How to make all headphones intelligent

Rutgers engineers can turn 'dumb' headphones into smart ones by turning them into sensors

RUTGERS UNIVERSITY

Research News

    SHARE

 PRINT  E-MAIL

IMAGE: ENGINEERS CONDUCTED EXPERIMENTS WITH "DUMB " HEADPHONES WITH ESTIMATED PRICES RANGING FROM $2.99 TO $15,000. HEADFI CAN TRANSFORM SUCH HEADPHONES INTO SMART ONES. view more 

CREDIT: XIAORAN FAN

How do you turn "dumb" headphones into smart ones? Rutgers engineers have invented a cheap and easy way by transforming headphones into sensors that can be plugged into smartphones, identify their users, monitor their heart rates and perform other services.

Their invention, called HeadFi, is based on a small plug-in headphone adapter that turns a regular headphone into a sensing device. Unlike smart headphones, regular headphones lack sensors. HeadFi would allow users to avoid having to buy a new pair of smart headphones with embedded sensors to enjoy sensing features.

"HeadFi could turn hundreds of millions of existing, regular headphones worldwide into intelligent ones with a simple upgrade," said Xiaoran Fan, a HeadFi primary inventor. He is a recent Rutgers doctoral graduate who completed the research during his final year at the university and now works at Samsung Artificial Intelligence Center.

A peer-reviewed Rutgers-led paper on the invention, which results in "earable intelligence," will be formally published in October at MobiCom 2021, the top international conference on mobile computing and mobile and wireless networking.

Headphones are among the most popular wearable devices worldwide and they continue to become more intelligent as new functions appear, such as touch-based gesture control, the paper notes. Such functions usually rely on auxiliary sensors, such as accelerometers, gyroscopes and microphones that are available on many smart headphones

CAPTION

"Dumb" headphones can be plugged into a HeadFi device that connects to a cellphone, turning them into intelligent headphones. Engineers are working on a smaller version of the device.

CREDIT

Siddharth Rupavatharam

HeadFi turns the two drivers already inside all headphones into a versatile sensor, and it works by connecting headphones to a pairing device, such as a smartphone. It does not require adding auxiliary sensors and avoids changes to headphone hardware or the need to customize headphones, both of which may increase their weight and bulk. By plugging into HeadFi, a converted headphone can perform sensing tasks and play music at the same time.

The engineers conducted experiments with 53 volunteers using 54 pairs of headphones with estimated prices ranging from $2.99 to $15,000. HeadFi can achieve 97.2 percent to 99.5 percent accuracy on user identification, 96.8 percent to 99.2 percent on heart rate monitoring and 97.7 percent to 99.3 percent on gesture recognition.

###

Rutgers co-authors include Siddharth Rupavatharam, an electrical and computer engineering doctoral student, and Research Professor Richard E. Howard, the senior author and co-primary inventor at Rutgers' Wireless Information Network Laboratory (WINLAB), a research center in the School of Engineering. Engineers at the University of Science and Technology of China, University of Massachusetts Amherst, Microsoft and Alibaba Group contributed to the paper. A patent is pending.

CAPTION

The HeadFi prototype.

CREDIT

Siddharth Rupavatharam

 

Polarization: From better sunglasses to a better way of looking at asteroid surfaces

Unique technique may help planetary defense prepare for asteroids on a collision course with Earth

UNIVERSITY OF CENTRAL FLORIDA

Research News

 

IMAGE: DYLAN HICKSON IS A RESEARCH SCIENTIST AT THE ARECIBO OBSERVATORY IN PUERTO RICO AND LEAD AUTHOR OF THE PAPER. view more 

CREDIT: CREDIT: ARECIBO OBSERVATORY/ISRAEL CABRERA

Using the same principles that make polarized sunglasses possible, a team of researchers at the Arecibo Observatory in Puerto Rico have developed a technique that will help better defend against asteroids on a collision course with Earth.

A new study recently published in The Planetary Science Journal found a better way to interpret radar signals bounced off asteroids' surfaces. The data can better tell us if an asteroid is porous, fluffy or rocky, which matters because there are hundreds of near-Earth asteroids that could potentially hit the planet.

"Learning more about the physical properties of asteroids is crucial in Planetary Defense," says Dylan Hickson the lead author and a research scientist at the Arecibo Observatory in Puerto Rico. "A porous, fluffy asteroid does not pose as much of an impact threat as a dense, rocky asteroid does. With our research we can better prepare for potential asteroid impact events.

Depending on their size and composition some asteroids will burn up in the atmosphere, but others could cause catastrophic damage. Knowing how to deflect these potential threats will depend on what we know about their makeup.

Data collected from 1999-2015 with the Arecibo's main dish in Puerto Rico were used to complete the study. Arecibo is a U.S. National Science Foundation facility, which UCF manages for NSF under a cooperative agreement with Universidad Ana G. Méndez and Yang Enterprises Inc. The main dish collapsed in December, but work continues throughout the rest of the facility, and scientists continue to use previously collected data.

"When we send a radar signal with Arecibo, we know the exact polarization of the light, but when it bounces off of a surface, that can change how it's polarized," Hickson says. "If the asteroid surface was a smooth mirror, for example, it will reverse polarization 'perfectly' when the signal is reflected. With a rough and rocky surface, the light will interact with rock edges, cracks, and grains -- and reflect in a completely different polarization."

When the team analyzed Arecibo data, they broke down the polarization of the received signal into various components to decipher what surface features produced them. Is more of the surface fine-grained, smooth dust, sand-like grains or big rocks? Or is the surface full of small rocks and fine grains of dust?

Using polarimetric decomposition (polarization technique) isn't new, but it isn't 100% reliable yet. For example, scientists on NASA's OSIRIS REx mission were surprised by how rocky asteroid Bennu was when they arrived last year to begin a sample collection mission. Images taken from the spacecraft found the surface to be much more rocky than initial radar data indicated, and the team had to adjust its sample target site.

"Our results provide a methodology to extract more information about the surface properties from observations, giving us a better picture of what these mysterious surfaces look like," Hickson says. "Not only can this methodology be applied to archival data, but it can also be applied to future observations, potentially vastly increasing our understanding of the broader asteroid population."

###

Hickson is a postdoctoral research scientist in the Planetary Science Group at the Arecibo Observatory since 2019. He has a doctorate in Earth and space science from York University in Toronto, Canada and bachelor's degrees in Earth and environmental science and physical science from McMaster University in Hamilton, Canada.

The rest of the team on the paper includes: Anne K. Virkki and Phil Perillat from the Arecibo Observatory, Michael C. Nolan from the Lunar and Planetary Laboratory at the University of Arizona, and Sriram S. Bhiravarasu from Space Applications Centre in India.

The secrets of the best rainbows on Earth

UNIVERSITY OF HAWAII AT MANOA

Research News

 

IMAGE: RAINBOW OVER EAST OAHU. view more 

CREDIT: STEVEN BUSINGER

Rainbows are some of the most spectacular optical phenomena in the natural world and Hawai'i has an amazing abundance of them. In a new publication, an atmospheric scientist at the University of Hawai'i at Mānoa makes an impassioned case for Hawaii being the best place on Earth to experience the wonder of rainbows. He begins by highlighting the Hawaiian cultural significance of rainbows, he reviews the science of rainbows and the special combination of circumstances that makes Hawai'i a haven for rainbows.

"The cultural importance of rainbows is reflected in the Hawaiian language, which has many words and phrases to describe the variety of manifestations in Hawai'i," said author Steven Businger, professor in the UH Mānoa School of Ocean and Earth Science and Technology. "There are words for Earth-clinging rainbows (uakoko), standing rainbow shafts (ka?hili), barely visible rainbows (punakea), and moonbows (a?nuenue kau po?), among others. In Hawaiian mythology the rainbow is a symbol of transformation and a pathway between Earth and Heaven, as it is in many cultures around the world."

Why is Hawai'i the rainbow capital of the world?

The essential ingredients for rainbows are, of course, rain and sunlight. To see a rainbow on flat ground the sun must be within about 40 degrees of the horizon. As the sun rises to higher angles in the sky during the morning, the height of the rainbow diminishes until no rainbow is visible above the horizon. The pattern is reversed as the sun lowers in the afternoon, with rainbows rising in the east and the tallest rainbows just prior to sunset.

Hawai'i's location in the subtropical Pacific means the overall weather pattern is dominated by trade winds, with frequent rain showers and clear skies between the showers.

Businger outlines four additional factors affecting the prevalence of rainbows throughout the islands.

"At night a warm sea surface heats the atmosphere from below, while radiation to space cools cloud tops, resulting in deeper rain showers in the morning that produce rainbows in time for breakfast," said Businger.

Another critical factor in producing frequent rainbows is Hawai'i's mountains, which cause trade wind flow to be pushed up, forming clouds and producing rainfall. Without mountains, Hawai'i would be a desert with a scant 17 inches annual rainfall.

A third factor conducive to rainbow sightings is daytime heating, which drives island-scale circulations. During periods of lighter winds, showers form over the ridge crests over Oahu and Kauai in the afternoon, resulting in prolific rainbows as the sun sets.

Due to the remoteness of the Hawaiian Islands, the air is exceptionally clean and free of pollution, continental dust, and pollen. This is the fourth factor that contributes to the numerous bright rainbows with the full spectrum of colors.

CAPTION

Rainbow over Honolulu Harbor with what appears to be its reflection. However, the reflected bow is not what it appears to be. See the paper for explanation.

CREDIT

Minghue Chen

Chasing rainbows

As Businger pursued his passion for finding and photographing these beautiful light displays, he began to imagine a smartphone app with access to Doppler radar data and high-resolution satellite data that could alert users when nearby conditions become conducive for rainbow sightings.

"After a few years of false starts, Paul Cynn and I finally connected with Ikayso, a Hawaiian smartphone app developer in April of 2020. I am very excited to say that our app, called RainbowChase, is now available to the public for free," said Businger.

###

RainbowChase is the only app that provides guidance to bring more rainbows into your life. Users can view radar and satellite images of rain and clouds, along with current and future weather, and collect rainbow photos.

CAPTION

An example of supernumerary bows beneath the primary bow.

CREDIT

Matt Champlin

 

Study of Redoubt and other volcanoes improves unrest detection

UNIVERSITY OF ALASKA FAIRBANKS

 

Volcanologists do what they can to provide the public enough warning about impending eruptions, but volcanoes are notoriously unpredictable. Alerts are sometimes given with little time for people to react.

That may soon change.

Work led by research assistant professor Társilo Girona, with the University of Alaska Fairbanks Geophysical Institute, has revealed a method by which scientists -- and the public -- can have perhaps years of advance warning about a potential eruption.

The solution lies in regular and widespread monitoring of the radiant temperature of a volcano's flanks before the appearance of any of the usual warning signs, such as glacier melting, sulfur odors, increased gas emissions, quaking and deformation.

Girona is the lead author of a paper published today in the journal Nature Geosciences titled "Large-Scale Thermal Unrest of Volcanoes for Years Prior To Eruption." The paper is co-authored by Vincent Realmuto and Paul Lundgren, research scientists at NASA's Jet Propulsion Laboratory in Pasadena, California. Lundgren supervises JPL's Earth Surface and Interior Group.

"This is showing that very large areas in the volcanoes are increasing the release of heat," Girona said. "It's a process which is going on in, we cannot say in the whole volcano itself, but in very large areas in the volcano. It's a large-scale process."

Girona also works with the Alaska Volcano Observatory, which is evaluating how best to integrate the research findings into its monitoring of Alaska volcanoes. The AVO is a cooperative organization among UAF, the U.S. Geological Survey and the Alaska Division of Geological and Geophysical Surveys.

David Fee, AVO coordinating scientist at UAF, said the findings can bolster volcano monitoring. That's important for the airline industry, particularly in Alaska and especially near Anchorage and other communities potentially in the path of an ash cloud.

"These results might provide critical information on how best to supplement existing monitoring networks, especially for difficult-to-monitor volcanoes in remote parts of Alaska," he said. "Any advance information on eruptions is helpful."

The research focused on five volcanoes that erupted or exploded in the past 20 years, that displayed a wide range of behaviors and characteristics, and that are considered representative of volcanoes worldwide: Mount Redoubt in Alaska, Mount Ontake in Japan, Mount Ruapehu in New Zealand, Calbuco in Chile and Pico do Fogo in Cabo Verde, an island nation off the west coast of Africa.

The researchers analyzed 16 ½ years of thermal infrared radiance data collected by NASA's Terra and Aqua satellites.

The satellite data had never been analyzed with an eye toward long-term early awareness of potential volcanic activity.

Girona, Realmuto and Lundgren wanted to answer this question: Does volcanic activity underground produce a noticeable increase in radiant temperature at the surface long before an eruption?

The data provided the answer for all five of the studied volcanoes: A clear "yes."

The researchers wrote that volcanoes can experience thermal unrest "for several years before eruption" and that the unrest "is dominated by a large-scale phenomenon operating over extensive areas of volcanic edifices." They also found that the heat increased regardless of the type of eruption.

Mount Redoubt, for example, had an increase of 0.85 degrees Fahrenheit, plus or minus 0.31 degrees (0.47 degrees Celsius, plus or minus 0.17), from mid-2006 to its major eruption of March 2009. Notably, the radiant temperature began increasing approximately one year earlier than the onset of other warning signs. Redoubt's radiant temperature began dropping quickly a year after the eruption and has remained low since 2014.

The researchers said their findings will allow scientists to anticipate eruptions that are difficult to forecast through other geophysical and geochemical methods.

"This is especially relevant for phreatic eruptions (volcanic gas explosions), such as the one at Ontake, Japan, in 2014," Girona said. "Phreatic eruptions are generally very difficult to anticipate with traditional methods."

The research, which Girona began at JPL and continued after moving to the Geophysical Institute, also provides insights into the interaction between a volcano's magmatic gases and its subsurface system of superheated water.

Lundgren said the new approach, combined with such tools as GPS or satellite radar measurements of surface displacements, can reveal even more about volcano processes.

For example, the team integrated surface heat emissions with surface displacements in another recent publication to better understand the behavior of Domuyo, a newly discovered deforming volcano in Argentina.

View east of Redoubt volcano and recent eruption deposits on the upper west-southwest flanks.

###

NOTE TO EDITORS:

Photographs of Mount Redoubt are available at https://avo.alaska.edu/images/image.php?id=17859 and http://www.avo.alaska.edu/images/image.php?id=17627.

Two graphics about Mount Redoubt are available at https://news.uaf.edu/wp-admin/post.php?post=128347&action=edit.

The research paper will be available at https://dx.doi.org/10.1038/s41561-021-00705-4.

 

Distant planet may be on its second atmosphere, NASA's Hubble finds

NASA/GODDARD SPACE FLIGHT CENTER

Research News

    SHARE

 PRINT  E-MAIL

IMAGE: THIS IS AN ARTIST'S IMPRESSION OF THE EARTH-SIZED, ROCKY EXOPLANET GJ 1132 B, LOCATED 41 LIGHT-YEARS AWAY AROUND A RED DWARF STAR. SCIENTISTS USING NASA'S HUBBLE SPACE TELESCOPE HAVE FOUND... view more 

CREDIT: CREDITS: NASA, ESA, AND R. HURT (IPAC/CALTECH)

Scientists using NASA's Hubble Space Telescope have found evidence that a planet orbiting a distant star may have lost its atmosphere but gained a second one through volcanic activity.

The planet, GJ 1132 b, is hypothesized to have begun as a gaseous world with a thick hydrogen blanket of atmosphere. Starting out at several times the diameter of Earth, this so-called "sub-Neptune" is believed to have quickly lost its primordial hydrogen and helium atmosphere due to the intense radiation of the hot, young star it orbits. In a short period of time, such a planet would be stripped down to a bare core about the size of Earth. That's when things got interesting.

To the surprise of astronomers, Hubble observed an atmosphere which, according to their theory, is a "secondary atmosphere" that is present now. Based on a combination of direct observational evidence and inference through computer modeling, the team reports that the atmosphere consists of molecular hydrogen, hydrogen cyanide, methane and also contains an aerosol haze. Modeling suggests the aerosol haze is based on photochemically produced hydrocarbons, similar to smog on Earth.

Scientists interpret the current atmospheric hydrogen in GJ 1132 b as hydrogen from the original atmosphere which was absorbed into the planet's molten magma mantle and is now being slowly released through volcanic processes to form a new atmosphere. The atmosphere we see today is believed to be continually replenished to balance the hydrogen escaping into space.

"It's super exciting because we believe the atmosphere that we see now was regenerated, so it could be a secondary atmosphere," said study co-author Raissa Estrela of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "We first thought that these highly irradiated planets could be pretty boring because we believed that they lost their atmospheres. But we looked at existing observations of this planet with Hubble and said, 'Oh no, there is an atmosphere there.'"

The findings could have implications for other exoplanets, planets beyond our solar system.

"How many terrestrial planets don't begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism that photo-evaporates the primordial atmosphere. This process works early in a planet's life, when the star is hotter," said lead author Mark Swain of JPL. "Then the star cools down and the planet's just sitting there. So you've got this mechanism where you can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it."

In some ways GJ 1132 b, located about 41 light-years from Earth, has tantalizing parallels to Earth, but in some ways it is very different. Both have similar densities, similar sizes, and similar ages, being about 4.5 billion years old. Both started with a hydrogen-dominated atmosphere, and both were hot before they cooled down. The team's work even suggests that GJ 1132 b and Earth have similar atmospheric pressure at the surface.

But the planets have profoundly different formation histories. Earth is not believed to be the surviving core of a sub-Neptune. And Earth orbits at a comfortable distance from our Sun. GJ 1132 b is so close to its red dwarf star that it completes an orbit around its host star once every day and a half. This extremely close proximity keeps GJ 1132 b tidally locked, showing the same face to its star at all times--just as our Moon keeps one hemisphere permanently facing Earth.

"The question is, what is keeping the mantle hot enough to remain liquid and power volcanism?" asked Swain. "This system is special because it has the opportunity for quite a lot of tidal heating."

Tidal heating is a phenomenon that occurs through friction, when energy from a planet's orbit and rotation is dispersed as heat inside the planet. GJ 1132 b is in an elliptical orbit, and the tidal forces acting on it are strongest when it is closest to or farthest from its host star. At least one other planet in the host star's system also gravitationally pulls on the planet.

The consequences are that the planet is squeezed or stretched through this gravitational "pumping." That tidal heating keeps the mantle liquid for a long time. A nearby example in our own solar system is Jupiter's moon Io, which has continuous volcanic activity due to a tidal tug-of-war from Jupiter and the neighboring Jovian moons.

Given GJ 1132 b's hot interior, the team believes the planet's cooler, overlying crust is extremely thin, perhaps only hundreds of feet thick. That's much too feeble to support anything resembling volcanic mountains. Its flat terrain may also be cracked like an eggshell due to tidal flexing. Hydrogen and other gases could be released through such cracks.

NASA's upcoming James Webb Space Telescope has the ability to observe this exoplanet. Webb's infrared vision may allow scientists to see down to the planet's surface. "If there are magma pools or volcanism going on, those areas will be hotter," explained Swain. "That will generate more emission, and so they'll be looking potentially at the actual geologic activity--which is exciting!"

###

The team's findings will be published an upcoming issue of The Astronomical Journal.

Artwork:
NASA, ESA, and R. Hurt (IPAC/Caltech) Science: NASA, ESA, and M. Swain (Jet Propulsion Laboratory)

CAPTION

The rocky exoplanet GJ 1132 b, similar in size and density to Earth, possesses a hazy atmosphere made up of volcanic gases. Scientists say GJ 1132 b, orbiting a red-dwarf star about 41 light-years away, has some features in common with worlds in our own solar system as well as vast differences. Its hazy appearance might compare to Titan, Saturn's largest moon, the only solar system moon with a substantial atmosphere - though Titan is much colder. Our own Earth might have had such a hazy appearance early in its history, although unlike Earth, the new planet is far too hot to be habitable. And GJ 1132 b likely has a "secondary atmosphere," created by volcanic activity after its first hydrogen-helium atmosphere was stripped away by radiation from its star.

CREDIT

Credits: NASA/JPL-Caltech/Lizbeth B. De La Torre

Uncovering exotic molecules of potential astrochemical interest

INSTITUTE OF PHYSICAL CHEMISTRY OF THE POLISH ACADEMY OF SCIENCES

Research News

 

IMAGE: CO-AUTHORS DR. ARUNLIBERTSEN LAWZER I DR. THOMAS CUSTER OF RESEARCH DEMONSTRATE THE MOLECULES OF THE ASTROCHEMICAL INTEREST AT THE PLANETARIUM OF THE COPERNICUS SCIENCE CENTRE. SOURCE: IPC PAS, GRZEGORZ KRZYZEWSKI... view more 

CREDIT: © INSTITUTE OF PHYSICAL CHEMISTRY, POLISH ACADEMY OF SCIENCES

Looking at the night sky, one's thoughts might be drawn to astrochemistry. What molecules inhabit the vast spaces between the stars? Would we see the same molecules that surround us here on Earth? Or would some of them be more exotic--something rarely observed or even unknown?

Recent research by a multinational team led by Prof. Robert Ko?os from the Institute of Physical Chemistry of the Polish Academy of Sciences has revealed an unusual molecule obtained and detected for the first time in laboratory conditions and also paved a smooth path to produce and further study another. Now that they can be seen and studied, they may prove worthy of wider astrochemical interest. Let's get a closer look at this scientific development.

Interstellar clouds - where the story begins...

The medium permeating the space between stars is mainly filled with hydrogen, helium, and cosmic dust. However, average distances between atoms or molecules in these interstellar clouds are so vast that entire days may pass before they collide. In the vacuum of space, the passage of time and the impact of radiation are crucial factors for the development of more advanced chemical compounds.

As the physical conditions found in interstellar clouds are drastically different from those on our planet, the detection of some of the chemical compounds found in them requires advanced studies on Earth. As part of this, scientists create molecules which are normally unstable under Earth conditions and then conduct research on their properties. They discover them on Earth first so that we can more easily detect them in space. Sounds interesting, but how does it look in practice?

Phosphorus menagerie

Jupiter and Saturn have been in the spotlight in our own solar system for more than two decades due to the detection of phosphine (PH3), ammonia's analog, in their atmospheres. In 2020, all eyes shifted towards Venus following claims that PH3 had been found in its atmosphere as well. The appearance of phosphine in an astronomical object is momentous because of its tremendous importance for living organisms. Molecules containing phosphorus are crucial for enzymatic processes which are responsible for the formation of the structural materials of our skeletons, nucleic acids like DNA and RNA, and even energy transport in all living cells. Although it is the 6th most abundant element in Earth's biomass and the 12th most abundant on the planet overall, it is a billion times less abundant in the interstellar medium. Due to their rarity, detecting P-containing molecules in interstellar clouds continues to intrigue scientists.

We know very little about the behavior and existence of P-containing molecules in extreme interstellar conditions. Only a few have been found and are limited to PN, CP, PO, HCP, CCP, PH3, and NCCP. Of these only PO and PN have been detected in molecular clouds. It is possible that the low abundance of reactants containing phosphorus in such media makes the formation of larger molecules quite rare and difficult to detect. We also need to characterize a wider variety of P-containing chemicals so that our search may be expanded to include a larger selection of appropriate targets. The search for new molecules is challenging since many known and promising P-containing species are unstable under typical laboratory conditions.

The IPC PAS researchers: Dr. Arun-Libertsen Lawzer, Dr. Thomas Custer, and Prof. Robert Ko?os, working in collaboration with Prof. Jean-Claude Guillemin of the Ecole Nationale Supérieure de Chimie de Rennes (France) have recently presented an efficient, UV-light-assisted cryogenic synthesis of the HCCP molecule, opening new possibilities for the spectroscopic investigation of this unusual chemical compound. It was detected using infrared and UV-vis spectroscopy. This characterization should be useful for possible future extraterrestrial detections.

"We use ultraviolet to dehydrogenate phosphorus containing organic molecules to produce exotic phosphorus species. We were able to produce triplet HCCP which is a molecule of astrochemical importance. The trick to detecting it lies in using the environment of a frozen inert gas." - remarks Dr. Lawzer.

The experiments performed as part of the project, and relevant theoretical studies show that the molecule has a linear shape and peculiar chemical bonding. Prof. Ko?os comments: "You may have heard in your school days that phosphorus was either 3- or 5-valent in its chemical compounds. Well, here it is monovalent, sporting a single bond to carbon. This is pretty unusual indeed."

The researchers also confirmed the existence of CH2=C=PH (phosphaallene), a molecule never observed before. It was formed along the route leading from CH3CP (the precursor species) to HCCP.

Experiments backed by quantum chemical computations, recently reported in Angewandte Chemie, have proven what was once but a theoretical construct. "If you asked a regular chemist, some of the most prominent species of the astrochemical menagerie would likely be ridiculed as mere molecular fragments rather than genuine molecules" - admits Prof. Ko?os.

The laboratory characterization of exotic compounds like HCCP and CH2=C=PH marks an important step towards their extraterrestrial detection. And such detections would greatly advance our knowledge concerning the astrochemistry of phosphorus. This should inspire even more scientists to look towards the stars above...

Not so fast, supernova: highest-energy cosmic rays detected in star clusters

MICHIGAN TECHNOLOGICAL UNIVERSITY

Research News

 

IMAGE: A 24 MICROMETER INFRARED MAP FROM THE COCOON REGION WITH SPITZERS MIPS OVERLAID WITH A GAMMA-RAY SIGNIFICANCE MAP FROM HAWC (GREENISH-YELLOW TO RED INDICATE HIGHER GAMMA-RAY SIGNIFICANCE). THE MAP IS... view more 

CREDIT: BINITA HONA

For decades, researchers assumed the cosmic rays that regularly bombard Earth from the far reaches of the galaxy are born when stars go supernova -- when they grow too massive to support the fusion occurring at their cores and explode.

Those gigantic explosions do indeed propel atomic particles at the speed of light great distances. However, new research suggests even supernovae -- capable of devouring entire solar systems -- are not strong enough to imbue particles with the sustained energies needed to reach petaelectronvolts (PeVs), the amount of kinetic energy attained by very high-energy cosmic rays.

And yet cosmic rays have been observed striking Earth's atmosphere at exactly those velocities, their passage marked, for example, by the detection tanks at the High-Altitude Water Cherenkov (HAWC) observatory near Puebla, Mexico. Instead of supernovae, the researchers posit that star clusters like the Cygnus Cocoon serve as PeVatrons -- PeV accelerators -- capable of moving particles across the galaxy at such high energy rates.

Their paradigm-shifting research provides compelling evidence for star forming regions to be PeVatrons and is published in two recent papers in Nature Astronomy and Astrophysical Journal Letters.

A characteristic of physics research is how collaborative it is. The research was conducted by Petra Huentemeyer, professor of physics at Michigan Technological University, along with recent graduate Binita Hona '20, doctoral student Dezhi Huang, former MTU postdoc Henrike Fleischhack (now at Catholic University/NASA GSFC/CRESST II), Sabrina Casanova at the Institute of Nuclear Physics Polish Academy of Sciences in Krakow, Ke Fang at the University of Wisconsin and Roger Blanford at Stanford, along with numerous other collaborators of the HAWC Observatory.

Huentemeyer noted that HAWC and physicists from other institutions have measured cosmic rays from all directions and across many decades of energy. It's in tracking the cosmic rays with the highest known energy, PeVs, that their origin becomes so important.

"Cosmic rays below PeV energy are believed to come from our galaxy, but the question is what are the accelerators that can produce them," Huentemeyer said.

Fleischhack said the paradigm shift the researchers have uncovered is that before, scientists thought supernova remnants were the main accelerators of cosmic rays.

"They do accelerate cosmic rays, but they are not able to get to highest energies," she said.

So, what is driving cosmic rays' acceleration to PeV energy?

"There have been several other hints that star clusters could be part of the story," Fleischhack said. "Now we are getting confirmation that they are able to go to highest energies."

Star clusters are formed from the remnants of a supernova event. Known as star cradles, they contain violent winds and clouds of swirling debris -- such as those noted by the researchers in Cygnus OB2 and cluster [BDS2003]8. Inside, several types of massive stars known as spectral type O and type B stars are gathered by the hundreds in an area about 30 parsecs (108 light-years) across.

"Spectral type O stars are the most massive," Hona said. "When their winds interact with each other, shock waves form, which is where acceleration happens."

The researchers' theoretical models suggest that the energetic gamma-ray photons seen by HAWC are more likely produced by protons than by electrons.

"We will use NASA telescopes to search for the counterpart emission by these relativistic particles at lower energies," Fang said.

The extremely high energy at which cosmic rays reach our planet is notable. Specific conditions are required to accelerate particles to such velocities.

The higher the energy, the more difficult it is to confine the particles -- knowledge gleaned from particle accelerators here on Earth in Chicago and Switzerland. To keep particles from whizzing away, magnetism is required.

Stellar clusters -- with their mixture of wind and nascent but powerful stars -- are turbulent regions with different magnetic fields that can provide the confinement necessary for particles to continue to accelerate.

"Supernova remnants have very fast shocks where the cosmic ray can be accelerated; however, they don't have the type of long confinement regions," Casanova said. "This is what star clusters are useful for. They're an association of stars that can create disturbances that confine the cosmic rays and make it possible for the shocks to accelerate them."

But how is it possible to measure atomic interactions on a galactic scale 5,000 light-years from Earth? The researchers used 1,343 days of measurements from HAWC detection tanks.

Huang explained how the physicists at HAWC trace cosmic rays by measuring the gamma rays these cosmic rays produce at galactic acceleration sites: "We didn't measure gamma rays directly; we measured the secondary rays generated. When gamma rays interact with the atmosphere, they generate secondary particles in particle showers."

"When particle showers are detected at HAWC, we can measure the shower and the charge of secondary particles," Huang said. "We use the particle charge and time information to reconstruct information from the primary gamma."

In addition to HAWC, the researchers plan to work with the Southern Wide-field Gamma-ray Observatory (SWGO), an observatory currently in the planning stages that will feature Cherenkov light detectors like HAWC but will be located in the southern hemisphere.

"It would be interesting to see what we can see in the southern hemisphere," Huentemeyer said. "We will have a good view of the galactic center that we don't have in the northern hemisphere. SWGO could give us many more candidates in terms of star clusters."

Future collaborations across hemispheres promise to help scientists around the world continue to explore the origins of cosmic rays and learn more about the galaxy itself.

###