Nothing, not even light, can escape the gravitational grasp of black holes.

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Scientists think that supermassive black holes, which have masses between millions and billions times more than the Sun, reside at the heart of almost every galaxy.

But these cosmic monsters are sucking in material relatively slowly, and nobody knows why.

At the current rate, it would take much more than a trillion years – about 100 times the present age of the Universe – for a black hole to absorb all of the matter in the Universe.

Barred spiral galaxy UGC 6093 is an active galaxy, meaning it has an active galactic nucleus. Material is dragged towards the central supermassive black hole, heating up and causing the galaxy's core to shine brightly. Credit: ESA/Hubble
Barred spiral galaxy UGC 6093 is an active galaxy, meaning it has an active galactic nucleus. Material is dragged towards the central supermassive black hole, heating up and causing the galaxy's core to shine brightly. Credit: ESA/Hubble

Whether or not they succeed in this timescale depends on what happens to the Universe in the future.

If the expansion of the Universe continues to speed up, then black holes have plenty of time to devour nearly everything, bar some cosmic material that may be pushed beyond their reach by the expansion.

Galaxies, galaxies everywhere - as far as the NASA/ESA Hubble Space Telescope can see. This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Called the Hubble Ultra Deep Field, this galaxy-studded view represents a "deep" core sample of the universe, cutting across billions of light-years. The snapshot includes galaxies of various ages, sizes, shapes, and colours. The smallest, reddest galaxies, about 100, may be among the most distant known, existing when the universe was just 800 million years old. The nearest galaxies - the larger, brighter, well-defined spirals and ellipticals - thrived about 1 billion years ago, when the cosmos was 13 billion years old. In vibrant contrast to the rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. These oddball galaxies chronicle a period when the universe was younger and more chaotic. Order and structure were just beginning to emerge. The Ultra Deep Field observations, taken by the Advanced Camera for Surveys, represent a narrow, deep view of the cosmos. Peering into the Ultra Deep Field is like looking through a 2.5 metre-long soda straw. In ground-based photographs, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is so empty that only a handful of stars within the Milky Way galaxy can be seen in the image. In this image, blue and green correspond to colours that can be seen by the human eye, such as hot, young, blue stars and the glow of Sun-like stars in the disks of galaxies. Red represents near-infrared light, which is invisible to the human eye, such as the red glow of dust-enshrouded galaxies. The image required 800 exposures taken over the course of 400 Hubble orbits around Earth. The total amount of exposure time was 11.3 days,
The Hubble Ultra Deep Field: a 'deep' core sample of the universe, cutting across billions of light-years.

At any rate, even the heaviest supermassive black holes, which weigh in at about 10 billion times the mass of the Sun, will disappear, or ‘evaporate’, after about 10¹ºº years (that’s 1 followed by 100 zeroes!).

If the expansion one day runs out of steam and the Universe re-collapses down to a ‘big crunch’, the Universe’s black holes will all merge.

It is only relatively recently that physicists have managed to simulate the merger of two black holes on a computer.

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If two black holes did merge, presumably the result would be one huge, ‘cosmic’ black hole.

Authors

Astronomer professor paul roche
Paul RocheAstronomer

Professor Paul Roche is Chair of Astronomy Education at Cardiff University.