The birth of Massive black holes in the early Universe visualised

Light from the areas around the first massive black holes is so intense it travels almost the entire Universe, for more than 13-billion light-years to reach our telescopes. Yet we do not quite know how these black holes formed. New research and an exciting visual simulation from the Georgia Institute of Technology aims to answer that question.

The new study finds that massive black holes form in dense starless regions that are growing rapidly, which is contrary the long-accepted belief that massive black hole formation was limited to regions bombarded by the powerful radiation of nearby galaxies. The conclusions of the study reported in the journal Nature, also finds that massive black holes are much more common in the universe than previously thought.

This two-part visualization by the Advanced Visualization Lab at the National Center for Supercomputing Applications starts shortly after the Big Bang and shows the evolution of the first galaxies in the universe over the first 400 million years, in increments of about 4 million years. The second part of the visualization stops time at the 400 million year mark, and flies the viewer through the data, breaking down the different variables that are being visualized — filaments of dense gas, pockets of elevated temperature, ionized gas, and ultraviolet light (Advanced Visualization Lab at the National Center for Supercomputing Applications)

John Wise, an associate professor in the Center for Relativistic Astrophysics at Georgia Tech and the paper’s corresponding author, says: “In this study, we have uncovered a totally new mechanism that sparks the formation of massive black holes in particular dark matter halos.

“Instead of just considering radiation, we need to look at how quickly the halos grow. We don’t need that much physics to understand it — just how the dark matter is distributed and how gravity will affect that. Forming a massive black hole requires being in a rare region with an intense convergence of matter.”

A 30,000 light-year region from the Renaissance Simulation centred on a cluster of young galaxies that generate radiation (white) and metals (green) while heating the surrounding gas. A dark matter halo just outside this heated region forms three supermassive stars (inset) each over 1,000 times the mass of our sun that will quickly collapse into massive black holes and eventually supermassive black holes over billions of year ( Advanced Visualization Lab, National Center for Supercomputing Applications)

Wise adds that the key criteria for determining where massive black holes formed during the universe’s infancy relates to the rapid growth of pre-galactic gas clouds that are the forerunners of all present-day galaxies, meaning that most supermassive black holes have a common origin forming in this newly discovered scenario. Dark matter collapses into halos that are the gravitational glue for all galaxies. The early rapid growth of these halos prevented the formation of stars that would have competed with black holes for gaseous matter flowing into the area.

John Regan, a research fellow in the Centre for Astrophysics and Relativity in Dublin City University adds that the discovery these black hole formation sites in the simulation initially left the team stumped as the previously accepted paradigm was that massive black holes could only form when exposed to high levels of nearby radiation. The earlier theory also relied on intense ultraviolet radiation from a nearby galaxy to inhibit the formation of stars in the black hole-forming halo.

Reagan says: “Previous theories suggested this should only happen when the sites were exposed to high levels of star-formation killing radiation

“As we delved deeper, we saw that these sites were undergoing a period of extremely rapid growth. That was the key. The violent and turbulent nature of the rapid assembly, the violent crashing together of the galaxy’s foundations during the galaxy’s birth prevented normal star formation and led to perfect conditions for black hole formation instead.”

The research was based on the Renaissance Simulation suite, a 70-terabyte data set created on the Blue Waters supercomputer between 2011 and 2014 to help scientists understand how the universe evolved during its early years.

To learn more about specific regions where massive black holes were likely to develop, the team examined the simulation data and found ten specific dark matter halos that should have formed stars given their masses but only contained a dense gas cloud. Using the Stampede2 supercomputer, they then re-simulated two of those halos — each about 2,400 light-years across — at much higher resolution to understand details of what was happening in them 270-million-years after the Big Bang.

Zoom of the inner 30 light-years of the dark matter halo. The rotating gaseous disk breaks apart into three clumps that collapse under their own gravity to form supermassive stars (Wise)

Wise says: “It was only in these overly-dense regions of the universe that we saw these black holes forming.

“The dark matter creates most of the gravity, and then the gas falls into that gravitational potential, where it can form stars or a massive black hole.”

The Renaissance Simulations are the most comprehensive simulations of the earliest stages of the gravitational assembly of the pristine gas composed of hydrogen and helium and cold dark matter leading to the formation of the first stars and galaxies. They use a technique known as adaptive mesh refinement to zoom in on dense clumps forming stars or black holes. In addition, they cover a large enough region of the early universe to form thousands of objects — a requirement if one is interested in rare objects, as is the case here.

The improved resolution of the simulation done for two candidate regions allowed the scientists to see turbulence and the inflow of gas and clumps of matter forming as the black hole precursors began to condense and spin. Their growth rate was dramatic.

Wise says: “Astronomers observe supermassive black holes that have grown to a billion solar masses in 800 million years.

“Doing that required an intense convergence of mass in that region. You would expect that in regions where galaxies were forming at very early times.”

Another aspect of the research is that the halos that give birth to black holes may be more common than previously believed.

Brian O’Shea, a professor at Michigan State University, says: “An exciting component of this work is the discovery that these types of halos, though rare, may be common enough.

“We predict that this scenario would happen enough to be the origin of the most massive black holes that are observed, both early in the universe and in galaxies at the present day.”

Future work with these simulations will look at the lifecycle of these massive black hole formation galaxies, studying the formation, growth and evolution of the first massive black holes across time. “Our next goal is to probe the further evolution of these exotic objects. Where are these black holes today? Can we detect evidence of them in the local universe or with gravitational waves?” Regan asked.

For these new answers, the research team — and others — may return to the simulations.

Regan concludes: “This research shifts the previous paradigm and opens up a whole new area of research.”