From The University of Oslo [Universitetet i Oslo](NO)
via
14 NOVEMBER 2021
DAVID NIELD
Dark matter ‘clumps’ between galaxies. S. Epps & M. Hudson/The University of Waterloo (CA))
There’s a lot we still don’t know about Dark Matter – that mysterious, invisible mass that could make up as much as 85 percent of everything around us – but a new paper outlines a rather unusual hypothesis about the very creation of the stuff.
In short: dark matter creates dark matter. The idea is that at some point in the early stages of the Universe, dark matter particles were able to create more dark matter particles out of particles of regular matter, which would go some way to explaining why there’s now so much of the stuff about.
The new research builds on earlier proposals [Physical Review Letters] of a ‘thermal bath’, where regular matter in the form of plasma produced the first bits of dark matter – initial particles which could then have had the power to transform heat bath particles into more dark matter.
“This leads to an exponential growth of the dark matter number density in close analogy to other familiar exponential growth processes in nature,” the international team of physicists, led by Torsten Bringmann from the University of Oslo in Norway, write in their newly published paper.
There are some unanswered questions about this new hypothesis, as is normal for anything to do with dark matter, but importantly it fits with the observations of dark matter we have today via the cosmic microwave background (CMB).
CMB per European Space Agency(EU) Planck.
While we can’t actually see dark matter directly, the behavior of the Universe, together with the electromagnetic radiation that makes up the CMB, strongly suggests that dark matter is out there somewhere – and in seriously large amounts.
There’s a variety of scenarios attempting to explain conditions that could constrain the proportions of dark matter we see. One, called a freeze-in scenario, proposes that however dark matter might have appeared in the hot bath of early plasma, nothing cancelled it out. As the Universe expanded, its gradual generation simply ceased, forever locking in a certain amount.
By contrast, a freeze-out model suggests dark matter appeared as rapidly as normal matter, but reached an equilibrium once antiparticles cancelled some out. Once again, the cooling of the expanding Universe chilled its generation but also its ability to quickly annihilate, leaving us with a set amount.
This new study proposes yet another possibility – more or less in between the two extremes. If it’s right, it would mean the amount of dark matter grew very quickly as the Universe expanded, with this growth slowing and eventually stopping as the expansion of the Universe has slowed down.
With regular matter and dark matter becoming more spaced out from one another over time, this dark matter production line has petered out. What’s more, according to the researchers, somewhere out there in the CMB there should be proof that this theory is correct, so the next job is to find it.
We have hugely sensitive dark matter detectors monitoring the cosmos, so it might not be too long before we hear more about this new approach to understanding dark matter production – in turn, teaching us more about the creation and the growth of the Universe.
“Our mechanism complements both freeze-in and freeze-out thermal production scenarios in a generic way,” write the researchers. “Further, and detailed, exploration of this new way of producing dark matter from the thermal bath thus appears highly warranted.”
The research has been published in Physical Review Letters.
See the full article here.
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Dark Matter Background
Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM, denied the Nobel, some 30 years later, did most of the work on Dark Matter.
Fritz Zwicky.
Coma cluster via NASA/ESA Hubble, the original example of Dark Matter discovered during observations by Fritz Zwicky and confirmed 30 years later by Vera Rubin.
In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.
Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).
Vera Rubin measuring spectra at the Department of Terrestrial Magnetism at the Carnegie Institution in Washington in about 1970. (Emilio Segre Visual Archives AIP SPL).
Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970.
Dark Matter Research
DAMA at Gran Sasso uses sodium iodide housed in copper to hunt for dark matter LNGS-INFN.
Yale HAYSTAC axion dark matter experiment at Yale’s Wright Lab.
The LBNL LZ Dark Matter Experiment (US) Dark Matter project at SURF, Lead, SD, USA.
PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China.
Inside the Axion Dark Matter eXperiment U Washington (US) Credit : Mark Stone U. of Washington. Axion Dark Matter Experiment.
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The University of Oslo [Universitetet i Oslo](NO), until 1939 named the Royal Frederick University is the oldest university in Norway, located in the Norwegian capital of Oslo. Until 1 January 2016 it was the largest Norwegian institution of higher education in terms of size, now surpassed only by the Norwegian University of Science and Technology [Norges teknisk-naturvitenskapelige universitet](NO). The Academic Ranking of World Universities has ranked it the 58th best university in the world and the third best in the Nordic countries. In 2015, the Times Higher Education World University Rankings ranked it the 135th best university in the world and the seventh best in the Nordics. While in its 2016, Top 200 Rankings of European Universities, the Times Higher Education listed the University of Oslo at 63rd, making it the highest ranked Norwegian university.
The university has approximately 27,700 students and employs around 6,000 people. Its faculties include (Lutheran) Theology (with the Lutheran Church of Norway having been Norway’s state church since 1536); Law; Medicine; Humanities; Mathematics; Natural Sciences; Social Sciences; Dentistry; and Education. The university’s original neoclassical campus is located in the centre of Oslo. It is currently occupied by the Faculty of Law. Most of the university’s other faculties are located at the newer Blindern campus in the suburban West End. The Faculty of Medicine is split between several university hospitals in the Oslo area. The university also includes some formally independent, affiliated institutes such as the Centre for International Climate and Environmental Research (CICERO); Norwegian Centre for Violence and Traumatic Stress Studies; and the Frisch Centre.
The university was founded in 1811 and was modeled after the University of Copenhagen [Københavns Universitet](DK) and the recently established Humboldt University of Berlin [Humboldt-Universität zu Berlin](DE). It was originally named for King Frederick VI of Denmark and Norway, and received its current name in 1939.
The Nobel Peace Prize was awarded in the university’s Atrium, from 1947 to 1989 and will be so again in 2020, making it the only university in the world to be involved in awarding a Nobel Prize. Since 2003, the Abel Prize is awarded in the Atrium. Five researchers affiliated with the university have been Nobel laureates.
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