These red dots represent some of the earliest galaxies known to astronomy. Located ten billion light-years away, they're only a few billion years older than the Big Bang. Their presence explains why we're now surrounded by massive elliptical galaxies.
The European Southern Observatory's APEX telescope has completed this survey of the universe's most distant galaxies, and for the first time we can see a clear link between these ancient starburst galaxies — so named because of the constant birth of new stars going on inside them — and the gigantic elliptical galaxies that we see in the modern universe. The galaxies tend to be clustered tightly together and surrounded by huge dark matter halos, which you can see in the image up top. These observations, coupled with computer simulations of how these halos should develop over billions of years, makes it extremely likely that these starburst galaxies eventually evolve into today's elliptical galaxies.
Crucially, the starburst period for these distant galaxies seems to have lasted only about 100 million years, which is nothing in cosmic terms. However, in just that very short period, the galaxies doubled their number of stars — and then, just like that, they suddenly stopped, never to form stars again. That fits well with the idea that these are juts early versions of modern elliptical galaxies, which we also know suddenly stopped forming stars eons ago.
Astronomers aren't totally sure why this happens, but they have a pretty shrewd idea: supermassive black holes. The way the starburst galaxies are clustered is very similar to that of quasars, which are ultra-energetic objects powered by a central black hole. The starburst galaxies likely helped fuel these early quasars by feeding them tons of excess material. Then, as the black holes became powerful enough, they actually blew away the starburst galaxies' extra gas. Without that gas, there was no way for stars to continue forming, and so ended 100 million years of frantic stellar activity.