At first glance, it’s almost like staring at a desktop screensaver: seemingly random bursts of color pulsate and sway on screen, as points of light spin, collide, and explode. But this is no screensaver. It's the simulated birth and evolution of a virtual galaxy — billions of years of space activity condensed into 120 seconds — created on a supercomputer by scientists at NYU Abu Dhabi.
The Numerical Investigations of Hundred Astrophysical Objects project (NIHAO) was envisioned by Andrea Macciò, project principal investigator and NYUAD associate professor of physics, in collaboration with researchers from China and Germany and now involves more than 20 scientists from around the world. At NYUAD, Macciò’s team includes three other researchers and four students.
Creating a galaxy with a computer is a lot like trying to develop a cake recipe just by looking at a picture of a cake. The basic ingredients might seem obvious but the quantity and ratio is a matter of constant trial and error.
It’s no different with galaxy simulations, Macciò explained. The code that he and other scientists developed on the project solves a set of equations with varying parameters that describe the physics behind the evolution of a galaxy and generates synthetic data for different kinds of galaxies, big and small.
“You can’t create a galaxy in a regular lab because they (galaxies) involve densities, time scales, and temperatures that are far beyond our reach,” Macciò said, “and that is why we do these on a computer.”
“You can’t create a galaxy in a regular lab because they (galaxies) involve densities, time scales, and temperatures that are far beyond our reach ... and that is why we do these on a computer.”
How are galaxy simulations used?
Simulations help astronomers and scientists overcome certain limitations when observing the cosmos. Telescopes and instruments provide them with a two-dimensional view of the galaxies in the sky whereas galaxy simulations can be moved, flipped, and rotated.
“The other important thing is that simulations also contain information about the distribution and abundance of dark matter inside the galaxy, a component which is invisible to telescopes. That helps to understand and explain some of the properties of real galaxies.”
Macciò further explained that scientists pore through and analyze the data generated by their simulations to help answer questions that are frequently raised about the formation and evolution of different galaxies.
“When you observe real galaxies in the universe, you’re looking at a particular instance in time in the life of that galaxy. With simulations we can ‘rewind’ time and go back to the beginning of that galaxy’s creation,” he explained.
When you observe real galaxies in the universe, you’re looking at a particular instance in time in the life of that galaxy. With simulations we can ‘rewind’ time and go back to the beginning of that galaxy’s creation.
Certain aspects of galaxies are similar, he continued. Galaxies as big as the Milky Way, for instance, have a lot of stars in them that are clustered together.
However, Yale University astronomers were stumped when they discovered a new class of galaxies called Ultra-Diffuse Galaxies (UDG) last year. Initial observations showed that these galaxies might be as massive as the Milky Way but everything else about them was different: they had fewer stars than scientists were expecting and these stars were spread over a larger area than normally observed. How was that possible? How were these galaxies formed?
Dr. Arianna Di Cintio from the University of Copenhagen’s DARK Cosmology Centre reached out to NIHAO looking for answers to these very questions. NIHAO’s database contained galaxies that resembled these newly discovered UDGs and by ‘rewinding’ time in their simulations Di Cintio and Macciò's team were able to unravel the ordinary beginnings of this class of unique galaxies.
UDGs, they determined, were created in the same way as other galaxies but simply evolved into something different.
“They formed as normal galaxies but also contained a lot of gas” and went through a phase of intense star formation, Macciò explained, which led to the explosion of several Supernovae. “Such explosions rattle the cosmic system and cause the stars to move away from the region where they were formed and spread out to where we see them now. These galaxies simply evolved and that makes them more plausible.” The findings were recently published by the Monthly Notices of the Royal Astronomical Society.
Phase one of the simulation project ended with publication of nearly 14 scientific papers in major journals across Europe and the United States and it won’t be long before the NYUAD supercomputer named Dalma is fed new code to generate a whole new family of virtual galaxies. Macciò is confident phase two will open up many new avenues like more intense study of black holes.
“The final goal is to understand: ‘What are the key physics phenomena that drive the evolution of galaxies through cosmic time?’ and the new phase of the NIHAO project is working in that direction.”