One of the biggest unanswered questions in Alzheimer’s research is why the disease affects people so differently. While many develop memory loss and dementia as Alzheimer’s progresses, others show little or no cognitive decline despite having the same underlying brain pathology.

“Around 30 percent of older adults who develop Alzheimer’s disease never experience its symptoms,” says senior author Evgenia Salta. “We really don’t know why. That’s a big mystery, and a very important one.”

Understanding what protects these individuals could eventually point scientists toward new ways to treat or even prevent dementia.

“If we understand what protects these brains, it could eventually lead to new therapeutic strategies.”

Can the aging brain replace damaged cells?

One possibility is that resilient brains are better at repairing themselves.

“Perhaps they can add new brain cells to a network that is degenerating,” Salta says.

This idea centers on adult neurogenesis, the process through which new neurons are generated in the adult brain. While adult neurogenesis is well documented in many animal species, scientists have long debated how much, if any, occurs in humans.

To investigate, Salta and her colleagues examined donated brain tissue from the Netherlands Brain Bank. The samples included healthy individuals, people with Alzheimer’s disease, and people whose brains showed Alzheimer’s pathology even though they never developed dementia.

The researchers concentrated on a small region within the brain’s memory center, one of the few places where new neurons may still develop.

“These cells are extremely rare, so we had to develop new ways to find them,” Salta says. “We really zoomed in on the exact spot where we expected them to be.”

The team also applied newly developed analytical methods designed specifically for human tissue, reducing reliance on assumptions based on animal studies.

Rare immature neurons persist into old age

The researchers identified the cells they were searching for: so called immature neurons, which resemble young neurons that have not yet fully matured.

“Even at an average age of over 80, we still found these immature neurons in all groups,” Salta says.

The result confirmed that these unusual cells remain present even in very old brains.

What surprised the researchers, however, was that resilient individuals did not have dramatically larger numbers of immature neurons than people with Alzheimer’s disease.

Brain cell behavior may matter more than numbers

Instead, the most important difference appeared to be how the cells behaved.

“In resilient individuals, these cells seem to activate programs that help them survive and cope with damage,” Salta says. “We also see lower signals related to inflammation and cell death.”

The findings suggest that these immature neurons may do more than simply replace cells lost during disease.

“It might not be (only) about replacing lost neurons,” Salta explains. “It could be that these cells support the surrounding tissue and help the brain stay functional and ‘youthful’. They may act as a sort of fertilizer in a garden that has started falling apart.”

Even so, Salta cautions that these ideas remain hypotheses. Because this study examined donated brain tissue, the researchers cannot directly observe how the cells function in living brains.

“We assume the cells’ function based on the data, but we cannot confirm it in this type of study,” she explains.

She also emphasizes that Alzheimer’s resilience is unlikely to have a single explanation.

“This is one piece of a very large puzzle,” she concludes. “There will never be just one factor that explains resilience.”

A new direction for Alzheimer’s research

The study also highlights a broader question about aging itself.

“Somewhere along this trajectory, there’s a kind of decision point,” Salta explains. “Some people remain stable, others develop dementia. We want to understand what drives that difference.”

Future research will explore how immature neurons communicate with other brain cells and whether those interactions help preserve memory and cognitive function.

Although the study does not explain why these cells behave differently in resilient individuals than in people who develop dementia, it reflects a growing shift in Alzheimer’s research. Instead of focusing only on how the disease damages the brain, scientists are increasingly asking why some brains can withstand that damage.

“Cognitive resilience is extremely exciting,” Salta says. “If we understand what protects these brains, it could eventually lead to new therapeutic strategies.”

For now, the findings add to growing evidence that the aging brain is more adaptable, and more complex, than scientists once believed.

Primordial black holes are thought to have formed during the first fraction of a second after the Big Bang, long before the first stars or galaxies existed. Unlike the black holes created by collapsing stars, these hypothetical objects could range in size from something as small as an asteroid to much larger bodies.

Although no primordial black hole has ever been confirmed, scientists believe they could answer several major questions about the universe. One of the biggest is the nature of dark matter, the invisible substance that makes up about 85 percent of all matter and provides the gravitational pull that helps hold galaxies together.

“We believe our study will aid in confirming that they actually do exist,” said Nico Cappelluti, an associate professor in the University of Miami’s Department of Physics, referring to research he conducted with Ph.D. student Alberto Magaraggia.

An Unusual LIGO Signal

Their work builds on a possible discovery reported by the Laser Interferometer Gravitational-Wave Observatory (LIGO), which late last year detected an unusual gravitational wave signal. Gravitational waves are ripples in spacetime produced by some of the universe’s most violent events, including collisions between black holes.

Most known black holes form after massive stars explode as supernovas. Their masses typically range from several times the mass of the Sun to billions of solar masses.

“The most common black holes form as the result of a supernova, the death of a massive star. So, their masses can range from a few times the Sun’s mass to billions of solar masses,” Cappelluti explained.

But in November, LIGO issued an automated alert for a merger in which at least one object appeared to have less than one solar mass. Such a small black hole would be difficult to explain through conventional stellar evolution and instead could point to a primordial black hole.

Not everyone is convinced. Some astrophysicists have suggested the signal may simply be noise within LIGO’s extremely sensitive detectors rather than evidence of a remarkable new discovery.

Could This Explain Dark Matter?

Cappelluti and Magaraggia argue that the detected object is best explained as a primordial black hole that formed in the dense conditions of the early universe, long before stars existed.

To test that idea, the researchers estimated how many primordial black holes might exist throughout the cosmos and how frequently LIGO should detect them.

“We attempted to estimate how many primordial black holes may exist in the universe and how many of them LIGO should be able to detect,” Magaraggia said. “And our results are encouraging. We predict that subsolar black holes like the one LIGO may have observed should indeed be rare, consistent with how infrequently such events have been seen so far.”

Their findings, published in The Astrophysical Journal, suggest that the mysterious LIGO signal has no conventional astrophysical explanation and is most consistent with a primordial black hole.

The study “suggests that the most plausible explanation for the LIGO signal, which lacks any conventional astrophysical explanation, is the detection of a primordial black hole,” Cappelluti said. “And our research indicates that these primordial black holes could account for a significant portion, if not all, of dark matter.”

Even so, both researchers emphasize that one detection is not enough to settle the question.

For now, scientists must wait to see whether LIGO and its international partners record additional events that match the same pattern.

“LIGO picked up what is very strong evidence that these types of black holes exist. But we’ll need to detect another such signal or even several others to get the smoking-gun confirmation that they are real,” Cappelluti said. “But what is clear is that they cannot be excluded as being real.”

A Theory Decades in the Making

The concept of primordial black holes dates back to the Cold War era, when Soviet scientists Yakov Zeldovich and Igor Novikov first proposed their existence. In the early 1970s, Stephen Hawking expanded on the idea, arguing that these objects could be abundant throughout the universe, emit radiation, and possibly explain dark matter.

LIGO later provided the first opportunity to search for evidence supporting those theories. On Sept. 14, 2015, the observatory made history by detecting gravitational waves for the first time, confirming a major prediction of Albert Einstein’s general theory of relativity and opening an entirely new way to study the universe.

The Future of Gravitational Wave Astronomy

LIGO consists of two observatories located in Hanford, Washington, and Livingston, Louisiana. Together with the Virgo detector in Italy and the underground KAGRA observatory in Japan, they form the international LVK collaboration, which searches for black holes, regions of space where gravity is so strong that not even light can escape.

Planned upgrades will make LIGO even more sensitive, increasing its chances of finding additional candidate primordial black holes. However, the observatory’s two L shaped detectors, each with 2.5 mile long vacuum arms, were designed to detect the high frequency gravitational waves produced by relatively recent cosmic collisions, not the waves generated directly during the Big Bang itself.

Future observatories will extend that reach much farther back in time. The European Space Agency’s Laser Interferometer Space Antenna (LISA), scheduled for launch in 2035, is expected to detect gravitational waves from the universe’s earliest epochs after the Big Bang.

Another planned facility, Cosmic Explorer, is currently in the design phase in the United States. Researchers expect it to be about 10 times more sensitive than LIGO, allowing it to detect black hole and neutron star mergers stretching back to the era when the first stars formed.

The international research team, led by Andrii Chumak of the University of Vienna, also uncovered an important insight. They found that the lifespan of magnons is not ultimately limited by the laws of physics, but by the quality of the material they travel through. Their findings were published in Science Advances.

What Are Magnons?

Magnons are tiny waves of magnetization that move through magnetic solids. They can be compared to ripples spreading across a pond after a stone is dropped into the water. Unlike photons, which travel through empty space or optical fibers, magnons remain inside magnetic materials.

Because their wavelengths can shrink to just a few nanometers, magnon-based circuits could potentially fit onto chips no larger than those already found in smartphones. Magnons also interact naturally with other fundamental quasiparticles, including phonons and photons, making them attractive building blocks for hybrid quantum systems and quantum metrology.

Solving the Magnon Lifetime Problem

For years, one of the biggest challenges facing magnon technology has been their extremely short lifetime. Since they could survive for only a few hundred nanoseconds, they disappeared far too quickly to reliably store or transfer quantum information.

The new study changes that picture. By increasing magnon lifetimes to as much as 18 microseconds, the researchers turned these once fleeting signals into long-lasting carriers of quantum information. Their performance now approaches the timescales needed for practical quantum technologies and makes magnons comparable to the superconducting qubits used in today’s leading quantum processors.

How the Researchers Achieved the Breakthrough

The breakthrough resulted from combining two important techniques.

First, instead of using conventional uniform magnons, the team generated short-wavelength magnons. These are naturally less sensitive to tiny defects on the crystal’s surface, which had shortened magnon lifetimes in previous experiments.

Second, the researchers cooled ultra-pure spheres of yttrium iron garnet (YIG) to just 30 millikelvin inside a mixed-phase cryostat. At temperatures only a fraction of a degree above absolute zero, the thermal processes that normally destroy magnons are effectively frozen out.

Materials, Not Physics, Set the Limit

Perhaps the most surprising discovery was identifying what now limits magnon lifetimes.

By testing three YIG spheres with different levels of purity, the researchers found a clear pattern. The purer the crystal, the longer the magnons survived. Even the least pure sample outperformed every previous experiment.

The results suggest that future improvements depend primarily on advances in materials science rather than overcoming an unavoidable law of nature. As researchers develop even purer magnetic materials, magnon lifetimes may continue to improve.

Why This Matters for Quantum Computing

With lifetimes reaching 18 microseconds, magnons become much more than temporary signals. They could serve as reliable quantum memory devices and low-loss communication channels that move quantum information across a chip.

The researchers say magnons could eventually connect hundreds of qubits through a shared pathway, creating a long-sought “quantum bus” that would help scale future quantum computers. Because magnons naturally interact with many different quantum systems, they could also act as universal translators, allowing technologies that normally cannot communicate with one another to work together.

The study is based on experiments carried out by Rostyslav Serha during his doctoral research. The project was led by the University of Vienna in collaboration with the University of Colorado, Colorado Springs, and research institutions in Germany, the United States, and Ukraine. Coauthor Kaitlin McAllister participated through the Vienna Doctoral School in Physics, which provides internships for outstanding master’s students from around the world.