The world of astronomy has mourned the recent passing of Dutch-American astronomer Maarten Schmidt, the first person to measure the distance of a quasar. His pioneering work in the 1960s greatly expanded the size of the known universe, providing one of the first clues that the Big Bang theory was correct. Schmidt died on Sept. 17 at his home in Fresno, California. He was 92 years old.
The history of quasars began several years before Schmidt focused his attention on them. Since the 1950s, astronomers have identified several sources of radio emissions in the sky. Many of these radio sources could be assigned to known objects, such as bright stars or nearby galaxies. But some have remained frustratingly elusive, having no visible counterpart. Whatever these strange radio sources were, they appeared as point objects, indicating that they were enormous in size but incredibly distant or small and close.
Astronomers, never slow to name a new category of celestial phenomena, quickly designated these radio sources as “near-stellar objects,” which were shortened to quasars.
Unraveling the Mysteries of Quasars
Schmidt, who earned his doctorate in philosophy from the University of Leiden in 1956 under the guidance of Dutch astronomer Jan Oort (famous for the Oort cloud), eventually moved to the California Institute of Technology to continue his studies on properties and evolution of galaxies. Among Schmidt’s numerous successes during his tenure there, he was the first to discover that the density of interstellar gas within galaxies was proportional to their star-forming rate, a relationship now known as Schmidt’s law (or, more recently , Kennicutt-Schmidt reads).
Schmidt then turned his attention to researching the light spectra of radio sources, in particular these mysterious quasars. By the early 1960s, astronomers had been able to identify the optical light counterparts of another quasar, but its spectrum remained poorly understood: its light output did not match 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 picked up the spectrum of this poorly understood object, and that spectrum had strange emission lines that, again, defined the explanation.
After several weeks of deep contemplation and very nervous about his home, Schmidt realized what he was looking at: a perfectly normal galaxy. All the emission lines of all the usual elements were there, like hydrogen and helium, but they were simply shifted very low towards the red end of the spectrum.
The light spectrum of an astronomical object can shift from two things. One is the Doppler effect: if an object moves away from us, the wavelength of its emitted light will lengthen and its emission lines will be shifted towards red. But the location of the 3C 273 emission lines implied a recession speed of about 100 million miles per hour, about 15 percent of the speed of light!
This redshift result was orders of magnitude greater than that found for any other known object.
Quasar: the bright nuclei of distant galaxies
Schmidt argued for another interpretation in his Nature article describing his discovery: the Big Bang. Distant objects are pushed away from us due to the expansion of space itself, which also causes a red shift. It was this awareness that allowed Edwin Hubble to lay the observational foundations for the Big Bang theory in the 1920s. But beyond Hubble’s insight, there was little else to anchor the Bang Bang in the observations. And so astronomers continued to debate its validity.
Schmidt’s work showed that 3C 273 was billions of light years away, making it the most distant astronomical object known at the time. This discovery of the first distance from a quasar has dramatically rewritten our understanding of the true scale of the cosmos.
For quasars to be detectable at such great distances, they must be incredibly bright. In fact, they must be the brightest objects in the universe. Schmidt believed that when we observe a quasar, we are seeing the light emitted as the gas violently swirls and grinds together around a giant black hole in a newly formed galaxy, which turned out to be the correct interpretation.
The existence of quasars has provided proponents of the Big Bang theory with an important observational victory. Quasars appear only in the distant universe; there are no objects as close as they are.
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 the modern one.
in 1966, time The magazine put Schmidt on the cover, comparing his discovery of the true nature of quasars to Galileo’s in its power to reshape our understanding of the universe. And such a result will surely live on.