Astronomy

A dark answer
Dark matter existed as a concept, first proposed by astronomers
like Jan Oort in 1932 and Fritz Zwicky in 1933, who also noticed
discrepancies in how much mass astronomers could see and how
much physics implied should be present. But few paid their work
any attention, writing their research off as little more than cosmological
oddities. And no one had bagged such solid evidence
of it before. And because no one had predicted what dark matter’s
existence might mean for galaxy dynamics, Rubin and Ford initially
didn’t recognize the meaning of their flat rotation curves.
“Months were taken up in trying to understand what I was
looking at,” Rubin told journalist Maria Popova. “One day I just
decided that I had to understand what this complexity was that I
was looking at, and I made sketches on a piece of paper, and suddenly
I understood it all.”
If a halo of dark matter graced each galaxy, she realized, the
mass would be spread throughout the galaxy, rather than concentrating
in the center. The gravitational force — and the orbital
speed — would be similar throughout.
Rubin and Ford had discovered the unseeable stuff that influences
not only how galaxies move, but how the universe came
to be and what it will become. “My entire education highlighted
how fundamental dark matter is to our current understanding of
astrophysics,” says Levesque, “and it’s hard for me to imagine the
field or the universe without it.”
Within a few years of the M31 observations, physicists like
Jeremiah Ostriker and James Peebles provided the theoretical
framework to support what Rubin and Ford had already shown, and
dark matter settled firmly into its celebrated place in the universe.
In more recent years, the Planck satellite measured the dark
matter content of the universe by looking at the cosmic microwave
background, the radiation left over from the Big Bang. The
clumps of matter in this baby picture of the universe evolved into
the galaxy superclusters we see today, and it was dark matter that
clumped first and drew the regular matter together.
Data from galaxy clusters now also confirms dark matter and
helps scientists measure how much of it exists within a given
group — a modern echo of Zwicky’s almost forgotten work. When
light from more distant sources passes near a cluster, the gravity
— from the cluster’s huge mass — bends the light like a lens.
The amount of bending can reveal the amount of dark matter.
Rubin measures spectra at the Carnegie Institution’s Department of
Terrestrial Magnetism. It was such measurements that revealed to Rubin
that the outer regions of galaxies rotated as fast as their inner regions —
indicating some huge amount of missing mass that would later be realized
as dark matter. AIP/EMILIO SEGRE VISUAL ARCHIVES
Rubin continued to work at the Carnegie Institution’s Department
of Terrestrial Magnetism until recently, still fascinated by galaxies
and studying how they move in the universe. AIP/EMILIO SEGRE VISUAL ARCHIVES
No matter which way or where scientists measure Rubin’s discovery,
it’s huge.
And while no one knows what all the dark matter is, scientists
have discovered that some small fraction of it is made of
neutrinos — tiny, fast-moving particles that don’t really interact
with normal matter. Measurements from the cosmic microwave
background, like those being taken by experiments called
POLARBEAR in Chile and BICEP2 and BICEP3 in Antarctica,
will help pin down how many neutrinos are streaming through
the universe and how much of the dark matter they make up.
Some setups, like the Gran Sasso National Laboratory in Italy
and the Deep Underground Science and Engineering Laboratory
in South Dakota, are trying to detect dark matter particles
directly, when they crash into atoms in cryogenically cooled
tanks filled with liquefied noble gases. So far, they haven’t managed
to capture a dark matter particle in action. But researchers
are taking dark matter — whatever it is — into account when
they think about how the universe evolves.
The Nobel committee may overlook Rubin, passing by her as
if they can’t see what all of astrophysics feels. But that won’t hurt
her legacy, says Levesque: It will hurt the legacy of the Nobel
itself. “It would then permanently lack any recognition of such
groundbreaking work,” Levesque says.
Rubin herself has never spoken about how she deserves a
Nobel Prize. She simply continued her scientific work until
recently, all the while influencing the origins, evolutions, and
fates of other scientists. “If they didn’t get a job or they didn’t get
a paper published, she would cheer people up,” says Bahcall. “She
kept telling her story about how there are ups and downs and you
stick with it and keep doing what you love doing.”
Rubin, herself, loves trying to understand the universe, and
in doing so, she has changed everyone’s understanding of it.
That carries more weight than some medal from Sweden. But let
Sweden recognize that for what it is: worthy of a prize.
WWW.ASTRONOMY.COM 31