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Hubble’s discovery suggests a major problem with our understanding of dark matter

It would be extremely optimistic to suggest that we have good dark matter management. But even with the slight understanding that we have something important may be missing.

New observations from the Hubble Space Telescope have found dark matter concentrations much higher than expected in some galaxies, by over an order of magnitude.

These concentrations are not consistent with theoretical models, suggesting that there is a large gap in our understanding: the simulations may be wrong or there may be a property of dark matter that we don’t fully understand, according to the research team.

“We did a lot of careful testing to compare the simulations and data in this study, and our discovery of the mismatch persists,”

; said astrophysicist Massimo Meneghetti of the National Institute of Astrophysics in Italy.

“One possible source of this discrepancy is that we may miss some key physical aspects in the simulations.”

Dark matter is one of the biggest thorns in our understanding of the Universe. Simply put, we don’t know what it is. It does not absorb, reflect or emit any electromagnetic radiation, making it completely undetectable directly. However, it interacts with the visible matter of the Universe via gravity.

This means that we can study how things like galaxies and stars are distributed and move in the Universe, calculate the gravity needed to produce those distributions and motions, and calculate and subtract the gravity produced by visible matter.

The gravity that remains indicates how much dark matter is present in the Universe, and from what we can tell, that’s a lot. Up to 85% of the matter in the Universe could be dark matter.

One of the ways we can indirectly “detect” dark matter is through the gravitational lens. Really massive objects, such as clusters of galaxies, create a gravitational field so intense that spacetime itself curves, meaning that any light traveling through that spacetime moves in a curved path.

Thus, objects at the edge of that gravitational field, such as distant galaxies, appear to us enlarged, stained, duplicated, and distorted.

lensGravitational lensing. (NASA, ESA and L. Calçada)

By studying these distortions and putting the galaxies back together, we can understand how the light was distorted, which means we can map the gravitational field – the greater the distortion, the stronger the gravitational field. Again, subtract the visible matter, et voila, a map of the dark matter inside that cluster of lenses. He is incredibly smart.

And that’s what Meneghetti and his team were doing, observing the observations of 11 clusters of galaxies using the Hubble Space Telescope and the Very Large Telescope of the European Southern Observatory in Chile.

“Clusters of galaxies are ideal laboratories for understanding whether computer simulations of the Universe reliably reproduce what we can infer about dark matter and its interaction with luminous matter,” he explained.

When the team sat down to analyze the data, they found that the large-scale lens effects expected to be produced by the galaxy as a whole. But they also found smaller lens effects nestled inside. These tiny lenses, produced by individual galaxies within clusters, did not appear in cluster simulations, suggesting an excess of dark matter.

To verify their findings, the team conducted spectroscopic observations of galaxies, using the displacement of light to calculate the speed of orbiting stars, a classic tool for measuring dark matter.

And they double-checked the distance calculations, because that can make a crucial difference to the dark matter calculations.

The researchers found that there is a much greater concentration of dark matter in those individual galaxies than the simulations allow. But the simulations were based on our better understanding of dark matter, so where does the additional mass come from?

Well, we don’t know. But it will be an exciting journey of discovery.

“For me personally, detecting a gnawing gap – a discrepancy of 10 in this case – between an observation and a theoretical prediction is very exciting,” said Yale University astrophysicist Priyamvada Natarajan.

“A key goal of my research has been to test theoretical models with improving data quality to find these gaps. It is these types of gaps and anomalies that have often revealed that we were missing something in the current theory, or point the way to a model. brand new, which will have more explanatory power. “

Either way, finding out what’s causing the mismatch between simulation and observation is likely to lead us to a stronger understanding of dark matter.

The research was published in Science.

Full cover image credit: NASA, ESA, G. Caminha (University of Groningen), M. Meneghetti (Observatory of Astrophysics and Space Science of Bologna), P. Natarajan (Yale University), the CLASH team, and M. Kornmesser ( ESA / Hubble)

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