The New Year started once again, as it always does, with two significant astronomical events.
First, on Jan. 4, our planet moved into the closest point in its orbit with the Sun, a position known as perihelion. This occurs during wintertime in the northern hemisphere, so while we enjoy the snow at the coldest time of the year, keep in mind that this relative proximity to the Sun keeps our winters a little milder than they would be otherwise.
And the second event? On the very same day, the American Astronomical Society gathered for its annual winter meeting.
While this year had the usual round of new discoveries, the most exciting aspect for me was the christening of the new Vera C. Rubin Observatory, the first national observatory named for a woman.
This recognition comes after a long history of women contributing to the science of astronomy. Some of the names include Caroline Herschel, rumored to be responsible for her brother’s observations of the planet Uranus; Annie Jump Cannon, who, working as a “computer” for Harvard astrophysicist Edward Pickering, developed our modern understanding of stellar classification; and Joycelyn Bell, the discoverer of neutron stars, whose adviser Antony Hewish was awarded the Nobel Prize for the discovery in 1974 — without her.
The list goes on. I’m beginning to detect a pattern.
Dr. Rubin, for her part, was responsible for discovering dark matter, the enigmatic material that makes up most of the mass in the universe.
If you’ve ever seen an image of a galaxy, you’ll notice that the brightest component is concentrated near the center. That led astronomers to deduce that most of the mass of the galaxy would also be located in the same region. Dr. Rubin’s project was an attempt to measure how much stuff happened to be there.
According to Newton’s Laws, the speed at which one object orbits another is determined by the mass of each and the distance between them. The farther one object is from another, the slower the speed of the orbit, as we see with the planets in the solar system. By observing the motion of the stars orbiting far from the galactic center, one can, in principle, deduce the mass of the galaxy itself.
But Dr. Rubin discovered a curious thing. As she observed the velocities of stars farther from the galactic center, she found they kept roughly the same speed, rather than falling off as she expected. This indicated there was some other unseen matter driving the motion of these stars, matter that was neither shining by its own light nor blocking the light of the other stars.
If this additional matter represented a small amount compared to the mass of the stars in the galaxy, it might be attributed to cool dust and gas or even some rogue planets. However, when she ran the numbers, she found the unseen dark matter accounted for 10 times more mass than all the visible stars in the galaxy.
Let that sink in for a moment. The lion’s share of the stuff that makes up galaxies is invisible to light. It doesn’t shine, it doesn’t reflect, and it doesn’t block the light from the stars that make up the other 10% of the mass.
This result was so shocking that many astronomers discounted it at the time. But observation after observation has supported the evidence that we can’t see 90% of the stuff in our universe that interacts only gravitationally with the other stuff that we can.
Now, this may seem unimportant. After all, if we can’t see it, why should we care? But due to the gravitational interaction, dark matter drives the formation of galaxies, which determine how stars are formed. Stars are the foundries for the elements that make up everything else in the universe, including other stars, planets and you.
So in a very real sense, you owe your very existence to all of this unseen matter in the universe. And certainly the discovery warrants some recognition.
Even though Dr. Rubin made her observations in 1970s, she never received a Nobel Prize for that effort. So I’m thrilled to see Dr. Rubin receive much more significant recognition in the form of a national observatory dedicated to studying the stuff she discovered. Formerly known as the Large Synoptic Survey Telescope, the instrument will image the entire night sky every couple of days, providing an unprecedented look into the variability of the deep cosmos.
That’s an incredible legacy for the woman who discovered most of the universe.