Milky Way: Not The Corpulent Conglomeration of Stellar-Stuff We Thought
Astronomers claim that the Milky Way is not as massive as we thought, especially when compared to our neighbor galaxy, Andromeda
Various methods that astronomers have used in the past to weigh galaxies have shown the Milky Way to be the heaviest member of our Local Group.
The Local Group is your home (broadly speaking of course). It is a collection of 35+ diverse galaxies that are gravitationally bound to each other. The standouts of this group (in terms of mass and beauty) are the Andromeda Galaxy and our very own Milky way.
Many of these methods however produce wildly varying results with very little firm agreement. Generally, these weighing sessions were all based on the movements of the many dwarf galaxies that orbit us and Andromeda. Clearly, we needed a more accurate scale.
Enter an international team of astronomers that have recently published their findings in the journal Monthly Notices of the Royal Astronomical Society. They claim a new more elaborate and accurate method for determining the mass of local galaxies.
What they do is look at the gravitational interactions between galaxies closest to us and integrate that data with the movements of other galaxies just outside our local group. This was the critical difference that allowed much greater accuracy. Galaxies within our group are getting closer. In fact, all of these galaxies may one day merge into one super galaxy. The other galaxies however, are not tied to our group. They therefore are subject to cosmic expansion that is making all galaxies not near us move increasingly farther and faster away from us.
This new method allows us (and by “us” I mean me and the astronomers 😉 to pinpoint the precise gravitational center of the entire Local Group which is, unsurprisingly, between the Milky Way and Andromeda. This then leads directly to an accurate assessment of the weight of both the normal luminous matter and the dark matter suffusing both our galaxies.
The results are in. The Milky Way has lost it’s top spot as the most massive galaxy in the Local Group. It is only half as massive as Andromeda. Not only that, both galaxies apparently are composed of 90% dark matter.
If this is upsetting for some reason, no worries. In 4 billion years we’ll merge with Andromeda and the whole point will be moot.