The genius idea that afternoon led Time magazine to compare him to Galileo

In his more than 50 years of academic career, Schmidt made outstanding contributions to human exploration of the universe with his extraordinary intelligence, keen intuition, advanced thinking, romantic feelings and tenacious will, and also won the due honor. He can rest in peace.

Written by | Wang Shanqin

On September 17, 2022, Maarten Schmidt (1929-2022), an outstanding astronomer and legend in the field of astronomy, passed away at the age of 92.

Martin Schmidt. Image source: [1]

A young and promising man with a distinguished background

Schmidt was born on December 28, 1929 in Groningen, the Netherlands. His father, Wilhelm Schmidt, was a government accountant, and his mother, Annie Wilhelmina Schmidt, was a housewife.[2]

Under the guidance of his uncle, a pharmacist and amateur astronomer, Schmidt built a telescope using two lenses and a paper tube. Due to the blackout during World War II, he was able to observe the stars from the center of the city. He sought out and read every astronomy book he could find. [2]

In 1949, Schmidt received a bachelor's degree from the University of Groningen and a master's degree one year later. Then, Schmidt entered the Leiden Observatory in the Netherlands to study for a doctorate under the master of astronomy Jan Hendrik Oort (1900-1992).

After spending a year as a doctoral student in Kenya observing stars and measuring their positions, Schmidt returned to Leiden University Observatory to map the morphology of the Milky Way using a radio telescope system to observe the 21-cm spectral line emitted by hydrogen molecular clouds in the spiral arms of the Milky Way.

In 1955, Schmidt married Cornelia Tom. [2] They had three daughters: Anne Schmidt, Marijke Schmidt and Elizabeth Schmidt. [3]

In 1956, Schmidt received his doctorate in astronomy, with the subject of his dissertation being to determine the mass distribution of the Milky Way using observations of the 21-cm spectral line.

For the next two years, Schmidt worked as a Carnegie Fellow at Mt. Wilson and Palomar Observatories, similar to today's postdoctoral work. This strange-sounding unit was formed by the merger of the former Mt. Wilson Observatory and Palomar Observatory.

In 1958, Schmidt returned to Leiden University. A year later, he was hired by Wilson and Palomar Observatory, and served as an associate professor at Caltech. [3] At that time, Palomar Observatory had a 200-inch (5.08-meter) Hale telescope, which was the largest and most powerful optical telescope in the world at that time. In astronomy, "optical" refers to visible light.

The main mirror of the Hale telescope in its polished state in December 1945. To reduce weight, its back has been hollowed out to create a honeycomb structure. Image source: [4]

In 1959, Schmidt published a paper[5] that linked the density of interstellar gas to the rate of star formation in it, a result known as the "Schmidt law." At the time, Schmidt was less than 30 years old.

Schmidt's paper has had a profound impact on the theory of star formation and has been cited at least two thousand times to date.

Mysterious radio sources, mysterious "stars"

Under the influence of his colleague, radio astronomer Thomas A. Matthews, Schmidt began to enter the field of radio sources. The so-called radio is radio. Radio sources refer to celestial bodies that emit radio radiation.

Since the 1950s, radio astronomy has flourished. Radio astronomers have discovered many radio sources in the sky. Astronomers in the Cambridge group compiled them into a table and kept updating it.

In 1959, this star catalog was updated and published as the "Third Cambridge Catalog of Radio Sources", which is the famous "3C Catalog". 3 stands for the third and C stands for Cambridge. All the radio source numbers in the 3C Catalog begin with "3C".

These radio sources are of great interest to astronomers, who image them with optical telescopes in order to identify their optical counterparts.

In the spring of 1960, Schmidt's colleague Rudolph Minkowski (1895-1976)[Note 1] confirmed that 3C 295 in the 3C table was a galaxy based on observations with the Hale telescope. Its redshift was 0.461[6], which was twice the record for the redshift of galaxies previously measured. Galaxies that emit strong radio radiation are called "radio galaxies."

In the summer of 1960, Matthews approached Allan Sandage (1926-2010) and asked him to use the Hale telescope to observe the 10 apparently small radio sources he had circled to determine whether they were radio galaxies.[7]

Alan Sandage. Image source: [8]

In September 1960, Sandage used the Hale telescope to observe the 48th radio source in the table, 3C 48, and detected a blue object similar to a star of about magnitude 16, surrounded by a small wisp of nebula-like material. Both Matthews and Sandage believed that this was a "radio star" that had never been seen before. [7]

Although a 16th-magnitude star is 10,000 times dimmer than the faintest star most people can see (6th magnitude), it is clearly bright in the "eye" of the Hale telescope.

Sandage photographed its spectrum and measured some of the emission lines in the spectrum, and found that they did not correspond to the spectral lines in the laboratory at all. Sandage took the spectrum of 3C 48 to communicate with Jesse Greenstein (1909-2002) and others. Greenstein was also unable to reach a clear conclusion.

In addition, Sandage's continuous observations also showed that the optical brightness of 3C 48 changes by half every 14 days, from which it can be inferred that the size of its luminous area is only a few times the size of the solar system. This result made Sandage more convinced that this is a star.

In 1962, Sandage photographed the position of 3C 273 in the 3C table and discovered a light blue star of about magnitude 13, 16 times brighter than 3C 48 of magnitude 16. Sandage also discovered a glowing "spine" in the middle of 3C 273 that resembled nebula. We now know that this "spine" is actually a jet ejected from 3C 273. [7]

Visible light image of 3C 273 (central bright spot) taken by the Hubble Space Telescope (Hubble) WFPC2. The columnar streak to the upper left of the central bright spot is the jet it emits, which is about 200,000 light-years long. Image source: [9]

But Sandage did not (or failed to) think deeply about the nature of this "star" and its "spikes." He also could not determine the more precise location of 3C 273 as a radio source, and therefore could not prove that 3C 273 and the 13th-magnitude "star" were exactly in the same position.

What Sandage didn't expect was that his colleague Schmidt would soon overtake him.

The ingenious idea behind a ruler

In the fall of 1962, Cyril Hazard and collaborators used the Parkes radio telescope to determine a more precise position of 3C 273, taking advantage of an obscuration of the moon over it. [10] They then sent the position to Matthews, who in turn forwarded it to Schmidt.

Hazzard observing from Jodrell Bank Observatory in the 1950s. Image credit: [11]

The precise location where Schmidt found 3C 273 coincided with the location where Sandage found the small, bright blue "star", which meant that the small blue "star" was the optical counterpart of 3C 273. A storm of astronomy was about to come.

On December 27, 1962, Schmidt took a spectrum of 3C 273 using the Hale telescope. It was so bright that the normal exposure time caused the film to be overexposed. [12] Schmidt successfully obtained its spectrum the second and third time.

Schmidt found that the spectrum of 3C 273 was very strange, with nine fairly wide emission lines. Among them, four emission lines with central wavelengths of 323.9 nanometers, 503.2 nanometers, 563.2 nanometers, and 579.2 nanometers were particularly prominent. Two other spectral lines at 459.5 nanometers and 475.3 nanometers were also identified. The central wavelengths of the remaining three spectral lines had a large error range.

Schmidt was unable to determine which chemical element these emission lines corresponded to. He tried many times to solve the mystery, but to no avail. He was so distressed that he wanted to give up.

At about the same time, Schmidt's colleague Beverley Oke used the 100-inch (254 cm) Hooker Telescope at Wilson Observatory to take a spectrum of 3C 273, which showed a strong emission line in the infrared band with a wavelength of 759.0 nanometers.

On the afternoon of Monday, February 5, 1963, Schmidt came to his office to continue thinking about his results. When he put the spectrum plate into the instrument, he suddenly realized that the distribution of three of the emission lines he had confirmed was very similar to that of the Balmer line series of hydrogen[Note 2].

Then, an idea that went against his ancestral teachings suddenly occurred to Schmidt: these spectral lines might be the emission lines of hydrogen, but they were moved to the red end ("redshifted").

This seemingly crazy idea excited Schmidt inexplicably. He immediately found a crude sliding ruler nearby, [7] and directly measured the amount of movement. He then immediately found that the red shift of 3C 273 was 0.158. In other words, these spectra were the spectral lines of hydrogen, but their wavelengths were stretched 0.158 times.

Schmidt followed up with his success and determined the nature of all the emission lines with confirmed wavelengths: the line photographed by Oak was the Hα line in the Balmer line system of hydrogen; four of the six lines he confirmed were the Hβ, Hγ, Hδ and Hε lines. [Note 3, Note 4] The other two emission lines were the once ionized magnesium (Mg II) and the twice ionized oxygen forbidden line ([O III]). [Note 5]

The optical spectrum of 3C 273 taken by Schmidt (top) and the comparison spectrum in the laboratory (Comparison Spectrum, bottom). Blue represents blue, Red represents red, and Red Shift represents redshift. The Hδ/410 nm, Hγ/434 nm, and Hβ/486 nm below are the three Balmer lines of hydrogen in the laboratory and their corresponding wavelengths. The same symbols above represent their positions after being redshifted. Image source: [13]

Schmidt walked out of the office excitedly. While walking in the corridor, he happened to meet Greenstein. He immediately told the latter about his discovery. Greenstein suddenly realized that he had previously imagined that the spectrum of 3C 48 had a significant red shift, but he gave up this idea because he believed it was a star in the Milky Way. With the confirmation of Schmidt's work, Greenstein strengthened his confidence. Greenstein and Schmidt only took 5 to 7 minutes to determine that the red shift of 3C 48 was 0.37, which was larger than the red shift of 3C 273.

The noise they made during their discussion startled Oak, who hurried over to ask what was going on. The three of them then spent the next few hours in the office discussing: In addition to the redshift explanation, are there any other explanations? They discussed until 6 p.m., but none of them could come up with another explanation. [12] So, the "redshift" explanation should be the most natural one.

After 6 o'clock, the three decided to go home. Schmidt was so excited that he did not go home immediately. Instead, he went to Greenstein's house with Oak to celebrate. Late at night, Schmidt returned home and said to his wife, "Something terrible happened at the office." [12]

He later recalled that his English expression might not be accurate[12], but he did say "terrible". Perhaps he meant "astonishing".

Schmidt's discovery was indeed shocking: combining the distance with the observed brightness, it can be calculated that the luminosity of 3C 273 is about 2 trillion times that of the sun (modern calculations show that the value is 4 trillion times), which is about 100 times the luminosity of the brightest radio galaxy confirmed at the time. An object much smaller than the Milky Way is much brighter than the galaxy, which was really shocking at the time.

What is it exactly?

"The core of the galaxy"

Schmidt soon wrote a paper discussing the spectrum of 3C 273 and interpreting the emission lines as hydrogen, magnesium, and oxygen lines redshifted by a factor of 0.158. The paper was published in Nature and was titled "3C 273: a large-redshifted quasi-object".[14]

In fact, that issue of Nature published four closely related papers in succession. The first was the paper by Hazard et al. measuring the precise position of 3C 273[10], the second was the paper by Schmidt determining the redshift of 3C 273[14], the third was the paper by Oak discovering the infrared emission lines of 3C 273[15], and the fourth was the paper by Greenstein and Matthews determining the redshift of 3C 48[16].

In this landmark paper of less than a page, Schmidt reported his observations and pointed out that the redshift of 3C 273 was basically not a "gravitational redshift" caused by the gravity of stars, but a "cosmological redshift" caused by the expansion of the universe.

Schmidt believed that 3C 273 was the core of a galaxy whose redshift was 0.158 and whose speed was 0.158 times the speed of light, or 47,400 kilometers per second.

Schmidt calculated that 3C 273 is about 500 million parsecs away from Earth, or about 1.6 billion light-years (2.44 billion light-years based on the modern Hubble constant). Schmidt also calculated that 3C 273's diameter is less than 1000 parsecs (3262 light-years, 1000 parsecs is just a rough estimate, not an exact value).

Schmidt not only correctly explained the redshift of 3C 273, but also correctly guessed that it was the core of a galaxy, showing his bold and advanced thinking.

In 1965, Schmidt published another important paper, announcing five new quasars that he had discovered,[17] three of which had a redshift of 1, and the farthest one had a redshift of 2. As he himself said, "We can now easily get very high redshifts, because these damn things are so bright."[Note 6]

Schmidt measuring the spectrum using a microscope in 1965. Image source: [18]

Successfully breaking the circle

It sounds incredible that such a small object can be much brighter than a very large galaxy, but it is very possible. Therefore, Schmidt's discovery shocked the entire astronomical community and many ordinary people.

People had already realized that a huge revolution in cosmology and astronomy had suddenly arrived. Schmidt became famous overnight. As he later recalled, "The night I discovered the red shift (of quasars), the prospects were excellent."[Note 7]

On March 11, 1966, Schmidt was featured on the cover of Time magazine, which compared Schmidt to the great physicist and astronomer Galileo Galilei (1564-1642): the 17th-century Italian astounded his contemporaries of scientists and theologians, and the 20th-century Dutchman astounded others of his time.

Schmidt appeared on the cover of Time magazine on March 11, 1966, for confirming quasars. Image source: [19]

With the help of Time magazine, Schmidt's fame successfully broke through the circle and became a media darling and celebrity.

Astronomers at the time called these mysterious celestial bodies "quasi-stellar radio sources" or "quasi-stellar objects" (QSOs). In 1964, Hong-Yee Chiu (1932-) thought the phrase "quasi-stellar radio sources" was too long in an article[20], so he simply called it "quasar", which literally means "similar star"; but domestic astronomy books also translate it as "quasar".

In 1965, Sandage, who had previously failed in his quest, discovered for the first time a quasar that does not emit radio radiation ("radio quiet"). [21] Studies have shown that 90% of quasars are radio quiet. Therefore, quasars contain quasi-stellar radio sources.

Since then, Schmidt has continued to search for and observe quasars, and has made important contributions to the identification, counting, statistics, spatial distribution, evolution, redshift-distance relationship, etc. For example, he found that the production rate of quasars in the universe with a redshift of about 2.5 is the highest.

Redshift and the mystery of energy

In the decade or so after the discovery of quasars, there has been controversy over their distance and energy sources. Schmidt and others believed that their red shift was "cosmological red shift", so they were very distant and bright objects; other astronomers opposed the former's view.

Despite this, the view of "cosmological redshift" still dominates. This inevitably leads to another question: how to explain their high luminosity?

In 1964, Edwin Salpeter (1924-2008) and Yakov Zel'dovich (1914-1987) proposed [22-23] that the supermassive black hole at the center of the galaxy devours the surrounding matter, and the particles inside the matter rub against each other to generate heat, heating the matter, which can explain the high luminosity of quasars.

In 1969, Donald Lynden-Bell (1935-2018), who had been a postdoctoral fellow under Schmidt, further developed this theory and proposed that supermassive black holes are common in the centers of galaxies and that nearby galaxies that emit strong radiation are old/dead quasars. [24] Lynden-Bell pointed out that there is no essential difference between ordinary galaxies, Seyfert galaxies, and quasars, except that the activity of the supermassive black holes at their centers and the surrounding matter disks are different.

An artistic conception of a quasar. Image source: [25]

However, the black hole model was not convincing enough at that time, because most astronomers and physicists did not believe in the existence of black holes. Therefore, throughout the 1960s, there was still no consensus on the redshift and energy of quasars.

Despite this, astronomers and physicists have clearly felt that even if quasars are not the result of the interaction between black holes and surrounding matter, they are likely related to some special physical processes in the center of the galaxy.

In addition, in order to enable the black hole model to explain quasars, theoretical physicists began to take black hole theory more seriously, and astronomers also enthusiastically searched for evidence of the existence of black holes.

Therefore, even in the somewhat chaotic 1960s, the discovery and research of quasars greatly promoted the development of astronomy and theoretical physics.

Ironclad evidence

The simplest and most powerful way to conclusively determine whether a quasar is the bright core of a galaxy is to find the galaxy it is in. If observational evidence can be found that a quasar is embedded in the center of a galaxy, Schmidt's idea will naturally be confirmed.

In 1973, Jerome Kristian photographed 26 quasars with the Hale telescope and found that some of them were clearly embedded in the centers of some galaxies. This strongly supported Schmidt's suggestion that "quasars are the cores of galaxies." However, opponents can still say that these coincidences may just be coincidences in line of sight.

In 1982, Todd A. Boroson and Oak discovered a galaxy around the quasar 3C 48 and confirmed that the redshift of this galaxy was the same as that of 3C 48. This directly proved that the redshift of the quasar was indeed the real cosmological redshift.

Quasars are the cores of galaxies. Schmidt's brilliant idea was correct.

Subsequent observations have also continuously confirmed Schmidt's idea. For example, after using the coronagraph to block the light of 3C 273, Hubble's ACS clearly photographed the matter next to it, which is the galaxy where 3C 273 is located; this strongly proves that 3C 273 is the core of a galaxy. For another example, in the image of "Quasar 0316-346" taken by Hubble's WFPC2, the galaxies around it are clearly visible.

An image of the galactic matter near 3C 273 taken by Hubble's ACS (left) and an optical image of the quasar 0316-346 taken by Hubble's WFPC2. In the left image, the light from the quasar has been blocked by the coronagraph, making the surrounding galactic matter easier to image. Image source: [26] (left); [27] (right).

Although there are still a few famous astronomers, such as Halton Arp (1927-2013), who ignore these iron facts and continue to insist that the redshift of quasars is not the cosmological redshift, they cannot shake the ironclad evidence of observations.

In addition to the ironclad evidence of redshift, a breakthrough has also been made in energy issues. Through indirect means, astronomers have proved that black holes do exist at the center of galaxies. In recent years, radio telescope arrays have directly photographed the supermassive black holes at the center of M87 and the Milky Way.

Academic Honors

In 1964, Schmidt was promoted to professor at Caltech.

He served as chairman of the Caltech Astronomy Department from 1972 to 1975 and as chairman of the Caltech Mathematics and Astronomy Group from 1976 to 1978.

From 1978 to 1980, he became the director of Hale Observatories, which was renamed from the Wilson and Palomar Observatories. As Wilson Observatory and Palomar Observatory had always been at odds, Schmidt decided to disband Hale Observatories in 1980 and restore them to their original two independent units. He thus became the last director of Hale Observatories.

Schmidt retired in 1996, but continued to conduct research and publish papers for about a decade.

Due to his important contributions to the identification of quasars and the understanding of various important properties of quasars, Schmidt has won many important awards since 1964. These awards include the Warner Prize in 1964, the Norris Russell Lecture in 1978, the Gold Medal of the Royal Astronomical Society in 1980, the James Craig Watson Medal in 1991, the Bruce Medal in 1992, and the first Kavli Prize for Astrophysics in 2008 (shared with Lyndon Bell).

In 2008, Schmidt (left) and Lyndon Bell (right) received the first Kavli Prize in Astrophysics. Image source: [28]

Romantic feelings and strong will

Quasars are recognized as one of the "four great discoveries" of the 1960s, along with microwave background radiation, pulsars, and interstellar molecules.

On Mount Palomar, where top players were everywhere and competition was extremely fierce, Schmidt seized the fleeting opportunity with his keen intuition and professional qualities, and was fortunate enough to become the first person to confirm a quasar.

Since then, humans have continued to discover more quasars, and their redshift values ​​have continued to break records. In 2021, astronomers discovered the quasar J0313-1806, and measured its redshift as high as 7.64. At that time, the universe was only 670 million years old (the age of the universe is between 13.8 and 14 billion years). This record will be quickly broken in the future.

At the height of Schmidt's career, he would ride the elevator into the "cage" at the prime focus of the Hale telescope after dark; after the elevator moved away, he would begin observing all night.

The Hale telescope is still in operation. Image source: [29]

On slightly chilly nights, he refused to put on more clothes to keep warm, because he believed that suffering a little in the cold night would make the stargazing process more romantic. He combined his romantic feelings with his strong will. [Note 8]

Of the nearly 1 million quasars discovered to date, 3C 273, confirmed by Schmidt, has a special status: not only is it the first quasar confirmed, it is also the only one that can be seen with a small telescope because it is relatively nearby (although it is not the nearest quasar) and extremely bright.

Schmidt. Image source: [3]

In his more than 50 years of academic career, Schmidt made outstanding contributions to human exploration of the universe with his extraordinary talent, keen intuition, advanced thinking, romantic feelings and tenacious will, and also won due honors.

He can rest in peace.

Schmidt. Image source: [3]

Notes

[Note 1] His uncle was the famous mathematician Hermann Minkowski (1864-1909), who made great contributions to the theory of relativity.

[Note 2] The Balmer lines of hydrogen are spectral lines emitted when hydrogen electrons transition from a higher energy level to the second energy level.

[Note 3] Hα, Hβ, Hγ, Hδ and Hε lines are spectral lines emitted when electrons in hydrogen atoms transition from the 3rd, 4th, 5th, 6th and 7th energy levels to the 2nd energy level. Their wavelengths are 656.3, 486.1, 434.1, 410.2 and 397.0 nanometers, respectively. Their colors are red, cyan, blue, violet and ultraviolet (colorless), respectively. However, because they are red-shifted by 0.158 times, they become 759.0 nanometers, 563.2 nanometers, 503.2 nanometers, 475.3 nanometers and 459.5 nanometers.

[Note 4] Some people believe that these spectral lines are actually doped with emission lines produced by the transition of electrons in once-ionized helium. Because when electrons in once-ionized helium transition from the 6th, 8th, and 10th energy levels to the 4th energy level, the wavelengths of the spectral lines emitted are 656.0nm, 485.9nm, and 433.9nm, which are equal to the wavelengths of Hα, Hβ, and Hγ lines, respectively. However, whether it is hydrogen, helium, or a mixture of hydrogen and helium, the fact that they are red-shifted is the essence of the matter, so Schmidt's explanation is not affected.

[Note 5] Forbidden lines are lines that cannot be produced in laboratories on Earth, but can be produced in the rarefied matter of space. Forbidden lines are represented by square brackets.

[Note 6] Original text: We could now easily get to very large redshifts, because these darn things are so bright.

[Note 7] Original text: The night I discovered the redshift, it was a fantastic prospect,...

[Note 8] Of course, romance does not mean stupidity. When it is very cold, he will still wear electric heating clothes.

References/Image sources

[1] http://phys-astro.sonoma.edu/brucemedalists/maarten-schmidt

[2] https://www.nytimes.com/2022/09/22/science/space/maarten-schmidt-dead.html

[3] https://www.caltech.edu/about/news/caltech-mourns-the-passing-of-maarten-schmidt-1929-2022

[4] Paul Calvert, Los Angeles Times

[5] Schmidt, M., The Rate of Star Formation, 1959, ApJ, 129, 243

[6] Minkowski, R., A New Distant Cluster of Galaxies, 1960, ApJ, 132, 908

[7] Dennis O., Lonely Hearts of the Cosmos, 1991, Little, Brown and Company, ISBN-13: 9780316648967

[8] ESTATE OF F. BELLO/SPL

[9] ESA/Hubble & NASA

[10] Hazard, C., Mackey, MB, & Shimmins, AJ Investigation of the Radio Source 3C 273 By The Method of Lunar Occultations, 1963, Nature, 197, 1037

[11] Miller Goss

[12] https://www.caltech.edu/about/news/fifty-years-quasars-38937

[13] https://www.parkes.atnf.csiro.au/people/sar049/3C 273/

[14] Schmidt, M. 3C 273: A Star-Like Object with Large Red-Shift, 1963, Nature, 197, 1040

[15] Oke, JB Absolute Energy Distribution in the Optical Spectrum of 3C 273, 1963Nature, 197, 1040

[16] Greenstein, JL & Matthews, TA Red-Shift of the Unusual Radio Source: 3C 48, 1963, Nature, 197, 1041

[17] Schmidt, M. Large Redshifts of Five Quasi-Stellar Sources, 1965, ApJ, 141, 1295

[18] Caltech Archives

[19] Time Inc

[20] Chiu, Hong-Yee. Gravitational Collapse, Physics Today, 17, 5, 21

[21] Sandage, A. The Existence of a Major New Constituent of the Universe: the Quasistellar Galaxies, 1965, ApJ, 141, 1560

[22] Salpeter, EE Accretion of Interstellar Matter by Massive Objects, 1964ApJ, 140, 796

[23] Zel'dovich, Ya. B. 1964, Dokl. Akad. Nauk SSSR, 155, 67 (also 158, 811)

[24] Lynden-Bell, D. Galactic Nuclei as Collapsed Old Quasars, 1969, Nature, 223, 690

[25] ESO/M. Kornmesser

[26] NASA, A. Martel (JHU), H. Ford (JHU), M. Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA

[27] John Bahcall, Mike Disney, and NASA/ESA

[28] https://www.kavliprize.org/prizes/astrophysics/2008

[29] Palomar/Caltech

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