The Universe: Pulsars & Quasars Infiltrate the Sky (S4, E10) | Full Episode | History

Henrietta Swan Leavitt’s contribution to the field of astronomy is that she gave us the tools to map out the stars in the universe. She discovered the correlation between Period and Luminosity. This helped turn the sky into a three-dimensional map allowing astronomers to solve the unknown in the equation: Distance.

A pulsar is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission. Wikipedia

A quasar is an extremely luminous active galactic nucleus, powered by a supermassive black hole, with mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Wikipedia

Pulsar vs Quasar

A pulsar (originally short for ‘pulsating star’) is a rapidly spinning neutron star – the remnant of a supernova explosion. A quasar (from ‘quasi-stellar radio source’) is in fact a distant galaxy with a fluctuating blaze of light and other radiations coming from its central regions.

Leavitt’s legacy

Leavitt died in 1921 as a mostly unknown astronomer, something that several biographies are working to correct today. After her death, her findings soon sparked a new understanding of the universe. Besides the work performed by Shapley, another American astronomer, Edwin Hubble, used Leavitt’s information to help him understand the distance to the nearest large galaxy to Earth, known as the Andromeda Galaxy (more officially known as M31). 

Andromeda’s distance of 2.5 million light-years was established in the 1920s using Cepheid variables, making it clear the galaxy was far outside the boundaries of the Milky Way. In other words, Hubble determined that there were other galaxies like our own in the universe. Subsequently, Hubble figured out that the universe was expanding by measuring the “redshift” of receding stars whose light was being pulled to the red side of the light spectrum.

“Leavitt’s discovery was so important that in 1924, Gösta Mittag-Leffler of the Swedish Academy of Sciences tried to nominate her for the Nobel Prize,” an article in Air and Space Smithsonian stated. “Unfortunately, Henrietta died of cancer three years before this, and the Nobel Prize is not awarded posthumously.”

Cepheid variables are still used today to help us understand the distance to astronomical objects. As astrophotography techniques continue to improve, these distances are refined. A famous example took place in 2012, when it was revealed that the North Star Polaris – a nearby Cepheid variable — is about 100 light-years to Earth closer than thought.

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Elizabeth Howell