In a paper published on Monday in the journal Nature, researchers from Harvard and the University of Cambridge, UK, report that, unlike many other large objects in the universe, black holes have a surface to which light can be attracted.
Black holes are made of matter, with masses as high as 10 billion times the mass of the sun.
A black hole’s surface is surrounded by a disk of gas and dust, but these are not in equilibrium.
A huge amount of energy is required to push the disk towards the centre of the black hole.
A white dwarf, on the other hand, is surrounded entirely by a white cloud of gas, surrounded by dust, and does not have a disk at all.
That means the white dwarf is able to absorb more light than its black counterpart.
The new research suggests that the disks that exist around stars, such as our sun, also reflect more light.
These white dwarfs may also be able to store more energy than a black hole, as well as producing more matter than a neutron star.
That, says astrophysicist James Pohl from the University College London, may explain why stars that are in the “habitable zone” (meaning the zone of temperature where liquid water can exist on its surface) of a star’s core may contain so much energy.
The researchers used the Subaru Telescope in Hawaii, which is designed to survey large swathes of the sky at once, to observe a star named KIC 8462852, which lies at the heart of a binary system.
That star is a remnant of a supernova explosion that took place a billion years ago, when the star was about 2.4 billion years old.
It has a white dwarf companion, but the astronomers were not able to see the light from this companion because it is invisible to the naked eye.
The scientists used a technique called gravitational lensing to observe the light reflected by the companion and then measured how it changed over time.
The star was much brighter in the sky, and the researchers found that the light that is reflected was about twice as bright as the light absorbed by the white companion.
The result was a decrease in the brightness of the star, but it was also reflected by its companion, and this helped to give the star its blue colour.
When a binary star like this one is destroyed, it can produce a supermassive black hole as it rotates around its parent star.
But the researchers were not expecting to find one in the binary system they studied, because they did not know whether the black holes contained a disk.
Instead, they observed the white dwarfed star to be a remnant in a disk, which they then calculated was larger than the disk around the blackhole itself.
“Our observations indicate that there is a very large black hole at the centre, and that it contains a very small white dwarf,” said lead author Matthew Hickey of Harvard’s Massachusetts Institute of Technology.
The team did not yet know whether a disk was contained by the black, white, or both white dwarfish, but they did calculate that the disk was more than 20 times larger than any previously observed disk.
The research suggests the disk may be a bit larger than we have ever thought, says Pohl, because it can absorb more than half the light in the black and white dwarf’s surrounding disk, but is still so far away from the black as to not have the potential to absorb any light at all at all, or even light at a wavelength that would be emitted from a nearby star.
“If you were to ask the question ‘What is that thing in the middle of the galaxy that’s going to be the centre and it absorbs everything’, we don’t know,” said Pohl.
But this is the first study to look at a disk containing a black and a white.
“We think this disk is very much like a white disk, except that it is smaller and there are more of them,” said Hickey.
“It’s really exciting, and it has exciting implications for understanding the behaviour of these very distant objects.”