SPACE

SPACE | Massive galaxies are being wiped out by voracious black holes: studies

WASHINGTON — Two independent studies show that the biggest black holes in the universe are growing faster than the rate of stars being formed in their galaxies, meaning that at last the voracious black holes may disappear those massive galaxies.

The findings released Thursday by the United States space agency NASA are based on data from NASA’s Chandra X-ray Observatory and other telescopes.

Over many years, astronomers have gathered data on the formation of stars in galaxies and the growth of supermassive black holes with millions or billions the mass of the Sun in their centers. These data suggested that the black holes and the stars in their host galaxies grow in tandem with each other.

“We are trying to reconstruct a race that started billions of years ago,” said Yang Guang of Pennsylvania State University who led one of the two studies. “We are using extraordinary data taken from different telescopes to figure out how this cosmic competition unfolded.”

Yang and his colleagues studied the growth rate of black holes in galaxies at distances of 4.3 to 12.2 billion light years from Earth.

They calculated the ratio between a supermassive black hole’s growth rate and the growth rate of stars in its host galaxy. A common idea is that this ratio is approximately constant for all galaxies.

Instead, Yang and colleagues found that this ratio is much higher for more massive galaxies.

For galaxies containing about 100 billion solar masses worth of stars, the ratio is about ten times higher than it is for galaxies containing about 10 billion solar masses worth of stars.

The co-author Niel Brandt, also from Penn State suggested that “maybe massive galaxies are more effective at feeding cold gas to their central supermassive black holes than less massive ones.”

Another team from Spain also found evidence that the most massive black holes’ growth has outstripped that of stars in their host galaxies.

Mar Mezcua from the Institute of Space Sciences in Spain and her colleagues studied 72 galaxies located at the center of galaxy clusters at distances ranging up to about 3.5 billion light years from Earth.

They found that the black hole masses were about ten times larger than masses estimated by another method using the assumption that the black holes and galaxies grew in tandem, implying that they’re gobbling up much more than previously thought.

— XINHUA

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