In 1974, the Nobel Prize in Physics was awarded to two men, Anthony Hewish and Sir Martin Ryle, for the discovery of pulsars, the dead remnants of massive stars left behind after the massive supernova explosions that ended their lives, a kind of star which had previously only been theorized to exist. However, the bulk of the work that led to the discovery from seven years earlier had actually been done by Jocelyn Bell Burnell, Hewish’s graduate student and one of the few female astronomers at the time.
Despite her incredibly important contributions being overlooked, Bell Burnell remained an active researcher. Last week, 50 years after her work as a graduate student, she earned the $3 million Special Breakthrough Prize in Fundamental Physics for her discovery of pulsars which revolutionized our understanding of the universe. Even more revolutionary, her personal experience has inspired her to donate the whole thing.
What Are Pulsars?
Pulsars are rapidly rotating dead stars that get their name because we detect them by their flashes of radio emission. But they only appear to pulse because their light is beamed into a search light that sweeps across our telescopes as they rotate. The most commonly used analogy is that of a lighthouse whose beacon of light scans the vast ocean for anyone who might be looking to detect it. The emission doesn’t actually blink on and off, it just appears to from our vantage point.
So how did pulsars get this way? Stars like our Sun, a relatively low mass star, spend much of their lives supporting themselves by burning through their supply of hydrogen. This act of fusion produces radiation which can exert an outward pressure which fights back against gravitational collapse. Stars that are more massive than our Sun move on to burn heavier and heavier elements, working their way down the periodic table of elements until they get to iron.
For elements heavier than iron, energy is no longer produced during their fusion but instead energy is required for them to form. So without this steady input of energy, stars halt the fusion process and thus no longer have a way to fight back against gravitational collapse. The outer layers of the star come crashing down on its core before being blown away in a supernova explosion.
Meanwhile, the core itself has become incredibly compact, so much so that electrons and protons have been squeezed together to form neutrons, the non-charged particles that like to hang out in the nuclei of atoms. Neutrinos are also formed in this process but they quickly escape. Eventually the neutrons are so tightly packed together that they cannot be forced any closer to their neighbors and so exert a pressure that again fights back against gravitational collapse, leaving a dead corpse star known as a neutron star.
Neutron stars are typically 10 to 20 kilometers across, which means they pack roughly one and a half times the mass of our Sun into a space comparable to the size of Manhattan. From another perspective, one teaspoon of neutron star weighs around 10 million tons.
The light emitted by a neutron star is beamed in two directions so that it shines out of opposite sides of the star instead of in all directions (like the light from our Sun) due in part to the star’s strong magnetic fields. Now, I’ll let you in on a little secret. When astronomers can’t explain a certain phenomenon, we often say, “it’s probably related to the magnetic fields” because magnetic fields can be quite challenging to study. But in this case, it really is true! The magnetic fields around neutron stars have been compressed and, as particles spiral around these very strong magnetic field lines, they produce emission leading to this relativistic beaming effect.
If the beam of a neutron star happens to be pointed in the right direction so that it sweeps over us here on Earth—like that lighthouse would over a ship in the ocean—then we call that neutron star a pulsar.
Who Discovered Pulsars?
In the 1960s, Jocelyn Bell Burnell and her advisor Anthony Hewish, along with a small team of other astronomers at the University of Cambridge, built a radio telescope in hope of finding quasars, powerful radio sources from the distant universe. And they did find about 100 quasars by studying the paper read outs produced by their spectrometer—computers were not readily available for this kind of research at the time so there was no way to write a handy search algorithm.
In 1967, Bell Burnell noticed a pulse of radio emission that repeated itself about once every 1.5 seconds. Hewish disregarded the signal as artificial and famously labeled it “LGM-1” short for “Little Green Men.” Luckily for us, and for science, Bell Burnell didn’t give up on the signal so easily. She was determined it was real. And then she found a few more. They published their work in 1968 and Hewish, along with another collaborator Sir Martin Ryle, were given the Nobel Prize in 1974.
Now we know of over 2,000 pulsars, including a few hundred so-called “millisecond pulsars” that can make one full spin in only a few milliseconds, and we expect there should be on the order of a billion neutron stars in our Milky Way galaxy alone.
With her discovery of pulsars, Bell Burnell had found an exotic kind of star that had previously only been dreamt up in theoretical explanations of what the end products of stars' lives must be. But more than that, pulsars produce gravitational waves so they provide information on this new way of exploring the universe, including helping us understand how some elements like gold are formed.
Pulsars also provide very precise clocks. Their pulses are so regular, in some cases down to the millisecond, that even tiny deviations reveal something about the pulsar’s environment like whether the dead star hosts any planets. Pulsar timing has been used to test Einstein’s theories of relativity and to estimate the weight of our solar system.
The Breakthrough Prize in Fundamental Physics
Dubbed the “Oscars of Physics,” the Special Breakthrough Prize was founded by physicist and entrepreneur Yuri Milner who we’ve discussed on this podcast before for his investments into searches for extraterrestrial life and plans for sending spacecrafts to our neighboring star Alpha Centauri. The prize is funded by wealthy scientists and innovators in the tech industry to acknowledge physicists who “make a significant contribution to human knowledge.” Previous awardees include Stephen Hawking and the LIGO team for their discovery of gravitataional waves.
Jocelyn Bell Burnell is noted as earning the $3 million prize not only for “the detection of radio signals from rapidly spinning, super-dense neutron stars,” but also for “a lifetime of inspiring scientific leadership.” She has spoken openly about her personal experiences with imposter syndrome, the feeling that everyone around you is qualified except for you, and an issue faced by many women and other under-represented groups in physics, as well as her dealings with societal pressure to quit academia once having her son.
In order to support others who may be experiencing the same pressures and lack of support, Bell Burnell will donate the entirety of her prize to the Institute of Physics to fund PhD tuition fees for people from under-represented groups. Thus her legacy will be to revolutionize the field of astronomy through the knowledge that pulsars have brought us and through the knowledge we will gain from these new researchers that would have been otherwise lost or forced out by a biased system.
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com. Image courtesy of shutterstock.
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