The Milky
Way galaxy weighs about 1 trillion times as much as our sun, according to a new
estimate.
Previous
estimates had ranged from 750 billion solar masses to up to 2 trillion. Lately,
researchers have been leaning toward the higher figure. But now astronomers
have used a more refined method to conclude that our galaxy's mass is slightly
less than 1 trillion solar masses.
The
galaxy's mass is a mix of stars, gas, dust and mysterious
dark matter.
The new
estimate is based on a large sample of stars in the galactic halo, a relatively
sparse sphere of stars that surrounds our galaxy's main disk. The speeds of
stars in the halo reveal the mass of the galaxy by allowing astrophysicists to infer
the amount of gravity required to keep those stars in orbit.
"The
galaxy is slimmer than we thought," said Xiangxiang Xue of the National
Astronomical Observatories of China, who led the international team of
researchers. "That means it has less dark matter than previously believed,
but also that it was more efficient in converting its original supply of
hydrogen and helium into stars."
The
finding, based on data from the Sloan Digital Sky Survey (SDSS-II), has broad
implications for our understanding
of the Milky Way, the researchers said in a statement.
"The
total mass of the galaxy is hard to measure because we're stuck in the middle
of it," explained collaborator Timothy Beers of Michigan State University.
"But it is the single most fundamental number we have to know if we want
to understand how the Milky Way formed or compare it to distant galaxies that
we see from the outside."
Previous
estimates had been based on 500 objects or fewer. The new math was based on
data for 2,400 stars.
The larger
data set "gives us a huge statistical advantage," said study team
member Hans-Walter Rix of the Max Planck Institute for Astronomy (MPIA) in
Heidelberg, Germany.
The
research will be detailed later this year in the Astrophysical Journal.
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