New research suggests that our universe has no dark matter

The current theoretical model for the composition of the universe is that it's made of 'normal matter,' 'dark energy' and 'dark matter.' A new uOttawa study challenges this.

A University of Ottawa study published today challenges the current model of the universe by showing that, in fact, it has no room for dark matter.

In cosmology, the term "dark matter" describes all that appears not to interact with light or the electromagnetic field, or that can only be explained through gravitational force.

We can't see it, nor do we know what it's made of, but it helps us understand how galaxies, planets and stars behave.

Rajendra Gupta, a physics professor at the Faculty of Science, used a combination of the covarying coupling constants (CCC) and "tired light" (TL) theories (the CCC+TL model) to reach this conclusion.

This model combines two ideas -- about how the forces of nature decrease over cosmic time and about light losing energy when it travels a long distance.

It's been tested and has been shown to match up with several observations, such as about how galaxies are spread out and how light from the early universe has evolved.

This discovery challenges the prevailing understanding of the universe, which suggests that roughly 27% of it is composed of dark matter and less than 5% of ordinary matter, remaining being the dark energy.

Challenging the need for dark matter in the universe

"The study's findings confirm that our previous work ("JWST early Universe observations and ΛCDM cosmology") about the age of the universe being 26.7billionyears has allowed us to discover that the universe does not require dark matter to exist," explains Gupta.

"In standard cosmology, the accelerated expansion of the universe is said to be caused by dark energy but is in fact due to the weakening forces of nature as it expands, not due to dark energy."

"Redshifts" refer to when light is shifted toward the red part of the spectrum.

The researcher analyzed data from recent papers on the distribution of galaxies at low redshifts and the angular size of the sound horizon in the literature at high redshift.

"There are several papers that question the existence of dark matter, but mine is the first one, to my knowledge, that eliminates its cosmological existence while being consistent with key cosmological observations that we have had time to confirm," says Gupta.

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Rare sighting of luminous jet spewed by supermassive black hole

What happens when a dying star flies too close to a supermassive black hole?

According to University of Maryland astronomer Igor Andreoni, several things happen: first, the star is violently ripped apart by the black hole's gravitational tidal forces -- similar to how the Moon pulls tides on Earth but with greater strength. Then, pieces of the star are captured into a swiftly spinning disk orbiting the black hole. Finally, the black hole consumes what remains of the doomed star in the disk. This is what astronomers call a tidal disruption event (TDE).

But in some extremely rare cases, the supermassive black hole launches "relativistic jets" -- beams of matter traveling close to the speed of light -- after destroying a star. Andreoni, who is a postdoctoral associate in the Department of Astronomy at UMD and NASA Goddard Space Flight Center, discovered one such case with his team in the Zwicky Transient Facility (ZTF) survey in February 2022. After the group publicly announced the sighting, the event was named "AT2022cmc." The team published its findings in the journal Nature on November 30, 2022.

"The last time scientists discovered one of these jets was well over a decade ago," said Michael Coughlin, an assistant professor of astronomy at the University of Minnesota Twin Cities and co-lead on the project. "From the data we have, we can estimate that relativistic jets are launched in only 1% of these destructive events, making AT2022cmc an extremely rare occurrence. In fact, the luminous flash from the event is among the brightest ever observed."

Before AT2022cmc, the only two previously known jetted TDEs were discovered through gamma-ray space missions, which detect the highest-energy forms of radiation produced by these jets. As the last such discovery was made in 2012, new methods were required to find more events of this nature. To help address that need, Andreoni and his team implemented a novel, "big picture" tactic to find AT2022cmc: ground-based optical surveys, or general maps of the sky without specific observational targets. Using ZTF, a wide-field sky survey taken by the Samuel Oschin Telescope in California, the team was able to identify and uniquely study the otherwise dormant-looking black hole.

"We developed an open-source data pipeline to store and mine important information from the ZTF survey and alert us about atypical events in real time," Andreoni explained. "The rapid analysis of ZTF data, the equivalent to a million pages of information every night, allowed us to quickly identify the TDE with relativistic jets and make follow-up observations that revealed an exceptionally high luminosity across the electromagnetic spectrum, from the X-rays to the millimeter and radio."

Follow up observations with many observatories confirmed that AT2022cmc was fading rapidly and the ESO Very Large Telescope revealed that AT2022cmc was at cosmological distance, 8.5 billion light years away.

Hubble Space Telescope optical/infrared images and radio observations from the Very Large Array pinpointed the location of AT2022cmc with extreme precision. The researchers believe that AT2022cmc was at the center of a galaxy that is not yet visible because the light from AT2022cmc outshone it, but future space observations with Hubble or James Webb Space Telescopes may unveil the galaxy when the transient eventually disappears.

It is still a mystery why some TDEs launch jets while others do not seem to. From their observations, Andreoni and his team concluded that the black holes in AT2022cmc and other similarly jetted TDEs are likely spinning rapidly so as to power the extremely luminous jets. This suggests that a rapid black hole spin may be one necessary ingredient for jet launching -- an idea that brings researchers closer to understanding the physics of supermassive black holes at the center of galaxies billions of light years away.

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Searching for traces of dark matter with neutron spin clocks

With the use of a precision experiment developed at the University of Bern, an international research team has succeeded in significantly narrowing the scope for the existence of dark matter. The experiment was carried out at the European Research Neutron Source at the Institute Laue-Langevin in France, and makes an important contribution to the search for these particles, of which little is known.

Cosmological observations of the orbits of stars and galaxies enable clear conclusions to be drawn about the attractive gravitational forces that act between the celestial bodies. The astonishing finding: visible matter is far from sufficient for being able to explain the development or movements of galaxies. This suggests that there exists another, so far unknown, type of matter. Accordingly, in the year 1933, the Swiss physicist and astronomer Fritz Zwicky inferred the existence of what is known now as dark matter. Dark matter is a postulated form of matter which isn't directly visible but interacts via gravity, and consists of approximately five times more mass than the matter with which we are familiar.

Recently, following a precision experiment developed at the Albert Einstein Center for Fundamental Physics (AEC) at the University of Bern, an international research team succeeded in significantly narrowing the scope for the existence of dark matter. With more than 100 members, the AEC is one of the leading international research organisations in the field of particle physics. The findings of the team, led by Bern, have now been published in the journal Physical Review Letters.

The mystery surrounding dark matter

"What dark matter is actually made of is still completely unclear," explains Ivo Schulthess, a PhD student at the AEC and the lead author of the study. What is certain, however, is that it is not made from the same particles that make up the stars, planet Earth or us humans. Worldwide, increasingly sensitive experiments and methods are being used to search for possible dark matter particles -- until now, however, without success.

Certain hypothetical elementary particles, known as axions, are a promising category of possible candidates for dark matter particles. An important advantage of these extremely lightweight particles is that they could simultaneously explain other important phenomena in particle physics which have not yet been understood.

Bern experiment sheds light on the darkness

"Thanks to many years of expertise, our team has succeeded in designing and building an extremely sensitive measurement apparatus -- the Beam EDM experiment," explains Florian Piegsa, Professor for Low Energy and Precision Physics at the AEC, who was awarded one of the prestigious ERC Starting Grants from the European Research Council in 2016 for his research with neutrons. If the elusive axions actually exist, they should leave behind a characteristic signature in the measurement apparatus.

"Our experiment enables us to determine the rotational frequency of neutron spins, which move through a superposition of electric and magnetic fields," explains Schulthess. The spin of each individual neutron acts as a kind of compass needle, which rotates due to a magnetic field similarly to the second hand of a wristwatch -- but nearly 400,000 times faster. "We precisely measured this rotational frequency and examined it for the smallest periodic fluctuations which would be caused by the interactions with the axions," explains Piegsa. The results of the experiment were clear: "The rotational frequency of the neutrons remained unchanged, which means that there is no evidence of axions in our measurement," says Piegsa.

Parameter space successfully narrowed down

The measurements, which were carried out with researchers from France at the European Research Neutron Source at the Institute Laue-Langevin, allowed for the experimental exclusion of a previously completely unexplored parameter space of axions. It also proved possible to search for hypothetical axions which would be more than 1,000 times heavier than was previously possible with other experiments.

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Astronomers discover widest separation of brown dwarf pair to date

A team of astronomers has discovered a rare pair of brown dwarfs that has the widest separation of any brown dwarf binary system found to date.

"Because of their small size, brown dwarf binary systems are usually very close together," said Emma Softich, an undergraduate astrophysics student at the Arizona State University (ASU) School of Earth and Space Exploration and lead author of the study. "Finding such a widely separated pair is very exciting."

The gravitational force between a pair of brown dwarfs is lower than for a pair of stars with the same separation, so wide brown dwarf binaries are more likely to break up over time, making this pair of brown dwarfs an exceptional find.

The study, which is based on observations the University of California San Diego (UC San Diego) Cool Star Lab conducted with W. M. Keck Observatory on Maunakea, Hawai'i Island, is published in today's issue of The Astrophysical Journal Letters.

Using Keck Observatory's Near-Infrared Echellette Spectrometer, or NIRES instrument, members of the UC San Diego Cool Star Lab, including Physics Professor Adam Burgasser and graduate students Christian Aganze and Dino Hsu, obtained infrared spectra of the brown dwarf binary system, called CWISE J014611.20-050850.0AB. The data revealed the two brown dwarfs are about 12 billion miles apart, or three times the separation of Pluto from the Sun. This distance confirms the unusual brown dwarf couple breaks the record for having the widest separation from each other.

"Keck's exceptional sensitivity in the infrared with this instrument was critical for our measurements," said co-author Burgasser, who leads the Cool Star Lab. "The secondary brown dwarf of this system is exceptionally faint, but with Keck we were able to obtain good enough spectral data to classify both sources and identify them as members of a rare class of blue L dwarfs."

"Wide, low-mass systems like CWISE J014611.20-050850.0AB are usually disrupted early on in their lifetimes, so the fact that this one has survived until now is pretty remarkable," said co-author Adam Schneider of the U.S. Naval Observatory, Flagstaff Station and George Mason University.

Brown dwarfs are celestial objects that are smaller than a normal star. These objects are not massive enough to sustain nuclear fusion and shine like normal stars, but are hot enough to radiate energy.

Many brown dwarfs have been discovered with data from NASA's Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, which solicits help from the public to search the WISE image data bank to find brown dwarfs and low-mass stars, some of the Sun's nearest neighbors.

For this study, the researchers inspected images of Backyard Worlds discoveries, where companion brown dwarfs may have been overlooked. In doing so, they discovered the rare CWISE J014611.20 050850.0AB brown dwarf binary system.

Softich went through about 3,000 brown dwarfs from Backyard Worlds one by one and compared the WISE images to other survey images, looking for evidence of a brown dwarf companion to the original target. The team then used data from the Dark Energy Survey (DES) to confirm that it was indeed a brown dwarf pair.

They then used Keck Observatory's NIRES to confirm the brown dwarfs have spectral types L4 and L8, and that they are at an estimated distance of about 40 parsecs, or 130.4 light-years from Earth, with a projected separation of 129 astronomical units, or 129 times the distance between the Sun and the Earth.

The team hopes this discovery will allow astronomers the chance to study brown dwarf binary systems and to develop models and procedures that will help in recognizing more of them in the future.

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Quantum physicists measure the smallest gravitational force yet

 Researchers have succeeded in measuring the gravitational field of a gold sphere, just 2 mm in diameter, using a highly sensitive pendulum -- and thus the smallest gravitational force. The experiment opens up new possibilities for testing the laws of gravity on previously unattained small scales.

Gravity is the weakest of all known forces in nature -- and yet it is most strongly present in our everyday lives. Every ball we throw, every coin we drop -- all objects are attracted by the Earth's gravity. In a vacuum, all objects near the Earth's surface fall with the same acceleration: their velocity increases by about 9.8 m/s every second. The strength of gravity is determined by the mass of the Earth and the distance from the center. On the Moon, which is about 80 times lighter and almost 4 times smaller than the Earth, all objects fall 6 times slower. And on a planet of the size of a ladybug? Objects would fall 30 billion times slower there than on Earth. Gravitational forces of this magnitude normally occur only in the most distant regions of galaxies to trap remote stars. A team of quantum physicists led by Markus Aspelmeyer and Tobias Westphal of the University of Vienna and the Austrian Academy of Sciences has now demonstrated these forces in the laboratory for the first time. To do so, the researchers drew on a famous experiment conducted by Henry Cavendish at the end of the 18th century.

During the time of Isaac Newton, it was believed that gravity was reserved for astronomical objects such as planets. It was not until the work of Cavendish (and Nevil Maskelyne before him) that it was possible to show that objects on Earth also generate their own gravity. Using an elegant pendulum device, Cavendish succeeded in measuring the gravitational force generated by a lead ball 30 cm tall and weighing 160 kg in 1797. A so-called torsion pendulum -- two masses at the ends of a rod suspended from a thin wire and free to rotate -- is measurably deflected by the gravitational force of the lead mass. Over the coming centuries, these experiments were further perfected to measure gravitational forces with increasing accuracy.

The Vienna team has picked up this idea and built a miniature version of the Cavendish experiment. A 2 mm gold sphere weighing 90 mg serves as the gravitational mass. The torsion pendulum consists of a glass rod 4 cm long and half a millimeter thick, suspended from a glass fiber a few thousandths of a millimeter in diameter. Gold spheres of similar size are attached to each end of the rod. "We move the gold sphere back and forth, creating a gravitational field that changes over time," explains Jeremias Pfaff, one of the researchers involved in the experiment. "This causes the torsion pendulum to oscillate at that particular excitation frequency." The movement, which is only a few millionths of a millimeter, can then be read out with the help of a laser and allows conclusions to be drawn about the force. The difficulty is keeping other influences on the motion as small as possible. "The largest non-gravitational effect in our experiment comes from seismic vibrations generated by pedestrians and tram traffic around our lab in Vienna," says co-author Hans Hepach: "We therefore obtained the best measurement data at night and during the Christmas holidays, when there was little traffic." Other effects such as electrostatic forces could be reduced to levels well below the gravitational force by a conductive shield between the gold masses.

This made it possible to determine the gravitational field of an object that has roughly the mass of a ladybug for the first time. As a next step, it is planned to investigate the gravity of masses thousands of times lighter.

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Gravitational forces in protoplanetary disks may push super-Earths close to their stars

Protoplanetary disc formation.

The galaxy is littered with planetary systems vastly different from ours. In the solar system, the planet closest to the Sun -- Mercury, with an orbit of 88 days -- is also the smallest. But NASA's Kepler spacecraft has discovered thousands of systems full of very large planets -- called super-Earths -- in very small orbits that zip around their host star several times every 10 days.

Now, researchers may have a better understanding how such planets formed.

A team of Penn State-led astronomers found that as planets form out of the chaotic churn of gravitational, hydrodynamic -- or, drag -- and magnetic forces and collisions within the dusty, gaseous protoplanetary disk that surrounds a star as a planetary system starts to form, the orbits of these planets eventually get in synch, causing them to slide -- follow the leader-style -- toward the star. The team's computer simulations result in planetary systems with properties that match up with those of actual planetary systems observed by the Kepler space telescope of solar systems. Both simulations and observations show large, rocky super-Earths orbiting very close to their host stars, according to Daniel Carrera, assistant research professor of astronomy at Penn State's Eberly College of Science.

He said the simulation is a step toward understanding why super-Earths gather so close to their host stars. The simulations may also shed light on why super-Earths are often located so close to their host star where there doesn't seem to be enough solid material in the protoplanetary disk to form a planet, let alone a big planet, according to the researchers, who report their findings in the Monthly Notices of the Royal Astronomical Society.

"When stars are very young, they are surrounded by a disc that is mostly gas with some dust -- and that dust grows into the planets, like the Earth and these super-Earths," said Carrera. "But the particular puzzle for us is that this disc doesn't go the all way to the star -- there's a cavity there. And yet we see these planets closer to the star than the edge of that disc."

The astronomers' computer simulation shows that, over time, the planets' and disk's gravitational forces lock the planets into synchronized orbits -- resonance -- with each other. The planets then begin to migrate in unison, with some moving closer to the edge of the disk. The combination of the gas disk affecting the outer planets and the gravitational interactions among the outer and inner planets can continue to push the inner planets very closer to the star, even interior to the edge of the disk.

"With the first discoveries of Jupiter-size exoplanets orbiting close to their host star, astronomers were inspired to develop multiple models for how such planets could form, including chaotic interactions in multiple planet systems, tidal effects and migration through the gas disk," said Eric Ford, professor of astronomy and astrophysics, director of Penn State's Center for Exoplanets and Habitable Worlds and Institute for CyberScience (ICS) faculty co-hire. "However, these models did not predict the more recent discoveries of super-Earth-size planets orbiting so close to their host star. Some astronomers had suggested that such planets must have formed very near their current locations. Our work is important because it demonstrates how short-period super-Earth-size planets could have formed and migrated to their current locations thanks to the complex interactions of multiple planet systems."

Carrera said more work remains to confirm that the theory is correct.

"We've shown that it's possible for planets to get that close to a star in this simulation, but it doesn't mean that it's the only way that the universe chose to make them," said Carrera. "Someone might come up with a different idea of a way to get the planets that close to a star. And, so, the next step is to test the idea, revise it, make predictions that you can test against observations."

Future research may also explore why our super-Earthless solar system is different from most other solar systems, Carrera added.

"Super-Earths in very close orbits are by far the most common type of exoplanet that we observe, and yet they don't exist in our own solar system and that makes us wonder why," said Carrera.

According to the researchers, the best published estimates suggest that about 30 percent of solar-like stars have some planets close to the host star than the Earth is to the Sun. However, they note that additional planets are could go undetected, especially small planets far from their star.

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