Milky Way ‘weighed’ more accurately

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THERE’S ONE OBVIOUS problem
facing anyone who wants to
weigh a galaxy – you can’t just
whip out a set of scales and
place it on them. Estimations of
the mass of our Galaxy, the Milky
Way, have therefore included a
huge margin of error. But now a
team at Columbia University has
developed a more accurate
method and used it to determine
that the mass of the Milky Way is
210 billion times that of the Sun.
The Milky Way consists of
roughly 100 billion stars that form
a gigantic disc around 100,000
light-years across. The whole
thing is orbited by a stream of
stars produced by dissolving
‘globular clusters’. Through
observing the motions of these
stars, the team were able to
figure out the gravitational
attraction created by the Milky
Way, and so infer its mass.
“Globular clusters are compact
groups of thousands to several
millions of stars that were born
when the Universe was still very
young,” said researcher Andreas
Küpper. “They orbit the Milky
Way and slowly disintegrate over
the course of billions of years,
leaving a unique trace behind.
Such star streams stick out from
the rest of the stars in the sky
much as contrails from airplanes
stick out from regular clouds.”
The researchers used data
from the Sloan Digital Sky
Survey, which scanned the sky
from the Northern Hemisphere
for 10 years to create a detailed
map of the stars in the sky. They
focused on the stream produced
by a globular cluster named
Palomar 5, which had a pattern
of wiggles in its path caused by
our Galaxy’s gravitational pull.
By creating millions of models
of our Galaxy using Columbia’s
Yeti supercomputer, the
researchers were able to find a
match and estimate the Milky
Way’s mass with an uncertainty
of just 20 per cent, compared to
the previous 400 per cent.