HD 163296 is representative of a typical protoplanetary disk viewed by the DSHARP collaboration. It has a central protoplanetary disk, outer emission rings, and gaps between them. There ought to be multiple planets in this system, and one can identify an odd artifact interior to the 2nd-from-the-outermost ring that may be a telltale sign of a perturbing planet. The scale bar at lower right is 10 AU, which corresponds to a resolution of only a few milliarcseconds. This can only be achieved through VLBI. (S. M. ANDREWS ET AL. AND THE DSHARP COLLABORATION, ARXIV:1812.04040)

Ask Ethan: How Does Very-Long-Baseline Interferometry Allow Us To Image A Black Hole?

It’s the technique, from the Event Horizon Telescope, that brought us a black hole’s image. Here’s how it works.

The Event Horizon Telescope has accomplished what no other telescope or telescope array has ever done: imaged the event horizon of a black hole directly. A team of more than 200 scientists using data from eight independent telescope facilities across five continents all joined together to achieve this monumental triumph. While there are many contributions and contributors that are well-deserving of being highlighted, there’s a fundamental physics technique that it all depended on: Very-Long-Baseline Interferometry, or VLBI. Patreon supporter Ken Blackman wants to know how that works, and how it enabled this remarkable feat, asking:

[The Event Horizon Telescope] uses VLBI. So what is interferometry and how was it employed by [the Event Horizon Telescope]? Seems like it was a key ingredient in producing the image of M87 but I have no idea how or why. Care to elucidate?

You’re on; let’s do it.