Astronomers produce better Milky Way mass estimate

An international team of scientists have come up with a better estimate for the mass of the Milky Way Galaxy.

Some might question why we need to know such a thing, but for the record it is 4.179 x 10^38 metric tonnes.

Astronomers at Columbia University led the study which is published this week in the Astrophysical Journal.

The Milky Way is our home galaxy and the Earth resides well away from the centre on one of the galaxy’s spiral-shaped arms.

The galaxy measures an average 150,000 light years across and consists of about 100 billion stars so getting a handle on its mass is no small matter.

By comparison measuring the mass of our sun is a snap using a formula based on knowing how long it takes the Earth to orbit the sun, at what distance and knowing the strength of the pull of gravity.

And this for the record is 1.98855 x 10^27 metric tonnes, scientists have found.

Earlier attempts to calculate this came up with levels of error that made the result almost meaningless, so this study represents a razor-sharp estimate with an uncertainty of just 10 per cent either way.

They used very old and slowly disintegrating streams of stars orbiting the galaxy in a cluster called Palomar 5.

These streams left behind over the last 11 billion years provided markers for calculating mass.

“Such star streams stick out from the rest of the stars in the sky as they are dense and coherent, much like contrails from aeroplanes easily stick out from regular clouds,” says Andreas Küpper of Columbia University who led the study.

The scientists also employed the kind of statistical mathematics used for studying the human genome and driving internet search engines.

The study showed that the mass of our galaxy within a radius of 60,000 light-years was 210 billion times the mass of the sun.

It took a supercomputer to come up with the numbers after running several million models so the scientists are confident they have got the numbers right.