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SOCIETY UPDATE 
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1/26/22 11:46 AM
1/26/22 11:46 AM

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FEEDBACK
DECEMBER 18, 2021 & JANUARY 1, 2022
Fine feather
A filament of cold, dense gas named the 
Gangotri wave may bridge two spiral 
arms near the Milky Way’s center, 
Lisa 
Grossman 
reported in “Scientists find the 
Milky Way’s first known ‘feather’ ” 
(
SN: 12/18/21 & 1/1/22, p. 4
).
Reader 
Doug Holcomb 
asked how 
this newfound “feather” differs from 
a galactic spur.
The language describing the dif-
ferent limbs of the Milky Way can get 
fuzzy, 
Grossman
says. In general, 
our galaxy has four primary spiral 
arms emanating from its center, and 
an unknown number of smaller arms. 
A spur tends to be an offshoot of an 
arm, but the line between spur and 
arm is not so strict.
“The main difference between the 
Gangotri wave and other galactic 
t endrils is that Gangotri runs perpen-
dicular to the larger arms of the galaxy, 
and crosses two of them,” 
Grossman
says. “That crossing of the two arms is 
unique, although researchers expect 
that there are probably more of them 
throughout the Milky Way that have 
yet to be discovered.”
Reader 
Jasmine Melvin 
wondered 
whether the Gangotri wave has stars.
“Many regions within the wave are 
sites of active star formation,” says 
astrophysicist 
Veena V.S. 
of the Max 
Planck Institute for Radio Astronomy 
in Germany. Future studies are needed 
to characterize the total number of stars 
within the structure, she says.