Team of scientists, led by the California Institute of Technology better known as Caltech, unveiled a distant protogalaxy connected to the cosmic web about 10 billion light-years away. It is a giant swirling disk of gas, still feeding from cool primordial gas tracing back to the Big Bang.
This protogalaxy is connected to a filament of the intergalactic medium, the cosmic web made of diffuse gas that crisscrosses between galaxies and extends throughout the universe and astronomers were able to image how such galaxies look like.
This is a very significant discovery as it provides new evidence supporting what is known as the cold-flow model of galaxy formation. It says that early in the development of the universe there was relatively cool gas that funnelled down from the cosmic web directly into galaxies and fuelled rapid star formation. Professor Christopher Martin, lead author of the study, noted that this discovery provides the strongest observational support yet for the cold-flow model of galaxy formation. He said: “Even as simulations and theoretical work have increasingly stressed the importance of cold flows, observational evidence of their role in galaxy formation has been lacking.”
The cold-flow model of galaxy formation was debated since 2003. The standard model said that when dark-matter halos collapse, they pull a great deal of normal matter in the form of gas along with them, heating it to extremely high temperatures. Afterwards gas cools down, which provides a steady but slow supply of cold gas that can form stars in growing galaxies.
However, in 1996 scientists discovered a distant population of galaxies producing stars at a very high rate only two billion years after the Big Bang, which could not be explained by that theory. The cold-flow model provided an explanation that relatively cool gas, delivered by filaments of the cosmic web, streams directly into protogalaxies, where it can quickly form stars. These new discoveries provide new evidence supporting this model.
This newly discovered protogalactic disk is about 400,000 light-years across—about four times larger in diameter than our Milky Way. The system in which it is situated in is dominated by two quasars. Quasar is extremely luminous object at the centre of a galaxy. Closest of these quasars, called UM287, is positioned so that its emission is beamed like a flashlight, helping to illuminate the cosmic web filament feeding gas into the spiralling protogalaxy.
In previous studies scientists thought to have discovered a large filament next to UM287. It was brighter than it should have been if indeed it was only a filament so it seemed that there must be something else there. Then astronomers used Cosmic Web Imager at Palomar Observatory, which allowed them to collect images around the UM287 at hundreds of different wavelengths simultaneously, revealing details of the system’s composition, mass distribution, and velocity.
Lead author of the study Professor Christopher Martin explaining the significance of the new discovery. Credit: Caltech Academic Media Technologies and Office of Strategic Communications
Images that were taken were combined to form a multiwavelength map of a patch of sky around the two quasars. These images showed that there is a rotating disc – scientists were able to notice that one side is moving closer and the other is moving away. Scientists took measurements, which indicate that the disk is rotating at a rate of about 400 kilometres per second – somewhat faster than the Milky Way’s own rate of rotation. There is also a filament that extends beyond the disk, which is funnelling gas into the disk at a fixed rate. When the gas merges with the disk inside the dark-matter halo it is pulled around by the spinning disc. Dark matter is a form of matter that we cannot see that is believed to make up about 27% of the universe.
Scientists say that this discovery is very significant. In fact, they it is very compelling evidence that cold-flow model is close to what actually happened at the beginning of formation of our universe. Simulations of this model show that as the gas falls in, it contains tremendous amounts of angular momentum, or spin, and forms extended rotating disks and this is exactly what scientists can observe now. However, now scientists will try to find out exactly what the gas falling into galaxies is actually doing, so the research will be continued.
The team has already identified two additional disks that appear to be receiving gas directly from filaments of the cosmic web in the same way, so we can only wonder what else will be discovered in the near future.