Category Archives: Cosmology

What Leads To Pair Production Process In Pulsar’s Magnetospheres? (Cosmology)

Zaza Osmanov and his collaborators studied the possibility of efficient pair production in a pulsar’s magnetosphere. They showed that, the electrostatic field exponentially amplifies, by means of the relativistic centrifugal force. As a result, the field approaches to Schwinger limit¹, leading to pair creation process in the light cylinder (LC) area². Their study recently appeared in Arxiv.

In 1969, Thomas Gold suggested that, since pulsars are rotating neutron stars, centrifugal effects might be very important. This is because, these can energise the pulsar’s magnetospheric particles to energies enough for producing high energy electromagnetic radiation.

Later, it has been shown by Z. Osmanov and colleagues that the centrifugal force in the LC area is different for different species of particles (magnetospheric electrons and positrons). This in turn, might lead to charge separation creating the Langmuir waves. On the other hand, since the centrifugal force is time dependent, it acts as a parameter, amplifying the electrostatic field, and after it inevitably reach the Schwinger limit, it results in a pair production process.

Now, Z. Osmanov and his collaborators, studied this completely new mechanism of pair creation in the pulsar magnetosphere.

“We consider the normal period pulsars and study the possibility of pair production by means of the centrifugally driven electrostatic fields.”, told Z. Osmanov, professor at Free University of Tbilisi and lead author of the study.

Considering the typical pulsar parameters they showed that the electric field exponentially increases and gradually reaches the Schwinger limit, when efficient pair creation might occur.

They also analysed constraints imposed on the process and found that the process is so efficient that the number density of electron-positron pairs exceeds the Goldreich-Julian density by five orders of magnitude.

In addition, it has been shown that, this novel mechanism of pair production not only changes the number density of electron-positron plasmas in pulsar’s magnetospheres but also, it significantly influences the physical processes there. In particular, it is evident that the processes of particle acceleration strongly depends on the plasma density.

Finally, they showed that, the emission spectral pattern will be influenced as well by the efficient pair creation. This in turn, might give rise to coherent radio emission, which seems to be quite promising in the light of modern enigma – fast radio bursts.

“Since all these problems are beyond the intended scope of the paper we are going to consider them very soon.”, concluded authors of the study.

1) Schwinger limit is a scale above which the electrostatic field is expected to become nonlinear.
2) Light Cylinder area is a hypothetical area where the linear velocity of rotation coincides with the speed of light.

Reference: Z. Osmanov, G. Machabeli, N. Chkheidze, “The novel mechanism of pair creation in pulsar magnetospheres”, Arxiv, pp. 1-5, 2021.

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Milky Way Not Unusual, Astronomers Find (Cosmology)

Detailed cross-section of another galaxy reveals surprising similarities to our home

The first detailed cross-section of a galaxy broadly similar to the Milky Way, published today, reveals that our galaxy evolved gradually, instead of being the result of a violent mash-up. The finding throws the origin story of our home into doubt.

The galaxy, dubbed UGC 10738, turns out to have distinct ‘thick’ and ‘thin’ discs similar to those of the Milky Way. This suggests, contrary to previous theories, that such structures are not the result of a rare long-ago collision with a smaller galaxy. They appear to be the product of more peaceful change.

And that is a game-changer. It means that our spiral galaxy home isn’t the product of a freak accident. Instead, it is typical.

The finding was made by a team led by Nicholas Scott and Jesse van de Sande, from Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and the University of Sydney.

“Our observations indicate that the Milky Way’s thin and thick discs didn’t come about because of a gigantic mash-up, but a sort-of ‘default’ path of galaxy formation and evolution,” said Dr Scott.

“From these results we think galaxies with the Milky Way’s particular structures and properties could be described as the ‘normal’ ones.”

This conclusion – published in The Astrophysical Journal Letters– has two profound implications.

“It was thought that the Milky Way’s thin and thick discs formed after a rare violent merger, and so probably wouldn’t be found in other spiral galaxies,” said Dr Scott.

“Our research shows that’s probably wrong, and it evolved ‘naturally’ without catastrophic interventions. This means Milky Way-type galaxies are probably very common.

“It also means we can use existing very detailed observations of the Milky Way as tools to better analyse much more distant galaxies which, for obvious reasons, we can’t see as well.”

The research shows that UGC 10738, like the Milky Way, has a thick disc consisting mainly of ancient stars – identified by their low ratio of iron to hydrogen and helium. Its thin disc stars are more recent and contain more metal.

(The Sun is a thin disc star and comprises about 1.5% elements heavier than helium. Thick disc stars have three to 10 times less.)

Although such discs have been previously observed in other galaxies, it was impossible to tell whether they hosted the same type of star distribution – and therefore similar origins. Scott, van de Sande and colleagues solved this problem by using the European Southern Observatory’s Very Large Telescope in Chile to observe UGC 10738, situated 320 million light years away.

The galaxy is angled “edge on”, so looking at it offered effectively a cross-section of its structure.

“Using an instrument called the multi-unit spectroscopic explorer, or MUSE, we were able to assess the metal ratios of the stars in its thick and thin discs,” explained Dr van de Sande.

“They were pretty much the same as those in the Milky Way – ancient stars in the thick disc, younger stars in the thin one. We’re looking at some other galaxies to make sure, but that’s pretty strong evidence that the two galaxies evolved in the same way.”

Dr Scott said UGC 10738’s edge-on orientation meant it was simple to see which type of stars were in each disc.

“It’s a bit like telling apart short people from tall people,” he said. “It you try to do it from overhead it’s impossible, but it if you look from the side it’s relatively easy.”

Co-author Professor Ken Freeman from the Australian National University said, “This is an important step forward in understanding how disk galaxies assembled long ago. We know a lot about how the Milky Way formed, but there was always the worry that the Milky Way is not a typical spiral galaxy. Now we can see that the Milky Way’s formation is fairly typical of how other disk galaxies were assembled”.

ASTRO 3D director, Professor Lisa Kewley, added: “This work shows how the Milky Way fits into the much bigger puzzle of how spiral galaxies formed across 13 billion years of cosmic time.”

Other co-authors are based at Macquarie University in Australia and Germany’s Max-Planck-Institut fur Extraterrestrische Physik.

Featured image: Galaxy UGC 10738, seen edge-on through the European Southern Observatory’s Very Large Telescope in Chile, revealing distinct thick and thin discs. © Jesse van de Sande/European Southern Observatory

Reference: Nicholas Scott, Jesse van de Sande et al., “Identification of an [α/Fe]—Enhanced Thick Disk Component in an Edge-on Milky Way Analog”, The Astrophysical Journal Letters, 913(1), 2021. Link to paper

Provided by ASTRO-3D

36 Dwarf Galaxies Had Simultaneous “Baby Boom” of New Stars (Cosmology)

Surprising finding challenges current theories on how galaxies grow

Three dozen dwarf galaxies far from each other had a simultaneous “baby boom” of new stars, an unexpected discovery that challenges current theories on how galaxies grow and may enhance our understanding of the universe.

Galaxies more than 1 million light-years apart should have completely independent lives in terms of when they give birth to new stars. But galaxies separated by up to 13 million light-years slowed down and then simultaneously accelerated their birth rate of stars, according to a Rutgers-led study published in the Astrophysical Journal.

“It appears that these galaxies are responding to a large-scale change in their environment in the same way a good economy can spur a baby boom,” said lead author Charlotte Olsen, a doctoral student in the Department of Physics and Astronomy in the School of Arts and Sciences at Rutgers University–New Brunswick.

“We found that regardless of whether these galaxies were next-door neighbors or not, they stopped and then started forming new stars at the same time, as if they’d all influenced each other through some extra-galactic social network,” said co-author Eric Gawiser, a professor in the Department of Physics and Astronomy.

Rutgers’ unexpected discovery challenges current theories on how galaxies grow and may enhance our understanding of the universe. © Rutgers University-New Brunswick

The simultaneous decrease in the stellar birth rate in the 36 dwarf galaxies began 6 billion years ago, and the increase began 3 billion years ago. Understanding how galaxies evolve requires untangling the many processes that affect them over their lifetimes (billions of years). Star formation is one of the most fundamental processes. The stellar birth rate can increase when galaxies collide or interact, and galaxies can stop making new stars if the gas (mostly hydrogen) that makes stars is lost.

Star formation histories can paint a rich record of environmental conditions as a galaxy “grew up.” Dwarf galaxies are the most common but least massive type of galaxies in the universe, and they are especially sensitive to the effects of their surrounding environment.

The 36 dwarf galaxies included a diverse array of environments at distances as far as 13 million light-years from the Milky Way. The environmental change the galaxies apparently responded to must be something that distributes fuel for galaxies very far apart. That could mean encountering a huge cloud of gas, for example, or a phenomenon in the universe we don’t yet know about, according to Olsen.

The scientists used two methods to compare star formation histories. One uses light from individual stars within galaxies; the other uses the light of a whole galaxy, including a broad range of colors.

“The full impact of the discovery is not yet known as it remains to be seen how much our current models of galaxy growth need to be modified to understand this surprise,” Gawiser said. “If the result cannot be explained within our current understanding of cosmology, that would be a huge implication, but we have to give the theorists a chance to read our paper and respond with their own research advances.”

“The James Webb Space Telescope, scheduled to be launched by NASA this October, will be the ideal way to add that new data to find out just how far outwards from the Milky Way this ‘baby boom’ extended,” Olsen added.

Rutgers co-authors include Professor Kristen B. W. McQuinnGrace Telford, a postdoctoral associate; and Adam Broussard, a doctoral student. Scientists at the University of Toronto, the Harvard-Smithsonian Center for Astrophysics, Johns Hopkins University and NASA’s Goddard Space Flight Center contributed to the study.

Featured image: The Milky Way-like galaxy NGC 1232 (center) shows the Milky Way’s location and relative size. Images of dwarf galaxies are centered close to their true locations but have been magnified for visibility. Credit: Charlotte Olsen

Reference: Charlotte Olsen, Eric Gawiser et al., “Star Formation Histories from Spectral Energy Distributions and Color–magnitude Diagrams Agree: Evidence for Synchronized Star Formation in Local Volume Dwarf Galaxies over the Past 3 Gyr”, Astrophysical Journal, 913(1), 2021.

Provided by Rutgers University

Plasma Jets Reveal Magnetic Fields Far, Far Away (Cosmology)

Radio telescope images enable a new way to study magnetic fields in galaxy clusters millions of light years away.

For the first time, researchers have observed plasma jets interacting with magnetic fields in a massive galaxy cluster 600 million light years away, thanks to the help of radio telescopes and supercomputer simulations. The findings, published in the journal Nature, can help clarify how such galaxy clusters evolve.

Galaxy clusters can contain up to thousands of galaxies bound together by gravity. Abell 3376 is a huge cluster forming as a result of a violent collision between two sub-clusters of galaxies. Very little is known about the magnetic fields that exist within this and similar galaxy clusters.

“It is generally difficult to directly examine the structure of intracluster magnetic fields,” says Nagoya University astrophysicist Tsutomu Takeuchi, who was involved in the research. “Our results clearly demonstrate how long-wavelength radio observations can help explore this interaction.”

An international team of scientists have been using the MeerKAT radio telescope in the Northern Cape of South Africa to learn more about Abell 3376’s huge magnetic fields. One of the telescope’s very high-resolution images revealed something unexpected: plasma jets emitted by a supermassive black hole in the cluster bend to form a unique T-shape as they extend outwards for distances as far as 326,156 light years away. The black hole is in galaxy MRC 0600-399, which is near the centre of Abell 3376.

The team combined their MeerKAT radio telescope data with X-ray data from the European Space Agency’s space telescope XXM-Newton to find that the plasma jet bend occurs at the boundary of the subcluster in which MRC 0600-399 exists.

“This told us that the plasma jets from MRC 0600-399 were interacting with something in the heated gas, called the intracluster medium, that exists between the galaxies within Abell 3376,” explains Takeuchi.

To figure out what was happening, the team conducted 3D ‘magnetohydrodynamic’ simulations using the world’s most powerful supercomputer in the field of astronomical calculations, ATERUI II, located at the National Astronomical Observatory of Japan.

The simulations showed that the jet streams emitted by MRC 0600-399’s black hole eventually reach and interact with magnetic fields at the border of the galaxy subcluster. The jet stream compresses the magnetic field lines and moves along them, forming the characteristic T-shape.

“This is the first discovery of an interaction between cluster galaxy plasma jets and intracluster magnetic fields,” says Takeuchi.

An international team has just begun construction of what is planned to be the world’s largest radio telescope, called the Square Kilometre Array (SKA).

“New facilities like the SKA are expected to reveal the roles and origins of cosmic magnetism and even to help us understand how the universe evolved,” says Takeuchi. “Our study is a good example of the power of radio observation, one of the last frontiers in astronomy.”

The study, “Jets from MRC 0600-399 bent by magnetic fields in the cluster Abell 3376,” was published in the journal Nature on May 5, 2021, at


James O. Chibueze, Haruka Sakemi, Takumi Ohmura, Mami Machida, Hiroki Akamatsu, Takuya Akahori, Hiroyuki Nakanishi, Viral Parekh, Ruby van Rooyen, and Tsutomu T. Takeuchi*  (* Graduate School of Science, Nagoya University)

Video (Credit: Takumi Ohmura, Mami Machida, Hirotaka Nakayama, 4D2U Project, NAOJ)

Featured image: A black hole (marked by the red x) at the centre of galaxy MRC 0600-399 emits a jet of particles that bends into a ‘double-scythe’ T-shape that follows the magnetic field lines at the galaxy subcluster’s boundary. (Image Credit: Modified from Chibueze, Sakemi, Ohmura et al. (2021) Nature Fig. 1(b))

Provided by Nagoya University

Astronomers Presented An Algorithm Which Computes N-point Correlation Functions Faster Than Any (Cosmology / Instrumentation)

Ever wanted to do cosmology from the four-point or the five-point function? Oliver Philcox and colleagues introduced a new estimator which computes the N-point galaxy correlation functions of Ng galaxies in O(Ng^2) time, *far* faster than the naive O(Ng^N) scaling!

𝑁-point correlation functions (NPCFs), or their Fourier-space counterparts, the polyspectra, are amongst the most powerful tools in the survey analyst’s workshop. These encode the statistical properties of the galaxy overdensity field at sets of 𝑁 positions, and may be compared to data to give constraints on properties such as the Universe’s expansion rate and composition.

Most inflationary theories predict density fluctuations in the early Universe to follow Gaussian statistics; in this case all the information is contained within the two-point correlation function (2PCF), or, equivalently, the power spectrum. For a homogeneous and isotropic Universe, both are simple functions of one variable, and have been the subject of almost all galaxy survey analyses to date.

The late-time Universe is far from Gaussian. Statistics beyond the 2PCF are of importance since the bulk motion of matter in structure formation causes a cascade of information from the 2PCF to higher-order statistics, such as the three- and four-point functions (3PCF and 4PCF).

“Correlation functions form the cornerstone of modern cosmology, and their efficient computation is a task of utmost importance for the analysis of current and future galaxy surveys.”

Now, Oliver Philcox and colleagues presented a new estimator/algorithm for efficiently computing the N-point galaxy correlation functions of Ng galaxies in O(Ng^2) time, *far* faster than the naive O(Ng^N) scaling!

By decomposing the N-point correlation function (NPCF) into an angular basis composed of products of spherical harmonics, the estimator becomes *separable* in r1, r2, r3, etc. It can be computed as a weighted sum of *pairs* of galaxies, for any N.

© Oliver Philcox et al

The algorithm is included in their new code *encore*:

It is written in C++ and computes the 3PCF, 4PCF, 5 PCF and 6 PCF of a BOSS-like galaxy survey in ~ 100 CPU-hours, including applying corrections for the non-uniform survey geometry. It can also be run on a GPU!

Whilst the complexity is technically O(Ng^2), for N>3, they practically found computation-time to scale *linearly* with the number of galaxies unless the density is very large! Below figure is the measurement of a few 5PCF components:

© Oliver Philcox et al.

This will allow future surveys like Euclid, DESI, and Roman to include higher-point functions in their analyses, giving sharper constraints on cosmological parameters, and testing new physics such as parity-violation!

Featured image: Strong scaling of the encore code: dependence of runtime, 𝑇 , on the number of CPU cores on a single node for different test cases. Dashed lines indicate linear relationships, and are calibrated at the single-CPU time © Philcox et al.

Reference: Oliver H. E. Philcox, Zachary Slepian, Jiamin Hou, Craig Warner, Robert N. Cahn, Daniel J. Eisenstein, “ENCORE: Estimating Galaxy N-point Correlation Functions in O(N2g) Time”, Arxiv, pp. 1-24, 2021.

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The Galaxy That Wags Its Tail (Cosmology)

It has a tail long two and a half million light years – twice as long as previously thought – and it even seems to “wag” one of the most massive galaxies at the center of the cluster Abell 1775, almost a billion light years away from us. This was discovered by an international team that includes several INAF researchers by analyzing images collected with the European Lofar radio telescope and NASA’s Chandra X-ray satellite.

The Galaxy clusters are the most massive structures in the universe. They enclose hundreds to thousands of galaxies bound together by the force of gravity. These orbit inside clusters with remarkable speed, so much so that they can move even thousands of kilometers in a single second. The space in which galaxies make their orbits is permeated by an extremely rarefied gas that reaches temperatures of tens or even hundreds of millions of degrees and extends for tens of millions of light years.

To study the gas that pervades the clusters of galaxies, astronomers have to resort to satellites that scan the sky in high energy, particularly in X-rays , a radiation that is absorbed by the Earth’s atmosphere. These observations reveal important information not only about clusters of galaxies but also about the formation of some strange sources recently discovered by analyzing these objects on the opposite side of the electromagnetic spectrum, in the radio band .

An international team of researchers combined observations in these two bands to study the Abell 1775 galaxy cluster , uncovering previously unseen details in this system that is just under a billion light-years from Earth. In the radio band, the group used data from three different radio telescopes including Lofar ( Low Frequency Array ), a large instrument made up of thousands of antennas distributed in the Netherlands and several European countries, managed by the Dutch Astron institute together with a international consortium which also includes the National Institute of Astrophysics. In X-rays, they pointed NASA’s Chandra satellite continuously for over a day at the cluster.

In the past, radio observations had revealed one of Abell 1775’s most spectacular phenomena: the presence of a particular galaxy , with a morphology that astronomers call ” head-tail “. This galaxy is one of the fastest in the cluster and hosts an “active” black hole at its center , which swallows the surrounding matter at a sustained rate and at the same time expels a part of it in the form of jets with strong radio band emission. Due to the galaxy’s high speed and the pressure exerted on it by the surrounding hot gas, these jets “bend” near the black hole, forming the “tail”, which is a very long trail of electrons and magnetic fields.

“In this study we found that the tail of this galaxy in the Abell 1775 cluster has an extension of about 2.5 million light years, one of the largest ever observed, and double that of past observations,” he explains. Andrea Botteon , researcher at the University of Leiden, in the Netherlands, and associate Inaf, first author of the article describing the results, published in the journal Astronomy & Astrophysics . “This discovery was made possible especially thanks to Lofar who, scanning the radio sky at wavelengths of about two meters, is sensitive to the radiation emitted in the region farthest from the ‘head’, where the black hole that generates the radio jets ».

The hot gas at the center of the Abell 1775 galaxy cluster observed in the X-band with the Chandra satellite. Note the mushroom structure, the density jump and the spiral structure of the gas. Credits: Nasa / Chandra / Botteon et al. 2021

The astronomers then realized that the tail region revealed by the new observations arises near a point where the trail of electrons and magnetic fields seems to break. This is where the tail changes direction slightly , as if the galaxy is “wagging its tail”.

“By analyzing Chandra’s X-ray data, we found that this transition point coincides with a region where the hot gas has a sharp change in density, and we believe that this is precisely the cause of its tail wagging,” adds Fabio Gastaldello , researcher Inaf in Milan and co-author of the study. “We think that the density jump is due to the gas motions inside Abell 1775, also highlighted by a ‘mushroom’ structure and a gas spiral in the center of the cluster, which we were able to bring out using particular techniques for processing the images”.

According to the new study, the movements of the hot gas inside the cluster would be responsible for the formation of other structures discovered by observing Abell 1775 in the radio band, such as the two filaments that are located near the head-tail galaxy. The large amount of data collected with two powerful tools such as Lofar and Chandra also allowed researchers to study in great detail the phenomena that contribute to accelerating electrons both in the tail of this galaxy and in the central region of the cluster.

“Lofar, with its very high sensitivity and angular resolution at frequencies of the order of one hundred MHz, is contributing substantially to our understanding of radio emission from galaxies and galaxy clusters”, comments co-author Tiziana Venturi , director of the Institute of Radioastronomy of INAF in Bologna. «Italy immediately saw the revolutionary potential of this instrument, and it has been part of the Lofar consortium for years. Soon a station of this radio telescope will be built at the Medicine Radio Astronomy Station and will be part of what is known as the International Lofar Telescope ».

Featured image: The radio emission from the huge “head-to-tail” galaxy at the center of the Abell 1775 cluster, observed by Lofar (in red) and superimposed on an optical band image. Credits: Lofar / Pan-Starrs / Botteon et al. 2021

To know more:

Provided by INAF

ALMA Discovers the Most Ancient Galaxy with Spiral Morphology (Cosmology)

Analyzing data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), researchers found a galaxy with a spiral morphology by only 1.4 billion years after the Big Bang. This is the most ancient galaxy of its kind ever observed. The discovery of a galaxy with a spiral structure at such an early stage is an important clue to solving the classic questions of astronomy: “How and when did spiral galaxies form?”

“I was excited because I had never seen such clear evidence of a rotating disk, spiral structure, and centralized mass structure in a distant galaxy in any previous literature,” says Takafumi Tsukui, a graduate student at SOKENDAI and the lead author of the research paper published in the journal Science. “The quality of the ALMA data was so good that I was able to see so much detail that I thought it was a nearby galaxy.”

The Milky Way Galaxy, where we live, is a spiral galaxy. Spiral galaxies are fundamental objects in the Universe, accounting for as much as 70% of the total number of galaxies. However, other studies have shown that the proportion of spiral galaxies declines rapidly as we look back through the history of the Universe. So, when were the spiral galaxies formed?

Tsukui and his supervisor Satoru Iguchi, a professor at SOKENDAI and the National Astronomical Observatory of Japan, noticed a galaxy called BRI 1335-0417 in the ALMA Science Archive. The galaxy existed 12.4 billion years ago [1] and contained a large amount of dust, which obscures the starlight. This makes it difficult to study this galaxy in detail with visible light. On the other hand, ALMA can detect radio emissions from carbon ions in the galaxy, which enables us to investigate what is going on in the galaxy.

The researchers found a spiral structure extending about 15,000 light-years from the center of the galaxy. This is one third of the size of the Milky Way Galaxy. The estimated total mass of the stars and interstellar matter in BRI 1335-0417 is roughly equal to that of the Milky Way.

“As BRI 1335-0417 is a very distant object, we might not be able to see the true edge of the galaxy in this observation,” comments Tsukui. “For a galaxy that existed in the early Universe, BRI 1335-0417 was a giant.”

Then the question becomes, how was this distinct spiral structure formed in only 1.4 billion years after the Big Bang? The researchers considered multiple possible causes and suggested that it could be due to an interaction with a small galaxy. BRI 1335-0417 is actively forming stars and the researchers found that the gas in the outer part of the galaxy is gravitationally unstable, which is conducive to star formation. This situation is likely to occur when a large amount of gas is supplied from outside, possibly due to collisions with smaller galaxies.

Video: Supercomputer simulation of spiral galaxy formation. Over a period of about 13.5 billion years, small galaxies merge one after another into a single giant spiral galaxy. Please note that this video was created in 2007 and is not a reproduction of the current study.
Credit: Takaaki Takeda, Sorahiko Nukatani, Takayuki Saito, 4D2U Project, NAOJ

The fate of BRI 1335-0417 is also shrouded in mystery. Galaxies that contain large amounts of dust and actively produce stars in the ancient Universe are thought to be the ancestors of the giant elliptical galaxies in the present Universe. In that case, BRI 1335-0417 changes its shape from a disk galaxy to an elliptical one in the future. Or, contrary to the conventional view, the galaxy may remain a spiral galaxy for a long time. BRI 1335-0417 will play an important role in the study of galaxy shape evolution over the long history of the Universe.

“Our Solar System is located in one of the spiral arms of the Milky Way,” explains Iguchi. “Tracing the roots of spiral structure will provide us with clues to the environment in which the Solar System was born. I hope that this research will further advance our understanding of the formation history of galaxies.”

Featured image: ALMA image of the galaxy BRI 1335-0417 at 12.4 billion years ago. ALMA detected emissions from carbon ions in the galaxy. Spiral arms are visible on both sides of the compact, bright area in the center of the galaxy.
Credit: ALMA (ESO/NAOJ/NRAO), T. Tsukui & S. Iguchi

Paper Information
These research results are presented in T. Tsukui & S. Iguchi “Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago” published online by the journal Science on THURSDAY, 20 May, 2021.

[1]The redshift of this object is z=4.41. Using the cosmological parameters measured with Planck (H0=67.3km/s/Mpc, Ωm=0.315, Λ=0.685: Planck 2013 Results), we can calculate the distance to the object to be 12.4 billion light-years. (Please refer to “Expressing the distance to remote objects” for the details.) 

Provided by ALMA

How Primordial Black Hole Forms? (Quantum / Cosmology)

Michael Baker and colleagues discussed the new mechanism of formation of primordial black holes (PBH’s) during a first-order phase transition in the early Universe. Their study recently appeared in Arxiv.

Primordial black holes are a hypothetical type of black hole that formed soon after the Big Bang. There are several possible formation mechanisms of primordial black holes (PBH’s): the most widely studied is collapse of density perturbations generated during inflation, while the collapse of topological defects, the dynamics of scalar condensates, or collisions of bubble walls during a first-order phase transition are viable alternatives.

Now, Michael Baker and colleagues, proposed a new mechanism of PBH production during a first-order cosmological phase transition.

“While previous papers on this topic have only considered the energy density stored in the bubble wall, we focused on a population of particles that interact with the bubble wall and showed that during a first-order phase transition, the energy density of the reflected particles can reach sufficient densities to trigger collapse into PBHs.”

— wrote M. Baker and his collaborators

They considered a particle species that interact/collides with the bubble wall. The mass of these particles may increase significantly during phase transitions due to either confinement or a Higgs mechanism. High-momentum particles can pass through the bubble wall into the true vacuum and gain a large mass, while low-momentum χ particles are reflected due to energy conservation (as shown in fig 1 below). The build-up of reflected particles (in front of the walls) creates a density perturbation which may lead to PBH formation.

(article continues below image)

A cartoon picture of the late stage of a first-order cosmological phase transition: regions of true vacuum (blue) are expanding with speed vw and coalescing, leaving an approximately spherical bubble of false vacuum (light red). High-momentum χ particles can pass through the bubble wall into the true vacuum and gain a large mass, while low-momentum χ particles are reflected due to energy conservation. The build-up of χ particles creates a density perturbation which may lead to PBH formation. The local coordinate system is also shown, along with the bubble wall thickness, lw. © M. Baker et al.

They track this process quantitatively by solving a Boltzmann equation, and demonstrated that the mass and density of the PBHs depend on the temperature at which the phase transition occurs and the probability that a black hole will form in a given volume.

Reference: Michael J. Baker, Moritz Breitbach, Joachim Kopp, Lukas Mittnacht, “Primordial Black Holes from First-Order Cosmological Phase Transitions”, Arxiv, pp. 1-7, 2021.

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Are We Boltzmann Brains? Which Processes Can Prevent Boltzmann Brains Domination In Future? (Cosmology / Quantum)

So say you’ve got a universe and there’s a kinda empty chunk of it. No planets, no big dust clouds… it’s pretty boring and could be considered “empty”. A few seconds later, there’s just a human brain floating there, in the middle of the space. Of course, like any human brain, it’s got no access to anything it needs to survive, so it stops working immediately.

The main idea is that it’s more likely for a human brain — complete with memories from an entire lifetime — to spawn in the middle of space than it is for science to develop the way it did. That’s the Boltzmann brain theory.

Where This Wacky Idea Exactly Came From?

The idea originated from an argument between physicists (like there aren’t a ton of those!) about the likelihood that science would evolve in the very specific way it did. The theory came (more specifically) from a reductio ad absurdum on Ludwig Boltzmann’s published paper that tried to explain reasons for low entropy in the universe.

According to this paper, while the entropy of a system (its measure of disorder always increases (moving towards disorder), there is some tiny possibility that a fluctuation can bring a system from disorder to order. Thus, it would decrease its entropy, moving it further away from equilibrium.

From the physicists work it follows that, theoretically, after a given period of thousands of years, atoms will come together and randomly form a human brain in the middle of space. This would happen due to random fluctuations that come from thermodynamic equilibrium. Since then, there has been debate on the topic between physicists whether, “we are Boltzmann brains or not”.

How it forms?

After thinking about the possibility of Boltzmann Brains, it turns out that there are actually two options which could result in the creation of a Boltzmann Brain:

  • Through nucleation. This would work if the current, observable universe isn’t a Minkowski space but is instead a de Sitter universe (the difference is the de Sitter is just a cosmological solution to the Einstein theory of relativity, the Minkowski is a combination of the three dimensional Euclidean space and four dimensional manifold).
  • Through quantum fluctuation. This would require a Minkowski vaccuum to occur, and it would simply play upon the idea of quantum fluctuation providing small amounts of energy to isolated activity. Through this random fluctuation of quantum energy, eventually by chance it would be put into the creation of a Boltzmann brain.

We focus completely on “creation of Boltzmann brain through nucleation” and by considering recent study of Ken Olum and colleagues, we are going to discuss why, “we are Boltzmann brains” is a nonsensical conclusion and what actually prevents Boltzmann brains domination in future!

If the dark energy is playing role in expansion of our universe, it will expand forever and will soon approach de Sitter space. So, there’s a possibility that Boltzmann brains can infinitely outnumber ordinary humans, and for this reason, you can’t say that, we are Boltzmann brains.

“Believing that we are Boltzmann brains is a nonsensical conclusion because our observation on which we base this conclusion would have no connection to the actual universe in which we live”, wrote Olum and his collaborators.

But, there is a possibility that, ordinary observers may dominate Boltzmann brains. If we want to know, what to expect in such situations, we need a procedure to regulate infinities and produce a sensible probability distribution. Thus, for this purpose, K. Olum and colleagues adopted scale factor cutoff measure. In this measure, the ratio of Boltzmann brains to ordinary observers in a given vacuum is roughly given by the ratio of the Boltzmann brain nucleation rate to the total decay rate of that vacuum.

“In the scale factor measure, this disaster is avoided when the rate of Boltzmann brain nucleation is smaller than the vaccum decay rate in each vaccum”, wrote Olum and his collaborators.

They found that there are two processes that are not always considered that influence the vacuum decay rate, thereby, preventing Boltzmann brain domination.

The first is the nucleation of small black holes. This process removes volume from the vacuum, and so contributes to total decay rate of vaccum.

“The rate is largest for the smallest black holes. It is always larger than the Boltzmann brain nucleation rate, if the minimum Boltzmann brain mass is larger than the Planck mass. Thus, we should not expect to be Boltzmann brains”, wrote Olum and his collaborators.

The other process is the nucleation of small regions of higher-energy inflating false vacuum. If vacua of high enough energies exist, this process also would prevent Boltzmann brain domination.

“It would be interesting to apply the considerations of our paper to the multiverse models like the one proposed by Vilenkin and colleagues, in which eternal inflation driven by inflating domain walls may still be possible..”, concluded authors of the study.

Reference: Ken D. Olum, Param Upadhyay, and Alexander Vilenkin, “Black holes and up-tunneling suppress Boltzmann brains” Arxiv, 2021.

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