May 20, 2024 May 13, 2024
Three Clemson University astrophysicists have received grants totaling more than $1 million through the NASA Astrophysics Data Analysis Program to study active galactic nuclei, their obscuring material, variability and periodicity.
Pablo Penil del Campo and Nuria Torres-Alba are postdoctoral researchers and Stefano Marchesi is an adjunct professor in the Department of Physics and Astronomy.
The highly competitive grant will support research focused on the analysis of publicly available archival data from NASA’s space astrophysics missions.
Pablo Péncillo del Campo studies quasi-periodic oscillations in blazars. His work may find evidence of the existence of binary supermassive black holes. Photo credit: NASA
4 blazers
Pennille will study quasi-periodic oscillations in blazars, a type of galaxy powered by a supermassive black hole that appears bright in all forms of light, including gamma rays (light with the highest levels of energy), when one of its jets of material points almost directly toward Earth.
The study will use NASA observations from missions spanning more than 30 years to study four blazars that show signs of periodic, long-term (2-4 years) emission in the gamma-ray band. Theoretical models are proposed to explain the physical mechanisms responsible for these possible periodicities, such as the presence of a binary system of supermassive black holes. In this project, Pennille will use NASA’s archived data to look for similar periodic behavior in the X-ray and ultraviolet visible bands.
“We aim to get a detailed and complete understanding of how and why these blazars change over time,” Pennille said.
Potentially, the results of this study could reveal evidence of a binary supermassive black hole at the center of one of these blazars, providing valuable insights into the evolution of galaxies.
Chaotic environment around a black hole
Marchesi and Torres-Alba will use publicly available observational data from NASA’s various X-ray telescopes to study the chaotic environments surrounding the supermassive black holes that exist at the centers of each galaxy. Their work will focus on the black holes closest to Earth in the “Local Universe.”
The environment around a massive black hole consists of gas that rotates around it and falls into it, feeding it and increasing its mass, producing light and energy in the process. However, very little is known about this environment, from its structure and density to the exact distance to the black hole.
The gas is so dense that it absorbs visible light, making it impossible to detect these sources with optical telescopes. X-ray photons, which are produced in the immediate vicinity of a supermassive black hole, are invisible to the human eye but are so energetic that they can penetrate the dense gas and be observed by space telescopes. This allows researchers to study and characterize the properties of supermassive black holes. However, even though the X-ray photons escape, they are affected by the gas in ways that vary based on the properties of the gas (density and structure). This also allows scientists to study all the unknown properties of black holes.
How efficiently black holes grow
Marchesi’s research is using these X-ray observations to learn more about the density of matter that may be related to how much energy a black hole can feed on and grow, while Torres Alba is using the multi-epoch observations to look at how matter changes over time.
Marchesi and Torres-Alba will study how efficiently black holes grow in mass by eating the gas around them, and how the energy released in this process affects the environment both nearby and much farther away.
“This work provides us with a unique understanding of what processes take place near the most extreme objects in the universe: black holes with hundreds of millions of times the mass of the Sun,” Marchesi said.
The sources the researchers chose for their analysis were selected from a much larger sample, using methods developed by a Clemson University graduate student working at Clemson University and INAF’s Compton Thick AGN Collaboration.
A new machine learning-based approach
The Marchesi sample was collected using a new machine learning-based method developed by former Clemson University graduate student Ross Silver. The Torres-Alba sample was drawn from the work of former Clemson University graduate student Shi-ului Zhao, who looked at data from over 100 sources, using multiple telescopes, and found that many of them are variable. Torres-Alba will look at all available observations from these sources to create the largest sample to date of known occulting variable supermassive black holes.
“We don’t yet know whether occultation variations are common, so this study will provide one of the greatest insights into the structure of black holes,” Torres-Alba said.
Both projects will leverage more than 20 years of observations from X-ray telescopes, including Chandra, NuSTAR, Swift-XRT and XMM-Newton, whose public catalogs contain hundreds of thousands of sources with X-ray data.
“This means we are entering an era in which we need effective selection criteria to extract from these catalogs the sources that are most suitable for analysis and to perform time-consuming dedicated analyses on only those, because it is not possible to do so on all known sources,” Marchesi said.
Marchesi and Torres-Alba’s study will allow researchers to evaluate the reliability of the methods developed at Clemson University.
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