Rotation curves of galaxies.

Rotation curves of galaxies. Worldpress

Vera Rubin receiving the National Medal of Science from President Clinton and Vice-President Gore in 1993.

Vera Rubin receiving the National Medal of Science from President Clinton and Vice-President Gore in 1993.
Emelio Segre Archive, American Institute of Physics

Vera Rubin installing equipment on the 2.1 meter telescope of Kitt Peak in 1965.

Vera Rubin installing equipment on the 2.1 meter telescope of Kitt Peak in 1965. NSF

by Kim Malville

Jan 31: Close approach of the moon to brilliant Venus, which will be first visible soon after sunset around 5:40pm. Venus will set around 9pm, depending on your horizon.

Feb 3: First quarter moon

February 10: Full Moon and partial eclipse of the moon. It will be a very subtle darkening of the moon, getting darkest at 5:45pm when it is close to setting, about two moon lengths above the horizon. See if you can detect it.

Feb 15: The moon and Jupiter are close in the morning sky

Feb 17: Venus achieves its greatest brightness tonight, visible as the sky darkens, it should first becomes visible in the western sky at around 5:55pm when it is 35° above the horizon. Venus should set around 7pm.

Feb 18: Last quarter moon.

Feb 26: New Moon and annular eclipse (when the moon appears too small to cover the sun entirely), visible in the southern hemisphere, Chile, Argentina, Zambia and the Democratic Republic of the Congo.

Dark matter & Vera Rubin

Most of the matter in the universe has never been seen. Dark matter reigns supreme in the universe. The best measurements of the effects of dark matter were made by Vera Rubin and her colleagues in the 1960s. For these fundamental measurements she truly deserved the Nobel Prize in Physics, which she never received.  She born was on July 23, 1928 and died aged 88 on December 25, 2016.

Vera Rubin received her PhD in astrophysics in 1954 at Georgetown University working under George Gamow. I first met Vera Rubin in the summer of 1960 when I, joined by my new bride, attended an International Summer Course on the structure of the galaxy at Nijenrode Castle in Breukelen, south of Amsterdam.  For me as a graduate student it was a heady experience, a feast of astronomy (and Dutch chocolate) that lasted for three weeks. We heard lectures from some of the world’s greatest astronomers and learned about the vexing problems that cried out to be solved.  Inspired by and energized by this remarkable conference, Vera took the torch and decided to measure the speeds of stars as they revolved about the centers of galaxies. Everyone thought they knew what she would find. The central regions of a galaxy rotate like a solid ball because of the tightly packed stars and speeds increase outward. Beyond that central region the stars would travel slower and slower due to weakening effects of gravity. It was so obvious, it hardly seemed necessary to measure.

A galaxy behaves like a solar system: planets move quickly in the central regions and slowly at the edge. Mercury zips around the sun at 29 miles per second while lonely non-planet Pluto plods along at 3 miles per sec. If Pluto were to travel faster, it would fly off like sparks on a grinding wheel. But that is not what Vera found. She and her colleague Kent Ford measured the rotation rates of stars in some 60 galaxies, and the results were always the same: their speeds didn’t drop off with increasing distance from the center but they stayed the same.  It was very, very puzzling and disturbing and a wonderful example why every well-established “fact” needs to be verified. Vera had estimated the gravitational mass of the galaxy by counting visible stars and clouds of glowing gas. Two things were wrong: (1) there wasn’t enough mass embedded in the center and (2) missing mass had to be distributed about the galaxy, not concentrated in the center. She and her colleagues speculated there might be many small stars, too faint to be visible. However, the required number of these dim stars was huge, some six times more than all the visible stars, which was completely at odds with studies of stars in our own neighborhood of the galaxy. Another possibility was that Newtonian gravity was significantly in error, but that would just open a terrible can of worms. Something different was required: particles of matter that couldn’t be seen were needed. If a halo of these dark particles surrounded each galaxy, she realized, the observed distribution could thus be explained. But what is this dark matter?

Today, after more than 35 years, it remains an enduring mystery. We have given a name to these dark particles, WIMPS (weakly interacting massive particles) but we don’t know exactly what they are. The mass-energy of the universe contains 5% of ordinary matter (people, planets, stars, visible galaxies), 27% dark matter, and a whopping 68% dark energy (which pushes the universe apart).   The bizarre and uncomfortable meaning of all of this is that we don’t understand the nature of 95% of the universe. We and everything we see with our eyes and through our telescopes are truly in the minority.

Most astronomers feel that Vera’s evidence for dark matter was a fundamental discovery in astrophysics and deserved the Nobel Prize. She was elected to the National Academy of Sciences in 1981, the first woman to receive the Royal Astronomical Society’s Gold Medal since Caroline Herschel in 1828, and was awarded the National Medal of Science in 1993. But for three decades she was passed over by the Nobel committee. Rules of the Nobel Prize prohibit posthumous awards

Only two women have ever received a Nobel Prize in physics, Marie Curie in 1903 and Maria Goeppert-Mayer in 1963. In 1978 Arno Penzias and Robert Wilson (who was also student with us at that extraordinary summer in the Netherlands in 1960) received the Nobel Prize for their accidental discovery of radiation from the big bang.  In 2006 another pair of male astronomers got the prize for mapping the same background radiation. In 2011 the prize was given to three men for discovering dark energy. No one yet, man or woman, has received the prize for dark matter. Usually the Nobel committee gets it right and rewards truly great scientific accomplishments. They missed this opportunity.skies-rotationcurves