New Understanding of Cosmic Rays, Neutrino Particles, and Gamma Rays

New model connects the origins of very high-energy neutrinos, ultrahigh-energy cosmic rays, and high-energy gamma rays with black-hole jets embedded in their environments.

One of the biggest mysteries in astroparticle physics has been the origins of ultrahigh-energy cosmic rays, very high-energy neutrinos, and high-energy gamma rays. Now, a new theoretical model reveals that they all could be shot out into space after cosmic rays are accelerated by powerful jets from supermassive black holes.

The model explains the natural origins of all three types of “cosmic messenger” particles simultaneously, and is the first astrophysical model of its kind based on detailed numerical computations. A scientific paper that describes this model, produced by Penn State and University of Maryland scientists, will be published as an Advance Online Publication on the website of the journal Nature Physics on January 22, 2018.

“Our model shows a way to understand why these three types of cosmic messenger particles have a surprisingly similar amount of power input into the universe, despite the fact that they are observed by space-based and ground-based detectors over ten orders of magnitude in individual particle energy,” said Kohta Murase, assistant professor of physics and astronomy and astrophysics at Penn State. “The fact that the measured intensities of very high-energy neutrinos, ultrahigh-energy cosmic rays, and high-energy gamma rays are roughly comparable tempted us to wonder if these extremely energetic particles have some physical connections. The new model suggests that very high-energy neutrinos and high-energy gamma rays are naturally produced via particle collisions as daughter particles of cosmic rays, and thus can inherit the comparable energy budget of their parent particles. It demonstrates that the similar energetics of the three cosmic messengers may not be a mere coincidence.”

Ultrahigh-energy cosmic rays are the most energetic particles in the universe — each of them carries an energy that is too high to be produced even by the Large Hadron Collider, the most powerful particle accelerator in the world. Neutrinos are mysterious and ghostly particles that hardly ever interact with matter. Very high-energy neutrinos, with energy more than one million mega-electronvolts, have been detected in the IceCube neutrino observatory in Antarctica. Gamma rays have the highest-known electromagnetic energy — those with energies more than a billion times higher than a photon of visible light have been observed by the Fermi Gamma-ray Space Telescope and other ground-based observatories. “Combining all information on these three types of cosmic messengers is complementary and relevant, and such a multi-messenger approach has become extremely powerful in the recent years,” Murase said.

Murase and the first author of this new paper, Ke Fang, a postdoctoral associate at the University of Maryland, attempt to explain the latest multi-messenger data from very high-energy neutrinos, ultrahigh-energy cosmic rays, and high-energy gamma rays, based on a single but realistic astrophysical setup. They found that the multi-messenger data can be explained well by using numerical simulations to analyze the fate of these charged particles.

“In our model, cosmic rays accelerated by powerful jets of active galactic nuclei escape through the radio lobes that are often found at the end of the jets,” Fang said. “Then we compute the cosmic-ray propagation and interaction inside galaxy clusters and groups in the presence of their environmental magnetic field. We further simulate the cosmic-ray propagation and interaction in the intergalactic magnetic fields between the source and the Earth. Finally we integrate the contributions from all sources in the universe.”

The leading suspects in the half-century old mystery of the origin of the highest-energy cosmic particles in the universe were in galaxies called “active galactic nuclei,” which have a super-radiating core region around the central supermassive black hole. Some active galactic nuclei are accompanied by powerful relativistic jets. High-energy cosmic particles that are generated by the jets or their environments are shot out into space almost as fast as the speed of light.

Gravitational Waves Measure The Universe

The direct detection of gravitational waves from at least five sources during the past two years offers spectacular confirmation of Einstein’s model of gravity and space-time. Modeling of these events has also provided information on massive star formation, gamma-ray bursts, neutron star characteristics, and (for the first time) verification of theoretical ideas about how the very heavy elements, like gold, are produced.

Astronomers have now used a single gravitational wave event (GW170817) to measure the age of the universe. CfA astronomers Peter Blanchard, Tarreneh Eftekhari, Victoria Villar, and Peter Williams were members of a team of 1314 scientists from around the world who contributed to the detection of gravitational waves from a merging pair of binary neutron stars, followed by the detection of gamma-rays, and then the identification of the origin of the cataclysm in a source in the galaxy NGC4993 spotted in images taken with various time delays at wavelengths from the X-ray to the radio.

An analysis of the gravitational waves from this event infers their intrinsic strength. The observed strength is less, implying (because the strength diminishes with distance from the source) that the source is about 140 million light-years away. NGC4993, its host galaxy, has an outward velocity due to the expansion of the universe that can be measured from its spectral lines. Knowing how far away it is and how fast the galaxy is moving from us allows scientists to calculate the time since the expansion began – the age of the universe: between about 11.9 and 15.7 billion years given the experimental uncertainties.

The age derived from this single event is consistent with estimates from decades of observations relying on statistical methods using two other sources: the cosmic microwave background radiation (CMBR) and the motions of galaxies. The former relies on mapping the very faint distribution of light dating from a time about four hundred thousand years after the big bang; the latter involves a statistical analysis of the distances and motions of tens of thousands of galaxies in relatively recent times. The fact that this one single gravitational-wave event was able to determine an age for the universe is remarkable, and not possible with every gravity wave detection. In this case there was an optical identification of the source (so that a velocity could be measured) and the source was neither too distant or too faint. With a large statistical sample of gravitational wave events of all types, the current range of values for the age will narrow.

The new result is intriguing for another reason. Although both the CMBR and the galaxy measurements are each quite precise, they seem to disagree with each other at roughly the ten percent level. This disagreement could just be observational error, but some astronomers suspect it might be a real difference reflecting something currently missing from our picture of the cosmic expansion process, perhaps connected with the fact that the CMBR arises from a vastly different epoch of cosmic time than does the galaxy data. This third method, gravitational wave events, may help solve the puzzle.

Precursor to Earth’s Magnetic Field Reversal

According to scientists’ best estimates, the Earth’s magnetic field is now weakening around 10 times faster than previously predicted, losing approximately 5% of its strength every decade. This finding indicates a magnetic pole reversal could be coming sooner rather than later.

 The geomagnetic dipole has decreased by nearly 6% per century since first measured by Gauss in the 1840s. This too is 10-20 times faster than the “Ohmic” decay rate. (The process by which the passage of an electric current through a conductor releases heat). The causes of this rapid decrease in Gauss stability, is the proliferation of reverse magnetic field on the core-mantle boundary. This has occurred especially beneath the South Atlantic with the transference of heat energy in a horizontal stream of the magnetic field from high to low latitudes.

The weakening of Earth’s magnetic field has two fundamental points. First: A weakened magnetic field allows charged particle events such as galactic cosmic rays, gamma rays, solar flares, and coronal mass ejections (CME), to produce enhanced consequences to extreme weather events that include earthquakes, volcanoes, hurricanes, tornadoes etc.

galactic_cosmic_rays_sun_magnetic_field_earths_core_scienceofcycles-com_m

Second: The second major consequence of a weakened magnetic field is its identification as the ‘precursor’ to a magnetic pole shift. It is estimated that Earth’s magnetic field reverses every few thousand years at low latitudes and every 10,000 years at high latitudes. It is believed we are far enough along the cycle that many living today will witness the bouncing back and forth of magnetic north as it swings reaching latitudes below 30°. Magnetic north can also move east and west longitudes.

Precursor First – Then Full Magnetic Flip
Individual magnetic reversal records show a remarkable degree of repeatability, including dipole collapse, rapid polarity change, and fast dipole intensity recovery stages. This is to say historical magnetic field reversals indicate that during the period of Earth’s magnetic field reduction, it will be in flux for several years before a full magnetic flip will incur. At this stage of magnetic minimization close to zero point, the magnetic field may have multiple swings north and south across the equator, additionally with large excursions of geomagnetic polar flux in east and west longitudes.

shifting_magnetic_pole

The final stage of reversal is when the dipole intensity partially recovers. An example of this phenomena would be magnetic north suddenly dropping down to at or below the equator, then rapidly snapping back to say and briefly exceeds the surface non-dipole intensity, which in turn is followed by a very rapid dipole intensity collapse, final reversal, and recovery of the dipole intensity in the new polarity position. The final latitudes and longitude positions are unknown. However, historical records indicate north will be south – and south will be north – but at what degrees North-South-East-West is anyone’s guess.

When the poles flip, having a compass that points South instead of North does not seem like too big of a deal to humans, but there is a question of what will happen other animals. Certain migratory animals like sea turtles and birds use the magnetic field in order to orient themselves. A reversal of the poles could interfere with their ability to do so.

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