Astronomers Think They Just Found The Edge of The Milky Way Galaxy

When you're right in the middle of something, it's pretty hard to tell exactly how big it is.

Like the Milky Way galaxy, for instance. We can't exactly go take a picture of it from the outside, so our best estimates rely on distance measurements to objects on the outskirts.

An estimate based on Gaia mapping data last year gave us a disc diameter of about 260,000 light-years, give or take.

But, just as the Sun's influence extends farther than the Kuiper Belt, the gravitational influence and density of the Milky Way - its invisible dark matter halo - extends farther than the disc.

How much farther? Well, as new calculations have found, quite a bit.

In a new paper submitted to the Monthly Notices of the Royal Astronomical Society and uploaded to arXiv, astrophysicist Alis Deason of Durham University in the UK and colleagues have revealed a diameter of 1.9 million light-years.

There's more to the Milky Way than the stuff we can see - the stars and gas all whirling in orbit around Sagittarius A*, the supermassive black hole at the galactic centre.