A newly published study has revealed that dark matter is being swallowed up by dark energy, offering valuable data not only about the nature and structure of these mysterious entities, but also about the future of the Universe.
Dark Matter and Dark Energy
In case you’re wondering, dark matter and dark energy are not Star Trek concepts – they’re real forms of energy and matter; at least that’s what most astrophysicists claim. Dark matter is a kind of matter hypothesized in astronomy and cosmology to account for gravitational effects that appear to be the result of invisible mass. The problem with it is that it cannot be directly seen with telescopes, and it neither emits nor absorbs light or other electromagnetic radiation at any significant level. It is believed that it does not react with light in any way; the only reason we know about it is that we see its effects. Basically, astronomers have consistently observed something causing a gravitational attraction, so therefore there has to be some matter with mass causing the attraction. They coined the term dark matter, and we still don’t really know what it’s made of.
Meanwhile, dark energy is a hypothetical form of energy which permeates all of space and tends to accelerate the expansion of the universe. Basically, ever since the 1990s, observations have revealed that the Universe is expanding at an accelerating rate. This baffled researchers; ok, it’s clear that it expands, but why is it expanding faster? If anything, it should expand slower, due to all the gravitational attraction. Well, dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate. The evidence for dark energy is indirect, just like with dark matter. Dark energy is thought to be very homogeneous, not very dense and have a negative pressure (acting repulsively) in order to explain the observed acceleration of the expansion of the universe.
According to modern measurements, on a mass–energy equivalence basis, the observable universe contains 26.8% dark matter, 68.3% dark energy (for a total of 95.1%) and 4.9% ordinary matter. So everything we know (humans and animals, planets, stars and galaxies) amounts for some 5% of the known Universe – the rest, the huge 95% is made out of dark energy and dark matter – something we still don’t know much about. Naturally, physicists and astronomers are trying to figure out how the two react with ordinary matter and with themselves.
Energy eats matter
Researchers in Portsmouth and Rome have made a stunning discovery, showing that dark matter is being slowly erased, swallowed up by dark energy. Professor David Wands, Director of Portsmouth’s Institute of Cosmology and Gravitation and one of the research member said:
“This study is about the fundamental properties of space-time. On a cosmic scale, this is about our Universe and its fate. If the dark energy is growing and dark matter is evaporating we will end up with a big, empty, boring Universe with almost nothing in it. Dark matter provides a framework for structures to grow in the Universe. The galaxies we see are built on that scaffolding and what we are seeing here, in these findings, suggests that dark matter is evaporating, slowing that growth of structure.”
Interestingly enough, there is no proposed mechanism to how or why this happens. What this type of study shows is that the Standard Model is no longer sufficient to explain all the interactions taking place at a cosmological scale. In other words, we’re missing something pretty important.
Research students Valentina Salvatelli and Najla Said from the University of Rome worked in Portsmouth with Dr Marco Bruni and Professor Wands, and with Professor Alessandro Melchiorri in Rome examined data from several surveys to reach this conclusion. Professor Wands said:
“Valentina and Najla spent several months here over the summer looking at the consequences of the latest observations. Much more data is available now than was available in 1998 and it appears that the standard model is no longer sufficient to describe all of the data. We think we’ve found a better model of dark energy.”
The models seem to support these claims; the fact that the Universe is accelerating, but at a slower pace than expected (following 90s observations) also seems to support their hypothesis.
“Since the late 1990s astronomers have been convinced that something is causing the expansion of our Universe to accelerate. The simplest explanation was that empty space – the vacuum – had an energy density that was a cosmological constant. However there is growing evidence that this simple model cannot explain the full range of astronomical data researchers now have access to; in particular the growth of cosmic structure, galaxies and clusters of galaxies, seems to be slower than expected.”
The community still hasn’t had a coherent reaction, but initial reviews seem to be positive. Professor Dragan Huterer, of the University of Michigan feels that other researchers should take not of these findings, and include them in future models and theories.
“The paper does look very interesting. Any time there is a new development in the dark energy sector we need to take notice since so little is understood about it. I would not say, however, that I am surprised at the results, that they come out different than in the simplest model with no interactions. We’ve known for some months now that there is some problem in all data fitting perfectly to the standard simplest model.”
To me, the fact that we can do so much, and yet know so little about 95% of the Universe we live in is stunning. There’s still so much to learn, and so much we have yet to understand. It’s a great time to be a scientist!
Journal Reference: Valentina Salvatelli, et al., “Indications of a Late-Time Interaction in the Dark Sector,” Physical Review Letters, 113, 181301, 30 October 2014; doi:10.1103/PhysRevLett.113.181301
