Did primordial black holes help or hinder formation of the universe’s first stars, eventually born about 100 million years later?

Supercomputer simulations helped investigate this cosmic question, thanks to simulations on the Stampede2 supercomputer of the Texas Advanced Computing Center (TACC), part of The University of Texas at Austin.

“We found that the standard picture of first-star formation is not really changed by primordial black holes,” said Boyuan Liu, a post-doctoral researcher at the University of Cambridge. Liu is the lead author of computational astrophysics research published August 2022 in the Monthly Notices of the Royal Astronomical Society.

In the early universe, the standard model of astrophysics holds that black holes seeded the formation of halo-like structures by virtue of their gravitational pull, analogous to how clouds form by being seeded by dust particles. This is a plus for star formation, where these structures served as scaffolding that helped matter coalesce into the first stars and galaxies.

However, a black hole also causes heating by gas or debris falling into it. This forms a hot accretion disk around the black hole, which emits energetic photons that ionize and heat the surrounding gas.

And that’s a minus for star formation, as gas needs to cool down to be able to condense to high enough density that a nuclear reaction is triggered, setting the star ablaze.

“We found that these two effects — black hole heating and seeding — almost cancel each other out and the final impact is small for star formation,” Liu said.

Depending on which effect wins over the other, star formation can be accelerated, delayed or prevented by primordial black holes. “This is why primordial black holes can be important,” he added.

Liu emphasized that it is only with state-of-the-art cosmological simulations that one can understand the interplay between the two effects.

Regarding the importance of primordial black holes, the research also implied that they interact with the first stars and produce gravitational waves. “They may also be able to trigger the formation of supermassive black holes. These aspects will be investigated in follow-up studies,” Liu added.

For the study, Liu and colleagues used cosmological hydrodynamic zoom-in simulations as their tool for state-of-the-art numerical schemes of the gravity hydrodynamics, chemistry and cooling in structure formation and early star formation.

“A key effect of primordial black holes is that they are seeds of structures,” Liu said. His team built the model that implemented this process, as well as incorporating the heating from primordial black holes.

They then added a sub-grid model for black hole accretion and feedback. The model calculates at each timestep how a black hole accretes gas and also how it heats its surroundings.

“This is based on the environment around the black hole known in the simulations on the fly,” Liu said.

XSEDE awarded the science team allocations on the Stampede2 system of TACC.

“Supercomputing resources in computational astrophysics are absolutely vital,” said study co-author Volker Bromm, professor and chair, Department of Astronomy, UT Austin.

Bromm explained that in theoretical astrophysics, the ruling paradigm for understanding the formation and evolution of cosmic structure is to use ab initio simulations, which follow the ‘playbook’ of the universe itself — the governing equations of physics.

The simulations use data from the universe’s initial conditions to high precision based on observations of the cosmic microwave background. Simulation boxes are then set up that follow the cosmic evolution timestep by timestep.

But the challenges in computational simulation of structure formation lie in the way large scales of the universe — millions to billions of light years and billions of years — mesh with the atomic scales where stellar chemistry happens.

“The microcosm and the macrocosm interact,” Bromm said.

“TACC and XSEDE resources have been absolutely vital for us to push the frontier of computation astrophysics. Everyone who is at UT Austin — faculty members, postdocs, students — benefits from the fact that we have such a premier supercomputing center. I’m extremely grateful,” Bromm added.

“If we look into one typical structure that can form the first stars, we need around one million elements to fully resolve this halo or structure,” Liu said. “This is why we need to use supercomputers at TACC.”

Liu said that using Stampede2, a simulation running on 100 cores can complete in just a few hours versus years on a laptop, not to mention the bottlenecks with memory and reading or writing data.

“The overall game plan with our work is that we want to understand how the universe was transformed from the simple initial conditions of the Big Bang,” explained Bromm.

The structures that emerged from the Big Bang were driven by the dynamical importance of dark matter.

The nature of dark matter remains one of the biggest mysteries in science.

The clues of this hypothetical yet unobservable substance are undeniable, seen in the impossible rotational speeds of galaxies. The mass of all the stars and planets in galaxies like our Milky Way do not have enough gravity to keep them from flying apart. The ‘x-factor’ is called dark matter, yet laboratories have not yet directly detected it.

However, gravitational waves have been detected, first by LIGO in 2015.

“It is possible that primordial black holes can explain these gravitational wave events that we have been detecting over the past seven years,” Liu said. “This just motivates us.”

Said Bromm: “Supercomputers are enabling unprecedented new insights into how the universe works. The universe provides us with extreme environments that are extremely challenging to understand. This also gives motivation to build ever-more-powerful computation architectures and devise better algorithmic structures. There’s great beauty and power to the benefit of everyone.”

The study, “Effects of stellar-mass primordial black holes on first star formation,” was published August 2022 in the Monthly Notices of the Royal Astronomical Society. The study authors are Boyuan Liu, Saiyang Zhang, and Volker Bromm of the University of Texas at Austin. Liu is now at the University of Cambridge.

To accomplish this, the researchers began with 3D-printed lattice materials and incorporated networks of air-filled channels into the structure during the printing process. By measuring how the pressure changes within these channels when the structure is squeezed, bent, or stretched, engineers can receive feedback on how the material is moving.

These lattice materials are composed of single cells in a repeating pattern. Changing the size or shape of the cells alters the material’s mechanical properties, such as stiffness or hardness. For instance, a denser network of cells makes a stiffer structure.

This technique could someday be used to create flexible soft robots with embedded sensors that enable the robots understand their posture and movements. It might also be used to produce wearable smart devices, like customized running shoes that provide feedback on how an athlete’s foot is impacting the ground.

“The idea with this work is that we can take any material that can be 3D-printed and have a simple way to route channels throughout it so we can get sensorization with structure. And if you use really complex materials, then you can have motion, perception, and structure all in one,” says co-lead author Lillian Chin, a graduate student in the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL).

Joining Chin on the paper are co-lead author Ryan Truby, a former CSAIL postdoc who is now as assistant professor at Northwestern University; Annan Zhang, a CSAIL graduate student; and senior author Daniela Rus, the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science and director of CSAIL. The paper is published in Science Advances.

Architected materials

The researchers focused their efforts on lattices, a type of “architected material,” which exhibits customizable mechanical properties based solely on its geometry. For instance, changing the size or shape of cells in the lattice makes the material more or less flexible.

While architected materials can exhibit unique properties, integrating sensors is notoriously challenging. Engineers typically must place sensors on the outside, which is tough because the lattice is full of holes so there is little material to work with. Also, when sensors are placed on the outside, they are not fully integrated with the material and can be affected by noise that comes from a soft material’s movements.

Instead, Chin and her collaborators used 3D printing to incorporate air-filled channels directly into the struts that form the lattice. When the structure is moved or squeezed, those channels deform and the volume of air inside changes. The researchers can measure the corresponding change in pressure with an off-the-shelf pressure sensor, which gives feedback on how the material is deforming.

Because they are incorporated into the material, these “fluidic sensors” are more accurate than sensors placed on the outside of a structure.

“If you stretch out a rubber band, it takes a little time to come back into place. But since we are using air and the deformations are relatively stable, we don’t get these same time-varying properties. The information that comes out of our sensor is a lot cleaner,” Chin says.

“Sensorizing” structures

The researchers incorporate channels into the structure using digital light processing 3D printing. In this method, the structure is drawn out of a pool of resin and hardened into a precise shape using projected light. An image is projected onto the wet resin and areas struck by the light are cured.

But as the process continues, the sticky resin tends to drip and get stuck inside the channels. The researchers had to work quickly to remove excess resin before it was cured, using a mix of pressurized air, vacuum, and intricate cleaning.

“We will have to do more brainstorming from the design side to think about that cleaning process, since it is the main challenge,” she says.

They used this process to create several lattice structures and demonstrated how the air-filled channels generated clear feedback when the structures were squeezed and bent.

Building off these results, they also incorporated sensors into a new class of materials developed for motorized soft robots known as handed shearing auxetics, or HSAs. HSAs can be twisted and stretched simultaneously, which enables them to be used as effective soft robotic actuators. But they are difficult to “sensorize” because of their complex forms.

They 3D printed an HSA soft robot capable of several movements, including bending, twisting, and elongating. They ran the robot through a series of movements for more than 18 hours and used the sensor data to train a neural network that could accurately predict the robot’s motion.

Chin was impressed by the results — the fluidic sensors were so accurate she had difficulty distinguishing between the signals the researchers sent to the motors and the data that came back from the sensors.

“Materials scientists have been working hard to optimize architected materials for functionality. This seems like a simple, yet really powerful idea to connect what those researchers have been doing with this realm of perception. As soon as we add sensing, then roboticists like me can come in and use this as an active material, not just a passive one,” she says.

“Sensorizing soft robots with continuous skin-like sensors has been an open challenge in the field. This new method provides accurate proprioceptive capabilities for soft robots and opens the door for exploring the world through touch” says Rus.

In the future, Chin looks forward to finding new applications for this technique, such as creating football helmets tailored to a specific player’s head that have sensing capabilities within the internal structure. This could increase the accuracy of feedback from on-field collisions and improve player safety. She is also interested in utilizing machine learning to push the boundaries of tactile sensing for robotics.

This research was supported, in part, by the National Science Foundation, the Schmidt Science Fellows Program in partnership with the Rhodes Trust, an NSF Graduate Fellowship, and the Fannie and John Hertz Foundation.

Meteorites from the Moon to Antarctica

During her doctoral research at ETH Zurich, Patrizia Will analysed six samples of lunar meteorites from an Antarctic collection, obtained from NASA. The meteorites consist of basalt rock that formed when magma welled up from the interior of the Moon and cooled quickly. They remained covered by additional basalt layers after their formation, which protected the rock from cosmic rays and, particularly, the solar wind. The cooling process resulted in the formation of lunar glass particles amongst the other minerals found in magma. Will and the team discovered that the glass particles retain the chemical fingerprints (isotopic signatures) of the solar gases: helium and neon from the Moon’s interior. Their findings strongly support that the Moon inherited noble gases indigenous to the Earth. “Finding solar gases, for the first time, in basaltic materials from the Moon that are unrelated to any exposure on the lunar surface was such an exciting result,” says Will.

Without the protection of an atmosphere, asteroids continually pelt the Moon’s surface. It likely took a high-energy impact to eject the meteorites from the middle layers of the lava flow similar to the vast plains known as the Lunar Mare. Eventually the rock fragments made their way to Earth in the form of meteorites. Many of these meteorite samples are picked up in the deserts of North Africa or in, in this case, the “cold desert” of Antarctica where they are easier to spot in the landscape.

Grateful Dead lyrics inspire lab instrument

In the Noble Gas Laboratory at ETH Zurich resides a state-of-the-art noble gas mass spectrometer named, “Tom Dooley” — sung about in the Grateful Dead tune by the same name. The instrument got its name, when earlier researchers, at one point, suspended the highly sensitive equipment from the ceiling of the lab to avoid interference from the vibrations of everyday life. Using the Tom Dooley instrument, the research team was able to measure sub-millimetre glass particles from the meteorites and rule out solar wind as the source of the detected gases. The helium and neon that they detected were in a much higher abundance than expected.

The Tom Dooley is so sensitive that it is, in fact, the only instrument in the world capable of detecting such minimal concentrations of helium and neon. It was used to detect these noble gases in the 7 billion years old grains in the Murchison meteorite — the oldest known solid matter to-date.

Searching for the origins of life

Knowing where to look inside NASA’s vast collection of some 70,000 approved meteorites represents a major step forward. “I am strongly convinced that there will be a race to study heavy noble gases and isotopes in meteoritic materials,” says ETH Zurich Professor Henner Busemann, one of the world’s leading scientists in the field of extra-terrestrial noble gas geochemistry. He anticipates that soon researchers will be looking for noble gases such as xenon and krypton which are more challenging to identify. They will also be searching for other volatile elements such as hydrogen or halogens in the lunar meteorites.

Busemann comments, “While such gases are not necessary for life, it would be interesting to know how some of these noble gases survived the brutal and violent formation of the moon. Such knowledge might help scientists in geochemistry and geophysics to create new models that show more generally how such most volatile elements can survive planet formation, in our solar system and beyond.”

Story Source:

Materials provided by ETH Zurich. Original written by Marianne Lucien. Note: Content may be edited for style and length.

Because this behavior is hypothesized to be perpetual, the universe should have no beginning and no end — only eternal cycles of growing and shrinking that extend forever into the future, and forever into the past.

It’s an appealing concept in part because it removes the need for a state called a singularity that corresponds to the “beginning of time” in other models.

But a new study by University at Buffalo physicists Will Kinney and Nina Stein highlights one way that cyclic or “bouncing” cosmologies fall flat.

The research shows that the latest version of this theory — a cyclic model that resolves long-standing concerns about entropy — introduces a new problem (or rather, returns to an old one). Cyclic universes described under this model must have a beginning, Kinney and Stein conclude.

“People proposed bouncing universes to make the universe infinite into the past, but what we show is that one of the newest types of these models doesn’t work,” says Kinney, PhD, professor of physics in the UB College of Arts and Sciences. “In this new type of model, which addresses problems with entropy, even if the universe has cycles, it still has to have a beginning.”

“There are a lot of reasons to be curious about the early universe, but I think my favorite is the natural human tendency to want to know what came before,” says Stein, a UB PhD student in physics, regarding the importance of such research. “Across cultures and histories, humans have told stories about creation, about ‘in the beginning.’ We always want to know where we came from.”

The study, funded by the National Science Foundation, was published in June in the Journal of Cosmology and Astroparticle Physics. The paper is titled, “Cyclic cosmology and geodesic completeness.”

If the universe had a beginning, how did it begin?

Kinney is author of a 2022 book titled, “An Infinity of Worlds,” which tells the epic story of cosmic inflation, a competing theory about the origins of the universe. Under this model, the early universe was characterized by a period of rapid expansion from a singularity, followed by the superhot Big Bang, which forged the primordial elements that went on to make galaxies and stars and planets, and the atoms in our bodies and all other living things.

Cosmic inflation is a leading theory. But it focuses on what happens during and after the age of rapid expansion. It doesn’t explain what came before that, and it doesn’t describe the conditions of the initial singularity.

A truly cyclic universe would circumvent these problems: If the universe is engaged in endless cycles of expansion and contraction, it need not have a beginning at all. But as Kinney notes, these bouncing models raise their own array of untenable questions.

“Unfortunately, it’s been known for almost 100 years that these cyclic models don’t work because disorder, or entropy, builds up in the universe over time, so each cycle is different from the last one. It’s not truly cyclic,” Kinney says. “A recent cyclic model gets around this entropy build-up problem by proposing that the universe expands a whole bunch with each cycle, diluting the entropy. You stretch everything out to get rid of cosmic structures such as black holes, which returns the universe to its original homogenous state before another bounce begins.”

“But,” he adds, “long story short, we showed that in solving the entropy problem, you create a situation where the universe had to have a beginning. Our proof shows in general that any cyclic model which removes entropy by expansion must have a beginning.”

“The idea that there was a point in time before which there was nothing, no time, bothers us, and we want to know what there was before that — scientists included,” Stein says. “But as far as we can tell, in models that address entropy, there must have been a ‘beginning.’ There is a point for which there is no answer to the question, ‘What came before that?’ “

And, of course, there are further research questions, Kinney says: “Our proof does not apply to a cyclic model proposed by Roger Penrose, in which the universe expands infinitely in each cycle. We’re working on that one.”

“Working with precious fossils is a challenge since it is important not to destroy or harm the specimen,” said the article’s senior author, Tilo Niemann, M.D., head of CT, and cardiac and thoracic radiology in the Department of Radiology at Kantonsspital Baden in Baden, Switzerland. “Even if there exist various imaging techniques to evaluate the internal structure, it was not possible to scan a whole tusk in toto without the need for fragmentation or at least having to do multiple scans that then had to be painstakingly assembled.”

The extinct woolly mammoth (Mammuthus primigenius) was the size of a modern-day African elephant and lived throughout Eurasia and North America. Most of the woolly mammoths went extinct with the conclusion of the last Ice Age, and the last specimens lived approximately 6,000 years ago. They belong to the order Proboscidea, which includes today’s elephants as well as other extinct mammoths, mastodons and gomphotheres.

Mammoths were covered in fur and had small ears and a small tail to abate frostbite. They also had tusks that they used for scraping bark off trees, digging on the ground for food and fighting. The tusks of proboscideans have allowed researchers to determine the age and identification of specific life-altering occurrences based on annual growth increment analysis.

Newer CT scanners have larger gantries, which is the ring or cylinder into which a patient, or in this case the tusk, is placed. The introduction of larger gantries now allows the opportunity for scanning larger objects that was not possible before, Dr. Niemann noted.

The tusk that the researchers examined was found in central Switzerland and excavated by the heritage and archaeology office of Canton Zug. The tusk is a total of 206 centimeters (cm) in length — nearly 7 feet. It has a basal (measurement at the base) diameter of 16 cm — just over 6 inches. The total object diameter — taking into account its helical, or spiral, curvature — is 80 cm, or just over 2.5 feet.

Tusks mostly consist of two types of material: cementum, a bonelike substance, and dentin, which lies beneath the cementum and accounts for the majority of the tusk’s mass. Mammoth tusks are internally structured by annual increments of dentin apposition which, when viewed in longitudinal section (as opposed to cross-section), resemble cone-shaped cups stacked on top of one another. The first “cone” a mammoth creates forms the tip of the tusk, while the cone at the tusk base is the most recent, generated just prior to the animal’s death. The cones in between are formed throughout the mammoth’s lifetime.

Using the larger-gantry CT scanner, researchers, in collaboration with the Institute of Evolutionary Medicine, University of Zurich, were able to capture a clear image of the entire tusk’s interior.

“It was fascinating to see the internal structure of the mammoth tusk,” Dr. Niemann said.

The researchers found a total of 32 cones, resulting in a minimum age of 32 years at the time of death. Even though the mammoth tusk is well-preserved, it is missing the tip, so the estimate obtained is slightly below the actual age of the animal at the time of death.

“Our mammoth had died at the age of around 32 years, approximately 17,000 years ago,” Dr. Niemann said.