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Click on the image to see the animation of how a black hole eats matter from a companion star and launches a jet.
Credit: International Centre for Radio Astronomy Research (ICRAR)
MAVERIC Survey
MAVERIC Survey
Milky Way ATCA and VLA Exploration of Radio Sources In Clusters = MAVERIC (Not Top Gun: MAVERICK!!)
Low-mass X-ray Binary (LMXRB) (Credit: Fender & Belloni 2012)
A central compact object either a black hole or neutron star or white dwarf accretes matter from a low-mass companion. The central jet emits radio synchrotron emission, while the accretion disk is bright at X-ray frequencies.
The existence of black holes (BHs) in the globular clusters (GCs) has been questioned several times over the last decades. Theoretical studies carried out in the past predicted that as a consequence of mass segregation and violent interaction in the cluster core, all BHs should kick out of GCs within a short timescale after the formation. However, in the last decade, this conjecture has been proven to be at least partially flawed with the discovery of a number of BH binaries in the extra-galactic and Galactic GCs.
With the discovery of the binary black hole coalescence in the local universe via the detection of gravitational waves by LIGO, there are broad scientific implications for the presence of stellar mass BHs in GCs. Besides, BHs are the primary enginees governing the dynamical evolution of GCs.
Owing to the high density of GCs (e.g., see top figure and/or the bottom left panel), close binaries are formed dynamically and efficiently in these clusters. A BH with an interacting low-mass companion (generally known as low-mas X-ray Binary; see left plot ) is expected to launch a bright radio jet, which allows us to identify a BH binary. This has motivated our group to start a systematic survey of 50 Milky Way globular clusters, spread in both northern and southern hemispheres, at radio wavelengths using the Karl G. Jansky VLA and Australia Telescope Compact Array (ATCA). The name of the survey is MAVERIC (Milky Way ATCA and VLA Exploration of Radio Sources In Clusters).
My research involves carrying out a multiwavelength (radio, X-ray, and optical) study of the compact variable sources in Milky Way GCs to unravel the true nature of the central compact object.
In my current study on GCs M22 and M4, I found there exists a mixed population of compact objects in both globular clusters with a few new BH candidates in these GCs (Kundu et a. in preparation).
In the future, I will extend this study to other GCs in our MAVERIC survey.
Left Image: VLA 5 GHz radio continuum image of M22, with two candidate BH binaries, M22-VLA1 and M22-VLA2, discovered by our group (Strader et al., Nature 2012).
Telescopes used for my multiwavelength study:
Radio wavelength: Very Large Array, USA & Australia Telescope Compact Array, Australia
X-ray wavelength: Space-based SWIFT and Chandra telescopes.
Optical wavelength: Space-based Hubble Space Telescope and ground-based telescopes such as SOAR & Multi Unit Spectroscopic Explorer of the European Southern Observatory.
Left Image: Optical counterpart of candidate BH binaries, M22-VLA1 and M22-VLA2, in the SOAR (left) and Hubble Space Telescope (right) images Strader et al., Nature 2012 .
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