Astronomers Find the Youngest Supermassive Black Hole Yet

Researchers this week announced they’ve spotted the youngest supermassive black hole observed to date, dating back to roughly 800 million years after the Big Bang. In cosmic terms, that’s practically an infant. And it’s a problem, because nothing about the standard picture of black hole growth explains how something that massive got that big that fast.

Here’s the tension. Supermassive black holes — the kind that sit at the centers of galaxies, including our own — are thought to grow gradually, feeding on gas and dust and merging with other black holes over billions of years. That process takes time. A black hole observed at 800 million years post-Big-Bang shouldn’t have had nearly enough of it. Yet there it is, already supermassive, already dominant enough in its region of the early universe to be detected across billions of light-years.

This isn’t the first early-universe black hole to raise this exact question, but it’s now the youngest one on the list, and that keeps narrowing the window theorists have to work with. Every time one of these gets found further back in cosmic time, the “how” gets harder to answer with existing models.

Why this keeps happening

Part of what’s going on is observational: instruments capable of picking out extremely distant, extremely faint quasar-like signals have gotten better, and astronomers have gotten better at knowing where to point them. So in one sense, it’s not surprising we keep finding these — we’re better equipped to look for them than we were even a few years ago.

But the surprising part isn’t that we’re finding them. It’s that they keep existing at all. A handful of isolated cases might be explained away as flukes or measurement quirks. A growing catalog of them, spanning different regions of the sky and different points in the early universe, starts to look like a pattern that current galaxy-formation models simply don’t account for.

The leading explanations on the table involve either unusually efficient accretion — black holes somehow pulling in and processing matter far faster than the standard rate — or “heavy seed” scenarios, where the black holes started out unusually massive to begin with rather than growing from smaller stellar remnants. Neither is fully satisfying yet, and this latest discovery doesn’t settle which one is right. What it does is add more weight to the argument that something in the early-universe growth story needs revising.

Expect this to keep being a live thread through 2021. Every new early black hole detection is effectively a stress test for how galaxies and their central monsters came together in the universe’s first billion years, and right now the models are failing that test more often than they’re passing it.