Independent test supports the ring-like M87 black hole shadow

A silhouette in deep space

When the first image of the giant black hole M87* appeared, it showed a glowing loop around a dark hub. Was that loop real, or was it a glitch born from code? To snap an object so far away, dishes across the globe join forces through interferometry. This method combines signals from distant dishes to act like one Earth-sized virtual dish. Yet the gaps between those dishes leave big holes in the data. Past critics wondered if the bright loop framing the dark black hole shadow was just a trick of software settings.

Testing the shape without hints

To test whether the loop was genuine, a team rebuilt the scene with an independent imaging tool. They fed their code data points that bypass local dish calibration errors. They also worked without morphological priors, which are mathematical assumptions about an object's expected shape. In other words, the computer had no hints telling it to hunt for a ring.

Even without hints, the ring clearly emerged from the data. The team found its angular width across the sky to be 42.2 ± 1.5 microarcseconds, an angular size far smaller than a pinpoint. From this size, and assuming nominal scaling parameters, they calculated that M87* holds a mass equal to 6.5 ± 0.5 billion times our Sun. They also found that we view the system at an inclination angle of about 20° from its approaching jet.

What questions remain?

Making pictures from this sparse data is still an inadequately constrained problem. Because global dishes are spaced so far apart, large blanks in the data remain. Different imaging methods still yield divergent representations when it comes to the finest details. While the ring-like black hole shadow itself now stands on firm footing, scientists must keep refining their tools to agree on every sharp detail.