University of Utah physicist led the design, construction, upgrade of the VERITAS instrument

The VERITAS array has confirmed the detection of high-energy gamma rays from the vicinity of a supermassive black hole located in a distant galaxy, TXS 0506+056. While these detections are relatively common for VERITAS, this blackhole is potentially the first known astrophysical source of high-energy cosmic neutrinos, a type of ghostly subatomic particle that can be made at astrophysical sources of ultra-high energy cosmic rays.

The University of Utah is one of the founding collaborating institutions of the VERITAS observatory. Co-author Dave Kieda, professor of physics and astronomy and the dean of the U’s graduate school, led the design, construction and upgrade of VERITAS that gave the instrument enhanced sensitivity to the lower-energy gamma rays critical to the discovery. Anushka Udara Abeysekara, research assistant professor of physics and astronomy at the U, is also a coauthor on the paper.

“This is the first time we’ve seen high-energy gamma-rays and neutrinos being generated by a common astrophysical source. This is evidence that nearby and faraway galaxies with supermassive blackholes at their centers are actively creating high-energy cosmic rays,” said Kieda. “It’s one of the pieces of the puzzle needed to solve the mystery of where these cosmic rays come from.”

The University of Utah also operates the Telescope Array cosmic ray observatory based in Delta, Utah. In 2015, the University of Utah Telescope Array Group identified a potential hotspot of ultra-high energy cosmic rays coming from a broad region of the sky containing numerous potential extragalactic cosmic-ray sources. Because our Galaxy’s magnetic field bends the trajectory of incoming cosmic particles, the Telescope Array was unable to pinpoint any individual galaxy as the origin of the high energy cosmic rays. The VERITAS gamma-ray discovery, in combination with the ICECUBE neutrino detection, provides a way to directly identify a single galaxy as a source of high energy cosmic rays. This “multi-messenger” approach to astronomy — employing joint observations of neutrinos, gamma-rays, X-rays and cosmic-rays — provides a major breakthrough in the understanding of the astrophysical origin of the most energetic particles in the universe.

“The era of multi-messenger astrophysics is here,” said National Science Foundation director France Córdova. “Each messenger — from electromagnetic radiation, gravitational waves and now neutrinos — gives us a more complete understanding of the universe, and important new insights into the most powerful objects and events in the sky. Such breakthroughs are only possible through a long-term commitment to fundamental research and investment in superb research facilities.”

Find the full release, written by the Smithsonian Astrophysical Observatory, below.

VERITAS Supplies Critical Piece to Neutrino Discovery Puzzle

The VERITAS array has confirmed the detection of gamma rays from the vicinity of a supermassive black hole. While these detections are relatively common for VERITAS, this black hole is potentially the first known astrophysical source of high-energy cosmic neutrinos, a type of ghostly subatomic particle.

On September 22, 2017 the IceCube Neutrino Observatory, a cubic-kilometer neutrino telescope located at the South Pole, detected a high-energy neutrino of potential astrophysical origin. However, IceCube is not capable of locating a source of neutrinos on the sky. For that, scientists needed more information.

Very quickly after the detection by IceCube was announced, telescopes around the world including VERITAS (which stands for the “Very Energetic Radiation Telescope Array System”) swung into action to identify the source. The VERITAS, MAGIC and H.E.S.S. gamma-ray observatories all looked at the neutrino position. In addition, other gamma-ray observatories that monitor much of the sky at lower and higher energies also provided coverage.

These follow-up observations of the rough IceCube neutrino position suggest that the source of the neutrino is a blazar, which is a supermassive black hole with powerful outflowing jets that can change dramatically in brightness over time. This blazar, known as TXS 0506+056, is located at the center of a galaxy about 4 billion light years from Earth.

Initially, NASA’s Fermi Gamma-ray Space Telescope observed that TXS 0506+056 was several times brighter than usually seen in its all-sky monitoring. Eventually, the MAGIC observatory made a detection of much higher-energy gamma rays about two weeks after the neutrino detection, while VERITAS, H.E.S.S. and HAWC did not see the blazar in any of their observations during the two weeks following the alert.

Given the importance of higher-energy gamma-ray detections in identifying the possible source of the neutrino, VERITAS continued to observe TXS 0506+056 over the following months, through February 2018, and revealed the source but at a dimmer state than what was detected by MAGIC.

The detection of gamma rays coincident with neutrinos is tantalizing, since both particles must be produced in the generation of cosmic rays. Since they were first detected over one hundred years ago, cosmic rays — highly energetic particles that continuously rain down on Earth from space — have posed an enduring mystery. What creates and launches these particles across such vast distances? Where do they come from?

“The potential connection between the neutrino event and TXS 0506+056 would shed new light on the acceleration mechanisms that take place at the core of these galaxies, and provide clues on the century-old question of the origin of cosmic rays,” said co-author and Spokesperson of VERITAS Reshmi Mukherjee of Barnard College, Columbia University in New York, New York.

“Astrophysics is entering an exciting new era of multi-messenger observations, in which celestial sources are being studied through the detection of the electromagnetic radiation they emit across the spectrum, from radio waves to high-energy gamma rays, in combination with non-electromagnetic means, such as gravitational waves and high-energy neutrinos,” said co-author Marcos Santander of the University of Alabama in Tuscaloosa.

A paper describing the deep VERITAS observations of TXS 0506+056 appears online in The Astrophysical Journal Letters on July 12, 2018. A paper on the IceCube and initial gamma-ray observations, including VERITAS’, appears in the latest issue of the journal Science.

VERITAS is a ground-based facility located at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory in southern Arizona. It consists of an array of four 12-meter optical telescopes that can detect gamma rays via the extremely brief flashes of blue “Cherenkov” light created when gamma rays are absorbed in the Earth’s atmosphere.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Read the full press release on the UNews website.

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From the Clark Planetarium's website.

Dr. Anil Seth
Thursday, July 26, 2018
Clark Planetarium

Big Black Holes

It’s not just your kids that need educational enrichment over the summer months. Clark Planetarium is excited to host a trio of free and engaging lectures that explore topics about our home planet and beyond.

So mark your calendars for Clark Planetarium’s free Summer Lecture Series and ensure that your learning never ends. Get your tickets here!

On Thursday, July 26th, from 6-7pm, we will have our last installment of our Summer Lectures Series with Dr. Seth. He will talk about how astronomers find black holes, focusing on his own efforts to figure out whether galaxies much smaller than the Milky Way have black holes at the centers. This work can reveal the origins of these mysterious objects.

 

Admission is free and open to the public!

Clark Planetarium
110 South 400 West
Salt Lake City, UT 84101
View Map

More information available here.

 

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ALL DETAILS PREDICTED BY CRITICAL THEORY WERE CONFIRMED ON REAL OBJECTS IN A LAB

The struggle to keep drinks cold during the summer is a lesson in classical phase transitions. To study phase transitions, apply heat to a substance and watch how its properties change. Add heat to water and at the so-called “critical point,” watch as it transforms into a gas (steam). Remove heat from water and watch it turn into a solid (ice).

Now, imagine that you’ve cooled everything down to very low temperatures — so low that all thermal effects vanish. Welcome to the quantum realm, where pressure and magnetic fields cause new phases to emerge in a phenomenon called quantum phase transitions (QPT). More than a simple transition from one phase to another, QPT form completely new properties, such as superconductivity, in certain materials.

Apply voltage to a superconductive metal, and the electrons travel through the material with no resistance; electrical current will flow forever without slowing down or producing heat. Some metals become superconducting at high temperatures, which has important applications in electric power transmission and superconductor-based data processing. Scientists discovered the phenomenon 30 years ago, but the mechanism for superconductivity remains an enigma because the majority of materials are too complex to understand QPT physics in details. A good strategy would be first to look at less complicated model systems.

Now, University of Utah physicists and collaborators have discovered that superconducting nanowires made of MoGe alloy undergo quantum phase transitions from a superconducting to a normal metal state when placed in an increasing magnetic field at low temperatures. The study is the first to uncover the microscopic process by which the material loses its superconductivity; the magnetic field breaks apart pairs of electrons, called Cooper pairs, which interact with other Cooper pairs and experience a damping force from unpaired electrons present in the system.

The findings are fully explained by the critical theory proposed by coauthor Adrian Del Maestro, associate professor at the University of Vermont. The theory correctly described how the evolution of superconductivity depends on critical temperature, magnetic field magnitude and orientation, nanowire cross sectional area, and the microscopic characteristics of the nanowire material. This is the first time in the field of superconductivity that all details of QPT predicted by a theory were confirmed on real objects in the lab.

“Quantum phase transitions may sound really exotic, but they are observed in many systems, from the center of stars to the nucleus of atoms, and from magnets to insulators,” said Andrey Rogachev, associate professor at the U and senior author of the study.“By understanding quantum fluctuations in this simpler system, we can talk about every detail of the microscopic process and apply it to more complicated objects.”

The study published online July 9, 2018 in Nature Physics.

THEORETICAL MEETS EXPERIMENTAL

Condensed matter physicists study what happens to materials with all of their heat removed in two ways — experimental physicists develop materials to test in a lab, while theoretical physicists develop mathematical equations to understand the physical behavior. This research tells the story of how the theory and experimental informed and motivated each other.

As a postdoctoral fellow, Rogachev showed that applying magnetic fields to nanowires under low temperatures distorts superconductivity. He understood the effects at finite temperatures but came to no conclusion as to what happens at the “critical point” where superconductivity falters. His work, however, inspired the young theoretical physicist Adrian Del Maestro, a graduate student at Harvard at the time, to develop a complete critical theory of the quantum phase transition.

In Del Maestro’s “pair breaking” theory, single electrons are unlikely to bump into the edges of the smallest wire since even a single strand of atoms is large compared to the size of an electron. But, said Del Maestro, “two electrons that form the pairs responsible for superconductivity can be far apart and now the nanoscale size of the wire makes it more difficult for them to travel together.” Then add in a powerful magnetic field, which disentangles pairs by curving their paths, and “the electrons are unable to conspire to form the superconducting state,” said Del Maestro.

“Imagine that the edges of the wire and the magnetic field act like some frictional force that makes electrons not want to pair up as much,” said Del Maestro. “That physics should be universal.” Which is exactly what his theory and the new experiment show.

“Only a few key ingredients—spatial dimension and existence of superconductivity—are essential when describing the emergent properties of electrons at quantum phase transitions,” he said. The amazing agreement between the conductivity values Del Maestro’s theory predicted over a decade ago and the values measured in the new experiment sets a powerful standard for “the experimental confirmation of quantum universality,” Del Maestro said, “and underscores the importance of fundamental physics research.”

STATE-OF-THE-ART NANOWIRES

To test Del Maestro’s theory, Rogachev needed nearly one-dimensional nanowires, with diameters smaller than 20-30 nanometers.

“In theoretical physics, one-dimensional systems play a very special role, since for them an exact theory can be developed” said Rogachev. “Yet one-dimensional systems are notoriously difficult to deal with experimentally.”

The MoGe nanowires are the crucial element of the whole study. In his postdoctoral days, Rogachev could only make such wires 100 nanometers long, too short to test the critical regime. Years later at the U, he and his then-student Hyunjeong Kim, lead author of the study, improved upon an existing method of electron beam lithography to develop a state-of-the-art technique.

Ninety-nine percent of physicists create nanostructures using a method called positive electron beam (e-beam) lithography. They shine a beam of electrons onto an electron-sensitive film, then remove the exposed part of the film to create needed structures. Far fewer physicists use negative e-beam lithography, in which they draw their structure with the e-beam but remove all of the unexposed film. This is the method that Kim bought to the state-of-the-art, fabricating thin nanowires with widths below 10 nm.

“It’s not just that we make them, but we can measure them,” said Rogachev. “Many people make really small particles, but to really be able to look at transport on these wires, it was like developing a new technique.”

To test the quantum phase transitions, Rogachev brought the wires to Benjamin Sacépé and Frédéric Gay at the Institut Néel in Grenoble where their facility is capable of cooling the material to 50 milliKelvin, applying magnetic field of various strengths and measuring the wires’ resistance to describe how the superconductivity breaks down. The French collaborators added to the group years of expertise in precise transport measurement, noise-rejection techniques and quantum physics of two-dimensional superconductors.

“After decades of intensive research, we are still far from fully understanding superconductivity” says Tomasz Durakiewicz, program director for condensed matter physics at the National Science Foundation, which co-funds this work. “These results significantly advance the field by closely linking the tangible, physical universe of nanowires and the field-driven phase transitions happening at the quantum scale. By merging theory and experiment, the team was able to explain the complex relationship between conductivity and geometry, magnetic fields and critical temperature, all while proposing a theory of quantum criticality that is in excellent agreement with experimental observations.”

BRINGING IT TO HIGHER TEMPERATURES

Rogachev is now preparing to test nanowires made of cuprates. Cuprates have a quantum phase transition between a magnetic state and a normal state, At the critical point, there are quantum fluctuations that, according to several theories, promote the emergence of superconductivity. The cuprates are often called high-temperature superconductors because they go to the superconducting state at the record-high temperature of 90-155 K, a contrast to the rather small critical temperature of MoGe alloys at 3 – 7 K. Rogachev wants to make wires out of cuprates to understand the microscopic mechanism of high-temperature superconductivity. Another avenue he wants to explore with his collaborators in Grenoble is quantum phase transition in superconducting films.

“Now we have this certain piece of physics worked out, we can move to more complicated objects where we basically don’t know exactly what is going on,” he said.

*****

The research was supported by the National Science Foundation and the ERC grant QUEST. Nanowire fabrication was carried out at the University of Utah Microfab and USTAR facilities.

Read the full press release on the UNews website. The published paper, "Pair-Breaking Quantum Phase Transition in Superconducting Nanowires", is available on the NSF website.

 

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A new study using data from NASA’s NuSTAR space telescope suggests that Eta Carinae, the most luminous and massive stellar system within 10,000 light-years, is accelerating particles to high energies — some of which may reach Earth as cosmic rays.

“We know the blast waves of exploded stars can accelerate cosmic ray particles to speeds comparable to that of light, an incredible energy boost,” said Kenji Hamaguchi, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the lead author of the study. “Similar processes must occur in other extreme environments. Our analysis indicates Eta Carinae is one of them.”

Astronomers know that cosmic rays with energies greater than 1 billion electron volts (eV) come to us from beyond our solar system. But because these particles — electrons, protons and atomic nuclei — all carry an electrical charge, they veer off course whenever they encounter magnetic fields. This scrambles their paths and masks their origins.

Eta Carinae, located about 7,500 light-years away in the southern constellation of Carina, is famous for a 19th century outburst that briefly made it the second-brightest star in the sky. This event also ejected a massive hourglass-shaped nebula, but the cause of the eruption remains poorly understood.

The system contains a pair of massive stars whose eccentric orbits bring them unusually close every 5.5 years. The stars contain 90 and 30 times the mass of our Sun and pass 140 million miles (225 million kilometers) apart at their closest approach — about the average distance separating Mars and the Sun.

“Both of Eta Carinae’s stars drive powerful outflows called stellar winds,” said team member Michael Corcoran, also at Goddard. “Where these winds clash changes during the orbital cycle, which produces a periodic signal in low-energy X-rays we’ve been tracking for more than two decades.”

NASA’s Fermi Gamma-ray Space Telescope also observes a change in gamma rays — light packing far more energy than X-rays — from a source in the direction of Eta Carinae. But Fermi’s vision isn’t as sharp as X-ray telescopes, so astronomers couldn’t confirm the connection.

To bridge the gap between low-energy X-ray monitoring and Fermi observations, Hamaguchi and his colleagues turned to NuSTAR. Launched in 2012, NuSTAR can focus X-rays of much greater energy than any previous telescope. Using both newly taken and archival data, the team examined NuSTAR observations acquired between March 2014 and June 2016, along with lower-energy X-ray observations from the European Space Agency’s XMM-Newton satellite over the same period.

“The key to accurately measuring eta Car’s X-rays and identifying the star system as the gamma ray source — and thus proving that the colliding winds of this binary system are accelerating cosmic rays — was to fully characterize NuSTAR’s background,” said coauthor Daniel Wik, assistant professor at the University of Utah.

Wik previously developed a multi-component background model for the NuSTAR mission, but eta Car’s location in the plane of the Milky Way caused the background of NuSTAR’s 9 separate observations to be more complicated than usual. He helped identify additional sources of background and how to account for them, allowing the link between Eta Carinae X-ray and gamma ray emission to become clear.

Eta Carinae’s low-energy, or soft, X-rays come from gas at the interface of the colliding stellar winds, where temperatures exceed 70 million degrees Fahrenheit (40 million degrees Celsius). But NuSTAR detects a source emitting X-rays above 30,000 eV, some three times higher than can be explained by shock waves in the colliding winds. For comparison, the energy of visible light ranges from about 2 to 3 eV.

The team’s analysis, presented in a paper published on Monday, July 2, in Nature Astronomy,shows that these “hard” X-rays vary with the binary orbital period and show a similar pattern of energy output as the gamma rays observed by Fermi.

The researchers say that the best explanation for both the hard X-ray and the gamma-ray emission is electrons accelerated in violent shock waves along the boundary of the colliding stellar winds. The X-rays detected by NuSTAR and the gamma rays detected by Fermi arise from starlight given a huge energy boost by interactions with these electrons.

Some of the superfast electrons, as well as other accelerated particles, must escape the system and perhaps some eventually wander to Earth, where they may be detected as cosmic rays.

“We’ve known for some time that the region around Eta Carinae is the source of energetic emission in high-energy X-rays and gamma rays”, said Fiona Harrison, the principal investigator of NuSTAR and a professor of astronomy at Caltech in Pasadena, California. “But until NuSTAR was able to pinpoint the radiation, show it comes from the binary and study its properties in detail, the origin was mysterious.”

NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR’s mission operations center is at UC Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission’s ground station and a mirror archive. Caltech manages JPL for NASA.

For more information on NuSTAR, visit:

https://www.nasa.gov/nustar

http://www.nustar.caltech.edu

Adapted from an original release written by Francis Reddy of NASA’s Goddard Space Flight Center, available online here: https://www.nasa.gov/feature/goddard/2018/nasas-nustar-mission-proves-superstar-eta-carinae-shoots-cosmic-rays

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