How Vera Rubin Transformed Astronomy
The Vera C. Rubin Observatory has just unveiled the most detailed view of the universe ever seen
A telescope powerful enough to spot a golf ball on the Moon. A camera so detailed you’d need 400 Ultra HD TVs just to view a single image in its full resolution. And the potential to uncover 20 billion galaxies.
Yesterday, the Vera C. Rubin Observatory released its very first images. Perched on a mountaintop in Chile, the $800 million marvel is being hailed as a once-in-a-generation leap for astronomy. One of the first images (above) shows a vibrant star-forming region 9,000 light-years from Earth.
Within hours the observatory had discovered more than 2,000 previously unknown asteroids, including seven near-Earth objects. In time, scientists believe it will increase the number of known objects in our solar system tenfold and capture images as far as 1.2 million light-years away.
More than 25 years in the making, the telescope will film the southern night sky in unprecedented detail for the next decade — building the most comprehensive survey of the universe ever attempted. Crucially, it could finally help solve one of science’s greatest puzzles: what exactly is dark matter, the mysterious yet abundant substance that makes up most of the universe?
There are some great write-ups of the observatory’s launch event on BBC News and Astronomy Magazine, and you can also see more on the Vera C. Rubin Observatory website.
But who was Vera Rubin, and how did she come to reshape our understanding of the cosmos? Here’s a short explainer video and newsletter that we first published in 2023 covering her incredible story.
The Discovery That Reshaped The Universe
What is dark matter? If it exists, then it is the most abundant matter in the universe. This would make its discovery one of the greatest in the history of science.
One of the leading figures who found evidence for its existence was the astronomer Vera Rubin. Rubin isn’t as well-known as Sir Isaac Newton, but she should be. After all, Rubin’s study of the rotation of galaxies transformed our understanding of the universe and forced astronomers to fundamentally rethink everything they thought they knew.
But there is a catch. While most scientists now believe in the existence of dark matter, we can’t be certain. And while we think that it makes up a quarter of the mass of the universe, we still don’t know what it actually is.
Watch my short explainer to find out more…
The biggest mystery in the universe
What is the universe made of? It’s one of science’s biggest unknowns.
Thanks to Rubin, we now believe that a sizeable portion of the cosmos is made up of matter that we are unable to see or interact with in any way. We call it dark matter because we can’t see it and, when it comes to working out what this abundant and mysterious substance is, we are still completely in the dark.
Considering that scientists have never directly observed dark matter and can’t even agree what it is, you might be wondering how we can be sure it’s actually there.
To answer this, we need to go back a few hundred years.
Standing on the shoulders of Kepler, Newton and Hubble
It seems incredible to think now, but just over 100 years ago it was generally agreed that our galaxy, the Milky Way, was the universe. That all changed in 1924 when astronomer Edwin Hubble confirmed the existence of another galaxy – M31, also known as Andromeda. By the end of the decade, he had found at least 20 more. We’ve now counted over 100 billion galaxies – confirmation that the Milky Way is no more than a metaphorical speck of dust on the canvas of an ever-growing universe.
Our ability to explore and understand the universe owes a lot to Sir Isaac Newton and the laws of gravity he developed in the 17th century. Building on German astronomer Johannes Kepler’s insights about the movement of planets, Newton identified that objects with mass attract each other. Newton’s law said that the force of gravity was proportional to the mass of objects and the distance between them. This explained why planets closest to the sun in our solar system spin the fastest, while the rotation of those on the outer edges is much slower.
It was Newton’s great insight that led to the discovery of Neptune. Astronomers working in the 19th century couldn’t ‘see’ the most distant planet in our solar system. Instead, they deduced its existence through a mathematical prediction based on the unusual orbit of Uranus. Even today, we still use Newton’s law to launch rockets and land them safely.
However, in the 1960s, a strange new discovery suggested a more complex universe than Newton imagined while sat underneath an apple tree 300 years earlier.
The genius of Vera Rubin
Astronomer Vera Rubin was relatively overlooked in her lifetime. She was never nominated for a Nobel prize. But as a trailblazer for women in science who forced us to rethink the rules of the universe, her legacy and achievements should be as celebrated as those of her more famous peers.
Rubin was born in 1928, just four years after Hubble proved that there was more to the universe than the Milky Way. As a child, she was fascinated by the stars she could see through her bedroom window, noticing how they moved through the night sky.
In many ways, it was an ideal time to grow up with a fascination for the workings of outer space. Just not if you were a girl.
Recalling her school days, Rubin said:
“The high school physics teacher did not know how to include the few young girls in the class, so he chose to ignore us. The first day of class, he defined two kinds of discoveries: those that took insight and brilliance (here his examples all came from males) and discoveries that required hard work but not brilliance (his example was the discoveries of Marie Curie). I was often angry in class for his similar comments. I rarely spoke, and the teacher never learned that I was interested in astronomy. The day I received mail informing me that I had been accepted to Vassar College with a needed scholarship, I met the physics professor in the hall and told him my good news. ‘You should do OK as long as you stay away from science,’ were his words.”
These kinds of obstacles continued to present themselves throughout her career. Like the time she was invited to share her Masters thesis with the American Astronomical Society, but only if the Chairman of Cornell University presented it on her behalf. Rubin refused and did it herself.
In 1965, she joined the Carnegie Institution in Washington to study the movement of galaxies and had to battle for use of the institute’s 200-inch telescope at the Palomar Observatory. Shortly after arriving, Rubin was told: “Your time on the observatory is limited, because we don’t have a women’s bathroom.” On her first tour of the facility, she taped over the ‘men’ sign on the toilet door with a drawing of a skirted woman.
It was here, at Palomar, that Rubin made her universe-shaking discovery. Working with Kent Ford, she set her sights on the outer edges of the Milky Way and our neighbouring galaxy Andromeda.
Rubin and Ford expected to see stars moving in the same way as they do in our solar system – objects nearer the centre moving faster than objects at the edge. But they didn’t. The outermost stars were moving way too fast given how far they were from the galaxy’s centre of mass.
Persuading astronomers to rethink the universe
The observations of Rubin and Ford seemed to pose two possibilities – either something was wrong with the data, or something was wrong with our entire picture of the physical universe. They began analysing other galaxies and in each one they discovered the same problem of fast-moving outer stars. What could explain it?
Rubin had an answer. “The universe has played a trick on us,” she said. Perhaps these observations could be explained by our current scientific models… if those galaxies contained huge quantities of some invisible, undetectable mass.
Throughout her academic career, Rubin had consistently faced doubts and scepticism. Perhaps with this in mind, she made relatively little fuss about these initial findings. Instead, she spent the next decade observing galaxy after galaxy, collecting more and more data until she had studied over 60 of them.
By the 1980s, Rubin felt the evidence was conclusive. She was now certain that dark matter wasn’t just a little secret sauce: it was a main ingredient, far outweighing all the visible matter we know about.
In 1985 she gave a landmark talk at the International Astronomical Union where she shared her findings. It was the pinnacle of years of perseverance. Rubin’s evidence was so conclusive that her fellow astronomers were left in little doubt. By popular consensus, it was now agreed that the universe contained an abundance of dark matter.
What is dark matter? MACHOs vs WIMPs vs axions
Although our understanding is still sketchy, we have made some strides in building on Rubin’s initial findings. In 2013, the Planck satellite gave an estimate that the universe is made up of 4.9% regular matter, 26.8% dark matter and 68.3% dark energy (the stuff that means the universe is expanding quicker than we would expect it to).
Two rival theories for explaining dark matter are MACHOs and WIMPs. The former posits that dark matter is made up of things that are very big, but not very bright, known as Massive Compact Halo Objects. The latter argues that dark matter is made up of very, very small things, known as Weakly Interacting Massive Particles (which are massive in the sense that they have mass).
If you’re thinking that MACHOs and WIMPs sound like the kind of juvenile names a group of teenage boys would have dreamt up, then you may be amused to learn that some of the projects launched in the 1990s to investigate them had names including OGLE and EROS. Decades on from Rubin’s bathroom battle, astrophysics still remained a male-dominated field.
None of these missions found decisive evidence of MACHOs and it now seems increasingly unlikely that MACHOs are the answer. WIMPs haven’t shown up either, but the hunt continues: the LUX-ZEPLIN dark matter detector, buried one kilometre below South Dakota, hopes to detect traces of WIMPs, while new data about deep space should soon be appearing courtesy of the Vera C. Rubin Observatory in Chile.
In recent years, an alternative theory has been gaining traction. Step in, the axion. Unlike MACHOs and WIMPs, these hypothetical particles are low in mass, but huge in number. It might be the case that an enormous quantity of axions were spat out during the Big Bang and are still hanging around billions of years later.
In April 2023, academics from the University of Hong Kong published research arguing that ‘Einstein rings’ – a visual effect seen around some galaxies – gives credence to the theory that dark matter consists of axions.
Rubin’s legacy
Dark matter is the best explanation we have for the phenomena observed by Vera Rubin, but we may one day find a better one.
Perhaps the problem with those speeding stars wasn’t the amount of mass holding them in place, but the law of gravity it was calculated with. In the 1980s, physicist Mordehai Milgrom wondered if a tweak to Newton’s law might be able to clear the whole thing up. He argued that the mass of observable matter is sufficient if, beyond a certain point, the effect of gravity doesn’t weaken as much as Newton’s law says it should. This theory, called Modified Newtonian Dynamics, or MOND, has its problems – like the way it hasn’t been tied into Einstein’s theory of relativity – and many have simply dismissed it. But not Vera Rubin.
Ultimately, “dark matter” isn’t really an answer. It’s a question. Rubin’s great discovery was to show us just how much we don’t know. It’s only when we are aware of the limits of our knowledge that we start asking the right questions. However much we think we know, there will always be a whole lot more to learn.
Shortly before her 81st birthday, Rubin attended a conference at Queen’s University in Canada to celebrate her incredible career. On the event’s final day, she was asked if she would be disappointed if her great revelation turned out to be disproved – if the movement of galaxies she spent her life studying ended up being explained by something other than dark matter.
“I would be delighted,” she replied.
As Rubin had said previously: “It is a strange and mysterious universe. But that’s fun.”
Recommended links and further reading
The first episode of Vox’s Unexplainable podcast Most of the Universe is Missing’. “She (Rubin) discovered that everything we can see, everything we can touch, everything we know, is just a tiny sliver of what the universe really is.”
Vera Rubin’s short memoir An Interesting Voyage, published online by the Annual Review of Astronomy and Astrophysics in 2011. On the sexism she faced, Rubin notes with some understatement that: “Women generally required more luck and perseverance than men did.”
The Hunt for Dark Matter: The Universe’s Mysterious Gravitational Glue (New Scientist) Kathryn Zurek at the California Institute of Technology says that the hunt for dark matter has “taught people to not be quite so dogmatic about how nature should behave. It’s useful and humbling.”
Dark matter is certainly one of the most interesting subjects in cosmology!
The observations of spiral galaxies in the 1970s not only opened our eyes to this “missing mass,” but also the integral role that it plays in galactic formation and dynamics!
Several candidates have been proposed for dark matter—including Weakly Interacting, axions and sterile neutrinos, and while each candidate offers a potential pathway to solving the dark matter mystery, we’re yet to uncover a direct detection.
The ongoing search sure is an exciting mission—thanks for sharing!