From Live Science : “We may finally be able to test one of Stephen Hawking’s most far-out ideas”

From Live Science

1.1.22
Paul Sutter

National Aeronautics Space Agency(USA)/European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Canadian Space Agency [Agence Spatiale Canadienne](CA) James Webb Infrared Space Telescope annotated. Scheduled for launch in 2011 delayed to October 2021 finally launched December 25, 2021.

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An artist’s impression of Dark Matter in the beginning of the universe. Image credit: Shutterstock.

We may soon be able to test one of Stephen Hawking’s most controversial theories, new research suggests.

In the 1970s, Hawking proposed that Dark Matter, the invisible substance that makes up most matter in the cosmos, may be made of black holes formed in the earliest moments of the Big Bang.

Now, three astronomers have developed a theory that explains not only the existence of Dark Matter, but also the appearance of the largest black holes in the universe.

“What I find personally super exciting about this idea is how it elegantly unifies the two really challenging problems that I work on — that of probing the nature of dark matter and the formation and growth of black holes — and resolves them in one fell swoop,” study co-author Priyamvada Natarajan, an astrophysicist at Yale University (US), said in a statement. What’s more, several new instruments — including the James Webb Space Telescope that just launched — could produce data needed to finally assess Hawking’s famous notion.

Black holes from the beginning

Dark Matter makes up over 80% of all the matter in the universe, but it doesn’t directly interact with light in any way. It just floats around being massive, affecting the gravity within galaxies.

It’s tempting to think that black holes might be responsible for this elusive stuff. After all, black holes are famously dark, so filling a galaxy with black holes could theoretically explain all the observations of Dark Matter.

Unfortunately, in the modern universe, black holes form only after massive stars die, then collapse under the weight of their own gravity. So making black holes requires many stars — which requires a bunch of normal matter.Scientists know how much normal matter is in the universe from calculations of the early universe, where the first hydrogen and helium formed. And there simply isn’t enough normal matter to make all the Dark Matter astronomers have observed.

Sleeping giants

That’s where Hawking came in. In 1971, he suggested that black holes formed in the chaotic environment of the earliest moments of the Big Bang. There, pockets of matter could spontaneously reach the densities needed to make black holes, flooding the cosmos with them well before the first stars twinkled. Hawking suggested that these “primordial” black holes might be responsible for Dark Matter. While the idea was interesting, most astrophysicists focused instead on finding a new subatomic particle to explain Dark Matter.

What’s more, models of primordial black hole formation ran into observational issues. If too many formed in the early universe, they changed the picture of the leftover radiation from the early universe, known as the cosmic microwave background [CMB].

CMB per European Space Agency(EU) Planck.

That meant the theory only worked when the number and size of ancient black holes were fairly limited, or it would conflict with measurements of the CMB. .

The idea was revived in 2015 when the Laser Interferometer Gravitational-Wave Observatory found its first pair of colliding black holes.

Caltech /MIT Advanced aLigo

The two black holes were much larger than expected, and one way to explain their large mass was to say they formed in the early universe, not in the hearts of dying stars.

A simple solution

In the latest research, Natarajan, Nico Cappelluti at The University of Miami (FL)(US) and Günther Hasinger at The European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU) took a deep dive into the theory of primordial black holes, exploring how they might explain the Dark Matter and possibly resolve other cosmological challenges.

To pass current observational tests, primordial black holes have to be within a certain mass range. In the new work, the researchers assumed that the primordial black holes had a mass of around 1.4 times the mass of the sun. They constructed a model of the universe that replaced all the Dark Matter with these fairly light black holes, and then they looked for observational clues that could validate (or rule out) the model.

The team found that primordial black holes could play a major role in the universe by seeding the first stars, the first galaxies and the first supermassive black holes (SMBHs). Observations indicate that stars, galaxies and SMBHs appear very quickly in cosmological history, perhaps too quickly to be accounted for by the processes of formation and growth that we observe in the present-day universe.

“Primordial black holes, if they do exist, could well be the seeds from which all supermassive black holes form, including the one at the center of the Milky Way,” Natarajan said.

And the theory is simple and doesn’t require a zoo of new particles to explain Dark Matter.

“Our study shows that without introducing new particles or new physics, we can solve mysteries of modern cosmology from the nature of Dark Matter itself to the origin of supermassive black holes,” Cappelluti said in the statement.

So far this idea is only a model, but it’s one that could be tested relatively soon. The James Webb Space Telescope, which launched Christmas Day after years of delays, is specifically designed to answer questions about the origins of stars and galaxies. And the next generation of gravitational wave detectors, especially the Laser Interferometer Space Antenna (LISA), is poised to reveal much more about black holes, including primordial ones if they exist.

Gravity is talking. Lisa will listen. Dialogos of Eide.

Together, the two observatories should give astronomers enough information to piece together the story of the first stars and potentially the origins of Dark Matter.

“It was irresistible to explore this idea deeply, knowing it had the potential to be validated fairly soon,” Natarajan said.

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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, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970.

Vera Rubin measuring spectra, worked on Dark Matter(Emilio Segre Visual Archives AIP SPL).
Dark Matter Research

LBNL LZ Dark Matter Experiment (US) xenon detector at Sanford Underground Research Facility(US) Credit: Matt Kapust.

Lamda Cold Dark Matter Accerated Expansion of The universe http scinotions.com the-cosmic-inflation-suggests-the-existence-of-parallel-universes. Credit: Alex Mittelmann.

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.

DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB (CA) deep in Sudbury’s Creighton Mine.

The LBNL LZ Dark Matter Experiment (US) Dark Matter project at SURF, Lead, SD, USA.

DAMA-LIBRA Dark Matter experiment at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS) located in the Abruzzo region of central Italy.

DARWIN Dark Matter experiment. A design study for a next-generation, multi-ton dark matter detector in Europe at The University of Zurich [Universität Zürich](CH).

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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