Supermassive black holes obscured by dust likely to grow when galaxies collide, new study shows

A new study by researchers from Newcastle University has found that supermassive black holes that are hidden by dust are more likely to grow and release significant amounts of energy when they are inside galaxies that are expected to collide with another galaxy. The research, published in Monthly Notices of the Royal Astronomical Society, sheds light on the mystery of what drives gas close enough to black holes for them to grow.

Galaxies, including our own Milky Way, contain supermassive black holes that grow by consuming gas that falls into them. However, the mechanism that drives the gas close enough to the black holes remains unknown. One possibility is that when galaxies are close together, they merge into a larger galaxy due to gravitational attraction.

The final stages of gas being consumed by a black hole produce a large amount of energy that is typically detected using visible light or X-rays. However, this study’s researchers were only able to detect growing black holes using infrared light from various telescopes, including the Hubble Space Telescope and infrared Spitzer Space Telescope.

To better understand the so-called ‘cosmic noon,’ a time when most of the Universe’s galaxy and black hole growth is expected to have taken place, the researchers developed a new technique to determine the likelihood of two galaxies being very close together and expected to collide in the future. They applied this method to hundreds of thousands of galaxies formed 2 to 6 billion years after the Big Bang.

Understanding how black holes grew during this time is crucial to modern-day galactic research, particularly as it may provide insight into the supermassive black hole in the Milky Way and how our galaxy evolved over time. However, measuring the distances of cosmic noon galaxies accurately is challenging due to their distance from us, making it difficult to determine with precision if any two galaxies are close to each other.

In a breakthrough discovery, researchers from Newcastle University have developed a statistical approach to determine galaxy distances, overcoming the challenges of accurately measuring the distances of galaxies and supermassive black holes at cosmic noon. The team’s new technique uses images at various wavelengths and removes the need for individual spectroscopic distance measurements.

The study’s lead author, Sean Dougherty, explains that their novel approach looks at hundreds of thousands of distant galaxies statistically to determine the likelihood of any two galaxies being close together and on a collision course.

The research team, which includes Dr. Chris Harrison, notes that these supermassive black holes are difficult to find using X-ray light as it is blocked by dust. However, they emit infrared light produced by the hot dust surrounding them, allowing for their detection.

The upcoming launch of the James Webb Space Telescope is expected to revolutionize studies in the infrared and uncover even more secrets about how these dusty black holes grow. Dr. Harrison believes that the telescope will be instrumental in finding and studying these hidden growing black holes, leading to a better understanding of the dust surrounding them and the number of hidden black holes in distant galaxies.

Source: Royal Astronomical Society

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