Sky & Telescope - October 2023 - 22

W. C. KEEL ET AL. / ASTRONOMICAL JOURNAL 2022, DOI 10.3847/1538-3881/AC517D / CC BY 4.0
Citizen Science Big Leagues
and we want to use it as efficiently as possible, " Brown says.
" We want to maximize the scientific return of the telescope. "
When he heard about the program, Keel thought, " Well,
this is just what we've been looking for. " Crafting a proposal,
he took to the discussion forum. " Help us collect the strangest
objects! " he wrote, and volunteers complied, combing
through old threads to find their favorites. Project scientists
shaped the categories of galactic " gems " that Keel eventually
proposed, but the list bore the fingerprints of the Zooites. For
categories with many candidates, participants voted on which
ones should make the final proposal - a process handled
partly by other volunteers.
This kind of project shows that citizen science isn't just a
machine, something " you put your project in and out comes
your result, " says Ivy Wong (Commonwealth Scientific and
Industrial Research Organisation, Australia), part of the Zoo
Gems team and a co-leader of Radio Galaxy Zoo, the radio
astronomy counterpart of the original effort. " It's not like
that at all. It's like any collaboration - the communication
has to be two ways. "
Galactic Weirdos
The Zoo Gems project, selected alongside two other gapfillers,
kicked off in 2018 and will run through late 2023.
Hubble has observed more than half of the mysterious targets,
including compact star factories known as " Green Peas, "
elliptical galaxies that are blue instead of the typical red, and
a rare class of radio galaxies.
SUPERIOR VIEW Zooites use Sloan Digital Sky Survey images (left) to
classify galaxies like the red spiral UGC 3935. The details of the galaxy's
swirl appear to great effect in the Hubble Space Telescope image (right)
taken as part of the Zoo Gems project.
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The breadth of unusual targets included in Zoo Gems is
special, says Samantha Brunker (University of Connecticut),
who was not involved in the project but has studied Green
Pea galaxies. " They were able to select objects in many different
categories, " she says, producing a broad dataset that's
" really beneficial for the community. "
Plus, says Brunker, unusual objects can sometimes serve as
tools for scientists as they untangle broader questions about
the cosmos. " In the early universe, things that we think of
as rare or unusual now might have been commonplace, " she
says. Take those Green Peas, first identified as a group by
participants during Galaxy Zoo's early years. They're named
for their small size and their color in Galaxy Zoo's groundbased
images. The galaxies' hot young stars emit high-energy
photons that excite the surrounding gas; the gas then belches
out that energy at a wavelength the images show in green.
Green Peas are rare in the nearby universe, but scientists
think they may be similar to the galaxies responsible for a
major transition in the universe's early life. They have high
star-formation rates and low metal content, and they leak
photons capable of stripping away the electrons of hydrogen
atoms. Those characteristics suggest they may be doppelgängers
of the early galaxies that spurred the Epoch of Reionization,
converting the universe's hydrogen into plasma (S&T:
April 2018, p. 14). If so, then studying the nearby analogs
could help us understand the traits of early galaxies, which
are more difficult to analyze.
In fact, Webb recently spotted some early galaxies that
researchers say look remarkably similar to the Peas. The
objects are compact, and their spectra reveal similar levels of
heavy elements as their modern-day counterparts. But Zoo
Gems images suggest the Green Peas might not be perfect
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22 OCTOBER 2023 * SKY & TELESCOPE
Sky & Telescope - October 2023

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