Research
Shanil Virani's research has primarily focused on three distinct areas: science education & communication, fundamental research related to astrophysical phenomena, and spacecraft science operations. An extensive and detailed bibliography can be found by clicking on the Publications tab.
Astrophysical Research
It is now recognized that every galaxy likely hosts a supermassive black hole that lurks at its center. Supermassive black holes that show signs of devouring material in its immediate vicinity are called "Active Galactic Nuclei" (AGN). Much of my astrophysical research has involved carrying out surveys and studies to better understand the AGN phenomenon and to understand the relationship between the supermassive black hole at the center and its host galaxy. In order to understand the nature of activity in galactic nuclei, in particular how it is initiated and maintained, it is reasonable to begin with the question, how do active galaxies compare with non-active galaxies? But any such statistical comparison is fraught with difficulty since this, at least ideally, requires an understanding of the biases in the samples selected. Moreover, it is not clear just which parameter(s) should be compared. Could an active nucleus, especially in the more luminous members of the active galactic nuclei (AGN) family, have a significant effect on "macroscopic" scales; that is, not only on the immediate circum-nuclear environment, but even on the structural parameters of the host galaxy? For these reasons, a comparison of the environments of AGN has been of particular interest in the past three decades, motivated largely by the widely held hypothesis that interactions and mergers play a significant role in initiating activity of the supermassive black hole.
My specific research goals have been to probe hidden populations of supermassive black holes heretofore missed in previous surveys of active galactic nuclei in both the nearby and distance Universe. Using the Chandra X-ray Observatory, a space-based, NASA "Great Observatory", we stared at what we thought was a blank region of the sky at least as it appears to be as seen by the eye. This "blank" area on the sky has now been imaged by the Hubble Space Telescope, the Spitzer Space Telescope, the Chandra X-ray Observatory, and virtually every major telescope on the ground. Using 250,000 second exposures of 4 flanking fields -- called the Extended Chandra Deep Field-South -- this is one of the largest and deepest surveys ever performed with this Observatory. As the Chandra X-ray image embedded in the text shows, this area is anything but blank! In fact, MOST of the sources you see in this image are active supermassive black holes in the centers of galaxies betrayed by the gas swirling around it! These sources have been extensively followed up from the ground using some of the largest ground-based telescopes located in Hawaii and Chile.
My specific research goals have been to probe hidden populations of supermassive black holes heretofore missed in previous surveys of active galactic nuclei in both the nearby and distance Universe. Using the Chandra X-ray Observatory, a space-based, NASA "Great Observatory", we stared at what we thought was a blank region of the sky at least as it appears to be as seen by the eye. This "blank" area on the sky has now been imaged by the Hubble Space Telescope, the Spitzer Space Telescope, the Chandra X-ray Observatory, and virtually every major telescope on the ground. Using 250,000 second exposures of 4 flanking fields -- called the Extended Chandra Deep Field-South -- this is one of the largest and deepest surveys ever performed with this Observatory. As the Chandra X-ray image embedded in the text shows, this area is anything but blank! In fact, MOST of the sources you see in this image are active supermassive black holes in the centers of galaxies betrayed by the gas swirling around it! These sources have been extensively followed up from the ground using some of the largest ground-based telescopes located in Hawaii and Chile.
In addition to my research related to the Extended Chandra Deep Field-South, I was also responsible for carrying out one of the deepest surveys of the hard X-ray sky ever done. We obtained 3 million seconds of time with the space-based International Gamma-Ray Astrophysical Laboratory (INTEGRAL) to find so heavily obscured AGNs in the nearby universe that they don't appear in traditional AGN surveys. I was also awarded time for follow-up observations with the Chandra X-ray Observatory and with Japan's Suzaku space observatory. One of my more exciting results was finding a "precocious" supermassive black hole in the early Universe. Using the Chandra X-ray Observatory, we imaged and characterized the X-ray spectrum of an AGN found at a redshift of 6, i.e., at a time when the Universe was only ~800 million years old. Our results for the energy index and α_ox are consistent with no strong evolution in the active galactic nucleus emission mechanism with redshift out to z~6 and therefore with the picture that massive black holes have already formed less than 1 Gyr after the Big Bang. The background image to this page shows an artistic creation of what the central engine of an AGN may look like. This research result was the subject of a NASA/Chandra press release and was also highlighted as a "High Energy Astrophysics Picture of the Week" entitled "Black Hole Too Young?". To understand how AGN activity may have impact on their host galaxies on "macroscopic" scales, I developed a technique that permitted the robust decomposition of the bulge and disk components of a local sample of Seyfert galaxies (i.e., in the nearby Universe), as well as a (control) sample of nonactive galaxies matched to the Seyferts in the distributions of redshift, luminosity, and morphological classification. The structural parameters of the host galaxies in both samples were measured. No statistically significant differences at greater than the 95% level are found in these parameters according to a Kolmogorov-Smirnov test. Similarly, I found no statistically significant differences between the control and active sample host galaxies in terms of light asymmetries-bars, rings, isophotal twisting, etc. Since AGN were first discovered some 50 years ago, much work still remains in attempting to resolve these enigmatic objects and the role they play in the formation and evolution of galaxies.
Spacecraft Science Operations
The Chandra X-ray Observatory is a space-based, "Great Observatory" that has revolutionized our view of the X-ray universe. It is NASA's flagship X-ray observatory, just like the Hubble Space Telescope is NASA's flagship optical observatory. Launched in 1999 onboard the space shuttle Columbia, the Chandra X-ray Observatory's unprecedented resolution allows high energy astrophysicists like me to find extreme objects in the Universe. In order to image the high energy universe at a sharp focus, the mirrors on the Chandra X-ray Observatory are exquisitely polished. If the state of Colorado was as smooth as Chandra's mirrors, Pikes Peak would be less than one inch tall! We new immediately what an incredible research facility this observatory was to become. The image below shows "Leon X-1", named after the Chandra Telescope scientist Dr. Leon VanSpeybroeck who designed the mirrors. It was detected in the very first image that was taken right after the Observatory opened its sunshade door to the X-ray universe.
This new X-ray source was found to be an unobscured active galactic nucleus at redshift z=0.3207 and had not been detected before. I will never forget that day when we commanded the Observatory door to open and the very first X-ray photons from the Universe began collecting on our instrument. It is a highlight of my life. Designed for a mission lifetime of 5 years, in 2001 NASA extended Chandra's lifetime to 10 years "based on the observatory's outstanding results." In 2014, NASA's Senior Review committee reviewed the Chandra X-ray Observatory, the Hubble Space Telescope, and all other NASA missions. In reviewing the scientific productivity of the Observatory, the committee once again endorsed an extension of the mission stating "Chandra is the most powerful facility for X-ray astrophysics, and its unique capabilities have no likely successor in the foreseeable future."
The Smithsonian Astrophysical Observatory, half of the Harvard-Smithsonian Center for Astrophysics located in Cambridge, MA, is charged with operating and carrying out its mission on behalf of NASA.For 5+ years, I was part of the Science Operations Team responsible for monitoring the health and safety of the Observatory and its instruments, as well as scheduling the Observatory to maximize its science return. The primary instrument onboard the Chandra X-ray Observatory, responsible for carrying out more than two-thirds of all observations is the Advanced CCD Imaging Spectrometer (ACIS). I was part of the ACIS Operations team at the Harvard-Smithsonian Center for Astrophysics and worked closely with the instrument teams at MIT and PSU. Specifically, since the Observatory only makes contact with the ground once every ~8 hours via NASA's Deep Space Network, I wrote several software programs that monitored the health and safety of the ACIS during every real-time contact with the Observatory. I also wrote software that automated the review and checks of the mission command schedule that would be uploaded every week to be executed by the Observatory autonomously to carry out its science observation schedule. One of the key contributions I made to operating and maintaining the Observatory happened very early after launch.
The Smithsonian Astrophysical Observatory, half of the Harvard-Smithsonian Center for Astrophysics located in Cambridge, MA, is charged with operating and carrying out its mission on behalf of NASA.For 5+ years, I was part of the Science Operations Team responsible for monitoring the health and safety of the Observatory and its instruments, as well as scheduling the Observatory to maximize its science return. The primary instrument onboard the Chandra X-ray Observatory, responsible for carrying out more than two-thirds of all observations is the Advanced CCD Imaging Spectrometer (ACIS). I was part of the ACIS Operations team at the Harvard-Smithsonian Center for Astrophysics and worked closely with the instrument teams at MIT and PSU. Specifically, since the Observatory only makes contact with the ground once every ~8 hours via NASA's Deep Space Network, I wrote several software programs that monitored the health and safety of the ACIS during every real-time contact with the Observatory. I also wrote software that automated the review and checks of the mission command schedule that would be uploaded every week to be executed by the Observatory autonomously to carry out its science observation schedule. One of the key contributions I made to operating and maintaining the Observatory happened very early after launch.
One month into the mission, we noticed that the instrument was suffering radiation damage. We quickly figured out that during perigee passage through the Earth's Van Allen belts, the mirrors on the Chandra X-ray Observatory were not only incredible at focussing X-ray photons from the Universe, they were also very good at focussing low energy protons from the Van Allen belts onto the instrument, causing "charge transfer inefficiency" (or CTI), which meant our spectral resolution was rapidly disappearing. Working with scientists at NASA's Marshall Space Flight Center, we quickly developed a brand new radiation model suitable for Chandra's elongated, elliptical orbit and used it to schedule science observations as well as when to shutdown for perigee passage through the Van Allen Belts. Not only did this new radiation model limit further degradation to the instrument, we also realized that we can more efficiently schedule the observatory such that we could regain up to 250,000 seconds of additional science time per year!
Working for a world-class research facility like the Chandra X-ray Observatory, I quickly learned that the images one typically sees in the press is literally the tip of the iceberg of what has to happen to make that observation possible. I also learned first-hand how incredibly smart, approachable, and dedicated the team of scientists and analysts responsible for the Observatory are in carrying out its mission. I was truly fortunate to have spent 5 years with such an outstanding team and my time at the CfA is definitely a highlight of my life!
Working for a world-class research facility like the Chandra X-ray Observatory, I quickly learned that the images one typically sees in the press is literally the tip of the iceberg of what has to happen to make that observation possible. I also learned first-hand how incredibly smart, approachable, and dedicated the team of scientists and analysts responsible for the Observatory are in carrying out its mission. I was truly fortunate to have spent 5 years with such an outstanding team and my time at the CfA is definitely a highlight of my life!
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