Milky Way Mystery: Is Our Galaxy Getting Even Bigger?

The Milky Way stretches about 100,000 light years in diameter yet scientists think that this giant bundle of gas, dust and several hundred billion stars could be getting even bigger.

However, since we sit inside the Milky Way, it's hard to get a good glimpse of its size and shape. Instead, astronomers look at other similar galaxies for clues to the workings of our own.

Predicted for years, researchers have quantified disk growth in two Milky Way-like galaxies for the first time by investigating the light at the edge of their disks. These galaxies could be growing at a speed of 550 yards per second. At that speed, you could circumnavigate the globe in about 22 hours.

On a galactic level, it isn't that quick. But over, time it amounts to a significant growth.

"It won't be quick, but if you could travel forward in time and look at [the Milky Way] in three billion years' time it would be about 5 percent bigger than today," researcher Cristina Martínez-Lombilla explained in a statement.

Martínez-Lombilla, a doctoral candidate at the Instituto de Astrofísica de Canarias in Tenerife, Spain, will present her team's work Tuesday afternoon at the 2018 European Week of Astronomy and Space Science in Liverpool, U.K.

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The bustling center of the Milky Way is imaged by the NASA Spitzer Space Telescope. JPL-Caltech/NASA

The Milky Way is a barred spiral galaxy. Its shape is determined by the interactions of matter—dust, gas and stars—and gravity. Our galaxy's matter lies mostly in the flat plane of a disk; arms of matter reach out from a bar across the center.

Read more: Planets Discovered Outside Milky Way Galaxy for First Time

Young, blue stars populate the galaxy's disk, while some star nurseries sit at the very edge. Older, dimmer stars are often found in the galaxy's halo and the bulge around its centre. For this reason, scientific models suggest the galaxy's disk should grow over time, in line with populations of bright, blue short-lived stars.

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In this artist's impression of the Milky Way, its two major arms can be seen attached to the ends of a thick central bar. JPL-Caltech/NASA

Martínez-Lombilla and team used ground-based and space telescopes to collect optical, near-UV and near-infrared data to detail the disk edges of other galaxies.

Observing the light in these regions, the team tracked how young blue stars moved up and down from the disk. Measuring this light allowed them to figure out how long it will take for stars to move from their nurseries, and how their galaxies were growing.

"The Milky Way is pretty big already," Martínez-Lombilla said. "But our work shows that at least the visible part of it is slowly increasing in size, as stars form on the galactic outskirts."

Read more: Andromeda Galaxy Brought Down To Size for Head-to-Head Collision With Milky Way

This growth, however, may be short-lived—astronomically speaking. Our galaxy is due to collide with the neighboring Andromeda Galaxy in about four billion years. When this happens, the size and shape of the galaxies will warp dramatically as they combine.