From everything we’ve been able to tell, the Milky Way is a fairly typical galaxy. It’s a medium-large spiral with several smaller satellite galaxies, and the disk spans some 120,000 light-years. It can be hard to tell what the galaxy looks like from the inside, though. A new analysis focusing on a class of very bright stars indicates the Milky Way might be stranger than we thought with a warped and uneven central disk.
Researchers at the University of Warsaw in Poland spent six years tracking a class of celestial objects known as cepheid variable stars. These “signpost” stars pulse at a stable frequency related to their brightness. Since we know from that pattern how bright the stars are, we can compare that with how much light reaches us to deduce the distance between Earth and the cepheid. The researchers point out the distance to cepheid stars is accurate to within five percent. With enough data points, it’s possible to measure many features of the galaxy.
The University of Warsaw team used the Warsaw Telescope in Chile to amass data from 2,431 cepheid stars. They integrated that data into a new 3D map of the galaxy. This is the first such map built using direct measurements of stellar distances. Thus, it’s the most accurate we have.
The 3D model of the Milky Way created by the researchers paints a picture of a galaxy that’s far from flat. Instead, the thickness of the galactic disk varies considerably, and it gets more variable the farther you get from the galactic core. In fact, the edges of the disk twist away from the core in opposite directions. The video below is in Polish, but it has a few useful visuals. Alien astronomers looking at the Milky Way from someplace else probably think our galaxy looks quite unusual.
Currently, astronomers can only speculate about the cause of this curvature. The leading hypotheses include interactions with dark matter or massive interstellar gas clouds. It’s also possible that the Milky Way had a close encounter with another galaxy at some point in the distant past.
In addition to mapping the Milky Way, the data on cepheid variable stars showed they were created in bunches. That suggests that star formation does not proceed at the same rate across the galaxy at all times, but happens in bursts. What causes these increases in star formation is unclear, but maybe it has something to do with the warped shape of the Milky Way?