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Now we know that the Milky Way and Andromeda are of similar masses, what have we learned? Importantly, we can now try to understand the role these galaxies played in the formation and evolution of the local universe. It and the Milky Way are equals in the local universe. While the calculation was complicated, the result was unequivocal: previous estimates had overstated the total mass of Andromeda. We figured that if we can trace out the escape velocity for stars within the massive gravitational halo of Andromeda, we can work out its gravitational pull, and the mass that is ultimately responsible.
Galactic clash war of galaxy free#
The key concept is escape velocity, or how fast you have to be moving to break free from the gravitational pull of a massive object.Īs Elon Musk and the Falcon Heavy rocket just showed, you need to get up to speeds of more than 11km per second to ensure that your Telsa electric car escapes Earth’s gravitational clutches. This is what we did in our new work, but with a twist.Įscape velocity is the key to measuring the mass of galaxies. American astronomer Vera Rubin figured out more than half a century ago that there is much more to the Andromeda galaxy than simply the stars we can see.Īs dark matter holds stars in their orbits, we can use their motions to measure the overall mass of the Andromeda galaxy, including the unseen dark matter.
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The rest, the significant majority, is this elusive dark matter that dominates all of the mass in the universe.īut it is the gravitational pull of this dark matter that holds the stars in their orbits, meaning we can measure its presence. The light side of a galaxy, the glowing stars and gas that we can see, accounts for only a couple of tens of percent of the total mass. The mass of a galaxy is dominated by its dark side, an immense amount of matter that is unseen by telescopes. Simply counting the number of stars in any galaxy, and adding their individual masses, won’t give you its total mass. Johnson (University of Washington), the PHAT team, and R. Our new work takes a new approach to measuring the mass of the Andromeda galaxy.Ī portion of the Andromeda galaxy (M31), our galactic next-door neighbour. For Andromeda, where observations are more difficult, astronomers have still struggled to measure an accurate mass. In our Milky Way, where we can get the best observational data, there has been a growing consensus among astronomers as to its mass.
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Until now, astronomers have been unable to pin down the galactic masses, with a lack of data and complex calculations yielding very uncertain answers.Īt times it seemed that our own Milky Way was more massive at others it appeared that Andromeda was the local Goliath. The answer to this question is vitally important if we are to understand the dynamic history of all nearby galaxies, both large and small, as the gravitational field of the most massive will command the action. But astronomers have struggled to work out which of these two galaxies is the most massive.Īnd knowing the masses of the two giant galaxies will help to reveal the details of our ultimate fate. The Andromeda and the Milky Way galaxies are very similar, giant spirals containing hundreds of billions of individual stars.