The Rock Star's Dusty Astronomy Thesis

"Astronomy's much more fun when you're not an astronomer- Brian May

I wholeheartedly agree, that's why I studied finance


I'm only 25 years old, so undoubtedly there's a ton of great music from the last century that I wasn't around for and won't ever fully appreciate. But of all the classic rock bands, I'd definitely say Queen is my favorite: Bohemian Rhapsody is still a kick-ass karaoke song, 46 years after its original release. Plus, Queen's lead guitarist Brian May happens to also hold a Ph.D. in astrophysics, which is all the more reason for me to like them! Just recently, I watched the Bohemian Rhapsody movie about Freddie Mercury and Queen, and it dawned on me I actually didn't know what exactly May wrote his thesis on, so I thought it'd be fun to try jump into it and provide a synopsis

At 73, Brian May is still making music! In 2019 he released a single called New Horizons after the spacecraft to Pluto

As an undergraduate, May had studied math and physics at Imperial College London and remained there from 1970 to 1974 to pursue a doctorate in astrophysics, but he decided to put his Ph.D. on hold after Queen's meteoric rise to fame. What he was studying was the zodiacal light, a faint glow visible in the night sky that can be seen just after twilight in the spring or just before dawn in the fall. This phenomenon has been observed and recorded for centuries; the Islamic prophet Muhammad referred to it as the "false dawn" and described how to distinguish it to avoid mistiming the 5 daily prayers in Muslim tradition. In modern times, we know this glow is caused by sunlight being scattered by the enormous, diffuse cloud of interplanetary dust that extends far beyond Earth's orbit. Researchers had analyzed the spectroscopy of the zodiacal light and realized that it had the exact same absorption spectrum as the sun, meaning it must be caused by reflections off solid objects, rather than a gas which would alter the sunlight's observed spectrum. Yet even after the Pioneer 10 spacecraft confirmed this in 1972, there remained another question: where did all this dust come from in the first place? 

Beautiful image of the zodiacal light, which is glowing even brighter than the Milky Way off to the right

That's where May comes in - by 2006, there still hasn't been much research done on the nature of the interplanetary dust cloud, so May picks up his dusty, unfinished thesis (pun intended!) from over 30 years ago and reregisters for his Ph.D. His paper, titled "A Survey of Radial Velocities in the Zodiacal Dust Cloud", depicted the overall motions of this dust cloud relative to Earth's orbit by examining the tiny redshifts/blueshifts in the cloud's absorption spectrum over repeated observations. Now unlike detecting redshift in a single star or galaxy rapidly expanding away from us, May's tasks was not as simple as examining the absorption spectrum from a single grain of dust: every observation is a sample of a bazillion particles, all moving haphazardly throughout the solar system. So what May was measuring was a change in the statistical distribution of the spectral lines from the dust cloud, and to do this he needed a device called a Fabry-Perot Interferometer

Some figures from May's actual thesis - bottom left illustrates the point about statistical distributions of redshifts and blueshifts

Similar to how a microscope allows a scientist to closely examine a small sample, a Fabry-Perot Interferometer allows an astronomer to zoom in on an extremely precise wavelength range of the electromagnetic spectrum for closer study. It lets light inside the device where it is partially reflected and partially transmitted between two closely spaced mirrors, then focused back onto a screen to create an interference pattern. Armed with his interferometer and a coelostat (basically a motorized mirror that tracks a fixed portion of the sky over time as it rotates overhead), May spent a bunch of time at Teide Observatory in Tenerife, Spain, making repeated observations of the zodiacal light to collect data on their absorption spectra. After crunching the numbers, he found the patterns were consistent with a flat interplanetary dust cloud that orbited the sun in the same direction as the Earth. This is a crucial finding because it suggests the dust cloud is generated by the asteroid belt, which rotates in the same direction as the rest of the solar system, as opposed to comet tails (which come into the solar system equally in prograde and retrograde orbits) or interstellar dust (which would come in at an angle completely different from the solar system)

Great animation of a Fabry-Perot Interferometer | Credit: YouTube

Two other points worth noting: first, May's conclusion that the zodiacal dust cloud originates from the asteroid belt is supported by observations made by the Infrared Astronomical Satellite (IRAS) in 1983, which revealed that the dust cloud had an internal structure of concentric disks, many of which lined up with known asteroid clusters. And second, why did astronomers believe that the zodiacal dust cloud had to "originate" from some source in the first place? Couldn't it have just been leftovers from the formation of the solar system? The reason is that if it weren't being constantly replenished, such a diffuse cloud of tiny particles would be washed out of the solar system within a few hundred thousand to a few million years by two forces: 1) solar wind would easily push the dust cloud off into interstellar space, and 2) another phenomenon known as Poynting-Robertson drag, whereby solar radiation reduces the angular momentum of an orbiting dust particle, causing it to fall into the sun. So the fact there is a dust cloud within the vicinity of the Earth, billions of years after the formation of the solar system, means it had to be produced relatively recently

The zodiacal dust cloud, as illustrated in May's thesis

There's a cool Wikipedia page titled "List of Celebrities With Advanced Degrees", and I saw that Dexter Holland, the lead singer for the band The Offspring (another band I like) has a Ph.D. in molecular biology, which is pretty neat! So, if Brian May can get his Ph.D. in astrophysics at the age of 60, then that means I have 35 more years to supplement my bachelors in finance with a degree in aerospace engineering!  

To learn more about his thesis on the zodiacal dust cloud, check out Scott Manley's fantastic video here

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