The discovery of the accelerated expansion of the Universe has often been attributed to the force known as dark energy. An intriguing new theory was put forward last year to explain this mysterious force; black holes could be the cause of dark energy! The theory goes on to suggest as more black holes form in the Universe, the stronger the pressure from dark energy. A survey from the Dark Energy Spectroscopic Instrument (DESI) seems to support the theory. The data from the first year of operation shows the density of dark energy increases over time and seems to correlate with the number and mass of black holes!
Cast your mind back 4 billion years to the beginning of the Universe. Just after the Big Bang, the moment when the Universe popped into existence, there was a brief period when the Universe expanded faster than the speed of light. Before you argue that nothing can travel faster than the speed of light we are talking of the very fabric of space and time expanding faster than the speed of light. The speed of light limit relates to travel through the fabric of space, not the fabric of space itself! This was the inflationary period.
This illustration shows the “arrow of time” from the Big Bang to the present cosmological epoch. Credit: NASAThe energy that drove the expansion in the early Universe shared similarities with dark energy, the repulsive force that seems to permeate the Universe and is driving the current day accelerated expansion of the Universe.
What is dark energy though? It is thought to make up around 68% of the Universe and, unlike normal matter and energy seems to have a repulsive force rather than attractive. The repulsive nature was first inferred from observations in the late 1990’s when astronomers deduced the rate of acceleration when observing distant supernova. As to the nature of dark energy, no-one really knows what it is or what it comes from, that is, until now.
Artist’s illustration of a bright and powerful supernova explosion. (Credit: NASA/CXC/M.Weiss)A team of researchers from the University of Michigan and other institutions have published a paper in the Journal of Cosmology and Astroparticle Physics. In their paper they propose that black holes are the source of dark energy. Professor Gregory Tarle said ‘Where in the later Universe do we see gravity as strong as it was at the beginning of the Universe?’ The answer, Tarle goes on to describe is the centre of black holes. Tarle and team propose that what happened during the inflation period runs in reverse during the collapse of a massive star. When this happens, the matter could conceivably become dark energy.
The team have used data from the Dark Energy Spectroscopic Instrument (DESI) which is mounted upon the 4m Mayall telescope at Kitt Peak National Observatory. The instrument is essentially 5,000 computer controlled fibre optics which cover an area of the sky equal to about 8 square degrees. The evidence of dark energy is achieved by studying tens of millions of galaxies. The galaxies are so far way their light takes billions of years to reach us. We can use the information to determine how fast the Universe is expanding with unprecedented precision.
Stu Harris works on assembling the focal plane for the Dark Energy Spectroscopic Instrument (DESI), which involves hundreds of thousands of parts, at Lawrence Berkeley National Laboratory on Wednesday, 6 December, 2017 in Berkeley, Calif.The data shows evidence that dark energy has increased with time. This is not perhaps in itself surprising but it seems to accurately mirror the increase in black holes over time too. Now that DESI is operational, more observations are required to hunt down the black holes and try to quantify their growth over time to see if there really is merit in this new exciting hypothesis.
