allan Sandage is Quasar Pioneer #3 because he had the vision to obtain the very first optical spectra of quasars. The very first was 3C 48 in collaboration with Thomas Matthews. Sandage and Matthews also observed two additional objects, 3C 196, and 3C 286. Sandage presented these spectra at the 107th Meeting of the American Astronomical Society in New York in December, 1960. Historically, this meeting marks the first public announcement of a quasi-stellar radio sources (quasar) even though their extragalactic nature and cosmological redshifts would not be deciphered until February 1963.
In 1965, Sandage published the first known absorption line in a quasar spectrum, which was associated CIV in peak of the CIV emission line of radio-quiet object BSO 1. This observation started a frenzy of activity to find additional examples of absorption lines, which were shortly found in the objects PHL 398 (Kinman 1966) and 3C 191 (M. Burbidge et al. 1966). As such, Sandage also made the first historical announcement that birthed the science of quasar absorption lines.
Sandage had one of the most notable careers in astronomy, making contributions across a board range of subfield, including measuring the Hubble-Lemaitre constant.
Selected Works:
Sandage, A. 1966, Intensity variations of quasi-stellar sources in optical wavelengths, ApJ, 144, 1234
Sandage, A. 1965, The existence of a major new constituent of the Universe: The quasi-stellar galaxies, ApJ, 141, 1560
Matthews, T.A., & Sandage, A., 1963, Optical identification of 3C 48, 3C 196, and 3C 286 with stellar objects, ApJ, 138, 30
A young Allan Sandage poses for his faculty portrait at Carnegie.
A prolific observer trained by Edwin Hubble himself, Sandage was at home in the prime focal cage of the 200-in Palomar telescope atop Mount Wilson.
#4 Marteen Schmidt
Marteen Schmidt
Marteen Schmidt, in December of 1962, took the spectrum of a star-like object nearest the coordinates sent to him by Cyril Hazard (this first set of coordinates were slightly off), but Schmidt had a hunch he should take the spectrum of the bright "star" first to rule it out. It was so bright, he saturated the plate. The next night he timed the exposure and saw the telltale signs of a quasi-stellar object: strange emission lines and a bright blue continuum. By February 1962, Schmidt determined that the emission was the Balmer hydrogen series redshift by 15%. The rest, as they say, is history. In his lifetime, Schmidt was recognized with several honors, including the Gold Medal of the Royal Astronomical Society, the Bruce Medal, and the Kavli Prize. He was a member of the National Academy of Science. Schmidt lived to be 92 years old.
Born: December 28, 1929
Died: September 17, 2022
PhD: Leiden University, 1956
Nationality: Dutch
Discovered that redshift emission lines and extragalactic nature of quasars
Marteen Schmidt is arguably at the pinnacle of the pantheon of the Quasar Pioneers. However, here, he is not ranked Quasar Pioneer #1 because his defining contribution was just a bit down the daisy chain of discovery events. He is Quasar Pioneer #4 because he discovered a new class of astronomical object. He was the first to decode the pattern of emission lines in the optical spectra of the "radio stars." He also correctly interpreted the implications of his findings.
The redshifted emission lines Schmidt measured indicated that these objects were extremely distant, powerful, and luminous (equal to 4 trillion suns) and were being carried away by cosmic expansion at a rate of 15% the speed of light. The heated debate as to whether quasi-stellar objects were Galactic radio stars or very distant radio galaxies was abruptly terminated. (Well, as we will see with Quasar Pioneer #6, a minority of individuals continued the debate as to the meaning of the quasar luminosity-distance relationships, arguing for non-cosmological redshifts). The energies were so great that it was quickly realized the physical process that powered quasars required a new phenomena be introduced to the astronomical sciences-- all known phenomena could not even come close to so much power output.
In my Blog #2 "A Modern Scientific Revolution," I describe how the discovery of quasars created a scientific revolution. Our paradigm of the Universe changed. Schmidt discovered not only an object that revolutionized our thinking about energy generation and the role of black holes in the formation and evolution of galaxies, he discovered a tool. This tool gave us a means to probe the depths of the cosmos in time and space. Before quasars, we had no experimental technique to measure the Universe across its epochs, and we certainly never would have "seen" (or conceived?) the cosmic web through its Lyman-alpha forest lines.
Selected Works:
Schmidt, M., & Greene, R.F. 1983, Quasar evolution derived from the Palomar bright quasar survey and other complete surveys, ApJ, 269, 352
Schmidt, M. 1969, Quasi-stelar objects, ARA&A, 7, 527
Schmidt, M., 1963, 3C 273: A star-like object with a large redshift, Nature, 197, 1040
This staged NY Times photo from 1963 shows Schmidt ostensibly studying the spectrum of 3C 273 using an intensity scanner.
How does a scientist make the cover of Time magazine? Simple. They change our world view. March 1966, Schmidt joins the likes of Einstein, Oppenheimer, Hubble, and Shapley.
Marteen Schmidt.
Nature, Volume 197, Issue 4872
(March 16, 1963)
Once 3C 273 was understood, Marteen Schmidt published his famous discovery paper in the March 16, 1963, issue of Nature (Volume 197, Issue 4872). As we mention above, Cyril Hazard also published his paper on the Moon occultation methods in the very same issue. In fact, four quasar-related companion papers were published in this issue of Nature. Together, these papers ushered in a new science of astronomy. Before this issues of Nature, the universe was known only locally. Within a few years, the Universe could be directly probed back in time roughly 12 billion years.
"Investigation of the Radio Source 3C 273 by the Method of Lunar Occultations" by C. Hazard, M. B. Mackey, and A. J. Shimmins.
"3C 273: A Star-Like Object with Large Redshift" by Maarten Schmidt. "
Absolute Energy Distribution in the Optical Spectrum of 3C 273" by J. B. Oke.
"Redshift of the Unusual Radio Source: 3C 48" by Jesse L. Greenstein and Thomas A. Matthews.
The fourth paper published the correct redshift of 3C 48, which was originally controversial (3C 48 was first published as a "radio star") but was finally accepted once the nature of 3C 273 was understood.
#5 Eleanor Margaret Burbidge
Margaret Burbidge
Margaret Burbidge was a Fellow of the Royal Astronomical Society, (RAS) and was awarded the a RAS Gold Medal, among many other career achievement awards. She has held several leadership posts such as Director of the Royal Greenwich Observatory, and President of both the American Astronomical Society and the American Association for the Advancement of Science. She helped develop the Faint Object Spectrograph for HST that was used for the now famous HST QSO Absorption Line Key Project. Burbidge finished out her career at UC San Diego, having lived 100 years.
Born: August 12, 1919
Died: April 5, 2020
PhD: University of London College, 1943
Nationality: British
Observed virtually all of the first quasars in the 1960s and early 1970s
Discovered broad absorption line quasars (also see Roger Lynds)
Made many first key insights and interpretations of quasar spectra
Proactively communicated/summarized quasar science to the broader scientific community
Margaret Burbidge is Quasar Pioneer #5 because she was both a prolific observer who rapidly built a database of quasar spectra and a key scientist in deciphering the complex patterns of absorption lines in these quasar spectra. Her worked super-charged the build up of the body of knowledge required to rule out countless interpretations and theories and narrow the number of viable interpretations. The large number of quasars she studied provided the diversity of information that allowed her to refine our understanding of what quasar absorption lines truly are. She also helped establish the luminosity-distance distributions for quasars and the fact that quasars are high-energy phenomena connected to supermassive black holes. During the first decade marked by a sea of confusing data, Burbidge was instrumental in distilling the essence of these objects and broadly communicating the nature of quasars to the scientific community.
In other news, Burbidge was part of the small cohort with Geoffrey Brubidge, William Fowler, and Sir Fred Hoyle (known as B2FH) to first correctly describe stellar nucleosynthesis. Margaret Burbidge was married to Quasar Pioneer #6, Geoffrey Burbidge. In 1967, the Burbidges co-authored the seminal book Quasi-Stellar Objects.
Selected Works:
Burbidge, E.M. 1970, Further spectroscopic observations of quasi-stellar objects and radio galaxies, ApJ, 160, 33
Burbidge, E.M. 1967, Quasi-stellar Objects, ARA&A, 5, 399
Burbidge, G.R. & Burbidge, E.M. 1967, Quasi-stellar objects, a series book in astronomy and astrophysics (San Francisco : W.H. Freeman)
Burbidge, E.M., Lynds, C.R., Burbidge, G.R. 1966, On the measurements and interpretation of absorption features in the spectrum of the quasi-stellar object 3C 191, ApJ, 144, 447
A young Burbidge was not allowed to observe at Mt. Wilson, but was allowed to "assist." She would take her husband along as the "observer" and have him assist her.
Burbidge delivers a lecture to her esteemed colleagues.
#6 Geoffrey Ronald Burbidge
Geoffrey Burbidge
Geoffrey Burbidge, occasionally and affectionately referred to as the "gadfly of the cosmos," was a formidable presence in the community. His sharp mind was finely tuned into observational details. His great talent was to see, articulate, and challenge percieved inconsistencies in the interpreations of the data. His direct challenges sharpened the dialog and drove follow-up observations for testing theories and hypotheses. Burbidge was a Fellow of the American Physical Society and was awarded the Warner Prize, the Bruce Medal, the Gold Medal of the Royal Astronomical Scoiety. He worked at Harvard, University of Chicago, Caltech, and Mt Wilson Observatory. In his early career, he would be the "observer of record" on behalf of his wife Margaret, Quasar Pioneer #5, who was a prolific observer. Burbidge lived to be 84 years old.
Born: September, 24, 1925
Died: January 26, 2010
PhD: University of London College, 1951
Nationality: British
Father of the quasar catalog (w/ Paul Hewitt)
Fierce proponent challenging alternative interpretations of quasar redshifts
Geoffrey Burbidge is Quasar Pioneer #6 because he was famous for challenging the status quo and highlighting inconsistencies in the countless ideas and theories about the nature of quasars, particularly regarding the interpretation of their cosmological redshifts. His main arguments involved the luminosity-distance distribution, which he argued was not consistent with the measured distributions of other cosmologically distributed astronomical objects. Burbidge remained a staunch supporter of a variation of Sir Fred Hoyle's 1948 Steady State Theory that he called the "Quasi-Steady State Theory." Because Burbidge so thoroughly studied all available quasar data, he compiled the data into a series of catalogs beginning in the mid-1970s that culminated in "the Bible" (a.k.a. "the phonebook") in 1993 w/ Paul Hewitt. SDSS quickly made his catalogs obsolete. However, for three decades, Burbidge's catalogs were a standard feature on the shelves of all quasar scientists and were carted to the summits of countless mountain tops for observing runs.
Burbidge was part of the small cohort with Margaret Brubidge, William Fowler, and Sir Fred Hoyle (known as B2FH) to first correctly describe stellar nucleosynthesis. Geoffrey Burbidge was married to Quasar Pioneer #5, Margaret Burbidge. In 1967, the Burbidges co-authored the seminal book Quasi-Stellar Objects.
Selected Works:
Hewitt, A., & Burbidge, G.R. 1993, A revised updated catalog of quasi-stellar objects, ApJS, 87, 451 (a.k.a. "the phonebook")
Burbidge, G.R. 1973, Problem of the redshifts, Nat. Phys, Sci, 246 (150), 17
Burbidge, G.R., & Burbidge, E.M. 1967, Limits to the distance of the quasi-stellar objects deduced from their absorption spectra, ApJ, 148, 107
Burbidge, G.R. & Burbidge, E.M. 1967, Quasi-stellar objects, a series book in astronomy and astrophysics (San Francisco : W.H. Freeman)
Burbidge posing for his 1962 faculty portrait at UC San Diego.
Burbidge affably chatting it up with colleagues. As pictured here, his famous cheshire smile and penetrating mischeiveious eyes were well known to telegraph a coming challenge and heated debate.
#7 Clarence Roger Lynds
Roger Lynds
Roger Lynds was an insightful observational astronomer and instrument builder who was key to the development of the science of quasar absorption lines. He had a very high aptitude for interpreting the more extreme manifestations of absorption lines in quasar spectra, such as the "forest" blueward of Lyman-alpha emission and extremely broad absorption troughs. He was instrumental in characterizing the flaw in the HST primary mirror shortly after its launch in 1990. Over his long career, Lynds worked at UC Berkeley, the Dominion Astrophysical Observatory, NRAO (yes, he also did radio astronomy!), and NOAO's Kitt Peak. In addition to his work on absorption lines in quasar spectra, he is famous for discovering gravitaional arcs behind galaxy clusters; he birthed the field of gravitational lenses. Lynds was a member of the National Academy of Sciences, a Miller Fellow (UC Brekeley), a Fellow of the Canada National Research Council, and a Fellow of the American Assocociation for the Advecement of Science. He lived to the age of 94.
Born: July 28, 1928
Died: April 16, 2023
PhD: University if California, Berkeley, 1955-56
Nationality: American
Early prolific observer of quasar spectra and instrumentalist
First to correctly proposed origin of Lyman-forest lines in quasar spectra
Discovered broad absorption line (BAL) quasars
C. Roger Lynds is Quasar Pioneer #7 because, (1) he was an early titan in the study of quasar absorption lines whose methods were adopted by many in the field, (2) he discovered the Lyman-alpha forest, and (3) he discovered broad absorption line (BAL) quasars and correctly interpreted them as high-velocity outflows on the order of 10,000 to 30,000 km/s.
Throughout the early 1960s, Lynds was on par with Margaret Burbidge for the number of quasar spectra he observed and published. He was famous for this efficiency at the telescope and became one of the most prolific observers of quasar spectra using the telescopes at Kitt Peak Observatory. In 1965, he determined that 3C 9 has a redshift of z=2.012. This was an astonishing discovery that instantly catapulted our look-back time into the universe from 4 to 10 billion years. It opened minds to the possibilities of probing back to the very edge and beginnings of the Universe.
In 1967, Lynds noted extreme absorption troughs carved out of the blue wings of the emission lines in the spectrum of PHL 5200. The classic P-Cygni profiles were similar to stellar wind signatures in stellar spectra and similar to the less extreme outflow signatures in the spectra of AGN. Lynds realized the features in PHL 5200 indicated a tremendous outflow with velocities up to 10-20% the speed of light (M. Burbidge found other early examples of BAL quasars).
In 1970, Lynds took the spectrum of 4C 05.34, which was the highest redshift quasar at the time (z=2.87). He noted a high line density blueward of the Lyman-alpha emission line and proposed that these lines were intervening Lyman-alpha absorption lines. In a Sky and Telescope article, he coined the moniker "Lyman-alpha forest," painting the image of the dense pattern of lines in the spectrum as a thicket of trees.
Selected Works:
Lynds, C.R., 1971, The absorption-line spectrum of 4C 05.34, ApJ, 164, L73
Lynds, C. R. 1967, A quasi-stellar source with a rapidly expanding envelope, ApJ, 147, 396
Lynds, C.R., Stockton, A.N., & Livingston, W.C. 1965, New spectroscopic observations of quasi-stellar sources, ApJ, 142, 1667
Lynds shown here posing for his faculty portrait for the NOAO.
Lynds was key in developing instrumentation for the national observatories and HST. Here, he is pictured inspecting instrumentation in the Cassegrain cage it the Mayall 4-m telescope. He pioneered speckle optics that enhanced "seeing" well before adaptive optics was declassified by the U.S. military.
#8 John Norris Bahcall
John Bahcall
John Bahcall made key early contributions to the interpretation of quasar absorption lines and was the Principle Investigator of the Hubble Space Telescope Quasar Absorption Lines Key Project. In addition, Bahcall was quite famous for his work on solar neutrinos, and was known as "The Godfather of Neutrinos." It is rare to be a giant contributor in one field, but Bahcall achieved that stature in two very different fields. He was a prolific scientist, having published over 600 refereed journal papers and nine books. His long list of awards and prizes includes the Gold Medal of the Royal Astronomical Society, the Fermi Award, the National Medal of Science, the Heineman Prize, and a NASA Distinguished Public Service Medal, and the Exceptional Scientific Achievement Award (posthumous). Bahcall lived to be 70 years old.
Born: December 30, 1934
Died: August 17, 2005
PhD: Harvard University, 1961
Nationality: American
Proposed Type I (associated) and Type II (intervening) Absorption Lines
Proposed metal lines arise in Clusters (w/ Ed Salpeter)
Proposed metal lines arise in extended halos of galaxies (w/ Lyman Spitzer)
Formulated Bahcall-Peeble Tests #1 and #2 (w/ Jim Peebles)
Architect and PI of the HST Quasar Absorption Line Key Project
John Bahcall is Quasar Pioneer #8 because he contributed to so many aspects of the science. He had an amazing insight and talent to infer what absorption line data were saying about the cosmos. He proposed the first objective methods for locating absorption systems by cross correlating redshifted standardized line lists. He proposed that metal lines could arise in galaxy clusters (w/ Ed Salpeter) and, soon after, that they arise in the halos of galaxies (w/ Lyman Sptizer). For the latter, he had to predict that these halos were highly extended around the galaxies, on the order of 100 kpc. And he was correct!
With Jim Peebles, Bahcall formulated two cosmological tests. Test #2 provided objective determination if a class of absorber was cosmologically distributed along the sightlines to quasars. It was instrumental in the work of Wal Sargent and collaborators, who applied it to MgII, CIV, and most famously, to Lyman-alpha forest lines.
Bahcall was Principal Investigator and Chief Scientist on the Hubble Space Telescope QSO Absorption Line Key Project. This project brought together the giants in the field with a single focus of efficiently acquiring and analyzing the ultraviolet (UV) spectra of quasars, a new spectral window opened by HST in the 1990s. This project started a legacy that evolved into the HST UV Initiative.
Selected Works:
Bahcall, J.N., Bergeron, J., Boksenberg, A., Hartig, G.F., Jannuzi, B.T., Kirhakos, S., Sargent, W.L.W., Savage, B.D., Schneider, D.P., Turnshek, D.A., Weymann, R.J., & Wolfe, A.M. 1993, The Hubble Space Telescope Quasar Absorption Line Key Projects. I. First observational results, including Lyman-alpha and Lyman-limit systems, ApJS, 87, 1
Bahcall, J.N., & Peebles P.J.E, 1969, Statistical tests for the origin of absorption lines observed in quasi-stellar sources, ApJ, 156, 7
Bahcall, J.N., & Spitzer, L, 1969, Absorption lines produced by galactic halos, ApJ, 156, 63
Bahcall, J.N., & Salpeter, E.E., 1965, On the interaction of radiation from distant sources with the intervening medium, AJ, 142, 1677
Bahcall was thinker and a doer. He wrote several theoretical papers on absorption line science that were decades ahead of the computing power required to solve the problems he tackled. He was prolific with ideas that influenced his fellow scientists and drove the direction of research. He was a talented manager and organizer and an inspiring team leader of observational programs.
Bahcall was also famous for his work on the solar neutrino problem. Here he is seen, hard hat on head, 2 miles down in a South Dakota mine, inspecting the Deep Underground Neutrino Experiment.
#9 Wallace Leslie William Sargent
Wal Sargent
Wal Sargent spent most of his career at Caltech. By many, he was considered to be the "father of quasar absorption line surveys." He led the second Palomar Sky Survey, which imaged ~50 millions galaxies. Sargent also took sevral lead roles in the developent of the W.M. Keck Observatory. He famously told the builder of the HIRES instrument, Steven Vogt, to design a "Quasar Eating Machine." Over the years, Sargent accumulated 100s of HIRES/Keck spectra (Wal's Vault) and mentored a string of Hubble Fellows to push the boundaries of our science. He was a Fellow of the American Academy of Arts and Sciences, a Fellow of the Royal Society, and a member of the National Academy of Sciences. Among other recognitions, he was awarded the Warner Prize, delivered an honorary Darwin Lecture to the Royal Astronomical Society, and received Heineman Prize and the Bruce Medal. Sargent lived to be 77 years old.
Born: February 15, 1935
Died: October 29, 2012
PhD: University of Manchester, 1959
Nationality: British
Creator of the unbiased uniform quasar absorption line survey (w/ Peter Young)
Established statistical nature of Lyman-alpha, Lyman-limit, CIV, and MgII absorbers
Pioneer of high-resolution (HIRES) studies
Wal Sargent is Quasar Pioneer #9 because he invented the modern methods to conduct quasar absorption lines surveys (w/ Peter Young) and then for decades led the these surveys and provided our first unbiased, statistically complete characterization of the four primary of absorber classes (MgII, CIV, LLSs, and Lyman-alpha forest). He was able to quantitative show that these absorbers are cosmologically distributed and was able to chart how they evolved with comsic time. He thus resolved several 20-year debates about the nature of absorption lines in quasar spectra. Much of Sargent's seminal work was in collaboration with Alex Boksenberg, who built and contributed his breakthrough instrument, the Image Photon Counting System (IPCS). This instrument was mated to the Palomar 200-inch telescope and provided exquisite quasar spectra. Sargent affectionately called their collaboration "Boksenberg's Flying Circus."
In addition to these foundational contributions (and countless other works), Sargent mentored an impressive array of students and quasar absorption lines scientists, such as Alex Filippenko, Tom Barlow, John Huchra, Lmin Lu, Michael Rauch, Rob Simcoe, Chuck Steidel, Ed Turner, and David Tytler, many of whom made remarkable and lasting contributions to absorption line science.
The far-reaching and lasting legacy of Wallace Sargent is profound and undeniable.
Selected Works:
Sargent, W.L.W., Boksenberg, A., & Steidel, C.C. 1989, A survey of Lyman-limit absorption in the spectra of 59 high-redshift QSOs, ApJS, 69, 703
Sargent, W.L.W., Boksenberg, A., & Steidel, C.C. 1988, CIV absorption in a new sample of 55 QSOs: Evolution and clustering of the heavy-element absorption redshifts, ApJS, 68, 539
Sargent, W.L.W., Steidel, C.C., & Boksenberg, A. 1988, MgII absorption in the spectra of high ans low redshift QSOs, ApJ, 334, 22
Sargent, W.L.W., Young, P.J., Boksenberg, A., & Tytler, D. 1980, The distribution of Lyman-alpha absorption lines in the spectra of six QSOs: Evidence for an extragalactic origin, ApJS, 42, 41 (eds. note: a seminal breakthrough paper!)
A young Sargent in his office at Caltech, no doubt in the midst of contemplating some absorption lines in a high-redshift quasar.
Sargent was honored with a statue outside Winterton Junior School in North Lincolnshire, UK, which he attended in his youth. It depicts Sargent looking up at the stars.
#10 Arthur Michael Wolfe
Art Wolfe
Art Wolfe was the Chancellor’s Associates Chair of Physics at UC San Diego. Over the span of his career he worked at the University of Cambridge, the Lebedev Physical Institute in Moscow, and the University of Pittsburgh before becoming a Professor in the Physics Department at UC San Diego and later the Director of the Center for Space Science. He was a Fellow of the American Academy of Arts and Sciences and the American Association for the Advancement of Science. He was a Sackler Fellow at the University of Cambridge and a recipient of the prestigious Jansky Prize. His research explored and impacted so many areas, including Zeeman splitting at high redshift and excited ions as indicators of star formation, for example. Wolfe lived to the the age of 74.
Born: April 29, 1939
Died: February 17, 2014
PhD: University of Texas Austin, 1967
Nationality: American
Discovered Sachs-Wolfe Effect (gravitational redshifting of CMB photons)
Established damped Lyman-alpha absorber (DLA) population
Pioneered HI mass density - global star formation evolution relations
Pioneered cosmic chemical evolution using DLAs
Engaged in the search of evolution in fine structure constant using absorption lines
Art Wolfe is Quasar Pioneer #10 because he was first to established the cosmic incidence of the population of damped Lyman Alpha Absorbers (DLAs). He had the vision to realize that these objects may constitute an important component of the Universe. He then trail blazed an array of studies exploiting DLA properties to measure cosmic evolution of metallicity and star formation rates. He also measured the HI mass density at high redshifts (w/ Lisa Storrie-Lombardi). With his students Ken Lanzetta, Limin Lu, Jason X. Prochaska, Regina Jorgenson, and Marc Rafelski, Wolfe made foundational and seminal contributions to high-resolution studies of the kinematics and chemical abundances of the metal-lines associated with DLAs.
Wolfe literally birthed a whole sub-branch of quasar absorption line science that continues to have far-reaching impacts on cosmology and galaxy formation and inspire generations of researchers to pursue DLA focused research.
Selected Works:
Wolfe, A.M., Gawiser, E. & Prochaska, J.X. 2005, Damped Ly-alpha Systems, ARA&A 43, 861
Wolfe, A.M., & Wills, B.J. 1977, A study of the optical and radio absorption-line systems in AO 0235+164, ApJ, 218, 39
Wolfe, A.M., Turnshek D.A, Smith, H.E., & Cohen, R.D. 1986, Damped Lyman-alpha absorption by disk galaxies with large redshifts. I. The Lick survey, ApJS, 61, 249
Damped Lyman-alpha absorption line shows the unique profile shape with a staurated core and broad damping wings. The wings directly yield the column density. Because the gas column density is so high, even the lowest-metallicity absorbers will exhibit substantial metal-line column densities. Thus, metallicity is measured with great sensitivity. Furthermore, because the gas is mostly neutral, ionization corrections are small to negligible. DLAs are ideal systems for studying cosmic chemical evolution.
#11 Jacqueline Andrée Bergeron
Jacqueline Bergeron
Jaqueline Bergeron was a pioneer in establishing the connection between galaxies and metal absorption lines in quasar spectra. Her seminal paper with Patrick Biossé in 1991 is foundational to the field. Throughout her career, she worked at Cambridge (w/ James Feldon), Cornell University, (w/ Ed Salpeter) Caltech (w/ Wal Sargent and Marteen Schmidt). She spent most of her career at the Institut d'Astrophysique de Paris. She served as the Director of ESO, and as General Secretary of IAU. She was inducted into France's most prestigious order, the Légion d’Honneur, for her sceintific contributions. Bergeron lived to be 82 years old.
Born: January 28, 1942
Died: December 20, 2024
PhD: Paris, 1972
Nationality: French
Predicted the true nature of the Lyman-alpha forst clouds (w/ Ed Salpeter)
First high resolution CIV and MgII kinematics (w/ Patrick Petitjean)
Firmly established MgII absorber arise in galaxy halos (w/ Patrick Biossé)
Pioneering work on high-ionization absorption line systems at high redshifts
Jacqueline Bergeron is Quasar Pioneer #11 because she was the first scientist to firmly establish the connection between low-ionization metal absorption lines and galaxies (w/ Patrick Boissé). By 1991, after half a decade of efforts, she observationally established that galaxies have highly extended gas halos, thus confirming the 1969 hypothesis of John Bahcall and Lyman Spitzer.
Bergeron (w/ Grazyna Sasinska) was also known for being first to demonstrate that photoionization models can explain the column density ratios in metal-line absorbers. This opened the field to analysis methods that allowed the chemical abundances and gas phase conditions to be estimated from measured column densities in quasar absorption lines. Today, these (now highly sophisticated) methods remain a cornerstone in the analysis of absorption lines systems.
In her very early career, still as a gradate student, she and Ed Salpeter were the first to correctly interpreted the nature of the Ly-alpha forest as warm HI clouds in the intergalactic medium ionized by a ubiquitous ultra-violet background of radiation from quasars and galaxies. In her later career, she broke scientific ground studying and characterising the properties of high-ionization absorbers at higher redshifts.
Selected Works:
Bergeron, J., Aracil, B., Petitjean, P. 2002, The warm-hot intergalactic medium at z~2.2: Metal enrichment and ionization source, A&A, 396, L11
Bergeron, J. & Boissé, P. 1991, A sample of galaxies giving rise to Mg II quasar absorption systems, A&A, 243, 344
Bergeron, J. & Stasinska, G. 1986, Absorption lines systems in QSO spectra: Properties derived from observations and from photoionization models, A&A, 169, 1
Bergeron, J., & Salpeter, E.E. 1970, Photo-ionization of intergalactic matter, Astrophysical Letters, 7, 115
This photo of Bergeron as a graduate student was taken in 1970, when she was 28 years old. This is the same year she worked out the physics of the ionization of the IGM by a UV background. (Cropped from a photo of the faculty and research staff at IoA, Cambridge; credit: Edward Leigh)
Bergeron reporting her most recent results at an international conference on quasar absorption line science.
Quasar Pioneers
Honorable Mentions
Jesse Greenstein
(Oct 15, 1909 - Oct 21, 2002). American astronomer Jesse Greenstein (Carnegie Observatories) was a close collaborator of Marteen Schmidt, Allan Sandage, and Tom Bolton at Caltech. He was part of the small elite group of astronomers that wrestled with the nature of emissions lines observed in the very first quasar spectrum of 3C 48. In a 1964 paper, Greenstein and Schmidt proposed that quasars must be supermassive compact objects fueled by intense gravitational infalling gas.
Notable students: Helmut Abt
Thomas Matthews
American astronomer Thomas Matthews (Caltech) is credited, along with Alaln Sandage and John Bolton. with being one of the discoverers of the very first quasi-setllar object, 3C 48. In 1960, we was a prime observer using the newly commissioned Owens Valley interferometer built by John Bolton.
Notable students: Richard Tully
Carl Seyfert
(Feb 11, 1911 - Jun 13, 1960) American astronomer Carl Seyfert was a student of the famous Harlow Shapley. Seyfert is best known for his pioneering studies of emission line galaxies in the 1940s. He essentially was the first to study and classify AGN (which would soon be called radio galaxies). Today, this class of galaxies bear his name. His life was tragically cut short by an auto accident. Ken Kellerman (one of John Bolton's students) has speculated as to how the course of the discovery quasars and the circuitous path to the realization they were high-redshift objects may have been shortened had Seyfert lived through the next decade.
Lyman Spitzer
(Jun 26, 1914 - Mar 31, 1997) American astrophysicists Lyman Spitzer (Princeton) made countless significant contributions to physics, astrophysics, and engineering. He was first to propose that hot diffuse gas was present around galaxies. As early as 1948, Spitzer proposed space telescopes to access the high-ionization ultraviolet absorption lines in bright background stars (quasar would not be discovered for another 17 years!). With Jon Rogerson and Don York, Spitzer was involved with the Copernicus space telescope to measure the first OVI absorption in the ISM of the Galaxy.
Notable students: Carl Heiles, Bev Oke, and Leonard Searle.
Quasar Absorption Trailblazers
Active years beginning in the 1960s
Alec Boksenberg
British astronomer Alex Boksenberg (a.k.a. Boskey, Cambridge University) is credited with breaking the field of quasar spectroscopy wide open in the 1970s with his highly sensitive high-resolution Image Photon Counting System (ICPS). It was highly sensitive with a linear response and no read noise. It boasted a resolution of 0.2 Å (12 km/s)! In collaboration with Wal Sargent, Boksey engaged in research ranging from MgII and CIV surveys to galaxy halo studies. In 2015, he authored the seminal work on CIV and SiIV kinematics at z~3.5 using the HIRES/Keck spectrograph.
Notable students: Erik Stengler
Robert Carswell
British astronomer Bob Carswell (Univ. of Sussex) is the primary author of the workhorse spectral fitting routine VPFIT (w/ John Webb). He pioneered Voigt profile fitting of both Lyman-alpha and metal-line absorbers in early (pre-Keck/VLT) high-resolution spectra. With Ray Weymann and Dennis Walsh, he is credited with identifying and studying the the spectra of the first lensed quasar pair. Carswell is also a co-author on 1981 seminal Annual Review article. "QSO Absorption Lines in the Spectra of Quasi-Stellar objects."
Notable students: Michael Rauch, John Webb, and Gerry Williger
James Gunn
American astronomer James Gunn (Princeton), while still in graduate school at Caltech i 1965, proposed the Gunn-Peterson (GP) Effect, which was observed 35 years later. The GP trough has been a key to understanding the Epoch of Reionization. Gunn conceived the Sloan Digitial Sky Survey (SDSS) and led efforts to bring it to fruition. Four-color selection was a key design component and SDSS was instrumental in finding some million high-redshift quasars, which forever transformed the field of quasar absorption lines.
Notable students: Augustus Oemler, Paul Schechter, and Don Schneider
Blair Savage
(Jul 7, 1941 - Jul 19, 2022) American astronomer Blair Savage (Univ. of Wisconsin, Madison) is notable for his work on the Galactic ISM, corona, and CGM, including high-velocity clouds (HVCs) and the Magellanic Stream. He broke new ground with every new space telescope (OAO-2, Copernicus, IUE, FUSE, and HST), and was primary member of the HST QSO Absorption Line Key Project. Savage was a prolific scientist , having contributed to more then 550 journal articles.
Notable students: Andrew Fox, Chris Howk, Ken Sembach, and Todd Tripp
Peter Strittmatter
British-born astronomer Peter Strittmatter (Univ. of Arizona) is best known for classification of quasars via study of peculiar spectral features. He proposed the class known as BL Lacertae Objects. In the early days, Strittmatter strongly argued that all quasar absorption lines were "intrinsic." meaning associated with the quasar environment. He lost that debate. He conducted early surveys of MgII and CIV and found an ionization proximity effect around quasars.
Notable students: Bradley Peterson.
Ray Weymann
American astronomer Ray Weymann (Carnegie Observatories) is highly recognized as the primary author of the 1981 Annual Review "Absorption Lines in the Spectra of Quasi-Stellar Objects," which was the foundational work for two generations of astronomers. During his active career, he was a prolific and versatile quasar absorption line astronomer- his work ranged from metal-line surveys to gravitational lenses, to the nature of galaxy halos He was a primary mmber of the HST Quasar Absorption Line Key Project, through which he characterized the evolution of the z<1.6 Lyman-alpha forest.
Notable students: Todd Boroson, and David Turnshek.
Donald York
(1944 - Dec 26, 2025) American astronomer Don York (Univ. of Chicago) is a giant in the field of ISM studies and quasar absorption lines. He is a member of the first team to measure D/H and OVI absorption in the Milky Way (w/ Jon Rogerson) using the revolutionary Copernicus satellite. He is a co-founder of SDSS and originator of the SDSS quasar catalog. He steadfastly challenged the notion of a single monolithic gas halo around galaxies, thus foreshadowing the baryon cycle and its various infalling and outflowing components.
Notable students: Jim Lauroesch, Gordon Richards, and Dan Vanden Berk.
Active years beginning in the 1970s
Frank Briggs
Frank Briggs pioneered radio-band 21-cm absorption in the spectra of quasars. He opened the door to probing the CNM and the WNM in HI absorption the ISM of high-redshift galaxies. He clearly established that the neutral ISM gas resides in a two-phase medium and in BAL quasar winds. His work has since been built on and comprehensive deep redshift path surveys of 21-cm absorbers have been conducted out to the very high redshifts. Future work will likely observed redshift drift and absorption agains the CMB.
Notable students: Wendy Lane, Sandhya Rao, and Martin Zwaan
Frederic Chaffee
American astronomer Fred Chaffee (SAO) contributed foundation insights into a broad range of quasar science. He is known for pushing high-resolution observations to their very limit before 10-meter class telescopes made it routine. He was first to resolve the Lyman-alpha forest and constrain the physical conditions of IGM clouds. He use gravitational lenses to constrain the sizes of metal-line absorbers, and was prolific in the field of BAL quasars studies, and constrained their frequency. He was an early pioneer of D/H studies. Chaffee rounded out his career by servinfgas Directory of the W.M. Keck Observatory.
Lenox Cowie
Scotland-born British astronomer Len Cowie (Univ. of Hawaii) is highly notable for his work on quasar absorption line systems observed with HIRES/keck. He has studied the evolution of the Lyman-alpha forest (with Ester Hu), early-epoch D/H, DLAs, and metal-enrichment evolution (including proving that the Lyman-alpha forest was not "pristine.") He conducted some of the very first observations characterizing the Epoch of HI Reionization (w/ Antoinette Songaila).
Notable students: Jiasheng Huang, Li-Yen Hsu
Max Pettini
Italian-born astronomer Max Pettini (Cambridge University) is renown for his research on the chemical evolution of galaxies, the intergalactic medium, D/H measurements, and high-redshift galaxies. He is a Fellow of the Royal Society (2010) and received the Herschel Medal from the Royal Astronomical Society (2008.) Pettini recently received the Gruber Cosmology Prize with Ryan Cooke for precision D/H measurements.
Notable students: Ryan Cooke, Sara Ellison, Anna Quidar
Donald Schneider
American astronomer Don Schneider (Penn State) was a stduent of James Gunn (of the Gunn-Peterson Effect). As part of the HST Quasar Absorption Line Key Project, Schneider developed objective absorption line detection algorithms that remain state of the art. He is renown for his pioneering use of color selection to find z>4 quasars, which paved the way for finding quasars up to z~10. Schneider has also contributed to studies of large scale structure and our understanding of extragalactic black holes.
Notable students: Jianjian Shen
J. Michael Shull
American astronomer Mike Shull (UC Boulder) is known for his breakthrough studies of the baryon budget of WHIM gas .At Boulder, he and collaborator John Stocke participated in the design and building of the COS instrument. They built a team of AGN/quasar absorption line researchers with which they did pioneering and highly thorough measurements of the properties of the z<0.4 IGM.
Shull has several notable students, including (but not limited to) Charles Danforth, and Jason Tumlinson
Beverly Wills
American astronomer Bev Wills (Univ. of Texas, Austin) is known for her long standing contributions and body of work in the field of AGN and quasars. She was instrumental in identifying the class of radio-quiet blazars, a subclass of active galaxies where the relativistic jet of ionized matter is directed almost directly toward the observer. She has extensively studied the broad absorption lines (BAL) quasars and has been instrumental in building insight into their black hole "engines," structure, and variability.
Notable students: Feng Ma, and Michael Brotherton.
Peter Young
(Jul 31, 1954 - Sep 5, 1981) British-born astrophysicist Peter Young was a brilliant researcher who died tragically while a postdoc at Caltech. He had recently finished his PhD under Wal Sargent at Caltech. which he accomplished in an amazing short 18 months. His few papers in the early 1980s wrote the book on how to undertake and analyze a uniform unbiased survey of a population of absorbers. Literally, all work in the field of quasar absorption lines since the early-1980s has deep roots in the methodologies he developed and pioneered.
Active years beginning in the early-1980s
Jill Bechtold
(??? - Jan 12, 2024) American astronomer Jill Bechtold (Univ. of Arizona) conducted large surveys of Lyman-alpha absorption using HST; she built the VizieR HST/FOS Spectral Atlas known as the "Bechtold Catalog." She pioneered studies of the low-redshift Lyman-alpha forest and proximity effect to measure the UV background spectrum. Bechtold also did early ground-breaking work on the kinematics of strong metal-line absorbers
Notable students: Jennifer Scott.
Patrick Biossé
French astronomer Patrick Biossé (Institut d'Astrophysique de Paris) was co-author on the seminal 1991 paper with Jaqueline Bergeron that established MgII absorbers arise in the halos of galaxies. His absorption line work included metal lines, Lyman-alpha forest ines, and DLAs. He was an early adopter of ionization modeling to gain insights into the chemical and ionization conditions of absorbing gas, especially small sub-parsec gas structures. Biossé participated in studies searching for time variations in intervening narrow metal-line absorbers at high redshifts.
Graig Foltz
American astronomer Craig Foltz (MMT Observatory) was a leading researcher who was instrumental in characterizing radio and optical properties of quasars. He was an important contributor to the seminal Large Bright Quasar Survey (LBQS), which was one of the first surveys to characterize the overall quasar population. He also conducted impactful and influential studies of BAL absorption and metal-line absorption, such a MgII and CIV. Foltz served as Directory of the MMT Observatory, Program Manager for ALMA, and then Astronomical Sciences Acting Deputy Division Director for the NSF.
Frederick Hamann
American astronomer Fred Hamann (UC Riverside) is a a leading expert on the broad absorption line (BAL) outflows of quasars. Using high-resolution spectra, he pioneered methods of analysis to study the complex nature of numerous BAL quasars, including their ionization, gas phases, metallicities, covering factors, and evolution. He is credited for the discovery of Extremely Red Quasars (ERQs) in the SDSS database.
Notable students: Chen Chen, and Paolo, Rodríguez Hidalgo
Antoinette Songaila
Antoinette Songaila (Univ. of Hawaii) engagd in ground-breaking work using HIRES/Keck to measure the column density distribution functions and gas mass densities of CIV and SiIV absorbers. She introduced her "super-POD" method, which used flux-decrement distributions of individual pixels. She explored the effects of HeII ionization in the IGM at z=3-4 and partook in early studies of the early-epoch D/H ratio.
David Tytler
British-born astronomer David Tyler (UC San Diego) is primarily known for his meticulous measurements of the D/H ratio at high redshifts for placing constraints on the cosmic baryon mass density. His early work characterized the properties of Lyman-limit systems (LLS) as well as established their importance astrophysically.
Notable students: Scott Burles, David Kirkman, and John O'Meara
David Turnshek
American astronomer David Turnshek (Univ .of Pittsburgh) is well known for his early breakthrough work on BAL quasars. He and his primary collaborator Sandya Rao pioneered efficient methods to select for z<1 DLAs using MgII/FeII absorption and studied the z<1 HI mass density and nature (morpologies, luminosities, etc.) of DLA-selected galaxies.
Notable students: Dan Nestor
C. Megan Urry
American astronomer Meg Urry (Yale) is best known for championing unification models of AGN, studies of the role of black holes in the evolution of galaxies, and for her leadership and body of work supporting women in the sciences. In all three areas she has had significant impact on the science and on the culture of science. She had received dozens of professional awards over her career.
Notable students: Arita Ghosh, and Matthew O'Dowd (yes, that Matt O'Dowd from PBS Spacetime).
John Webb
British astronomer John Webb (Univ. of New South Wales) is best known for his breakthrough "many-multiplet" analysis methods for studying the evolution of the fine-structure constant using quasar absorption lines. He has also played a large role in the development of VPfit. Webb was highly involved in the flurry of D/H ratio measurements being conducted in the 1990s.
Notable students: Neil Crighton, and Michael Murphy
Active years beginning in the late 1980s
Jane Charlton
American astronomer Jane Charlton (Penn State) was a child prodigy who earned her B.S, in Physics and Chemistry at the age of 18. In her early career, she is known for her theoretical work with Ed Salpeter. Transitioning into the 1990s, Charlton began experimenting with multi-phase ionization modeling of absorbers and over the years has pioneered techniques to extract the detailed cloud-by-cloud densities, temperatures, kinematics, and metallicities. Her work was foundational leading to Bayesian inference and MCMC methods (w/ Sameer) that have yielded significant insights into metal-line absorbers and the CGM.
Notable Students: Ragib Ganguly, Anand Naryanan, and Jane Rigby
Kenneth Lanzetta
American astronomer Ken Lanzetta (SUNY Stoneybrook) was a student of Art Wolfe and worked with David Turnshek. In his early career, Lanzetta studied MgII absorbers and DLAs. In a series of papers in the mid-1990s, he established the HI extent of galaxy halos using Lyman-alpha absorbers He had written the first modern notes on Quasar Absorption Lines for graduate classes. In his later career, Lanzetta became involved in private ventures and remains active using the Condor Array Telescope to image filaments in the cosmic web.
Notable students: Hsiao-Wen Chen.
Karen Leighly
American astronomer Karen Leighly (Univ. of Oklahoma) is recognized for her work on the X-ray variability of narrow-line Seyfert galaxies and extensive research on the nature of broad absorption lines (BALs). She has developed the state-of-the-art spectral synthesis code SimBAL, which is capable of forward modeling using Bayesian "calibration" and MCMC to constraint the physical conditions of BALs. Coupled with her use of infrared spectroscopy, she has learned how to penetrate deep into these winds and extract accurate column densities, gas densities, and ionization states.
Patrick Petitjean
French astronomer Patrick Petitjean (Institut d'Astrophysique de Paris) is well known for his work on MgII, CIV, and DLA systems. He has advanced research in the areas of high-resolution studies of the IGM, precision spectroscopy to verify the constancy of the fine-structure constant, and absorption line measurements of the temperature of the CMB in the early universe. Petitjean often collaborated with Jaqueline Bergeron.
Notable Students: Cédric Ledoux, Bastian Aracil, and Pasquier Noterdaeme.
Kenneth Sembach
American astronomer Ken Sembach (STScI) was a student of Blair Savage. He was a past Director of STScI and Deputy Project Scientists for the Far Ultraviolet Spectroscopic Explorer (FUSE). He pioneered ultraviolet absorption line spectroscopy (SiIV, CIV, OVI and NV) of the diffuse ISM and CGM gas in the Milky Way galaxy. In colaboration with Blair Savage, Sembach was instrumental in early characterizations of the chemical composition, kinematics, and ionization conditions of Galactic gas.
Charles Steidel
American astronomer Chuck Steidel (Caltech) was a student of the late great Wal Sargent. Steidel is known for early large absorption lines surveys of MgII and CIV, and LLS absorber classes. He is well known for his work establishing the sizes and kinematics of galaxy halos using MgII absorbers. In the mid-1990s, Steidel broke open the redshift 2.5 universe using Lyman Break Galaxies. He is PI of the highly successful Keck Baryonic Structure Survey.
Steidel has several notable students including (but not limited to) Dawn Erb, Gwen Rudie, and Alice Shapley.
This blog has been fully written by the author. There has been no AI assistance with the writing or grammar; however, NASA/ADS, Wikipedia, and Google AI assisted searches were employed. This blog made use of the Astronomy Genealogy Project (astrogen.aas.org).
Copyright 2026 Christopher W. Churchill
60 Years of Quasars in Two Volumes
Order Your Copies Today!
Volume 1 : Cambridge university Press | Amazon
Volume 2 : Cambridge university Press | Amazon
Page updated
Google Sites
Report abuse