Biggest black holes may grow faster than the host galaxies

An image from the Chandra X-ray Observatory’s Deep Field-South. The Chandra image (blue) is the deepest ever obtained in X-rays. It is combined with an optical and infrared image from the Hubble Space Telescope, in the colors red, green and blue. Each Chandra source is produced by hot gas falling in towards a supermassive black hole at the centre of galaxies, as shown in the artist’s illustration.

(X-ray: NASA/CXC/Penn. State/G. Yang et al. & NASA/CXC/ICE/M. Mezcua et al.; Optical: NASA/STScI; Illustration: NASA/CXC/A. Jubett)

A number of the most monstrous black holes in the universe are growing faster than their host galaxies, new research suggests.

Supermassive black holes are believed to exist in the centers of most, if not all, large galaxies, where they feed on surrounding gas, dust, and other material. Two new studies suggest that these massive black holes are much larger than expected on the basis of the exchange rate of the surrounding stars formed, the researchers said.

“We are trying to reconstruct a contest that began billions of years ago,” Guang Yang, a researcher at Penn State and lead author of one of the studies, said in a statement. “We are using special data coming from different telescopes to find out how this cosmic game unfolded.” [Images: Black Holes of the Universe]

Using data from NASA’s Chandra X-ray Observatory and other telescopes, Yang the study examined the speed at which the black holes grow in galaxies 4.3 billion to 12.2 billion light-years from Earth. The researchers compared the growth of a black hole to the growth of the stars in the galaxies.

Previous research has shown that black holes and the stars in their host galaxies, in general, grow in combination with each other. However, the new findings, which are available on and will be published in the April issue of the journal Monthly Notices of the Royal Astronomical Society, shows that the larger the galaxy, the greater the ratio between the growth of the black hole and the stars.

“An obvious question is ‘Why’?” Niel Brandt, a researcher at Penn State and co-author of the study, said in the same statement. “Maybe massive galaxies are more effective in feeding gas to their central supermassive black holes is less heavy.”

In a second study, which also used Chandra data, a team of researchers found that, in larger galaxies, black holes grow about 10 times faster than the galaxy’s stars are formed.

“We find the black hole are much bigger than we had expected,” Mar Mezcua, lead author of the second study and a researcher at the Institute of Space Sciences in Barcelona, Spain, said in the statement. “Maybe they got a head start in this competition to grow, or maybe they had a speed edge of the growth that it took billions of years.”

For the study, the researchers focused on black holes in some of the “brightest and most massive galaxies in the universe”, the statement said. She looked at the 72 galaxies in the centre of clusters is about 3.5 billion light-years from Earth.

Together with the Chandra X-ray Observatory, the researchers used data from the Australia Telescope Compact Array, the Karl G. Jansky Very Large Array and the Very Long Baseline Array. The researchers were able to estimate the masses of supermassive black holes based on the corresponding X-ray and radio emissions. The team found that the black holes were approximately 10 times greater than estimated using traditional methods that assumed that black holes and their galaxies grow in tandem.

In addition, almost half of the black holes that the researchers studied weighed in yet larger “ultramassive” black holes, instead of only supermassive black holes, according to the statement.

Whereas supermassive black holes are generally millions of times heavier than our sun, “ultramassive” black holes are estimated to harbor at least 10 billion solar masses.

“We know that black holes are extreme objects,” J. Hlavacek-Larrondo, co-author of the second study and a researcher at the University of Montreal, said in the statement. “So it may not come as a surprise that the most extreme examples of them would break the rules we thought that they would have to follow.”

The second study was published Feb. 11 in the journal Monthly Notices of the Royal Astronomical Society. The full text of the article is also available on

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