The Event Horizon Telescope

“It is conceptually interesting, if not astrophysically very important, to calculate the precise apparent shape of the black hole... Unfortunately, there seems to be no hope of observing this effect.”

— Bardeen (1973,1974)

Imaging a Black Hole. At left is a model image for Sgr A* using a semi-analytic accretion flow (Broderick et al. 2011). Light is gravitationally lensed by the black hole to form a distinctive “ring” encircling the black hole’s “shadow” (Falcke … — **Imaging a Black Hole.** At left is a model image for Sgr A* using a semi-analytic accretion flow (Broderick et al. 2011). Light is gravitationally lensed by the black hole to form a distinctive “ring” encircling the black hole’s “shadow” (Falcke et al. 2000). The ring diameter is ~5 Schwarzschild radii . The image is bright on the approaching side of the accretion disk and faint on the receding side because of Doppler effects. At right, a sample image shows expected EHT performance in 2017-2018 (Fish, Johnson, et al. 2014).

The EHT is an international collaboration to create a worldwide very long baseline interferometry array observing at 1.3-millimeter wavelength. When the EHT is complete, it will be able to make images of black holes with a resolution of 10-20 microarcseconds. This resolution is fine enough to resolve the event horizons of the supermassive black holes in the center of our own Milky Way and of M87. You can see the official EHT website here; a Scientific American blog, written by Seth Fletcher, provides many great articles here. For a lot of great answers to common questions about the EHT, check out this reddit AMA. I recently gave a public lecture about the EHT that you can watch here.

My main role in the EHT is to study polarization. Because the submillimeter emission near supermassive black holes in synchrotron radiation, it is expected to be highly polarized. This polarization is a tracer of the underlying magnetic fields and of the strongly-curved spacetime itself. Read about out latest results (published December 4) here!

I have also worked on time-variability studies. One exciting finding was that the EHT can track the motion of compact, polarized flares near Sgr A*, even with only one or two baselines (see here). In another project, we showed that the EHT can determine the direction and angular velocity of an accretion flow around Sgr A*, if we are viewing it close to face-on (see here). Ultimately, we would like to expand these techniques to reconstruct movies of the dynamics near Sgr A*, to witness the final fate of material approaching the event horizon.