Size Matters

Look: A “mini monster” could help explain how black holes form

Did they grow quickly, or were they always that big?

NASA/CXC/A. Hobart

Don’t let the term dwarf galaxy fool you.

Despite their size, these bodies can still host supermassive black holes, like the one at the center of the Milky Way.

However, it’s a lot trickier for astronomers to spot them.

Since dwarf galaxies have lower concentrations of stars, they tend to be dimmer. And sometimes black holes can be buried in their galaxies.

NASA/CXC/Dartmouth Coll./J. Parker & R. Hickox; Optical/IR: Pan-STARRS

NASA/CXC/A. Hobart

On January 10, researchers announced that they identified a supermassive black hole hidden inside the dwarf galaxy Mrk 462.

Mkr 462 hosts one of the smallest supermassive black holes ever found. But it raises some big questions.

NASA/CXC/Dartmouth Coll./J. Parker & R. Hickox; Optical/IR: Pan-STARRS

NASA/CXC/Dartmouth Coll./J. Parker & R. Hickox; Optical/IR: Pan-STARRS

It was obscured by layers of gas and dust, which indicates to astronomers that there may be more supermassive black holes lurking in numerous dwarf galaxies.

“This is important because it could help address a major question in astrophysics: How did black holes get so big so early in the universe?”

Ryan Hickox, Dartmouth astrophysicist who studied Mrk 462

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NASA/CXC/A. Hobart

Looking at dwarf galaxies — which are small and mostly untouched because they haven’t merged with other galaxies — can give astronomers a window into the past.

NASA/JPL-Caltech

One hypothesis about the origin of black holes is that the first stars in the universe created “seeds” that quickly grew into large black holes.

NASA/CXC/A. Hobart

If astronomers find even more supermassive black holes in dwarf galaxies, it could give this hypothesis greater weight.

These discoveries are already happening.

A study published November 2021 reported evidence of at least 81 dwarf galaxies hosting supermassive black holes.

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On the other hand, there’s the idea that black holes could have started out giant, instead of quickly growing.

NASA/CXC/A. Hobart

NASA/CXC/Dartmouth Coll./J. Parker & R. Hickox; Optical/IR: Pan-STARRS

If it turns out that a low proportion of dwarf galaxies host supermassive black holes, there would be stronger evidence for this idea.

“We can’t make strong conclusions from one example, but this result should encourage much more extensive searches for buried black holes in dwarf galaxies.”

Jack Parker, Dartmouth astronomer who studied Mrk 462

NASA/CXC/Dartmouth Coll./J. Parker & R. Hickox; Optical/IR: Pan-STARRS