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Such primordial black holes (PBHs) could account for all or part of dark matter, be responsible for some of the observed gravitational waves signals, and seed supermassive black holes found in the center of our Galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material. In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. The 2020 Nobel Prize in physics was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since black holes are known to exist in nature, they make a very appealing candidate for dark matter.

The recent progress in fundamental theory, astrophysics, and astronomical observations in search of PBHs has been made by an international team of particle physicists, cosmologists and astronomers, including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.

To learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would create a black hole. However, cosmological perturbations that seeded galaxies are known to be much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the black holes to form.

Scientists hope to answer three specific questions: Do the observed black holes really have event horizons? Are they as featureless as the no-hair theorem says? And do they distort spacetime exactly as the Kerr metric predicts?

How do you prove that you’re observing a bizarre, featureless hole in the fabric of space and time?

From an observatory high above Chile’s Atacama Desert, astronomers have taken a new look at the oldest light in the universe.

Their observations, plus a bit of cosmic geometry, suggest that the universe is 13.77 billion years old – give or take 40 million years. A Cornell researcher co-authored one of two papers about the findings, which add a fresh twist to an ongoing debate in the astrophysics community.

The new estimate, using data gathered at the National Science Foundation’s Atacama Cosmology Telescope (ACT), matches the one provided by the standard model of the universe, as well as measurements of the same light made by the European Space Agency’s Planck satellite, which measured remnants of the Big Bang from 2009 to ’13.

Astronomers have made the cosmic distant ladder more accurate, but that has only made the mystery of cosmic expansion even worse.

Measuring the expansion of the universe is hard. For one thing, because the universe is expanding, the scale of your distance measurements affects the scale of the expansion. And since light from distant galaxies takes time to reach us, you can’t measure what the universe is, but rather what it was. Then there is the challenge of the cosmic distance ladder.

The distance ladder stems from the fact that while we have lots of ways to measure cosmic distance, none of them work at all scales. For example, the greatest distances are determined by measuring the apparent brightness of supernovae in distant galaxies. That works great across billions of light-years, but there aren’t enough supernovae in the Milky Way to nearby measure distances. Perhaps the most accurate distance measurement uses parallax, which measures the apparent shift in the position of a star as the Earth orbits the Sun. Parallax is a matter of simple geometry, but it’s only accurate to a couple of thousand light-years.

Continue reading “Astronomers Improve Their Distance Scale for the Universe. Unfortunately, it Doesn’t Resolve the Crisis in Cosmology” »

AP Exclusive: The Chinese government is tightly controlling all COVID-19 research under orders from President Xi Jinping, internal documents obtained by The AP show. As a result, China’s search for the origins of the virus has been cloaked in secrecy. In a sign of how sensitive research has become, police stopped scientists and confiscated their samples at a mineshaft where the closest known relative of the COVID-19 virus was found.

MOJIANG, China (AP) — Deep in the lush mountain valleys of southern China lies the entrance to a mine shaft that once harbored bats with the closest known relative of the COVID-19 virus.

The area is of intense scientific interest because it may hold clues to the origins of the coronavirus that has killed more than 1.7 million people worldwide. Yet for scientists and journalists, it has become a black hole of no information because of political sensitivity and secrecy.

Continue reading “China clamps down in hidden hunt for coronavirus origins” »

The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) is home to many interdisciplinary projects which benefit from the synergy of a wide range of expertise available at the institute. One such project is the study of black holes that could have formed in the early universe, before stars and galaxies were born.

Such primordial black holes (PBHs) could account for all or part of dark matter, be responsible for some of the observed gravitational waves signals, and seed supermassive black holes found in the center of our Galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material.

In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. The 2020 Nobel Prize in physics was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since black holes are known to exist in nature, they make a very appealing candidate for dark matter.

Over the past few decades, many experimental physicists have been probing the existence of particles called axions, which would result from a specific mechanism that they think could explain the contradiction between theories and experiments describing a fundamental symmetry. This symmetry is associated with a matter-antimatter imbalance in the Universe, reflected in interactions between different particles.

If this mechanism took place in the early Universe, such a particle might have a very small mass and be ‘invisible. Subsequently, researchers proposed that the axion might also be a promising candidate for dark matter, an elusive, hypothetical type of matter that does not emit, reflect or absorb light.

While dark matter has not yet been experimentally observed, it is believed to make up 85% of universe’s mass. Detecting axions could have important implications for ongoing dark matter experiments, as it could enhance the present understanding of these elusive particles.

Circa 2012 o.o

“Repulsive gravity”—a powerful repulsion between matter and antimatter—could explain the force known as dark energy, a new theory claims.

Circa 2012

(PhysOrg.com) — During the past few years, CERN physicist Dragan Hajdukovic has been investigating what he thinks may be a widely overlooked part of the cosmos: the quantum vacuum. He suggests that the quantum vacuum has a gravitational charge stemming from the gravitational repulsion of virtual particles and antiparticles. Previously, he has theoretically shown that this repulsive gravity can explain several observations, including effects usually attributed to dark matter. Additionally, this additional gravity suggests that we live in a cyclic Universe (with no Big Bang) and may provide insight into the nature of black holes and an estimate of the neutrino mass. In his most recent paper, published in Astrophysics and Space Science, he shows that the quantum vacuum could explain one more observation: the Universe’s accelerating expansion, without the need for dark energy.

“The quantum vacuum was predicted theoretically more than 60 years ago,” Hajdukovic told PhysOrg.com. “Today, there is significant experimental evidence that the quantum vacuum exists. I have decided to combine one reality (the quantum vacuum) with one hypothesis (the negative gravitational charge of antiparticles) and to study the consequences. The hypothesis of the gravitational repulsion between matter and antimatter is older than half a century, but before me no one has used it in the combination with the quantum vacuum. … The results are surprising; there is potential to explain [the Universe’s accelerating expansion] in the framework of the quantum vacuum enriched with the gravitational repulsion between matter and antimatter.”

According to Hajdukovic, gravity in the quantum vacuum arises from the gravitational repulsion between the positive gravitational charge of matter and the (hypothetical) negative gravitational charge of antimatter. While matter and antimatter are gravitationally self-attractive, they are mutually repulsive. (This part is similar to Massimo Villata’s theory from part 1, in which negatively charged antimatter exists in voids rather than in the quantum vacuum.) Although the quantum vacuum does not contain real matter and antimatter, short-lived virtual particles and virtual antiparticles could momentarily appear and form pairs, becoming gravitational dipoles.