36 DISCOVERMAGAZINE.COM
THIS PAGE: BOISSIER/A&A/ESO/CFHT. OPPOSITE: P. VAN DOKKUM/YALE UNIVERSITY (2)the Milky Way with 50 times its mass. Yet, bizarrely,
the galactic titan is rendered profoundly dim by its
wispy spiral arms, spaced 10 times farther apart than
in conventional spiral galaxies.
“It’s impossible to understand how that object
exists,” says Bothun. “All our models do not produce
objects anywhere near Malin 1.” The dim giant proved
there might be more to the universe’s galaxies than
anyone suspected.FOUND AND LOST
Galvanized by the discovery of Malin 1, astronomers
pored over the previous decades’ photographic
plates for hints of unnoticed, low-surface-brightness
galaxies. (In fact, they still do — there are a lot of
plates.) Although less grand than Malin 1, thousands
more materialized throughout the 1990s.
Further aiding in the search were charge-coupled
devices (CCDs), a far more light-sensitive imaging
technology that took off in the 1980s and dominates
astronomy today. “Discovering low-surface-brightness
galaxies was a thrilling thing to do,” says Karen
O’Neil, then a student of Bothun’s and now the
director of Green Bank Observatory in West Virginia.
“It’s always fun to go out and look for the unknown.”
Though intriguing, next to the billions of known
luminous galaxies, these hundreds of dim ones
still didn’t amount to a hill of beans, cosmically
speaking. The phantom universe, so far, was just a
phantom niche.
But ironically, it was work by Disney himself
that ended up slamming the door shut on the field.
He helped install a powerful receiver at the ParkesObservatory radio dish in Australia in 1997, hoping
to wrangle many Malin 1-esque galaxies and finally
blow the lid off the dim universe. In data collected
over several years, more than 4,000 concentrations of
hydrogen gas turned up — promising candidates as
low-surface-brightness galaxies.
By 2005, however, optical telescope follow-ups
on these sources suggested they were almost all just
hydrogen clouds in normal galaxies. “Not one looked
to be a hidden galaxy,” says Disney. The discovery was
a crushing result, seeming to prove beyond doubt that
Malin 1 and its ilk were just bizarre freaks, not part of
a larger phantom universe.
“That killed the subject off,” says Disney. “Even
I gave up.”... AND FOUND AGAIN?
But the subject did not give up on him, for other
skygazers thought Disney was on to something.
At a 2009 conference in the Caucasus region, Disney
met Ukrainian astronomer Valentina Karachentseva,
who suggested some of those thousands of hydrogen
clouds in the Parkes survey were indeed galaxies. Over
her career, through keen eyesight alone, Karachentseva
has identified numerous dim galaxies on photographic
plates. She told Disney she’d spotted standalone
galaxy-like objects right where the Parkes survey had
found gas clouds identified as merely extended parts
of nearby bright galaxies.
Thunderstruck, Disney returned to Wales and tried
something new. He went over calculations affirming
just how clustered the universe’s galaxies are. They’re
fundamentally social creatures, piling up practically
on top of each other, leaving immense, desolate
voids between clusters. Could his unseen galaxies
be hidden among these huddled galactic herds, with
their separate gas clouds mistaken as belonging to the
closest, resplendent galactic neighbor?
Disney came to realize that the Parkes observations
lacked the resolution, the fineness of detail, to make
out dim galaxies tightly bunched with luminous
galaxies. He tried to convince study colleagues and an
astronomical journal of the possible error, but none
was receptive. “I was a bit of a figure crying in the
darkness,” says Disney, “literally.”
He eventually found a way to settle the matter. In
early 2015 Disney was awarded time on the upgraded,
exquisitely sensitive Karl G. Jansky Very Large
Array (VLA) of radio dishes in New Mexico. He
rescanned a sample of 19 hydrogen clouds from the
4,000 candidates in the Parkes survey. Fourteen of
the clouds, it turned out, had no visible counterpart
galaxy in the new data.
“Bingo,” says Disney. Straightaway, it was clear that
the gas cloud radio wave sources shouldn’t have been
lumped together with nearby, optically bright galaxies.
He was onto something.
Despite being
the largest
known
spiral galaxy,
Malin 1 is
so dim and
its arms so
faint that
it remained
undetected
until the
1980s.