Measuring the total mass of our home galaxy is a tough puzzle. It’s difficult to see it all at once, buried as we are within one of its spiral arms. And there’s a huge portion of the Milky Way we can never see, since it’s made up of dark matter, which doesn’t emit light at all. So to get an accurate number, researchers need to weigh both the visible and invisible material that makes up the galaxy.
Now scientists have done just that, using new data from the Hubble Space Telescope combined with the Gaia spacecraft. This latest mass measurement of the Milky Way weighs in at 1.5 trillion times heavier than our sun.
Now, how heavy is the universe? Assuming the Milky Way is an average galaxy, and there are 200 billion galaxies in the universe, then all galaxies combined would weigh 300 sextillion (300,000,000,000,000,000,000,000) times the mass of the sun, and that’s not counting all the stuff drifting around between galaxies.