The mass of the Milky Way is only 50 percent of the original estimates of its mass compared to the mass of the nearest neighboring galaxy called Andromeda. The difference is suspected to be caused by dark matter. Dr. Jorge Peñarrubia, of the University of Edinburgh's School of Physics and Astronomy, led a group of scientists from the University of British Colombia, Carnegie Mellon University, and NRC Herzberg Institute of Astrophysics in determining the new findings. The research was published in the July 29, 2014, edition of the journal Monthly Notices of the Royal Astronomical Society.
Measuring the mass of a galaxy is not easy. One cannot just estimate the weight of a galaxy from telescopic measurements from all the suns, moons, planets, and other celestial bodies that are a part of a given galaxy. This effort would eliminate the mass of that which is too small to be seen and that which cannot be seen in visible light or any other type of light that is presently used in telescopes.
The researchers used the most recently recorded distance from the center of the Milky Way to the center of the Andromeda galaxy. The researchers collected records of all the movements of the two galaxies recorded by space telescopes and Earth telescopes to produce the most accurate estimate of the velocity of rotation of each galaxy. Rotation is a function of mass and gravity. The accumulated data produced a computer model that determined the most accurate mass of both galaxies to date.
The study found that both galaxies contain about 90 percent matter that is invisible. The research also showed that the two galaxies are expanding at a rate consistent with the expected rate of the expansion of the universe. The scientists found that Andromeda weighs twice as much as the Milky Way. This discovery is a first because previous thought was that both galaxies weighed the same because they are almost the same physical size.
The difference in mass is attributed to the presence of more dark matter in Andromeda than in the Milky Way. This discovery affords a close source to study dark matter. Andromeda is 2.5 million light years from the Milky Way. The research also agrees with NASA’s recent finding that some of the arms of the Andromeda galaxy will intrude on the Milky Way in about four billion years.