I have been an Assistant Professor of Astronomy in the Caltech astronomy department since 2019. Between 2015-18, I was a Millikan Fellow in Astronomy at Caltech, and I spent 2018-19 as a Clay Fellow at the Center for Astrophysics | Harvard and Smithsonian. My detailed CV and publications list can be found here. My professional focus is on exploring, understanding and bulding radio- and optical-wavelength instruments to observe the relativistic and unseen universe. I study neutron stars and black holes, and associated phenomena that vary on time-scales of nanoseconds to years. I also seek to understand the distribution and physical nature of diffuse/hot baryons within, around and in between galaxies, and dark matter. My research interests are detailed below.
I am an Australian of Indian origin. Educated at the Valley School, Bangalore, and Narrabri High School, NSW Australia, (and by my astronomer parents!), I studied physics as part of the Bachelor of Philosophy (PhB) at the Australian National University (ANU). The PhB also offered remarkable research opportunities: as an undergrad, I worked in a Bose-Einstein condensate lab, and I also investigated new ways of modelling the Earth's climate. I undertook Honours research with Prof. Dayal Wickramasinghe and Dr. George Hobbs on coherent radio emission from stars. While at ANU I resided at Burgmann College.
I spent the Fall of 2008 on exchange at the University of California, Berkeley. An undergraduate research apprentice program with Prof. Charles Townes and the Infrared Spatial Interferometer group led to my employment at UC Berkeley during 2010-11 as a Junior Specialist. I studied yearly changes in the atmosphere of Betelgeuse, and worked with the CASPER group to develop an instrument to image shells of water around similarly evolved stars.
I completed my PhD between 2011-15 at the University of Melbourne, with Prof. Stuart Wyithe and Dr. George Hobbs (at CSIRO Astronomy and Space Science). I developed predictions for gravitational-wave signals from orbiting pairs of supermassive black holes in merging galaxies, and tested these using decade-long timing data on millisecond pulsars from Murriyang, the Parkes telescope. My work provided the theoretical basis for two papers published in Science, and resulted in major thesis prizes.
During and immediately after my PhD, I also engaged in a selection of madcap ventures: investigations into an ultra-broadband pulsar system for the Australia Telescope Compact Array, searches for off-pulse emission and wind nebulae associated with a large pulsar sample, constraining the equation of state of matter at nuclear densities with gamma-ray burst and fast radio burst observations, and successful searches for fast radio bursts. I worked with Prof. Matthew Bailes and his group at Swinburne University on the nascent upgrade of the Molonglo Observatory to form a fast transient, pulsar and wide-field imaging instrument (UTMOST).
To hear about some of the things I do, you can check out recent colloquia of mine in the Caltech and Stanford physics departments.
A major motivation of astronomy is the discovery of objects and phenomena that expand our knowledge of what is possible, and which stretch physical theories. Neutron stars and black holes, and the electromagnetic and gravitational-wave emissions they power, are outstanding examples. Via a wide array of observational and sometimes theoretical investigations, I study the formation and life cycles of these objects, and the astrophysics of associated relativistic phenomena. At present, I am focused on the origins of fast radio bursts (FRBs) at extragalactic distances. FRBs are likely emitted by magnetars (neutron stars powered by magnetic-field decay), but the origins of the magnetars that emit FRBs (and perhaps all magnetars!) and the emission mechanisms remain in question. I also study the spectacular results of massive black holes (MBHs) disrupting and accreting nearby stars via extreme tidal forces. Tidal disruption events (TDEs) trace nearly all regimes of accretion and jet-launching from MBHs, and are beginning to reveal the theorized population of intermediate-mass MBHs. Stemming from my PhD research, I maintain an interest in using millisecond-pulsar timing observations to detect sources of gravitational waves from MBH binaries. Looking forward, I am developing a transformational fast-time-domain survey for pulsars and fast-transient emission with the DSA-2000 radio telescope. This survey will increase the known pulsar population by a factor of seven, and deliver around 10,000 arcsecond-localized FRBs each year, enabling paradigm-shifting discoveries of extreme astrophysical objects.
Around 85% of the gravitating material in the Universe is dark, of unknown composition. Most of the remaining 15%, which everything that we see is made of, itself exists as hot diffuse gas around and in between galaxies, making it very difficult to directly observe and characterize. I am developing a selection of novel techniques to shed light on the unseen parts of the Universe. First, it turns out that FRBs may be our best tools yet to measure the total content and physical conditions of the diffuse baryons. Imprinted on all FRBs are measures of the gas column density, level of density fluctuations, and magnetization along their lines of sight. I am using unprecedented samples of FRBs discovered and localized to individual galaxies by the DSA-110 instrument to trace the baryon distribution within galaxy halos and in the intergalactic medium. Besides being of central importance in the complex processes of galaxy formation and evolution, the baryon distribution that FRBs can trace is a major uncertainty in cosmological parameter inference with galaxy-redshift and weak-lensing surveys. In the coming years, I will use the orders of magnitude larger FRB samples from the DSA-2000 to fully characterize the the baryon distribution. Furthermore, I am growing a group to use the full suite of DSA-2000 surveys to perform a series of searches for signatures of dark-matter constituents. For example, annihilations, decays and conversions of the leading particle dark matter candidates - Weakly Interacting Massive Particles (WIMPs) and QCD axions - can result in radio emission in astrophysical magnetic fields.
A major theme of my career has been the development of new instrumentation to support and fulfill my scientific interests. Much of this work has been in collaboration with staff at the Owens Valley Radio Observatory. The Deep Synoptic Array (DSA) program of radio interferometers is my primary focus. I led the construction and commissioning of and science with the DSA-10 and DSA-110 instruments; the latter is now the leading instrument for the simultaneous discovery and arcsecond-localization of FRBs. DSA-10 receivers and digital signal processing equipment were used for the STARE-2 experiment, which co-discovered a Galactic FRB. I led the development and demonstration of the first phase of the SPRITEly instrument, a two-element interferometer for time-domain astronomy at millimeter wavelengths. I am also interested in high time resolution and interferometry systems in the optical and IR windows. For example, with collaborators at Fermilab, I studied the optical properties of the Crab pulsar by developing new instrumentation based on a high-speed photomultiplier tube for the 200-inch Hale telescope at Palomar. With the Infrared Spatial Interferometer, I helped develop a spectrometer to map warm gas around evolved stars. Now, with my group and the broader radio astronomy community at Caltech/OVRO, I am focused on designing and delivering the DSA-2000. The DSA-2000 will provide an unprecedented view of the radio sky, carrying out a series of imaging and time-domain surveys that are orders of magnitude more performant than any current equivalent.
From 2011 to 2015, I worked with Prof. Stuart Wyithe (University of Melbourne), and Dr. George Hobbs (CSIRO Astronomy and Space Science) and the Parkes Pulsar Timing Array team, on predicting the gravitational wave signal from orbiting pairs of supermassive black holes in merging galaxies. Gravitational waves - travelling perturbations to space itself - are a long-standing prediction of Einstein's general relativity, and are expected from compact, massive astrophysical systems. In a pair of reports in the journal Science, Dr. Ryan Shannon and I tested my predictions using a decade of the most accurate timing data on millisecond pulsars ever obtained, from the Parkes telescope. We showed that previous models for the evolution of binary black holes in galactic-centre environments required significant refinement. In particular, we found that either some binaries never reach small-enough separations to emit detectable gravitational waves, or that they rapidly evolve through the gravitational-wave emitting stage because of external influences. My thesis was awarded the Charlene Heisler prize of the Astronomical Society of Australia, and the Stefano Braccini prize selected by the Gravitational Wave International Committee.
I have been and am fortunate to work with outstanding students, postdoctoral scholars and staff. I am indebted to them for their trust in my leadership and mentorship, and for their dedication and enthusiasm. A full listing of past and present undergraduate and graduate students and postdoctoral scholars who have worked with me is in my CV.
Information for prospective group members. I welcome new students, postdocs and research staff to my group. In the coming years, my focus will be on the DSA-2000, and I look forward to supporting related projects in both instrumentation development and pure science. Undergraduate research can be carried out via Caltech's undergraduate research programs, and for Caltech undergrads via a senior thesis. I can advise graduate students who have been admitted to graduate studies at Caltech, including in Astronomy, Physics, and even a selection of options in Engineering and Applied Science. For prospective postdocs and staff, please look out for DSA-2000 advertisements on the standard astronomy job sites. Postdocs interested in applying for Caltech independent fellowships (e.g., EXP, Burke, Brinson) or independently funded fellowships should reach out to me first to discuss and refine their research plans. Finally, I encourage anyone interested in working with me to contact me and/or any member of my group to discuss possibilities!
CONTACT DETAILS
I can be found in office #272 in the Cahill Center for Astronomy on the Caltech campus in Pasadena, CA.
Cahill Center for Astronomy and Astrophysics
California Institute of Technology
MC 249-17, 1216 E California Blvd
Pasadena, CA 91125, USA.
Tel. +1 626 395 4286
Mail. vikram@caltech.edu