The invisible force has an effect on our Universe. We can not see it, and we can not see it – but we can observe how it interacts gravityally on things we can see and see, like light.
Now a global astronomer team has used one of the world's most powerful telescopes to study that effect across 10 million galaxies in the context of Einstein's overall relativity. The result? The most comprehensive map of dark matter throughout the history of the Universe to date.
Peer review has not been completed yet, but the map proposes an unexpected thing – that dark-structured objects may progress more slowly than previously predicted. ["Kungangkaragdagangdataaynagpapakitanatayoaytamaitoaynagpapahiwatigngisangbagaynanawawalamulasaatingkasalukuyangpag-unawasaStandardModelatsapangkalahatangteoryangrelativity"sabingphysicistChiakiHikagengKavliInstituteparasaPhysicsandMathematicsng
We do not know what the dark thing is. What we know is that the effects of gravitational we see in the Universe can not be attributed to just by seeing things. For example, the speed of rotation of the galaxies is different if it is based solely on gravity from the striking mass.
We also know that gravity can bend the path of light, as we can see in gravitational lensing. This effect can also be used to map dark matter – once you subtract the gravitational effect of the visible object, your rest is the gravitational effect of dark matter.
This is a common way to find dark objects, and this is what the Hikage team used. They placed the 870-megapixel Hyper Suprime-Cam with the 8.2-meter Subaru telescope to reach the galaxies of billions of light-years away.
Since their light lasts long enough to reach us, we see them as billions of years have passed, which means that the map covers a huge historical title of the Universe, allowing the astronomers observe how dark things have grown in billions of years.
The resulting 3D map shows the lumpy layout of dark matter in the Universe, consistent with the findings of previous research – except for the speed at which the structures is changing. According to this new map, it occurs more slowly than predicted by past results.
Not much, but enough to stand out differently. That said, the jury is still in what it means. This may indicate that something is missing from the Standard Model, which will be amazingly amazing; or it may indicate statistical fluctuation in the data.
It may be a while before we know, too. The team has been working on this project since 2014, using just the amount of first-year observations, or 11 percent of the Hyper Suprime-Cam survey, which has not yet been completed. Picture-taking is scheduled to end in 2020 at a time.
So do not be too excited – there is still a full mothership load of work to be done. But this is an intriguing result, and we wait for more information with bated breath.
"In a little work, if we can get better accuracy, we can find something concrete," said Hikage. "This is a great cause for me."
The research team was accepted at the Publication of the Astronomical Society of Japan and can be read in full on arXiv's pre-printed server.