Yan Zhou's lab receives Gentec EO gift

UNLV Department of Physics & Astronomy is pleased to acknowledge the recent donation of high-tech laser measuring technology by Gentec EO. The QE-25LP is a pyroelectric laser detector that provides a reliable and accurate solution to measure high-energy pulsed lasers in our department. In addition to scientific research impact, it will also improve the laser safety.

The equipment will be housed in the research lab of Assistant Professor, Yan Zhou, in UNLV's Cold and Ultracold Molecular Ions Lab and support research efforts on: (1) exploring new physics beyond the Standard Model by precision measurements using ultracold molecular ions and (2) investigating astrochemistry by emulating the interstellar environment in the laboratory.

Russell Frank Astronomy Lecture: Francis Halzen: IceCube: A Neutrino Window on the Universe. Thursday February 23, 2023 7:30PM. Bigelow Physics Building 102.

Francis Halzen: IceCube: A Neutrino Window on the Universe

The IceCube project at the South Pole melted 86 holes over 1.5 miles deep, in the Antarctic icecap, to construct an enormous observatory. The experiment discovered a flux of neutrinos reaching us from the cosmos, with energies more than a million times those of neutrinos produced at accelerator laboratories. These cosmic neutrinos are astronomical messengers from the extreme universe that is opaque to light. We discuss the IceCube telescope and recent discoveries that some high-energy neutrinos originate from sources powered by supermassive black holes.

This talk is intended for a general audience including enthusiasts of all backgrounds and ages.

The mission of the Russell Frank Astronomy Lecture Series is to bring distinguished scientists to UNLV to present lectures aimed at communicating cutting edge science to the general public. The lectures are free and are held once each semester. They are intended for a general audience and we encourage enthusiasts of all backgrounds and ages to attend.

The sponsor of the series, Russell Frank, is a New Jersey native who has multiple degrees and has taught at several prestigious institutions. Frank says: "I have enjoyed the various courses I have taken at UNLV and providing the astronomy and physics lecture series to the community is my way of giving back to the university."

Astrophysicists from UNLV and Nanjing University revise theoretical framework of Gamma Ray Bursts

Tony Allen from UNLV News Center summarized the work.

The mysteries of the cosmos continue to amaze astronomers, and with each new observation comes a chance to deepen – or upend – our understanding of the universe.

In the Dec. 7 issue of the journal Nature, an international team of astrophysicists report the discovery of a unique cosmological gamma-ray burst (GRB) that defies prevailing theories of how the violent cosmic explosions form. This “oddball” burst led the team to propose a new model, or source, for certain types of GRBs.

Gamma-ray bursts are the most luminous and violent explosions in the universe. They signify the deaths of stars or collisions of stellar remnants. Observed GRBs are typically placed into two categories: short- or long-duration GRBs. Long GRBs originate from the deaths of massive stars, and are typically associated with bright optical transients named supernovae. Short GRBs have a duration of less than two seconds and originate from the collisions of two neutron stars or a neutron star and a black hole, and are typically associated with more faint optical transients known as kilonovae.

For decades, GRBs nestled nicely into these cozy categories. Until now.

On Dec.11, 2021, a GRB triggered several gamma-ray detectors in space, including NASA’s Fermi Gamma-ray Telescope and the Neil Gehrels Swift Observatory. This burst, with a duration of nearly 70 seconds, would typically be regarded as a normal long GRB. That is, until multiple teams from the U.S. and Europe performed follow-up observations and discovered a surprising signature.

“This GRB includes two parts: a 13-second long hard spike and a 55-second softer extended emission,” said UNLV alumnus and study corresponding author Bin-Bin Zhang, who’s currently with China’s Nanjing University. “The duration of the 13-second hard spike should have completely excluded this burst from the short GRB category.”

In other words, instead of showing a much brighter supernova, as expected, the observation was consistent with a kilonova that is more typically associated with a short GRB.

“Such a peculiar GRB was the first of its kind ever detected,” said UNLV astrophysics professor Bing Zhang, co-corresponding-author of the Nature paper. “This discovery not only challenged our understanding of GRB origins, it also requires us to consider a new model for how some GRBs form.”

The research team believes that this unique GRB, known as GRB 211211A, likely formed through collision between a neutron star and a white dwarf, what’s known as a WD-NS merger.

White dwarfs are earth-sized objects that form from the death of low-mass stars – those with a mass smaller than that of about eight of our Suns. Neutron stars form when more massive stars, those with a mass of between about eight and 20 Suns, die off. When even larger stars die, they form black holes directly.

Massive, low-density stars make long-duration GRBs whereas high-density stars, including neutron stars, make short duration GRBs. According to UNLV’s Zhang, white dwarfs have intermediate densities, which make them ideal origins for the type of GRB discovered in 2021 as it displays an intermediately long duration without involving a massive star.

“Despite the relatively large number of GRBs observed each year, the unique signature of GRB 211211A pushed the envelope of our current categorial systems and required a new way of thinking,” said Zhang. “After careful review, the only merger scenario that made sense was that of a white dwarf and neutron star.”

UNLV doctoral student Shunke Ai and a student from Nanjing University collaborated to develop a detailed model to interpret the peculiar kilonova signature observed by GRB 211211A. Ai found that if a WD-NS merger leaves behind a rapidly spinning neutron star, known as a magnetar, the additional energy injection from the magnetar combined with the nuclear reaction energy from the material thrown during the burst can account for the kilonova emission observed for GRB 211211A. About the Study

The study, “A long-duration gamma-ray burst with a peculiar origin”, appeared Dec. 7 in the journal Nature. The paper includes 10 co-authors from 4 institutions, with UNLV and Nanjing University being the lead institutions. Published in the same issue are three parallel papers that report the detection of the kilonova. This paper focuses on the peculiar gamma-ray emission itself and proposes the WD-NS merger model to interpret the data.

 

(Image credit: Anyu Lei and Jing Chen, Nanjing University School of Arts)

International Team of Astronomers closer to an understanding of Fast Radio Bursts

Author: Tony Allen from UNLV News Center.

Nearly 15 years after the discovery of fast radio bursts (FRBs), the origin of the millisecond-long, deep-space cosmic explosions remains a mystery.

That may soon change, thanks to the work of an international team of scientists – including UNLV astrophysicist Bing Zhang – which tracked hundreds of the bursts from five different sources and found clues in FRB polarization patterns that may reveal their origin. The team’s findings were reported in the March 17 issue of the journal Science.

FRBs produce electromagnetic radio waves, which are essentially oscillations of electric and magnetic fields in space and time. The direction of the oscillating electric field is described as the direction of polarization. By analyzing the frequency of polarization in FRBs observed from various sources, scientists revealed similarities in repeating FRBs that point to a complex environment near the source of the bursts.

“This is a major step towards understanding the physical origin of FRBs,” said Zhang, a UNLV distinguished professor of astrophysics who coauthored the paper and contributed to the theoretical interpretation of the phenomena.

To make the connection between the bursts, an international research team, led by Yi Feng and Di Li of the National Astronomical Observatories of the Chinese Academy of Sciences, analyzed the polarization properties of five repeating FRB sources using the massive Five-hundred-meter Aperture Spherical radio Telescope (FAST) and the Robert C. Byrd Green Bank Telescope (GBT). Since FRBs were first discovered in 2007, astronomers worldwide have turned to powerful radio telescopes like FAST and GBT to trace the bursts and to look for clues on where they come from and how they’re produced.

Though still considered mysterious, the source of most FRBs is widely believed to be magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the universe. They typically have nearly 100% polarization. Conversely, in many astrophysical sources that involve hot randomized plasmas, such as the Sun and other stars, the observed emission is unpolarized because the oscillating electric fields have random orientations.

That’s where the cosmic detective work kicks in.

In a study the team originally published last year in Nature, FAST detected 1,652 pulses from the active repeater FRB 121102. Even though the bursts from the source were discovered to be highly polarized with other telescopes using higher frequencies – consistent with magnetars – none of the bursts detected with FAST in its frequency band were polarized, despite FAST being the largest single-dish radio telescope in the world.

“We were very puzzled by the lack of polarization,” said Feng, first author on the newly released Science paper. “Later, when we systematically looked into other repeating FRBs with other telescopes in different frequency bands – particularly those higher than that of FAST, a unified picture emerged.”

According to Zhang, the unified picture is that every repeating FRB source is surrounded by a highly magnetized dense plasma. This plasma produces different rotation of the polarization angle as a function of frequency, and the received radio waves come from multiple paths due to scattering of the waves by the plasma.

When the team accounted for just a single adjustable parameter, Zhang says, the multiple observations revealed a systematic frequency evolution, namely depolarization toward lower frequencies.

“Such a simple explanation, with only one free parameter, could represent a major step toward a physical understanding of the origin of repeating FRBs,” he says.

Di Li, a corresponding author of the study, agrees that the analysis could represent a corner piece in completing the cosmic puzzle of FRBs. “For example, the extremely active FRBs could be a distinct population,” he says. “Alternatively, we’re starting to see the evolutionary trend in FRBs, with more active sources in more complex environments being younger explosions.”

The study, “Frequency-dependent polarization of repeating fast radio bursts—implications for their origin,” appeared March 17 in the journal Science. It includes 25 co-authors from 11 institutions and is part of long-running collaboration among institutions. In addition to UNLV and NAOC, collaborating institutions also include Yunnan University, Princeton University, Western Sidney University, Peking University and Green Bank Observatory, USA. 

(Image credit: Jingchuan Yu, Beijing Planetarium)

International Team of Astronomers Reports on Largest-ever Observed Set of Mysterious Fast Radio Bursts

Reported by Tony Allen in UNLV News Center.

An international team of astronomers recently observed more than 1,650 fast radio bursts (FRBs) detected from one source in deep space, which amounts to the largest set – by far – of the mysterious phenomena ever recorded.

More than a decade after the discovery of FRBs, astronomers are still baffled by the origins of the millisecond-long, cosmic explosions that each produce the energy equivalent to the sun’s annual output.

In a study published in the Oct. 13 issue of the journal Nature, scientists – including UNLV astrophysicist Bing Zhang – report on the discovery of a total of 1,652 independent FRBs from one source over the course of 47 days in 2019. The source, dubbed FRB 121102, was observed using the Five-hundred-meter Aperture Spherical Telescope (FAST) in China, and represents more FRBs in one event than all previous reported occurrences combined.

“This was the first time that one FRB source was studied in such great detail,” said Zhang, one of the study’s corresponding authors. “The large burst set helped our team hone in like never before on the characteristic energy and energy distribution of FRBs, which sheds new light on the engine that powers these mysterious phenomena.”

Since FRBs were first discovered in 2007, astronomers worldwide have turned to powerful radio telescopes like FAST to trace the bursts and to look for clues on where they come from and how they’re produced. The source that powers most FRBs is widely believed to be magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the universe. And while scientists are gaining greater clarity on what produces FRBs, the exact location of where they occur is still a mystery.

A mystery that recent results may be starting to unravel.

According to Zhang, there are two active models for where FRBs come from. One could be that they come from magnetospheres, or within a magnetar’s strong magnetic field. Another theory is that FRBs form from relativistic shocks outside the magnetosphere traveling at the speed of light.

“These results pose great challenges to the latter model,” says Zhang. “The bursts are too frequent and - given that this episode alone amounts to 3.8% of the energy available from a magnetar - it adds up to too much energy for the second model to work.”

The bursts were measured by FAST within a total of 59.5 hours over 47 days from Aug. 29 to Oct. 29, 2019. 

“During its most active phase, FRB 121102 included 122 bursts measured within a one-hour period, the highest repeat rate ever observed for any FRB,” said Pei Wang, one of the article’s lead authors from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

Researchers expect that FAST will continue to systematically investigate a large number of repeating FRBs in the future.

“As the world’s largest antenna, FAST’s sensitivity proves to be conducive to revealing intricacies of cosmic transients, including FRBs,” said Di Li, the study’s lead researcher from NAOC.

The study includes more than 30 co-authors from 16 institutions in four countries and is part of a long-running collaboration among the institutions. In addition to UNLV and NAOC, collaborating institutions include Guizhou Normal University, Cornell University, Max Planck Institute for Radio Astronomy, West Virginia University, CSIRO Astronomy and Space Science, University of California Berkeley, and Nanjing University.

Publication Details: “A bimodal burst energy distribution of a repeating fast radio burst source,” was published in the Oct. 13, 2021 issue of the journal Nature.

Professor Monika Mościbrodzka. Imaging Magnetic Fields at the Edge of M87's Black Hole. Thursday April 29, 2021 at 7PM PDT (ONLINE).

The Russell Frank Astronomy Lecture Series
UNLV Physics and Astronomy Department
7:00PM PDT Thursday April 29, 2021
2:00AM GMT Friday April 30, 2021
Webex link https://unlv.webex.com/unlv/j.php??MTID=m9b77c4799c5efce726b9afdbd984e08a

Two years ago, scientists presented the first image of a black hole at the center of a galaxy. We see a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. Last month, for the first time, observations revealed the signature of magnetic fields close to the edge of a black hole. These new images are the key to explaining how the black hole is able to launch energetic jets. Dr. Mościbrodzka will discuss how these images of the black hole were made and their meaning.

This talk is intended for a general audience including enthusiasts of all backgrounds and ages.

Bing Zhang contributes to understanding the physical mechanisms of fast radio bursts in three papers published in Nature.

Authored by Shane Bevell for the UNLV News Center, November 4, 2020.

Fast radio bursts, or FRBs – powerful, millisecond-duration radio waves coming from deep space outside the Milky Way Galaxy – have been among the most mysterious astronomical phenomena ever observed. Since FRBs were first discovered in 2007, astronomers from around the world have used radio telescopes to trace the bursts and look for clues on where they come from and how they’re produced.

UNLV astrophysicist Bing Zhang and international collaborators recently observed some of these mysterious sources, which led to a series of breakthrough discoveries reported in the journal Nature that may finally shed light into the physical mechanism of FRBs.

The first paper, for which Zhang is a corresponding author and leading theorist, was published in the Oct. 28 issue of Nature.

“There are two main questions regarding the origin of FRBs,” said Zhang, whose team made the observation using the Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, China. “The first is what are the engines of FRBs and the second is what is the mechanism to produce FRBs. We found the answer to the second question in this paper.”

Two competing theories have been proposed to interpret the mechanism of FRBs. One theory is that they’re similar to gamma-ray bursts (GRBs), the most powerful explosions in the universe. The other theory likens them more to radio pulsars, which are spinning neutron stars that emit bright, coherent radio pulses. The GRB-like models predict a non-varying polarization angle within each burst whereas the pulsar-like models predict variations of the polarization angle.

The team used FAST to observe one repeating FRB source and discovered 11 bursts from it. Surprisingly, seven of the 11 bright bursts showed diverse polarization angle swings during each burst. The polarization angles not only varied in each burst, the variation patterns were also diverse among bursts.

“Our observations essentially rules out the GRB-like models and offers support to the pulsar-like models,” said K.-J. Lee from the Kavli Institute for Astronomy and Astrophysics, Peking University, and corresponding author of the paper.

Four other papers on FRBs were published in Nature on Nov. 4. These include multiple research articles published by the FAST team led by Zhang and collaborators from the National Astronomical Observatories of China and Peking University. Researchers affiliated with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Survey for Transient Astronomical Radio Emission 2 (STARE2) group also partnered on the publications.

“Much like the first paper advanced our understanding of the mechanism behind FRBs, these papers solved the challenge of their mysterious origin,” explained Zhang.

Magnetars are incredibly dense, city-sized neutron stars that possess the most powerful magnetic fields in the universe. Magnetars occasionally make short X-ray or soft gamma-ray bursts through dissipation of magnetic fields, so they have been long speculated as plausible sources to power FRBs during high-energy bursts.

The first conclusive evidence of this came on April 28, 2020, when an extremely bright radio burst was detected from a magnetar sitting right in our backyard – at a distance of about 30,000 light years from Earth in the Milky Way Galaxy. As expected, the FRB was associated with a bright X-ray burst.

“We now know that the most magnetized objects in the universe, the so-called magnetars, can produce at least some or possibly all FRBs in the universe,” said Zhang.

The event was detected by CHIME and STARE2, two telescope arrays with many small radio telescopes that are suitable for detecting bright events from a large area of the sky.

Zhang’s team has been using FAST to observe the magnetar source for some time. Unfortunately, when the FRB occurred, FAST was not looking at the source. Nonetheless, FAST made some intriguing “non-detection” discoveries and reported them in one of the Nov. 4 Nature articles. During the FAST observational campaign, there were another 29 X-ray bursts emitted from the magnetar. However, none of these bursts were accompanied by a radio burst.

“Our non-detections and the detections by the CHIME and STARE2 teams delineate a complete picture of FRB-magnetar associations,” Zhang said.

To put it all into perspective, Zhang also worked with Nature to publish a single-author review of the various discoveries and their implications for the field of astronomy.

“Thanks to recent observational breakthroughs, the FRB theories can finally be reviewed critically,” said Zhang. “The mechanisms of producing FRBs are greatly narrowed down. Yet, many open questions remain. This will be an exciting field in the years to come.”

Read More

• "No pulsed radio emission during a bursting phase of a Galactic magnetar," published in the Nov. 4 issue of Nature.
• "The physical mechanisms of fast radio bursts," published in the Nov. 4 issue of Nature.
• "Diverse polarization angle swings from a repeating fast radio burst source," published in the Oct. 28 issue of Nature.