Early Universe’s supermassive black holes grew in cocoons like butterflies

Initial analyzes suggested that if the dots were in fact supermassive black holes, they should be almost as massive as their host galaxies, varying between 10 and 100% of their total mass. The problem was that the dots were visible at a very high redshift, meaning that astronomers were seeing them as they were when the Universe was about 1 billion years old. A “supermassive” black hole as heavy as its entire galaxy in a billion-year-old universe raised the question of how something could grow that big, that fast – we had no answer to that question.

But then Rusakov and his colleagues began to notice strange things in the JWST data. “We normally expect other signals from supermassive black holes, like X-rays, and we didn’t see these signals,” says Rusakov. The oddities don’t stop with the lack of X-rays.

The broad lines

Because black holes cannot be observed directly, astronomers measure their mass by observing the gas orbiting around them. As the gas swirls in the black hole, it heats up and glows. The gravity of a supermassive black hole pulls this gas in at incredible speeds, with the material reaching thousands of kilometers per second. This speed causes what is called the Doppler effect, which broadens where light from gas moving toward the observer on Earth changes to blue, and gas moving away changes to red, stretching the spectral lines into a broad, flat shape. By measuring the width of these lines, we calculate the speed of the gas and, by extension, the mass of the black hole.

In the case of the Little Red Dots, the lines appeared incredibly broad, leading to these staggering mass estimates. The shape of the lines seemed strange, however. It was not a typical rounded bell curve, but rather a sharp triangle sitting atop broad wing-like tails.