Research Seminar: Searching for giants and dwarves: searches for compact objects
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10:15 PM IST
Dr. Debnandini Mukherjee is a postdoctoral researcher at the Center of Space Plasma and Aeronomic Research (CSPAR). She works in NASA's Marshall Space Flight Center in Huntsville Alabama, with Tyson Littenberg's group. She works in the area of gravitational wave data analysis and astrophysics. Her work involves looking for gravitational waves from inspiralling compact object binaries comprising neutron stars, black holes or both. She has been working with the LIGO-VIrgo-KAGRA (LVK) Collaboration and using data collected by the same to look for signatures of gravitational waves and gleaning astrophysical implications of such observations. Her focus has been on the search for intermediate-mass black-hole (IMBH) binaries which is an interesting astrophysical source for the LISA mission as well. She is also involved in developing searches for gravitational waves for the LISA mission. In particular, she is interested in developing early warning (pre-merger) searches, aimed at sending out early alerts for gravitational waves. Debnandini completed her PhD from the University of Wisconsin Milwaukee in 2018. Before joining CSPAR, she was a postdoctoral scholar at the Pennsylvania State University.
The discovery of gravitational waves in 2015, added a new channel for multi-messenger observations of powerful astrophysical phenomena. Besides telescope observations using the pre-existing electromagnetic channels like X-rays, Gamma rays and Optical light, many such observations can also be supplemented and corroborated using gravitational waves. On the more massive end of the mass spectrum of compact objects, the intermediate mass black holes (IMBHs) are expected to have masses in the range of 100 to 100,000 solar masses, making up the mass space between the stellar mass and the supermassive black holes. GW190521, the heaviest black hole binary coalescence seen by the end of the last observation run in data from LIGO-Virgo, with its total mass being about 150 solar masses, has been the first clear observation of an IMBH. The rates of observation of gravitational wave sources with at least one IMBH component, to which the detectors are currently sensitive, would help constrain their formation channel, which so far remains uncertain. Their observations could also point to a missing link between stellar mass and super massive black holes. On the other end of the mass spectrum, GW170817 was not only the first observed binary neutron star (BNS) event in gravitational waves but it also started a new-era in multi-messenger astronomy through its observation and detection in other channels. Such multi-channel observations can lead to a more robust understanding of the physics that can be gleaned from BNS mergers. Such BNSs are expected to spend several minutes before merging in LIGO-Virgo's sensitive band, at design sensitivity. This can be leveraged to send out early alerts to multi-messenger partners, to enable observation of such events in multiple bands.
The space based laser interferometer LISA, expected to be operational in the next decades, will be able to probe the millihertz frequency band. This will make it sensitive to a vast array of compact object mergers, including the massive black holes or MBHs. These black holes, straddling the intermediate and supermassive types of black holes, have masses extending above a minimum of 1000 Mⵙ. They are expected to be observable within the LISA band for several weeks to months before they merge. This makes them excellent candidates for low latency, pre-merger observations. Also, some mergers of MBHs are expected to have electromagnetic counterparts due to the presence of gas or disks. Pre-merger alerts with sky location information from LISA data analysis sent out to the astronomy community, would enable early detections of such mergers in electromagnetic bands. Such multi-messenger observations stand to further our knowledge of astrophysics, including that of black hole formation and evolution.
In my talk I will discuss the search for the presently observable gravitational wave sources in LIGO-Virgo data and the possibility of future observations of more massive sources using LISA and explore the possibility of sending out pre-merger alerts for electromagnetically observable sources, to enable multi-messenger observations.
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