Sky & Telescope - March 2023 - 21

1,000-year-old O and B stars. Two surveys, the Americanbased
Bar and Spiral Structure Legacy (BESSEL) and Japan's
VLBI Exploration of Radio Astrometry (VERA), use these
freshly minted massive stars to precisely trace the spiral
structure over about half of our galaxy. (The farside is still
largely out of reach because the masers become too faint to
accurately measure.)
The Sloan Digital Sky Survey, or SDSS (S&T: Jan. 2023,
p. 20) also contributes to the effort by mapping stellar
motions and compositions. For example, when groups of stars
move together, astronomers generally surmise they were born
together. But knowing their composition can tease apart the
their birth group from other effects.
" Sometimes stars tend to have similar motions not
because they're born together, but because they feel the same
influence from the arms, " D'Onghia says. " With the Gaia
era, and SDSS V, we will learn a lot about where these regions
are, where such resonances happen. "
Here, There & Everywhere
Perhaps the best way to test spiral scenarios is a both/and
approach. " You can get much more information about the
Milky Way, " Master says, " but the Milky Way is just one
example of a galaxy. "
Other galactic examples are, of course, far away and thus
much fainter, but they win in terms of sheer number and
180°
210°
240°
15,000 l-y
150°
120°
variety. Legions of citizen scientists participating in Galaxy
Zoo (galaxyzoo.org), of which Masters is the principal
investigator, have classified millions of galaxy images. Over
the past 15 years, this web-based project has advanced from
simply classifying galaxy type (e.g., spiral vs. elliptical) to
identifying more complex properties, such as how tightly
spiral arms are wound. Astronomers have used these detailed
data to test - and overturn - predictions.
Nor are spirals limited to the relatively nearby universe; we
see them almost as far back as we can see disks. In one of the
most distant examples, Takafumi Tsukui and Satoru Iguchi
(both at SOKENDAI, Japan) used the Atacama Large Millimeter/submillimeter
Array in Chile to image the spiral shape
of a galaxy that existed just 1.4 billion years after the Big
Bang. The newly operational James Webb Space Telescope, or
JWST (S&T: Nov. 2022, p. 12), could also reveal spirals in the
early universe, when galaxies were first emerging. " This is the
new challenge, trying to see when they form these features, "
D'Onghia says.
With insights now coming in from a multitude of sources,
a field that was once starved of data is now swimming in it.
" It's a very exciting time, and it's a complicated time, " Benjamin
says. " But at least we have a lot more data to work with. "
¢ News Editor MONICA YOUNG practiced making cream spirals
in many coffees while writing this article.
270°
Sun
90°
300°
60°
45,000 l-y
60,000 l-y
330°
75,000 l-y
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Galactic longitude
FROM ABOVE These two images conceptualize what the Milky Way would look like from the outside, each one based on multiple datasets.
Depending on how the data are analyzed, interpreted, and prioritized, different views of our galaxy are possible.
sk yand tele scope .o r g * MARCH 2023 21
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ARTIST'S CONCEPT OF MILKY WAY: R. HURT / JPL-CALTECH; ANOTHER ARTIST'S
CONCEPT OF MILKY WAY: XING-WU ZHENG & MARK REID / BESSEL / NJU / CFA
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http://www.galaxyzoo.org

Sky & Telescope - March 2023

Table of Contents for the Digital Edition of Sky & Telescope - March 2023