Black holes are often described as voracious and monstrous, with sloppy eating habits that cause X-rays to be coughed up and spat out willy nilly.

Pushing the dietary analogy a bit further, scientists now say that regardless of where black holes dine, they have the same culinary habits.

Supermassive black holes, which anchor many galaxies, feed just like smaller "stellar" black holes, the researchers announced last week. The finding supports some implications of Einstein's relativity theory that black holes of all sizes have similar properties.

The conclusion comes from a large observing campaign of the spiral galaxy M81, which is about 12 million light-years from Earth. In the center of M81 is a black hole about 70 million times more massive than the sun. It pulls gas from the central region of the galaxy inward at high speed.

Stellar mass black holes typically weigh just a few solar masses and have a different source of food. They pull gas from an orbiting companion star.

In both cases, when black holes dine, material spirals inward and becomes superheated, giving off X-rays and other forms of radiation.

Researchers wondered if they'd have the same feeding mechanism. A study of the X-rays, optical light and radio waves emitted from the jowls of both black hole varieties suggests they do.

Scientists used the Chandra X-ray Observatory and multiple ground-based telescopes to take detailed observations of the huge black hole at the center of the M81 galaxy, and compared these to observations of smaller black holes. They found that while the total energy coming out of the massive black hole was larger, the relative amounts of energy being emitted at different wavelengths — from radio to infrared to X-ray light — were roughly the same.

"The shape of the light curves looks very much the same," said researcher Michael Nowak of MIT. "The only difference is the total energy coming out. The characteristic energy of the matter and the speeds of the jets all seem to work the same way. It's just that big black holes have more matter."

Even the material falling onto the black hole seems to travel at the same speed, regardless of the black hole's size. But since a more massive black hole has a wider event horizon, or distance within which matter cannot escape, it takes material longer to fall in.

"Everything around this huge black hole looks just the same except it's almost 10 million times bigger," Nowak said.

The findings help scientists understand how black holes work on a fundamental level.