HomeScienceOuter SpaceMaarten Schmidt, father of quasars, dies at age 92

Maarten Schmidt, father of quasars, dies at age 92

The world of astronomy mourned the recent death of Dutch-American astronomer Maarten Schmidt, the first person to measure the distance to a quasar. His seminal work in the 1960s vastly expanded the size of the known universe, providing one of the first indications that the big bang theory was right. Schmidt died on September 17 at his home in Fresno, California. He was 92 years old.

The story of quasars began several years before Schmidt turned his attention to them. Beginning in the 1950s, astronomers identified several sources of radio emissions into the sky. Many of those radio sources can be mapped to known objects, such as bright stars or nearby galaxies. But some remained frustratingly elusive and had no visible counterpart. Whatever these strange radio sources were, they appeared as point-like objects, indicating that they were either huge but incredibly far away or small and close.

Astronomers, never slow to name a new category of celestial phenomena, were quick to refer to these radio sources as “quasi-stellar objects,” which was shortened to quasars.

Unraveling the mysteries of quasars

Schmidt, who obtained his PhD in philosophy from Leiden University in 1956 under the tutelage of the Dutch astronomer Jan Oort (van Oort cloud fame), eventually moved to the California Institute of Technology to continue his studies of the properties and evolution of galaxies. Among Schmidt’s many accomplishments during his tenure there, he was the first to discover that the density of interstellar gas in galaxies was proportional to their rate of star formation, a relationship now known as the Schmidt law (or, more recently, the Kennicutt-Schmidt Act).

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Schmidt then turned his attention to finding the light spectra of radio sources, especially these mysterious quasars. By the early 1960s, astronomers were able to identify optical light counterparts from another quasar, but its spectrum remained poorly understood — its light output was not matched by any other known type of astronomical object.

In 1963, Schmidt used the Palomar Observatory’s 200-inch Hale telescope to discover the optical counterpart of the quasar known as 3C 273, one of the first to be discovered. He also collected the spectrum of this poorly understood object, and that spectrum contained strange emission lines that, again, defied explanation.

After several weeks of deep contemplation and lots of nervous pacing around his house, Schmidt realized what he was looking at: a perfectly normal galaxy. All the emission lines of all the usual elements were there, such as hydrogen and helium, but they were just shifted way down to the red end of the spectrum.

The light spectrum of an astronomical object can shift from two things. One is the Doppler effect: as an object moves away from us, the wavelength of the emitted light lengthens and the emission lines become red-shifted. But the position of 3C 273’s emission lines implied a recession speed of about 100 million mph, about 15 percent of the speed of light!

This redshift result was orders of magnitude greater than that found for any other known object.

Quasars: The Luminous Cores of Distant Galaxies

Schmidt argued for a different interpretation in his Nature paper describing his discovery: the big bang. Distant objects are pulled away from us by the expansion of space itself, which also causes a redshift. It was this realization that allowed Edwin Hubble to lay the observational foundation for the big bang theory in the 1920s. But beyond Hubble’s insight, there was little left to anchor the Bang Bang in observations. And so astronomers continued to argue about its validity.

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Schmidt’s work showed that 3C was 273 billion light-years away, making it the most distant astronomical object known at the time. This discovery of the first distance to a quasar dramatically redefined our understanding of the true extent of the cosmos.

To detect quasars at such great distances, they need to be insanely luminous. In fact, they must be the most luminous objects in the universe. Schmidt believed that when we observe a quasar, we see the light emitted as gas swirls and grinds violently around a giant black hole in a newly formed galaxy, which turned out to be the correct interpretation.

The existence of quasars provided proponents of the big bang theory with an important observational gain. Quasars only appear in the distant universe; there are no nearby objects like them.

In the Big Bang model, the universe changes and evolves as it continues to cool and expand. And since quasars are only found far, far away, they must have existed only in the early universe, not in our modern one.

in 1966, Time Schmidt magazine on their cover, comparing his discovery of the true nature of quasars to that of Galileo in his power to reshape our understanding of the universe. And such an achievement will surely live on.

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