Researchers say that our Milky Way galaxy is just half of the nearest spiral galaxy, Andromeda.

Andromeda is nearly 2.5 million light years away from Earth and is in the Andromeda constellation. Even though it is the nearest spiral galaxy to the Milky Way, it is not the nearest galaxy. Andromeda is the largest galaxy of the Local Group, which contains the Milky Way and about 30 other smaller galaxies.

Previously, scientists estimated the mass of both the galaxies taking into account their smaller satellite dwarf galaxies, which suggested that Andromeda was smaller than Milky Way.

A recent study conducted by an international team of researchers, which has been published in the journal Monthly Notices of the Royal Astronomical Society, suggests that Andromeda is in fact two times the size of Milky Way.

"Historically, estimations of the Milky Way's mass have been all over the map," says Matthew Walker, an assistant professor of physics at Carnegie Mellon University's McWilliams Center for Cosmology, who is also a part of the study's research team.

Walker says that they studied both the galaxies as well as the galaxies that surround them. The scientists observed the gravity and expansion of the galaxies to find the accurate mass that is contained within Milky Way and Andromeda. Scientists have able to measure these two things simultaneously for the first time to confirm their findings.

Both the galaxies are believed to have similar structure and extent; however, Andromeda is believed to have more mass than the Milky Way. The extra mass in Andromeda is made from the dark matter, which is an invisible substance that binds a galaxy together with its gravity.

Scientists say that they have been able to find that Andromeda has more mass than the Milky Way, but do not know how much dark matter is present in Andromeda. Dr. Jorge Penarrubia, who led the research, says that they suspected that Andromeda was bigger than the Milky Way. Dr. Penarrubia also says that measuring the weight of both the galaxies simultaneously was a challenging task.

Dr. Yin-Zhe Ma, a postdoctoral fellow at the University of British Columbia in Canada, who was involved with the new study, says that the latest research will give scientists an opportunity to understand about dark matter more from within the Milky Way.