University of Utah physicist led the design, construction, upgrade of the VERITAS instrument
Dr. Dave Kieda
Dr. Anushka Udara Abeysekara
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.”
ALL DETAILS PREDICTED BY CRITICAL THEORY WERE CONFIRMED ON REAL OBJECTS IN A LAB
PHOTO CREDIT: Andrey Rogachev, adapted from a figure in Nature Physics 10.1038/s41567-018-0179-8. This schematic diagram shows the quantum phase transition of a superconducting metal to a normal metal at zero temperature. As the magnetic field increases in strength, the superconductivity breaks down until the critical point at which the material becomes a normal metal.
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.”
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.
Dr. Daniel Wik
“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.”
PHOTO CREDIT: NASA, ESA, and the Hubble SM4 ERO Team. Eta Carinae’s great eruption in the 1840s created the billowing Homunculus Nebula, imaged here by Hubble. Now about a light-year long, the expanding cloud contains enough material to make at least 10 copies of our Sun. Astronomers cannot yet explain what caused this eruption.
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.
PHOTO CREDIT:NASA/CXC and NASA/JPL-Caltech Eta Carinae shines in X-rays in this image from NASA’s Chandra X-ray Observatory. The colors indicate different energies. Red spans 300 to 1,000 electron volts (eV), green ranges from 1,000 to 3,000 eV and blue covers 3,000 to 10,000 eV. For comparison, the energy of visible light is about 2 to 3 eV. NuSTAR observations (green contours) reveal a source of X-rays with energies some three times higher than Chandra detects. X-rays seen from the central point source arise from the binary’s stellar wind collision. The NuSTAR detection shows that shock waves in the wind collision zone accelerate charged particles like electrons and protons to near the speed of light. Some of these may reach Earth, where they will be detected as cosmic ray particles. X-rays scattered by debris ejected in Eta Carinae’s famous 1840 eruption may produce the broader red emission
“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.
Henry White, the Dean of the College of Science has announced that Dr. Pearl Sandick will serve as the next Associate Chair of the Department of Physics & Astronomy, effective July 1st. The department and Dr. Sandick are both very excited for her to take on this new role and help usher in the next phase of growth in the department.
Pearl Sandick
Dr. Pearl Sandick, is an Assistant Professor in the Department of Physics & Astronomy at the University of Utah. She earned a Ph.D. from the University of Minnesota in 2008 and was a postdoctoral fellow in the Theory Group at the University of Texas at Austin before moving to Utah in 2011. Professor Sandick is a theoretical particle physicist studying physics beyond the Standard Model, including supersymmetric theories and possible explanations for the dark matter in the Universe.
In addition to her research, she’s passionate about teaching, mentoring students, and making science accessible and interesting to non-scientists. Professor Sandick currently serves on the APS Committee on the Status of Women in Physics, is the Chair of the National Organizing Committee for the APS Conferences for Undergraduate Women in Physics (CUWiPs), and is the founder and faculty sponsor of the University of Utah Women in Physics and Astronomy (WomPA).
