The VERITAS experiment measured gamma rays coming from the Crab Pulsar at such large energies that they cannot be explained by current scientific models of how pulsars behave, the researchers said.
The results, published today in the journal Science, outline the first observation of photons from a pulsar system with energies greater than 100 billion electron volts -- more than 50 billion times higher than visible light from the sun.
"This is the highest energy pulsar system ever detected," said Rene Ong, a UCLA professor of physics and astronomy and spokesperson for the VERITAS collaboration. "It is a completely new and surprising phenomenon for pulsars."
Data were acquired for 107 hours over the course of three years by VERITAS's ground-based gamma ray observatory, which is part of southern Arizona's Whipple Observatory, a facility managed by the Harvard–Smithsonian Center for Astrophysics. VERITAS (Very Energetic Radiation Imaging Telescope Array System) observes gamma rays using a network of four telescopes, each 12 meters in diameter.
Ong noted that all previous observations of pulsars indicated that the radiation cuts off at the high energies the team observed.
"It means the radiation we detect must be a new component that was completely unexpected," he said.
Gamma rays, the most energetic type of electromagnetic radiation, cannot be directed by lenses or bounced off mirrors like ordinary visible light, Ong said. Because the rays are invisible to the human eye, the only way telescopes on Earth can detect them is by observing the path they take as they are absorbed in the planet's atmosphere.
Gamma rays are ejected from the Crab Pulsar, and they smash into Earth's atmosphere, causing "the electromagnetic equivalent of a sonic boom," Ong said. This collision creates a shower of visible light more than 6 miles above the ground that is recorded by VERITAS.
"The atmosphere is an integral part of our measurement system, which makes VERITAS different from conventional telescopes," Ong said.
One of the most widely studied astronomical objects in the northern hemisphere, the Crab Nebula, which is some 6,500 light-years from Earth, was formed when a massive star exploded in a supernova event that was observed on Earth in the year 1054. While it is most typical for pulsars to be ejected from the stellar wreckage during a supernova, in the case of the Crab system, the pulsar remained at its center, producing radiation that covers the entire electromagnetic spectrum, Ong said.
He calls the Crab system the "Rosetta Stone of astronomy," because astronomers and astrophysicists have observed this object at every conceivable wavelength of light.
"The Crab Pulsar is considered among the best understood systems in all of astronomy, yet here we have found something totally new," he said. "It is astronomy in a completely new light; we are seeing phenomena that you just can't explore with optical light or X-rays, or even low-energy gamma rays."
The Crab Pulsar is a highly magnetized neutron star with a surface magnetic field a trillion times stronger than that of the Earth. The star spins at the dizzying rate of about 30 times a second and emits gamma rays through "curvature radiation," an effect that creates a lighthouse-like beacon that winks on when the beam faces the Earth and off when the star pivots away.
Light detected by the VERITAS experiment cannot be explained by curvature radiation, however, and likely comes from regions well outside the high–magnetic field region close to the neutron star, Ong said. While such energetic gamma rays have been observed elsewhere in the galaxy, the actual mechanism of how they are created in a pulsar is not fully understood.
"The pulse duration of the radiation we see is almost three times shorter than that seen at other gamma ray energies," he said. "This was very surprising and means this new radiation is probably coming from a different physical region of the star's outer magnetosphere."
The VERITAS experiment looks for radiation emanating from celestial objects such as pulsars, active galaxies, the center of the Milky Way and supermassive black holes. It has collected data for nearly 1,000 hours every year since it began operating in 2007.
"We are trying to understand processes out in the cosmos that can create particles at these extreme energies, beyond what can be produced here on Earth," Ong said. "We are also very interested in seeing if these processes indicate some sort of new physics."
Ong hopes his research may shed some light on the mystery of cosmic rays.
"We are bombarded by high-energy particles from all over the cosmos that reach unimaginable energies," he said. "These cosmic rays are an important energy source in our galaxy, yet we have no clue where they are coming from.
"This measurement indirectly gives us clues to the highest energies in the cosmos, telling us about particles and energies that we can't generate here on Earth but that nature's accelerators are able to create for us."
Ong is currently helping to plan the next-generation ground-based gamma ray observatory, called the Cherenkov Telescope Array (CTA). Covering more than one-half square mile with dozens of telescopes, the CTA will be 10 times more sensitive than VERITAS, allowing radiation from fainter and more distant objects to be accurately resolved.
The 95 co-authors of the Science paper on the Crab Pulsar include scientists from 26 institutions in five countries who are part of the VERITAS collaboration. UCLA co-authors include Vladimir Vassiliev, an associate professor of physics and astronomy; Pratik Majumdar, a postdoctoral scholar in physics and astronomy; and Timothy Arlen, a graduate student.
This research is supported by the U.S. Department of Energy, the U.S. National Science Foundation, the Smithsonian Institution, the National Sciences and Engineering Research Council of Canada, the U.K.'s Science and Technology Facilities Council, and the Science Foundation Ireland.
UCLA is California's largest university, with an enrollment of nearly 38,000 undergraduate and graduate students. The UCLA College of Letters and Science and the university's 11 professional schools feature renowned faculty and offer 337 degree programs and majors. UCLA is a national and international leader in the breadth and quality of its academic, research, health care, cultural, continuing education and athletic programs. Six alumni and five faculty have been awarded the Nobel Prize.
For more news, visit the UCLA Newsroom and follow us on Twitter.
Stuart Wolpert | EurekAlert!
Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center
Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
18.10.2017 | Materials Sciences
18.10.2017 | Physics and Astronomy
18.10.2017 | Physics and Astronomy