New Theory of Gravity Might Explain Dark Matter

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by invoking dark matter. Prof. Erik Verlinde, renowned expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, published a new research paper today in which he expands his groundbreaking views on the nature of gravity.

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In 2010, Erik Verlinde surprised the world with a completely new theory of gravity. According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.

Newton’s law from information

In his 2010 article (On the origin of gravity and the laws of Newton), Verlinde showed how Newton’s famous second law, which describes how apples fall from trees and satellites stay in orbit, can be derived from these underlying microscopic building blocks. Extending his previous work and work done by others, Verlinde now shows how to understand the curious behaviour of stars in galaxies without adding the puzzling dark matter.

The outer regions of galaxies, like our own Milky Way, rotate much faster around the centre than can be accounted for by the quantity of ordinary matter like stars, planets and interstellar gasses. Something else has to produce the required amount of gravitational force, so physicists proposed the existence of dark matter. Dark matter seems to dominate our universe, comprising more than 80 percent of all matter. Hitherto, the alleged dark matter particles have never been observed, despite many efforts to detect them.

No need for dark matter

According to Erik Verlinde, there is no need to add a mysterious dark matter particle to the theory. In a new paper, which appeared today on the ArXiv preprint server, Verlinde shows how his theory of gravity accurately predicts the velocities by which the stars rotate around the center of the Milky Way, as well as the motion of stars inside other galaxies.

“We have evidence that this new view of gravity actually agrees with the observations, ” says Verlinde. “At large scales, it seems, gravity just doesn’t behave the way Einstein’s theory predicts.”

At first glance, Verlinde’s theory presents features similar to modified theories of gravity like MOND (modified Newtonian Dynamics, Mordehai Milgrom (1983)). However, where MOND tunes the theory to match the observations, Verlinde’s theory starts from first principles. “A totally different starting point,” according to Verlinde.

Adapting the holographic principle

One of the ingredients in Verlinde’s theory is an adaptation of the holographic principle, introduced by his tutor Gerard ‘t Hooft (Nobel Prize 1999, Utrecht University) and Leonard Susskind (Stanford University). According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct – part of the information in our universe is contained in space itself.

This extra information is required to describe that other dark component of the universe: Dark energy, which is believed to be responsible for the accelerated expansion of the universe. Investigating the effects of this additional information on ordinary matter, Verlinde comes to a stunning conclusion. Whereas ordinary gravity can be encoded using the information on the imaginary sphere around the universe, as he showed in his 2010 work, the result of the additional information in the bulk of space is a force that nicely matches that attributed to dark matter.

On the brink of a scientific revolution

Gravity is in dire need of new approaches like the one by Verlinde, since it doesn’t combine well with quantum physics. Both theories, crown jewels of 20th century physics, cannot be true at the same time. The problems arise in extreme conditions: near black holes, or during the Big Bang. Verlinde says, “Many theoretical physicists like me are working on a revision of the theory, and some major advancements have been made. We might be standing on the brink of a new scientific revolution that will radically change our views on the very nature of space, time and gravity.”

Realistic Solar Corona Loops Simulated In Lab

Caltech applied physicists have experimentally simulated the Sun’s magnetic fields to create a realistic coronal loop in a lab.

solar-loop

Coronal loops are arches of plasma that erupt from the surface of the Sun following along magnetic field lines. Because plasma is an ionized gas—that is, a gas of free-flowing electrons and ions—it is an excellent conductor of electricity. As such, solar corona loops are guided and shaped by the Sun’s magnetic field.

The Earth’s magnetic field acts as a shield that protects humans from the strong X-rays and energized particles emitted by the eruptions, but communications satellites orbit outside this shield field and therefore remain vulnerable. In March 1989, a particularly large flare unleashed a blast of charged particles that temporarily knocked out one of the National Oceanic and Atmospheric Administration’s geostationary operational environmental satellites that monitor the earth’s weather; caused a sensor problem on the space shuttle Discovery; and tripped circuit breakers on Hydro-Québec’s power grid, which caused a major blackout in the province of Quebec, Canada, for nine hours.

“This potential for causing havoc—which only increases the more humanity relies on satellites for communications, weather forecasting, and keeping track of resources—makes understanding how these solar events work critically important,” says Paul Bellan, professor of applied physics in the Division of Engineering and Applied Science.

Although simulated coronal loops have been created in labs before, this latest attempt incorporated a magnetic strapping field that binds the loop to the Sun’s surface. Think of a strapping field like the metal hoops on the outside of a wooden barrel. While the slats of the barrel are continually under pressure pushing outward, the metal hoops sit perpendicularly to the slats and hold the barrel together.

The strength of this strapping field diminishes with distance from the Sun. This means that when close to the solar surface, the loops are clamped down tightly by the strapping field but then can break loose and blast away if they rise to a certain altitude where the strapping field is weaker. These eruptions are known as solar flares and coronal mass ejections (CMEs).

CMEs are rope-like discharges of hot plasma that accelerate away from the Sun’s surface at speeds of more than a million miles per hour. These eruptions are capable of releasing energy equivalent to 1 billion megatons of TNT, making them potentially the most powerful explosions in the solar system. (CMEs are not to be confused with solar flares, which often occur as part of the same event. Solar flares are bursts of light and energy, while CMEs are blasts of particles embedded in a magnetic field.)

The simulated loops and strapping fields provide new insight into how energy is stored in the solar corona and then released suddenly. Bellan worked with Caltech graduate student Bao Ha (MS ’10, PhD ’16) to create the strapping field and coronal loop. The results of their experiments were published in the journal Geophysical Research Letters on September 17, 2016.

Bellan and his colleagues have been working on laboratory-scale simulations of solar corona phenomena for two decades. In the lab, the team generates ropes of plasma in a 1.5-meter-long vacuum chamber.

“Studying coronal mass ejections is challenging, since humans do not know how and when the Sun will erupt. But laboratory experiments permit the control of eruption parameters and enable the systematic explorations of eruption dynamics,” says Ha, lead author of the GRL paper. “While experiments with the same eruption parameters are easily reproducible, the loop dynamics vary depending on the configuration of the strapping magnetic field.”

Simulating a strapping field with strength that fades over the relatively short length of the vacuum chamber proved difficult, Bellan says. In order to make it work, Ha and Bellan had to engineer electromagnetic coils that produce the strapping field inside the chamber itself.

After more than three years of design, fabrication, and testing, Bellan and Ha were able to create a strapping field that peaks in strength about 10 centimeters away from where the plasma loop forms, then dies off a short distance farther down the vacuum chamber.

The arrangement allows Bellan and Ha to watch the plasma loop slowly grow in size, then reach a critical point and fire off to the far end of the chamber.

Next, Bellan plans to measure the magnetic field inside the erupting loop and also study the waves that are emitted when plasmas break apart.

Russian Scientists Use Cosmic Rays to Forecast Hurricanes

Scientists from the National Research Nuclear University MEPhI (Russia) appear to have found a way to better predict hurricanes by measuring changes in the atmosphere which precede giant atmospheric vortexes with air pressure subsiding to the center with very high speed of the airflow.

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This can now be done with the use of a ‘muon hodoscope’. Muons are a byproduct of cosmic rays particles. A hodoscope is a type of detector commonly used in particle physics that make use of an array of detectors to determine the trajectory of an energetic particle – in this case cosmic rays.

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Lead researcher Professor Igor Yashin of Moscow Engineering Physics Institute states: “The hurricane muon hodoscope is able to observe and analyze – on a real-time basis, modulations of the flow of secondary cosmic rays on the Earth’s surface provoked by processes in the heliosphere, magnetosphere and atmosphere of Earth. The uniqueness of our hodoscope is that in the real-time mode, it allows reconstruction of each muon’s track and obtaining muonographs.

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It is hard to overstate the necessity of precise hurricane forecasting. Before artificial satellites, the only way to track hurricanes was via airplanes flying above the cyclones. But even today, satellites can’t provide comprehensive information. For example, they can’t detect the inner barometric pressure of the hurricane or the exact wind speed. Moreover, thick clouds obscure nascent cyclones from satellites. Despite the availability of satellite systems, sensors, and radars, aviation still plays an important role in forecasting.

cosmic-ray-muon-hodoscope

According to scientists, the new hodoscope provides precise forecasts. To watch the atmosphere over Russia, which spans 10,625,447,387 miles (17.1 million km), the need for four hodoscopes are required. Considering that hurricanes are a fraction of that size, and the majority of tropical cyclones are formed between 10 and 30 degrees of latitude of both hemispheres, the number of hodoscope necessary to monitor this territory is low.

“Muon diagnostics developed at MEPhI offers the possibility to model the flow of cosmic rays in the atmosphere and magnetosphere. But to study such processes, it is necessary to create a network of similar, adjustable muon hodoscopes. Such hodoscopes were developed at MEPhI,” Yashin says.

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Burst of Galactic Cosmic Rays Produces Crack in Earth’s Magnetic Field

The world’s largest and most sensitive cosmic ray monitor, located in India, has recorded a burst of galactic cosmic rays which produced a crack in the Earth’s magnetic shield, according to scientists.

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This is to say, a large fast moving coronal mass ejection (CME) from our Sun acting as an offensive front line making an opening in Earth’s magnetic field which then allowed an unusual large flow of galactic cosmic rays (GCR) to enter our atmosphere.

cosmic-ray-spectrum-gap

This event is unusual due to the fact that during times of high solar activity, the larger solar particles push aside the smaller but more harmful and damaging cosmic rays particles which produce high levels of radiation. Galactic cosmic rays come from outside our solar system generated from various celestial events such as exploding stars or supernovas occurring throughout our galaxy Milky Way.

The GRAPES-3 muon telescope located at the Tata Institute of Fundamental Research’s Cosmic Ray Laboratory in Ooty recorded a burst of galactic cosmic rays last year lasting for two hours.

grapes-3-cosmic-ray-telescope

The burst occurred when a giant cloud of plasma ejected from the solar corona, and moving with a speed of about 1.56 million per hour (2.5 million km) struck our planet, causing a severe compression of Earth’s magnetosphere from 11 to 4 times the radius of Earth. It triggered a severe geomagnetic storm that generated aurora borealis and radio signal blackouts in many high latitude countries, according to the study published in the journal Physical Review Letters this week.

Earth’s magnetosphere extends over a radius of 620,000 miles (1,000,000,000 kilometers), which acts as the first line of defense, shielding us from the continuous flow of solar and galactic cosmic rays, thus protecting life on our planet from these high intensity energetic radiations.

Detour Via Gravitational Lens Makes Distant Galaxy Visible

Never before have astrophysicists measured light of such high energy from a celestial object so far away. Around 7 billion years ago, a huge explosion occurred at the black hole in the center of a galaxy. This was followed by a burst of high-intensity gamma rays. A number of telescopes, MAGIC included, have succeeded in capturing this light. An added bonus: it was thus possible to reconfirm Einstein’s General Theory of Relativity, as the light rays encountered a less distant galaxy en route to Earth — and were deflected by this so-called gravitational lens.

gravitational-waves

The object QSO B0218+357 is a blazar, a specific type of black hole. Researchers now assume that there is a supermassive black hole at the center of every galaxy. Black holes, into which matter is currently plunging are called active black holes. They emit extremely bright jets. If these bursts point towards Earth, the term blazar is used.

Full moon prevents the first MAGIC observation

The event now described in “Astronomy & Astrophysics” took place 7 billion years ago, when the universe was not even half its present age. “The blazar was discovered initially on 14 July 2014 by the Large Area Telescope (LAT) of the Fermi satellite,” explains Razmik Mirzoyan, scientist at the Max Planck Institute for Physics and spokesperson for the MAGIC collaboration. “The gamma ray telescopes on Earth immediately fixed their sights on the blazer in order to learn more about this object.”

One of these telescopes was MAGIC, on the Canary Island of La Palma, specialized in high-energy gamma rays. It can capture photons — light particles — whose energy is 100 billion times higher than the photons emitted by our Sun and a thousand times higher than those measured by Fermi-LAT. The MAGIC scientists were initially out of luck, however: A full moon meant the telescope was not able to operate during the time in question.

Gravitational lens deflects ultra-high-energy photons

Eleven days later, MAGIC got a second chance, as the gamma rays emitted by QSO B0218+357 did not take the direct route to Earth: One billion years after setting off on their journey, they reached the galaxy B0218+357G. This is where Einstein’s General Theory of Relativity came into play.

This states that a large mass in the universe, a galaxy, for example, deflects light of an object behind it. In addition, the light is focused as if by a gigantic optical lens — to a distant observer, the object appears to be much brighter, but also distorted. The light beams also need different lengths of time to pass through the lens, depending on the angle of observation.

This gravitational lens was the reason that MAGIC was able, after all, to measure QSO B0218+357 — and thus the most distant object in the high-energy gamma ray spectrum. “We knew from observations undertaken by the Fermi space telescope and radio telescopes in 2012 that the photons that took the longer route would arrive 11 days later,” says Julian Sitarek (University of ?ódz, Poland), who led this study. “This was the first time we were able to observe that high-energy photons were deflected by a gravitational lens.”

Doubling the size of the gamma-ray universe

The fact that gamma rays of such high energy from a distant celestial body reach Earth’s atmosphere is anything but obvious. “Many gamma rays are lost when they interact with photons which originate from galaxies or stars and have a lower energy,” says Mirzoyan. “With the MAGIC observation, the part of the universe that we can observe via gamma rays has doubled.”

The fact that the light arrived on Earth at the time calculated could rattle a few theories on the structure of the vacuum — further investigations, however, are required to confirm this. “The observation currently points to new possibilities for high-energy gamma ray observatories — and provides a pointer for the next generation of telescopes in the CTA project,” says Mirzoyan, summing up the situation.

Tsunami Of Stars And Gas Produces Dazzling Eye-Shaped Feature In Galaxy

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered a tsunami of stars and gas that is crashing midway through the disk of a spiral galaxy known as IC 2163. This colossal wave of material — which was triggered when IC 2163 recently sideswiped another spiral galaxy dubbed NGC 2207 — produced dazzling arcs of intense star formation that resemble a pair of eyelids.

star-tsunami

“Although galaxy collisions of this type are not uncommon, only a few galaxies with eye-like, or ocular, structures are known to exist,” said Michele Kaufman, an astronomer formerly with The Ohio State University in Columbus and lead author on a paper published in the Astrophysical Journal.

Kaufman and her colleagues note that the paucity of similar features in the observable universe is likely due to their ephemeral nature. “Galactic eyelids last only a few tens of millions of years, which is incredibly brief in the lifespan of a galaxy. Finding one in such a newly formed state gives us an exceptional opportunity to study what happens when one galaxy grazes another,” said Kaufman.

The interacting pair of galaxies resides approximately 114 million light-years from Earth in the direction of the constellation Canis Major. These galaxies brushed past each other — scraping the edges of their outer spiral arms — in what is likely the first encounter of an eventual merger.

Using ALMA’s remarkable sensitivity and resolution, the astronomers made the most detailed measurements ever of the motion of carbon monoxide gas in the galaxy’s narrow eyelid features. Carbon monoxide is a tracer of molecular gas, which is the fuel for star formation.

The data reveal that the gas in the outer portion of IC 2163’s eyelids is racing inward at speeds in excess of 100 kilometers a second. This gas, however, quickly decelerates and its motion becomes more chaotic, eventually changing trajectory and aligning itself with the rotation of the galaxy rather than continuing its pell-mell rush toward the center.

“What we observe in this galaxy is very much like a massive ocean wave barreling toward shore until it interacts with the shallows, causing it to lose momentum and dump all of its water and sand on the beach,” said Bruce Elmegreen, a scientist with IBM’s T.J. Watson Research Center in Yorktown Heights, New York, and co-author on the paper.

“Not only do we find a rapid deceleration of the gas as it moves from the outer to the inner edge of the eyelids, but we also measure that the more rapidly it decelerates, the denser the molecular gas becomes,” said Kaufman. “This direct measurement of compression shows how the encounter between the two galaxies drives gas to pile up, spawn new star clusters and form these dazzling eyelid features.”

Computer models predict that such eyelid-like features could evolve if galaxies interacted in a very specific manner. “This evidence for a strong shock in the eyelids is terrific. It’s all very well to have a theory and simulations suggesting it should be true, but real observational evidence is great,” said Curtis Struck, a professor of astrophysics at Iowa State University in Ames and co-author on the paper.

“ALMA showed us that the velocities of the molecular gas in the eyelids are on the right track with the predictions we get from computer models,” said Kaufman. “This critical test of encounter simulations was not possible before.”

Astronomers believe that such collisions between galaxies were common in the early universe when galaxies were closer together. At that time, however, galactic disks were generally clumpy and irregular, so other processes likely overwhelmed the formation of similar eyelid features.

The authors continue to study this galaxy pair and currently are comparing the properties (e.g., locations, ages, and masses) of the star clusters previously observed with NASA’s Hubble Space Telescope with the properties of the molecular clouds observed with ALMA. They hope to better understand the differences between molecular clouds and star clusters in the eyelids and those elsewhere in the galaxy pair.

Significant Bronze Age city discovered in Northern Iraq

Archeologists from the Institute for Ancient Near Eastern Studies (IANES) at the University of Tübingen have uncovered a large Bronze Age city not far from the town of Dohuk in northern Iraq. The excavation work has demonstrated that the settlement, which is now home to the small Kurdish village of Bassetki in the Autonomous Region of Kurdistan, was established in about 3000 BC and was able to flourish for more than 1200 years. The archeologists also discovered settlement layers dating from the Akkadian Empire period (2340-2200 BC), which is regarded as the first world empire in human history.

bronze

Scientists headed by Professor Peter Pfälzner from the University of Tübingen and Dr. Hasan Qasim from the Directorate of Antiquities in Dohuk conducted the excavation work in Bassetki between August and October 2016. As a result, they were able to preempt the construction work on a highway on this land. The former significance of the settlement can be seen from the finds discovered during the excavation work. The city already had a wall running around the upper part of the town from approx. 2700 BC onwards in order to protect its residents from invaders. Large stone structures were erected there in about 1800 BC. The researchers also found fragments of Assyrian cuneiform tablets dating from about 1300 BC, which suggested the existence of a temple dedicated to the Mesopotamian weather god Adad on this site. There was a lower town about one kilometer long outside the city center. Using geomagnetic resistance measurements, the archeologists discovered indications of an extensive road network, various residential districts, grand houses and a kind of palatial building dating from the Bronze Age. The residents buried their dead at a cemetery outside the city. The settlement was connected to the neighboring regions of Mesopotamia and Anatolia via an overland roadway dating from about 1800 BC.

Bassetki was only known to the general public in the past because of the “Bassetki statue,” which was discovered there by chance in 1975. This is a fragment of a bronze figure of the Akkadian god-king Naram-Sin (about 2250 BC). The discovery was stolen from the National Museum in Baghdad during the Iraq War in 2003, but was later rediscovered by US soldiers. Up until now, researchers were unable to explain the location of the find. The archeologists have now been able to substantiate their assumption that an important outpost of Akkadian culture may have been located there.

Although the excavation site is only 45 kilometers from territory controlled by the Islamic State (IS), it was possible to conduct the archeological work without any disturbances. “The protection of our employees is always our top priority. Despite the geographical proximity to IS, there’s a great deal of security and stability in the Kurdish autonomous areas in Iraq,” said Professor Peter Pfälzner, Director of the Department of Near Eastern Archaeology at the IANES of the University of Tübingen. The research team consisting of 30 people lived in the city of Dohuk, which is only 60 kilometers north of Mosul, during the excavation work.

In another project being handled by the “ResourceCultures” collaborative research center (SFB 1070), Pfälzner’s team has been completing an archeological inspection of territory in the complete area surrounding Bassetki as far as the Turkish and Syrian borders since 2013 — and 300 previously unknown sites have been discovered. The excavations and the research work in the region are due to be continued during the summer of 2017. “The area around Bassetki is proving to be an unexpectedly rich cultural region, which was located at the crossroads of communication ways between the Mesopotamian, Syrian and Anatolian cultures during the Bronze Age. We’re therefore planning to establish a long-term archeological research project in the region in conjunction with our Kurdish colleagues,” says Pfälzner. The excavation work is being funded by the Fritz Thyssen Foundation.