Gravity seminar - Ziri Younsi Seminar

Abstract: Black holes possess gravitational fields so intense that they are
characterised by the presence of an event horizon, a boundary within
which nothing, not even radiation, can escape. Whilst it is now
widely-accepted that supermassive black holes reside at the centres of
galaxies, powering energetic phenomena like accretion and relativistic
jets, the evidence for their existence has until recently been indirect
in nature. With the advent of radio VLBI and access to
micro-arcsecond-scale resolutions, the Event Horizon Telescope (EHT)
revealed the historic first "image" of a black hole. This image, from
the M87 supermassive black hole, exhibits an asymmetrically-luminous,
ring-like structure. The synchrotron-emitting plasma circulating around
the central black hole, coupled with powerful Doppler effects and
gravitational lensing act in concert to produce this image. Furthermore,
the polarised structure of this image was recently revealed in April
2021, showing coherent, ordered magnetic field structure on event
horizon-scales. In this talk I will review the current status of black hole-imaging and
the EHT, with a focus on the M87 black hole result and its very recent
follow-up polarisation work. I will focus in particular on the
theoretical studies underpinning these results and our physical
understanding of M87 thus far, as well as presenting a discussion of
ongoing and future work within the EHT on our Galactic Centre black
hole, Sagittarius A*.