The Universe is too heavy.
The normal matter in the Universe is not enough to account for the strength of the effects we can see.
The quest to figure out what is making up the rest of the mass is both confusing and consuming.
There are multiple possibilities for the term 'dark matter' for this mass. A new paper is making a new case for primordial black holes, a candidate first proposed in the 1970s by Stephen Hawking and Bernard Carr.
"Our study predicts how the early Universe would look if black holes formed during the Big bang and dark matter was made by them," says physicist Nico Cappelluti of the University of Miami.
This would have a number of important implications. We wouldn't need new physics to explain dark matter. One of the most compelling questions of modern astrophysics is how the early Universe could have grown so big so fast.
They wouldn't have had enough time to form because of the mechanisms we observe in the modern Universe. The mass of a galaxy is always proportional to the mass of the black hole in its center.
Black holes are not a good candidate for dark matter. They are an attractive one, but like dark matter, they are hard to detect, and you can only observe their effect on the surrounding space.
The sheer amount of dark matter is a problem physicists face. Normal matter makes up just 15 percent of the Universe. 85 percent is dark matter.
It's difficult to make up with black holes. There aren't enough massive stars to generate that number of black holes according to our models. Red dwarfs are the majority of the Universe's stars.
They have seen something of a revival as a dark matter candidate in the last few years. These are black holes that could have formed from overdensities in the primordial plasma that filled the Universe immediately after the Big bang.
These black holes could be the seeds from which other black holes grow, but others could also have remained small enough to escape detection.
This explanation could help explain how supermassive black holes get so huge. At the moment, the question is hard to answer. The team's calculations show that these giants could have grown in the early Universe by merging with other primordial black holes.
"If there are primordial black holes, they could be the seeds from which all the supermassive black holes form, including the one at the center of the Milky Way," says astronomer and physicist Priyamvada Natarajan of Yale University.
The idea of unifying the two challenging problems that I work on, probing the nature of dark matter and the formation and growth of black holes, and resolving them in one fell swoop is exciting to me.
Black holes could help explain the excess of radiation in the Universe. The team believes that black holes would produce the same signature.
There are still some questions that need to be answered, even though it would be nice to solve so many mysteries in one fell swoop.
When light travels through a black hole's field, it bends, but we haven't detected it often enough to account for all the black holes that make up 85% of the matter in the Universe.
It's possible that we haven't done the right surveys. The team's paper was to lay out a case for the existence of primordial black holes so that we could find out what we need to look for.
We may be able to get some answers with the James Webb Space Telescope, which is due to launch soon.
"If the first stars and galaxies formed in the so-called 'dark ages', the European Space Agency believes that the first stars and galaxies will be seen by the telescope," says astronomer Gnther Hasinger.
The research is available on arXiv.
