“This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies. Perhaps we have been blind to the fact that early “dead” galaxies could in fact be disks, simply because we haven’t been able to resolve them.” -Sune Toft
How do galaxies form and grow? The theory behind it is simple and straightforward. You start with a collection of normal-and-dark matter, the normal matter collects in the center, pancakes, and forms stars over time. A little later, more gas falls in, and the galaxy continues to form new stars over time. It’s only when a gravitational interaction or a major merger occurs that a galaxy goes from active to “dead and red,” in the form of a giant elliptical.
At least, that’s the theory. But a new analysis of a very unusual galaxy, MACS2129-1, shows that despite being just 3 billion years old, it’s already “dead and red,” but it’s somehow still a spiral! With no evidence for a major merger and no conventional explanation for this otherwise, this young, dead galaxy creates a huge puzzle for astronomers.