VIKRAM RAVI

Millikan postdoc fellow in astronomy, Caltech

ABOUT ME

I am a Millikan fellow in the Caltech astronomy department. My professional focus is the physics of the ephemeral Universe. I study phenomena that occur on time-scales of nanoseconds to years, such as fast radio bursts, radiation statistics of astrophysical masers and lasers, neutron-star behaviour, and binary supermassive black holes. 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. 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 (more below). While at University, I took lodgings 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 the evolution of 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 (accepted Jan 2015) at the University of Melbourne, with Prof. Stuart Wyithe and Dr. George Hobbs (at CSIRO Astronomy and Space Science). I developed predictions for gravitational waves from orbiting pairs of supermassive black holes in merging galaxies, and tested these using decade-long timing data on millisecond pulsars from the Parkes telescope. My work provided the theoretical basis for two papers published in Science, led by Dr. Ryan Shannon, and resulted in me being invited to talk (video below) at a Kavli Frontiers of Science meeting in Makassar, Indonesia.

During my PhD, I also engaged in a selection of madcap ventures: insvestigations 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 then spent a part of 2014-15 working 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 behemoth (UTMOST).

My detailed CV and publications list can be found here.

LATEST HAPPENINGS

26 Oct: Caltech astronomy colloquium

I gave a colloquium at Caltech on "Fast Radio Bursts from Across the Universe?". A recording of this colloquium can be found here.

20 Oct: UCLA Physics and Astronomy colloquium

I gave a colloquium at UCLA on "Fast Radio Bursts from Across the Universe?". I reviewed the current status of the field, and presented recent empirical results on the FRB population. abstract

10 - 14 Oct: Hotwired 5 meeting, Villanova University

I attended and presented an invited review on FRBs at the fifth Hotwiring the Transient Universe meeting in Villanova University, PA.


29 Aug - 2 Sep 2016: GRAMPA meeting, IAP Paris

I presented an invited review on astrophysics with pulsar timing arrays at the GRavitational-wave Astronomy Meeting in PAris (GRAMPA). abstract

July 2016 onwards: Project scientist, DSA-10

Based on work by myself and collaborators on bright FRBs, we have been awarded a Caltech President's Discretionary Fund award to construct a 10-element Deep Synoptic Array prototype over the coming year (PIs Shri Kulkarni, Jonathon Kocz). I have been appointed project scientist. Nature article on current FRB efforts.

June 2016: Thesis prizes

I was notified that I have been awarded two prizes for my PhD thesis: the Charlene Heisler prize of the Astronomical Society of Australia, and the Stefano Braccini prize selected by the Gravitational Wave International Committee. Details on the latter award are here.

RESEARCH INTERESTS

Enigmatic outbursts from deep space

There is much that we don't know about the Universe, but most astrophysical phenomena are at least associated with known classes of objects. Among the most compelling of astrophysical mysteries, to me, are those transients for which we have no explanations at all. I study "fast radio bursts" (FRBs), which are intense millisecond-duration events that likely originate well beyond the Milky Way in rare cataclysms. With Dr. Ryan Shannon, I discovered one in the direction of the Carina dwarf spheroidal galaxy in 2013, and with Dr. Paul Lasky, I have speculated on possible neutron-star progenitors. At Caltech, with Prof. Shri Kulkarni, Dr. Harish Vedantham, and Prof. Gregg Hallinan, I am investigating and following up further events, analysing the population, and building instrumentation to localise new events. Using the unparalleled optical observatories associated with Caltech, I pursue other unexplained, unassociated events, such as astrophysical neutrinos, and soft gamma-ray and X-ray transients.

Astrophysical masers and lasers

We've all heard of, seen, or even played with lasers. Lasers are useful as extremely efficient light sources; the efficiency is derived from many resonators - atoms or molecules - radiating as one. Such "coherent" sources of radiation, mainly at radio wavelengths, are common in space, and are associated with planets, stars, and dense molecular clouds. However, our understanding of these systems is mainly circumstantial. By directly studying the statistics of the radiation fields of astrophysical coherent emitters, I hope to better understand the currently unknown underlying emission physics. I am investigating molecular masers with unprecedented spectral resolution and sensitivity with the giant Arecibo telescope. With collaborators at Fermilab, I am studying the optical properties of the Crab pulsar to search for evidence of coherence by developing new instrumentation for the 200-inch Hale telescope at Palomar. I also maintain a keen interest in electron-cyclotron maser emission from stars, and radio pulsar emission phenomenology.

Millisecond pulsars and gravitational waves

A career in research never entirely departs from themes explored in one's doctorate. I maintain a broad research interest in pulsar timing physics and gravitational radiation from binary supermassive black holes. With Prof. Tom Prince, I am involved in high-frequency searches for millisecond pulsars in the centre of the Milky Way, and in globular clusters. Such pulsars promise to enable dramatic tests of general relativity in strong gravitational regimes. I am more broadly interested in the millisecond pulsar population of the Galaxy, which will be probed by upcoming large telescopes, and in traditional searches for binary supermassive black holes radiating detectable gravitational waves.


PHD RESEARCH


From 2011 to 2014, 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. My work garnered significant media attention. For popular write-ups, see my piece on The Conversation, and, for example, an excellent article on Mashable. Video presentations of mine are linked below.


Video produced with Swinburne Astronomy Productions.
Presentation at the 2015 Kavli Frontiers of Science symposium in Makassar, Indonesia.


OTHER / PAST PROJECTS

UTMOST


With Prof. Matthew Bailes and his Swinburne group, I helped refurbish the venerable Molonglo Observatory into a fast transient, pulsar and wide-field imaging behemoth.

Coherent radio emission from stars


Rapidly rotating stars with strong magnetic fields, such as Ap and Bp objects and ultracool dwarfs, produce maser-like radio emission that provides insights into their magnetospheres. I studied such systems during my ANU Honours year. Read more in this article (pdf) I wrote for ATNF News.

Radio pulsar behaviour


Radio pulsars are among the most extreme astrophysical objects, and two Nobel prizes have been awarded for pulsar-related work. I have studied various aspects of pulsars; my first paper was on the beam geometries of young and millisecond pulsars.

Infrared Spatial Interferometer


While working at the UC Berkeley Infrared Spatial Interferometer, I led a five-year study of the warm molecular and dusty atmosphere of the red supergiant star Betelgeuse. We concluded that asymmetries associated with giant convection cells were responsible for launching large-scale dust outflows.



Publications

Click below for a list of my publications on ADS Bumblebee.

CV

Click below to download my short-form CV (PDF).

CONTACT DETAILS

I can be found in office #232 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 4015
Mail. vikram@caltech.edu