Title：Multi-messaging prelude: precursors of gravitational wave emitters at the milliarcsecond scale

Speaker：Leonid Gurvits（Delft University of Technology ）

Time：3:00 pm Oct. 10th (Thursday)

Tencent Meeting：42915400486 password: 6360

Location: Lecture Hall, 3rd floor

Abstract：

Formation of super-massive black hole binaries (SMBHB) is deemed to be inevitable in various cosmological models. Their search poses one of the most challenging problems of modern observational astrophysics. Dissipation of kinetic energy in SMBHB controls the evolution of these objects and leads to coalescing into a single black hole. This process (often called “inspiralling”) is accompanied by increasingly intensive emission of gravitational waves (GW) and ends with the final GW burst (a “chirp”). While the first direct detection of GW made by the LIGO and Virgo collaboration in 2015 dealt with coalescence of stellar-mass black holes, recent results by multiple Pulsar Timing Arrays (PTA) increased attention to the SMBHB population as a likely source of the GW background. SMBHB objects remain rather elusive: at present, there are only several dozens of candidates of which just a handful can be treated as certain cases. Direct detections of the components of SMBHB at the sub-parsec scales remain beyond reach for today’s observing techniques at all domains of the electromagnetic spectrum.  Recently several AGNs distinguished by oscillating astrometric positions at the milliarcsecond angular scale with periods of several years attracted our attention as SMBHB candidates. Our study does not allow us to “see” directly the components of possible SMBHBs. But we see a “smoking gun” of orbital motion in these potential SMBHBs. Several examples of such the oscillating behaviour are detected with VLBI astrometry. We analyse the evolution of these binary systems leading to coalescence and associated with this GW outburst.  The estimates presented in this work provide inputs into design studies of future mm/sub-mm VLBI systems with spaceborne radio telescopes. Such the systems will allow us to resolve images of binary SMBHBs at the microarcsecond angular scales, principally unachievable with the Earth-based observational facilities.

CV：

Professor Leonid Gurvits, Senior Scientist Emeritus, specializes in VLBI studies of extragalactic radio sources and their cosmological applications. He has been involved in various capacities in several Space VLBI projects, including the Japanese-led VSOP and Russia-led RadioAstron missions. Leonid Gurvits has been the Principal Investigator of the VLBI Tracking Experiment with the ESA’s Huygens Probe on Titan and Planetary Radio Interferometry and Doppler Experiment (PRIDE) of the ESA’s Jupiter Icy Moons explorer (JUICE). He is currently involved in science working teams of several next generation spaceborne VLBI missions and the ESA’s gravitational wave Laser Interferometer Space Antenna (LISA) mission. Leonid Gurvits worked at the Joint Institute for VLBI in Europe as a Head of Space Science and Innovative Applications department through 2022. He is currently Professor Emeritus of the Faculty of Aerospace Engineering of the Delft University of Technology. Academician of the International Academy of Astronautics. Since September 2024, Leonid Gurvits is a Visiting Professor at the Shanghai Astronomical Observatory under the Chinese Academy of Sciences President's International Fellowship Initiative.

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