The mass of our Milky Way galaxy has been estimated to be about 700 billion times that of our Sun, say researchers who developed a new method to overcome the galactic challenge.
The Sun has a mass of two nonillion (that is 2 followed by 30 zeroes) kilogrammes, or 330,000 times the mass of Earth.
“And our galaxy is not even the biggest galaxy,” said Gwendolyn Eadie from McMaster University in Canada.
Measuring the mass of our home galaxy, or any galaxy, is particularly difficult, researchers said.
A galaxy includes not only stars, planets, moons, gases, dust and other objects and material, but also a big helping of dark matter, a mysterious and invisible form of matter that is not yet fully understood and has not been directly detected in the lab.
Astronomers and cosmologists, however, can infer the presence of dark matter through its gravitational influence on visible objects.
Eadie, a PhD candidate in physics and astronomy at McMaster, used the velocities and positions of globular star clusters that orbit the Milky Way to study the mass of our galaxy and its dark matter component.
The orbits of globular clusters are determined by the galaxy’s gravity, which is dictated by its massive dark matter component. What is new about Eadie’s research is the technique she devised for using globular cluster (GCs) velocities.
The total velocity of a GC must be measured in two directions: one along our line-of-sight, and one across the plane of the sky (the proper motion).
Researchers have not yet measured the proper motions of all the GCs around the Milky Way.
Eadie, however, has developed a way to use these velocities that are only partially known, in addition to the velocities that are fully known, to estimate the mass of the galaxy.
Her method also predicts the mass contained within any distance from the centre of the galaxy, with uncertainties, which makes her results easy to compare with other studies.
The research appears in the Astrophysical Journal.