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Science details:
Rubin created galaxy rotation curves by measuring the velocity of rotating clouds of partially ionized hydrogen at various radii of the galaxy. These clouds are known as HII regions, and are regions in which star formation has recently taken place. HII regions are found in spiral and irregular galaxies, distributed across the galaxy.
The strongest hydrogen emission line, H-alpha line at 656.3nm, is detectable by telescopes and gives the regions their characteristic red colour. H-alpha emission is produced when an electron transitions from the n=3 to n=2 energy level in hydrogen, and is used to trace ionized hydrogen. After ionization, electrons and protons can recombine and the electron will cascade down to ground state, emitting photons in the process. About 50% of these cascades include the n=3 to n=2 transition, and therefore provides a way to detect hydrogen ionization.
Measuring the doppler shift of these emission lines allowed Rubin to deduce the orbital velocities of different regions of the galaxy.
Citations and resources:
https://en.wikipedia.org/wiki/H-alpha
https://en.wikipedia.org/wiki/H_II_region
https://en.wikipedia.org/wiki/Vera_Rubin
Figures:
Leftmost: illustration of the Doppler effect from an orbiting emission region https://jila.colorado.edu/~ajsh/courses/astr1120_03/text/chapter1/L1S5.html
Bottom right: Sixty seven HII regions seen in the Andromeda Galaxy. Ultraviolet photograph. http://cdsads.u-strasbg.fr/pdf/1970ApJ...159..379R
Top right: Rotational velocities of HII regions in Andromeda, as a function of distance from centre of galaxy. http://cdsads.u-strasbg.fr/pdf/1970ApJ...159..379R
Science details:
By observing visible matter in the Andromeda galaxy, it was expected that at high radii the velocity of the orbiting material would slow down, as the mass contained within their orbit would eventually begin to stagnate with larger and larger radii. Rubin and Ford observed that this was not the case, and velocities did not drop as quickly as they expected. This could be explained by the existence of additional 'dark' mass surrounding the galaxy, now known as a dark matter halo.
Citations and resources:
https://en.wikipedia.org/wiki/Vera_Rubin
Figures:
Left: (Left panel) Mass contained within a certain radius to the center of Andromeda. (Right panel) Density of mass at that radius. http://cdsads.u-strasbg.fr/pdf/1970ApJ...159..379R
Right: Rotation curve of the spiral galaxy M33, along with a predicted curve (dashed line) from the distribution of visible matter. Data and model predictions from Corbelli and Salucci 2000. The observations indicate the existence of dark matter, as the higher velocities must be sustained by more mass than accounted for just by visible matter. https://en.wikipedia.org/wiki/Galaxy_rotation_curve#/media/File:Rotation_curve_of_spiral_galaxy_Messier_33_(Triangulum).png
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General speaker notes
During her Master's, Rubin studied how galaxies move through our universe. She discovered a plane of density which would later be identified as the "supergalactic plane", but her paper was never published and she received harsh pushback. In her PhD, she discovered how galaxies tended to clump together, another controversial idea that when later pursued was proved to be true.
At the Carnegie Institution, Rubin collaborated with Kent Ford, an instrumentalist astronomer who had developed a state-of-the-art spectrometer. Using the spectrometer, Rubin and Ford measured the rotation rates of the nearby Andromeda Galaxy (M31), focusing on Hydrogen-II (HII) regions orbiting at various distances from the galaxy's centre. As they measured out to larger and larger radii, the HII regions seemed to move at the same speed, defying the supposed distribution of mass in the galaxy surmised from starlight observations. This prompted them to test this observation on other galaxies, and they eventually saw the same phenomena in each observation.
The data suggested that a halo of dark matter surrounded each galaxy, creating an even distribution of mass at larger galaxy radii and explained the constant velocities of the orbiting visible matter. Fritz Swicky had theorized the existence of dark matter in 1933 and his work was mostly overlooked, but this discovery provided the first solid evidence of its existence. The nature of dark matter is now one of the most pursued questions in modern astronomy.
Vera Rubin was born 1928 in Philadelphia, Pennsylvania. Her parents were Jewish immigrants from Eastern Europe, who both worked at Bell Telephone company.
Vera Rubin developed an interest in astronomy at the age of 10 from watching stars from her window. She earned a BSc in astronomy in 1948 at the all-women Vassar College, New York. After being barred from entering Princeton due to her gender, Rubin was accepted to Harvard as a postgraduate, but turned the offer down to attend Cornell with her husband. Rubin graduated with her masters degree in 1951, and obtained her PhD in 1954 from Georgetown University, Washington, D.C.
Throughout her graduate studies, Rubin encountered discouraging sexism and experienced imposter syndrome frequently. However, she routinely broke through barriers and defied stereotypes.
Rubin held academic positions at Montgomery College and Georgetown University, before finally joining the Carnegie Institution of Science in 1965 as a staff member where she remained for the rest of her career.
The existence of dark matter is now fundamental to the understanding of astrophysics and modern cosmology. Since it's initial discovery by Rubin and Ford, the Planck satellite was able to measure the dark matter content of the universe through the clumping of the cosmic microwave background. In addition, measurements of gravitational lensing by galaxy clusters again confirmed the existence of dark matter. It has been calculated that dark matter accounts for approximately 85% of the matter in the universe.
The true nature of dark matter is still unknown, and remains one of the largest mysteries in modern astronomy. Physicists are searching for dark matter both on earth and in space.
In recognition of her achievements, Rubin was elected to the National Academy of Sciences, and was awarded the National Medal of Science in 1993. Most recently, the Large Synoptic Survey Telescope in Chile was renamed the Vera C. Rubin Observatory in recognition of her contributions to the study of dark matter and her outspoken advocacy for the equal treatment and representation of women in science.
Slides by: Katherine Savard