From ASU via Science News: “The recipes for solar system formation are getting a rewrite”

From Arizona State University

Science News

May 11, 2018
Lisa Grossman

Exoplanets: Left to right Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f, with Earth-except for Earth these are artists’ concepts. Image credit: NASA Ames/ JPL-Caltech

With a mortar and pestle, Christy Till blends together the makings of a distant planet. In her geology lab at Arizona State University in Tempe, Till carefully measures out powdered minerals, tips them into a metal capsule and bakes them in a high-pressure furnace that can reach close to 35,000 times Earth’s atmospheric pressure and 2,000° Celsius.

In this interplanetary test kitchen, Till and colleagues are figuring out what might go into a planet outside of our solar system.

“We’re mixing together high-purity powders of silica and iron and magnesium in the right proportions to make the composition we want to study,” Till says. She’s starting with the makings of what might resemble a rocky planet that’s much different from Earth. “We literally make a recipe.”

Scientists have a few good ideas for how to concoct our own solar system. One method: Mix up a cloud of hydrogen and helium, season generously with oxygen and carbon, and sprinkle lightly with magnesium, iron and silicon. Condense and spin until the cloud forms a star surrounded by a disk. Let rest about 10 million years, until a few large lumps appear. After about 600 million years, shake gently.

GET COOKING Geologist Christy Till mixes up a mock exoplanet from powdered minerals in her Arizona lab. Abigail Weibel Photography

But that’s only one recipe in the solar systems cookbook. Many of the planets orbiting other stars are wildly different from anything seen close to home. As the number of known exoplanets has climbed — 3,717 confirmed as of April 12 — scientists are creating new recipes.

Seven of those exoplanets are in the TRAPPIST-1 system, one of the most exciting families of planets astronomers have discovered to date.

A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. NASA

The TRAPPIST-1 star, an ultracool dwarf, is orbited by seven Earth-size planets (NASA).

At least three TRAPPIST-1 planets might host liquid water on their surface, making them top spots to look for signs of life (SN: 12/23/17, p. 25).

Yet those planets shouldn’t exist. Astronomers calculated that the small star’s preplanet disk shouldn’t have contained enough rocky material to make even one Earth-sized orb, says astrophysicist Elisa Quintana of NASA’s Goddard Space Flight Center in Greenbelt, Md. Yet the disk whipped up seven.

TRAPPIST-1 is just one of the latest in a long line of rule breakers.
Other systems host odd characters not seen in our solar system: super-Earths, mini-Neptunes, hot Jupiters and more. Many exoplanets must have had chaotic beginnings to exist where we find them.

These oddballs raise exciting questions about how solar systems form. Scientists want to know how much of a planet’s ultimate fate depends on its parent star, which ingredients are essential for planet building and which are just frosting on the planetary cake.

NASA’s Transiting Exoplanet Survey Satellite, or TESS, which launched April 18, should bring in some answers.

NASA/TESS

TESS is expected to find thousands more exoplanets in the next two years. That crowd will help illuminate which planetary processes are the most common — and will help scientists zero in on the best planets to check for signs of life.

CAKE POP PLANETS Yes, baking actually makes a nice analogy for planet formation. Take a look.

Beyond the bare necessities

All solar system recipes share some basic elements. The star and its planets form from the same cloud of gas and dust. The densest region of the cloud collapses to form the star, and the remaining material spreads itself into a rotating disk, parts of which will eventually coalesce into planets. That similarity between the star and its progeny tells Till and other scientists what to toss into the planetary stand mixer.

“If you know the composition of the star, you can know the composition of the planets,” says astronomer Johanna Teske of the Carnegie Observatories in Pasadena, Calif. A star’s composition is revealed in the wavelengths of light the star emits and absorbs.

When a planet is born can affect its final makeup, too. A gas giant like Jupiter first needs a rocky core about 10 times Earth’s mass before it can begin gobbling up gas. That much growth probably happens well before the disk’s gas disappears, around 10 million years after the star forms. Small, rocky planets like Earth probably form later.

Finally, location matters. Close to the hot star, most elements are gas, which is no help for building planets from scratch. Where the disk cools toward its outer edge, more elements freeze to solid crystals or condense onto dust grains. The boundary where water freezes is called the snow line. Scientists thought that water-rich planets must either form beyond their star’s snow line, where water is abundant, or must have water delivered to them later (SN: 5/16/15, p. 8). Giant planets are also thought to form beyond the snow line, where there’s more material available.

But the material in the disk might not stay where it began, Teske says. “There’s a lot of transport of material, both toward and away from the star,” she says. “Where that material ends up is going to impact whether it goes into planets and what types of planets form.” The amount of mixing and turbulence in the disk could contribute to which page of the cookbook astronomers turn to: Is this system making a rocky terrestrial planet, a relatively small but gaseous Neptune or a massive Jupiter?

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Birthplace

In the disk around a star, giant planets form beyond the “snow line,” where water freezes and more solids are available. Turbulence closer in knocks things around.

Source: T. Henning and D. Semenov/Chemical Reviews 2013
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Some like it hot

Like that roiling disk material, a full-grown planet can also travel far from where it formed.

Consider “Hoptunes” (or hot Neptunes), a new class of planets first named in December in Proceedings of the National Academy of Sciences. Hoptunes are between two and six times Earth’s size (as measured by the planet’s radius) and sidled up close to their stars, orbiting in less than 10 days. That close in, there shouldn’t have been enough rocky material in the disk to form such big planets. The star’s heat should mean no solids, just gases.

Hoptunes share certain characteristics — and unanswered questions — with hot Jupiters, the first type of exoplanet discovered, in the mid-1990s.

“Because we’ve known about hot Jupiters for so long, some people kind of think they’re old hat,” says astronomer Rebekah Dawson of Penn State, who coauthored a review about hot Jupiters posted in January at arXiv.org. “But we still by no means have a consensus about how they got so close to their star.”

Since the first known hot Jupiter, 51 Pegasi b, was confirmed in 1995, two explanations for that proximity have emerged. A Jupiter that formed past the star’s snow line could migrate in smoothly through the disk by trading orbital positions with the disk material itself in a sort of gravitational do-si-do. Or interactions with other planets or a nearby star could knock the planet onto an extremely elliptical or even backward orbit (SN Online: 11/1/13). Over time, the star’s gravity would steal energy from the orbit, shrinking it into a tight, close circle. Dawson thinks both processes probably happen.

Hot Jupiters are more common around stars that contain a lot of elements heavier than hydrogen and helium, which astronomers call metals, astronomer Erik Petigura of Caltech and colleagues reported in February in The Astronomical Journal. High-metal stars probably form more planets because their disks have more solids to work with. Once a Jupiter-sized planet forms, a game of gravitational billiards could send it onto an eccentric orbit — and send smaller worlds out into space. That fits the data, too; hot Jupiters tend to lack companion worlds.

Hoptunes follow the same pattern: They prefer metal-rich stars and have few sibling planets. But Hoptunes probably arrived at their hot orbits later in the star’s life. Getting close to a young star, a Hoptune would risk having its atmosphere stripped away. “They’re sort of in the danger zone,” Dawson says. Since Hoptunes do, in fact, have atmospheres, they were probably knocked onto an elliptical, and eventually close-in, orbit later.

One striking exception to the hot loner rule is WASP-47b, [ApJL] a hot Jupiter with two nearby siblings between the sizes of Earth and Neptune. That planet is one reason Dawson thinks there’s more than one way to cook up a hot Jupiter.

Rock or gas

Hot Jupiters are so large that astronomers assume these exoplanets have thick atmospheres. But it’s harder to tell if a smaller planet is gassy like Neptune or rocky like Earth.

To make a first guess at a planet’s composition, astronomers need to know the planet’s size and mass. Together, those numbers yield the planet’s density, which gives a sense of how much of the planet is solid like rock or diffuse like an atmosphere.

HOME SWEET HOMES New images from the Very Large Telescope in Chile reveal that dust disks around young stars can take on many different forms. The shape of a disk can affect – and be affected by – the presence of baby planets.

ESO VLT Platform at Cerro Paranal elevation 2,635 m (8,645 ft)

ESO/H. Avenhaus et al./E. Sissa et al./DARTT-S and SHINE collaborations

The most popular planet detection strategies each measure one of those factors. The transit method, used by the Kepler space telescope, watches a star wink as the planet passes in front.

NASA/Kepler Telescope

Planet transit. NASA/Ames

Comparing the star’s light before and during the transit reveals the planet’s size. The radial velocity method, used with telescopes on the ground, watches the star wobble in response to a planet’s gravity, which reveals the planet’s mass.

Radial velocity Image via SuperWasp http http://www.superwasp.org-exoplanets.htm

Radial Velocity Method-Las Cumbres Observatory

[Left out of the discussion, Direct Imaging.

Direct imaging-This false-color composite image traces the motion of the planet Fomalhaut b, a world captured by direct imaging.

To me, this is a lapse in journalistic coverage as Direct Imaging is becomeing ao more powerful tool with new telescope capabilities.]

Most of the stars observed by Kepler are too far away and too dim for direct, accurate measures of planet masses. But astronomers have inferred a size cutoff for rocky planets. Last June, researchers analyzing the full Kepler dataset noticed a surprising lack of planets between 1.5 and two times Earth’s size and suggested those 1.5 times Earth’s radius or smaller are probably rocky; two to 3.5 times Earth’s radius are probably gassy (SN Online: 6/19/17).

Dozens more planets have had their masses inferred indirectly, mostly those in multiplanet systems where astronomers can observe how planets tug on one another. From what astronomers can tell, super-Earths — planets between one and about 10 times Earth’s mass — come in a wide range of compositions.

The Kepler mission is about to end, as the spacecraft’s fuel is running out. TESS will pick up where Kepler leaves off. The new planet-hunting space telescope will revolutionize the study of super-Earth densities. It will scan 85 percent of the sky for bright, nearby stars to pick out the best planets for follow-up study. As part of its primary mission, TESS will find at least 50 planets smaller than Neptune that can have their masses measured precisely, too. “Having masses … will help us understand the compositions,” says Quintana, a TESS team member. “We can see: Is there a true transition line where planets go rocky to gaseous? Or is it totally random? Or does it depend on the star?”

Star power

All kinds of planets’ fates do, in fact, depend on the stars, Petigura’s recent work suggests. In a February report in The Astronomical Journal, he and colleagues measured the metal contents of 1,305 planet-hosting stars in Kepler’s field of view.

The researchers learned that large planets and close-in planets — with orbital periods of 10 days or less — are more common around metal-rich stars. But the team was surprised to find that small planets and planets that orbit far from their stars show up around stars of all sorts of compositions. “They form efficiently everywhere,” Petigura says.

That could mean that metal-rich stars had disks that extended closer to the stars. With enough material close to the star, hot super-Earths could have formed where they currently spin. The existence of hot super-Earths might even suggest that hot Jupiters can form close to the star after all. A super-Earth or mini-Neptune could represent the core of what was once a hot Jupiter that didn’t quite gather enough gas before the disk dissipated, or whose atmosphere was blown off by the star (SN Online: 10/31/17).

Weird water

Some scientists are looking to stars to reveal what’s inside a planet. The help is welcome because density is a crude measure for understanding what a planet is made of. Planets with the same mass and radius can have very different compositions and natures — look at hellish Venus and livable Earth.

Take the case of TRAPPIST-1, which has seven Earth-sized worlds and is 39 light-years away. Astronomers are anxious to check at least three of the planets for signs of life
(SN: 12/23/17, p. 25). But those planets might be so waterlogged that any signs of life would be hard to detect, says exogeologist Cayman Unterborn of Arizona State. So much water would change a planet’s chemistry in a way that makes it hard to tell life from nonlife. Based on the planets’ radii (measured by their transits) and their masses (measured by their gravitational influence on one another), Unterborn and colleagues used density to calculate a bizarre set of interiors for the worlds, which the team reported March 19 in Nature Astronomy.

The TRAPPIST-1 planets have low densities for their size, Unterborn says, suggesting that their masses are mostly light material like water ice. TRAPPIST-1b, the innermost planet, seems to be 15 percent water by mass (Earth is less than 0.1 percent water). The fifth planet out, TRAPPIST-1f, may be at least half water by mass. If the planet formed with all that water already in it, it would have had 1,000 Earth oceans’ worth of water. That amount of water would compress into exotic phases of ice not found at normal pressures on Earth. “That is so much water that the chemistry of how that planet crystallized is not something we have ever imagined,” Unterborn says.

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Size it up

Measuring a planet’s mass and radius gives astronomers a sense of planetary makeup. This plot compares the TRAPPIST-1 planets (purple) with Earth, Venus, an exoplanet named K2-229b and a couple of other worlds.

Source: A. Santerne et al/Nature Astronomy 2018

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But there’s a glitch. Unterborn’s analysis was based on the most accurate published masses for the TRAPPIST-1 worlds at the time. But on February 5, the same day his paper was accepted in Nature Astronomy, a group led by astronomer Simon Grimm of the University of Bern in Switzerland posted more precise mass measurements at Astronomy and Astrophysics. Those masses make the soggiest planets look merely damp.

Clearly, Unterborn says, density is not destiny. Studying a planet based on its mass and radius has its limits.

Looking deeper

As a next step, Unterborn and colleagues have published a series of papers suggesting how stellar compositions can tell the likelihood that a group of planets have plate tectonics, or how much oxygen the planet atmospheres may have. Better geologic models may ultimately help reveal if a single planet is habitable.

But Unterborn is wary of translating composition from a star to any individual planet — existing geochemical models aren’t good enough. The recent case of K2-229b makes that clear. Astronomer Alexandre Santerne of the Laboratory of Astrophysics of Marseille in France and colleagues recently tried to see if a star’s composition could describe the interior of its newly discovered exoplanet, K2-229b. The team reported online March 26 in Nature Astronomy that the planet has a size similar to Earth’s but a makeup more like Mercury’s: 70 percent metallic core, 30 percent silicate mantle by mass. (The researchers nicknamed the planet Freddy, for Queen front man Freddie Mercury, Santerne wrote on Twitter.) That composition is not what they’d expect from the star alone.

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Hints from the star

Based on its mass and radius, an exoplanet named K2-229b is about Earth’s size but more similar to Mercury in composition, astronomers suggest.

Source: A. Santerne et al/Nature Astronomy 2018

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Geologic models need to catch up quickly. After TESS finds the best worlds for follow-up observations, the James Webb Space Telescope, due to launch in 2020, will search some of those planets’ atmospheres for signs of life (SN: 4/30/16, p. 32). For that strategy to work, Unterborn says, scientists need a better read on the exoplanet cookbook.

Christy Till’s pressure-packed test kitchen may help. Till is primarily a volcanologist who studies how magma erupting onto Earth’s surface can reveal conditions in Earth’s interior. “The goal is to start doing that for exoplanets,” she says.

Till and colleagues are redoing some foundational experiments conducted for Earth 50 years ago but not yet done for exoplanets. The experiments predict which elements can go into planets’ mantles and cores, and which will form solid crusts. (Early results that Till presented in December in New Orleans at the American Geophysical Union meeting suggest that multiplying the sun’s magnesium-to-silicon ratio by 1.33 still bakes a rocky planet, but with a different flavored crust than Earth’s.)

Till uses three piston cylinders to squash and singe synthetic exoplanets for 24 hours to see what minerals form and melt at different pressures and temperatures. The results may help answer questions like what kind of lava would erupt on a planet’s surface, what would the crust be made of and what gases might end up in the planet’s atmosphere.

It’s early days, but Till’s recipe testing may mean scientists won’t have to wait decades for telescopes to get a close enough look at an exoplanet to judge how much like home it really is. With new cookbook chapters, Unterborn says, “we can figure out which stars are the best places to build an Earth.”

Related journal articles
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Please help promote STEM in your local schools.

Stem Education Coalition

ASU is the largest public university by enrollment in the United States.[11] Founded in 1885 as the Territorial Normal School at Tempe, the school underwent a series of changes in name and curriculum. In 1945 it was placed under control of the Arizona Board of Regents and was renamed Arizona State College.[12][13][14] A 1958 statewide ballot measure gave the university its present name.
ASU is classified as a research university with very high research activity (RU/VH) by the Carnegie Classification of Institutions of Higher Education, one of 78 U.S. public universities with that designation. Since 2005 ASU has been ranked among the Top 50 research universities, public and private, in the U.S. based on research output, innovation, development, research expenditures, number of awarded patents and awarded research grant proposals. The Center for Measuring University Performance currently ranks ASU 31st among top U.S. public research universities.[15]

ASU awards bachelor’s, master’s and doctoral degrees in 16 colleges and schools on five locations: the original Tempe campus, the West campus in northwest Phoenix, the Polytechnic campus in eastern Mesa, the Downtown Phoenix campus and the Colleges at Lake Havasu City. ASU’s “Online campus” offers 41 undergraduate degrees, 37 graduate degrees and 14 graduate or undergraduate certificates, earning ASU a Top 10 rating for Best Online Programs.[16] ASU also offers international academic program partnerships in Mexico, Europe and China. ASU is accredited as a single institution by The Higher Learning Commission.

ASU Tempe Campus

From ScienceNews: “New ideas about how stars die help solve a decades-old mystery”

From ScienceNews

May 7, 2018
Maria Temming

Simulations show even small stars can heat up fast enough to form colorful planetary nebulae.

GOING OUT IN STYLE New insights into the death throes of sunlike stars help solve a decades-old mystery about planetary nebulae, such as the seven captured by the Hubble Space Telescope in this composite image. Clockwise from top left: D. Thompson/Large Binocular Telescope Observatory, C.R. O’Dell/Vanderbilt Univ., NASA, ESA; Hubble Heritage Team/STScl/AURA, NASA, ESA; Hubble SM4 ERO Team, NASA, ESA; Hubble SM4 ERO Team, NASA, ESA; Raghvendra Sahai and John Trauger /JPL, the WFPC2 Science Team, NASA; Andrew Fruchter, the ERO team/STScI, NASA, ESA; Hubble SM4 ERO Team, NASA, ESA

New insights into how stars like the sun die might help explain why astronomers find bright planetary nebulae where they’re least expected. Simulations of how these stellar remnants form suggest that smaller stars have cores that heat up fast enough to produce bright nebulae upon their demise, researchers report online May 7 in Nature Astronomy.

A planetary nebula is what’s left over when a sunlike star sheds its outer envelope of gas. Radiation from the stellar core, now exposed, sets the expanding shell of gas aglow, creating the kind of candy-colored clouds seen in spectacular Hubble Space Telescope images, like that of the Cat’s Eye Nebula and the butterfly-shaped NGC 6302 (SN Online: 9/5/13).

The full beauty of the Cat’s Eye Nebula (NGC 6543) is revealed in this new, detailed view from NASA’s Hubble Space Telescope. The image from Hubble’s Advanced Camera for Surveys (ACS) shows a bull’s eye pattern of eleven or even more concentric rings, or shells, around the Cat’s Eye. Each ‘ring’ is actually the edge of a spherical bubble seen projected onto the sky – that’s why it appears bright along its outer edge.

NASA/ESA Hubble ACS

NGC 6302
STELLAR VIEW Sharp images of the planetary nebula NGC 6302 reveal that carbon atoms (yellow) congregate near the center of the dying star. ALMA, Hubble Space Telescope

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

NASA/ESA Hubble Telescope

Astronomers had thought a star’s mass dictated what sort of nebula it produced, with more massive stars creating the brightest nebulae and stars with lower masses, like the sun, making nebulae too faint to see from another galaxy.

But that idea didn’t match observations: The brightest planetary nebulae in older elliptical galaxies — thought to be home to only low-mass stars — are just as luminous as those in younger, spiral galaxies, where massive stars abound. The puzzle vexed astronomers for decades.

Now, astrophysicist Albert Zijlstra at the University of Manchester in England, and colleagues have simulated planetary nebulae formation based on a new theory of stellar evolution. This theory says that after smaller stars shed their outer envelopes, their bare cores heat up more quickly than previously thought. That allows the cinderlike stellar core to pump more energetic radiation into the surrounding nebula before the gas expands too far out into space, ultimately making for a brighter nebula, explains Christophe Morisset, an astronomer at the National Autonomous University of Mexico in Mexico City not involved in the work.

Simulations showed that stars ranging from 1.1 to three times the mass of the sun produce nebulae with similar brightness. That result could explain why nebulae found in galaxies with stars that are 7 billion years old can be just as bright as those found in galaxies chock-full of 1-billion-year-old stars.

This finding marks “an important step forward” in understanding the universe’s population of planetary nebulae, says Penn State astronomer Robin Ciardullo, who was not involved in the work.

But some mystery still remains: For the most ancient elliptical galaxies with very small stars over 7 billion years old, the simulations didn’t produce planetary nebulae bright enough to match what astronomers see in the sky. So there’s still “a little ways to go” before astronomers can explain why bright nebulae are so ubiquitous, he says.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “Neutron stars shed neutrinos to cool down quickly”

ScienceNews

May 2, 2018
Emily Conover

GETTING CHILLS After swiping material from a partner star, a neutron star (illustrated) quickly cooled off by spewing out particles called neutrinos.

The process removes heat ‘the way the casino removes money from tourists’ pockets’.

For some neutron stars, the quickest way to cool off isn’t with a frosty beverage, but with lightweight, subatomic particles called neutrinos.

Scientists have spotted the first solid evidence that some neutron stars, the collapsed remnants of exploded stars, can rapidly cool their cores by emitting neutrinos. The result adds to evidence that scientists are gathering to understand the ultradense matter that is squished deep within a neutron star’s center.

The new evidence comes from a neutron star that repeatedly gobbled material from a neighboring star. The neutron star rapidly cooled off after its meals, scientists determined. X-rays emitted by the neutron star showed that the fast cooldown rate was consistent with a theorized effect called the direct Urca process, in which neutrinos quickly ferry energy away from a collapsed star, astrophysicist Edward Brown and colleagues report in the May 4 Physical Review Letters.

Neutron stars are known to emit neutrinos by a similar process that cools the star slowly. But previously, there wasn’t clear evidence for faster cooling. The team analyzed observations of the neutron star, located about 35,000 light-years from Earth, as it cooled during a 15-year interlude between feeding sessions. Neutrinos carried away energy about 10 times faster than the rate energy is radiated by the sun’s light — or about 100 million times quicker than the slow process, says Brown, of Michigan State University in East Lansing.

Although some other neutron stars have shown hints of such a quick chill, “this is basically the first object for which we can see the star actively cooling before our eyes,” says astrophysicist James Lattimer of Stony Brook University in New York, who was not involved with the research.

The direct Urca process, named by physicists George Gamow and Mário Schenberg in the 1940s, took its moniker from the now-defunct Urca casino in Rio de Janeiro. “The joke being that this process removes heat from the star the way the casino removes money from tourists’ pockets,” Brown says.

In the process, neutrons in the star’s core convert into protons and emit electrons and antineutrinos (the antimatter partners of neutrinos). Likewise, protons convert into neutrons and emit antielectrons and neutrinos. Because neutrinos and antineutrinos interact very rarely with matter, they can escape the core, taking energy with them. “The neutrino is a thief; it robs energy from the star,” says physicist Madappa Prakash of Ohio University in Athens, who was not involved with the research.

The observation may help scientists understand what goes on deep within neutron stars, the cores of which are squeezed to densities far beyond those achievable in laboratories. Although the simplest theory holds that the cores are crammed with neutrons and a smaller number of protons and electrons, scientists have also proposed that the collapsed stars may consist of weird states of matter, containing rare particles called hyperons or a sea of free-floating quarks, the particles that make up protons and neutrons (SN: 12/23/17, p. 7).

The direct Urca process can happen only if the fraction of protons in the center of the neutron star is larger than about 10 percent. So if the process happens, “that already tells us a lot,” says astrophysicist Wynn Ho of Haverford College in Pennsylvania, who was not involved in the research. Such observations could eliminate theories that would predict lower numbers of protons.

However, the scientists weren’t able to determine the mass of the neutron star, limiting the conclusions that can be drawn. But, says Prakash, if the mass of such a quickly cooling neutron star is measured, the neutron star’s interior makeup could be nailed down.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “A DIY take on the early universe may reveal cosmic secrets”

ScienceNews

April 27, 2018
Emily Conover

A rapidly expanding ring of ultracold atoms mimics the physics just after the Big Bang.

COSMIC LOOP A rapidly expanding ring of ultracold atoms imitates the physics of the universe just after the Big Bang. E. Edwards/JQI.

A DIY universe mimics the physics of the infant cosmos, a team of physicists reports. The researchers hope to use their homemade cosmic analog to help explain the first instants of the universe’s 13.8-billion-year life.

For their stand-in, the scientists created a Bose-Einstein condensate — a state of matter in which atoms are chilled until they all take on the same quantum state. Shaped into a tiny, rapidly expanding ring, the condensate grew from about 23 micrometers in diameter to about four times that size in just 15 milliseconds. The behavior of that widening condensate re-created some of the physics of inflation, a brief period just after the Big Bang during which the universe rapidly ballooned in size (SN Online: 12/11/13) before settling into a more moderate expansion rate.

Alan Guth, Highland Park High School and M.I.T., who first proposed cosmic inflation

HPHS Owls

Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

Alan Guth’s notes:

In physics, seemingly unrelated systems can have similarities under the hood. Scientists have previously used Bose-Einstein condensates to simulate other mysteries of the cosmos, such as black holes (SN: 11/15/14, p. 14). And the comparison between Bose-Einstein condensates and inflation is particularly apt: A hypothetical substance called the inflaton field is thought to drive the universe’s extreme expansion, and particles associated with that field, known as inflatons, all take on the same quantum state, just as atoms do in the condensate.

Scientists still don’t fully understand how inflation progressed, “so it’s hard to know how close our system is to what really happened,” says experimental physicist Gretchen Campbell of the Joint Quantum Institute in College Park, Md. “But the hope is that our system can be a good test-bed” for studying various theories. Already, the scientists have spotted several effects in their system similar to those predicted in the baby cosmos, the team reports April 19 in Physical Review X.

As the scientists expanded the ring, sound waves that were traveling through the condensate increased in wavelength. That change was similar to the way in which light became redshifted — stretched to longer wavelengths and redder colors — as the universe enlarged.

Nice ring to it
To mimic the physics of inflation in the early universe, scientists rapidly expanded a ring-shaped Bose-Einstein condensate, which decreased in density as it expanded over 15 milliseconds.

S. Eckel et al/Physical Review X 2018

Likewise, Campbell and colleagues saw a phenomenon akin to what’s known as Hubble friction, which shows up as a decrease in the density of particles in the early universe. In the experiment, this effect appeared in the guise of a weakening in the strength of the sound waves in the condensate.

And inflation’s finale, an effect known as preheating that occurs at the end of the rapid expansion period, also had a look-alike in the simulated universe. In the cosmic picture, preheating occurs when inflatons transform into other types of particles. In the condensate, this showed up as sound waves converting from one type into another: waves that had been sloshing inward and outward broke up into waves going around the ring.

However, the condensate wasn’t a perfect analog of the real universe: In particular, while our universe has three spatial dimensions, the expanding ring didn’t. Additionally, in the real universe, inflation proceeds on its own, but in this experiment, the researchers forced the ring to expand. Likewise, there were subtle differences between each of the effects observed and their cosmic counterparts.

Despite the differences, the analog universe could be useful, says theoretical cosmologist Mustafa Amin of Rice University in Houston. “Who knows?” he says. “New phenomena might happen there that we haven’t thought about in the early universe.”

Sometimes, when research crosses over between very different systems — such as Bose-Einstein condensates and the early universe — “sparks can fly,” Amin says.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

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From ScienceNews: “Spooky quantum entanglement goes big in new experiments”

ScienceNews

DRUMMING UP ENTANGLEMENT Two teams of scientists demonstrated quantum linkages between two specially designed jiggling structures: drumheadlike objects (illustrated) and silicon beams (not shown). Petja Hyttinen/Aalto University, Olli Hanhirova/ARKH Architects.

Quantum entanglement has left the realm of the utterly minuscule, and crossed over to the just plain small. Two teams of researchers report that they have generated ethereal quantum linkages, or entanglement, between pairs of jiggling objects visible with a magnifying glass or even the naked eye — if you have keen vision.

Physicist Mika Sillanpää and colleagues entangled the motion of two vibrating aluminum sheets, each 15 micrometers in diameter — a few times the thickness of spider silk. And physicist Sungkun Hong and colleagues performed a similar feat with 15-micrometer-long beams made of silicon, which expand and contract in width in a section of the beam. Both teams report their results in the April 26 Nature Stabilized entanglement of massive mechanical oscillators and Remote quantum entanglement between two micromechanical oscillators.

“It’s a first demonstration of entanglement over these artificial mechanical systems,” says Hong, of the University of Vienna. Previously, scientists had entangled vibrations in two diamonds that were macroscopic, meaning they were visible (or nearly visible) to the naked eye. But this is the first time entanglement has been seen in macroscopic structures constructed by humans, which can be designed to meet particular technological requirements.

Entanglement is a strange feature of quantum mechanics, through which two objects’ properties become intertwined. Measuring the properties of one object immediately reveals the state of the other, even though the duo may be separated by a large distance (SN: 8/5/17, p. 14).

Quantum mechanics’ weird rules typically apply to small fry — atoms, electrons and other tiny particles — and not to larger things such as cats, chairs or buildings. But that division leads to a confounding puzzle. “Atoms behave like atoms, and cats behave like cats, and so where is that transition in between?” says physicist Ben Sussman of the National Research Council of Canada in Ottawa, who was not involved in the research.

Now, scientists are extending the dividing line to larger and larger objects. “One of our motivations is to keep on testing how far we can push quantum mechanics,” says Sillanpää, of Aalto University in Finland. “There might be some fundamental limit for how big objects can be” and still be quantum.

In Sillanpää’s experiment, two tiny aluminum sheets — consisting of about a trillion atoms and just barely visible with the naked eye — vibrate like drumheads and interact with microwaves bouncing back and forth in a cavity. Those microwaves play the role of drum major, causing the two drumheads to sync up their motions. In many previous demonstrations of entanglement, the delicate quantum link is transient. But this one was long-lived, persisting as long as half an hour in experiments, Sillanpää says, and, in theory, even longer. “Our entanglement lasts forever, basically.”

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In unison

Physicists have entangled the motions of pairs of wiggling structures. Seen in these electron microscope images are the different types of devices that two teams used: vibrating drumheadlike objects (one at left) and expanding and contracting silicon beams (similar to that shown at right).

Mika Sillanpää/Aalto University, R. Riedinger et al/Nature 2016
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Taking a different tactic, Hong and colleagues demonstrated entanglement with two silicon beams, big enough to be seen with a magnifying glass. Within a region of each beam, in a 1-micrometer-long section composed of about 10 billion atoms, the structure expanded and contracted — as if taking deep breaths in and out — in response to being hit with light. Instead of microwaves, Hong and colleagues’ work used infrared light of the wavelength typically transmitted in telecommunications networks made of optical fibers, which means it could be incorporated into a future quantum internet. “From a technology standpoint, that really is crucial,” says physicist John Teufel of the National Institute of Standards and Technology in Boulder, Colo., who was not involved with the work.

Scientists could use such vibrating structures within a quantum network to convert quantum information from one type to another, transitioning from particles of light to vibrations, for example. Once constructed, a quantum internet could allow quantum computers to communicate and provide unhackable communication across the globe (SN: 10/15/16, p. 13).

The ability to entangle these specially designed structures moves scientists a step closer to that vision. “You can really start to think about building real devices with these things,” Sussman says.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “Astronomers can’t figure out why some black holes got so big so fast”

ScienceNews

March 16, 2018
Lisa Grossman

These behemoths defy expectations of how quickly black holes feed.

TOO BIG, TOO SOON Supermassive black holes that are actively feeding on gas and dust, like the one shown in this artist’s rendition, have been spotted in the early universe — before they should have had time to grow. NAOJ.

The existence of supermassive black holes in the early universe has never made much sense to astronomers. Sightings since 2006 have shown that gargantuan monsters with masses of at least a billion suns were already in place when the universe was less than a billion years old – far too early for them to have formed by conventional means.

One or two of these old massive objects could be dismissed as freaks, says theoretical astrophysicist Priyamvada Natarajan of Yale University. But to date, astronomers have spotted more than 100 supermassive black holes that existed before the universe was 950 million years old. “They’re too numerous to be freaks now,” she says. “You have to have a natural explanation for how these things came to be.”

The usual hypotheses are that these black holes were either born unexpectedly big, or grew up fast. But recent finds are challenging even those theories and may force astronomers to rethink how these black holes grow.

In the modern universe, black holes typically form from massive stars that collapse under their own gravity at the ends of their lives. They usually start out smaller than 100 solar masses and can grow either by merging with another black hole (SN: 3/19/16, p. 10) or by accreting gas from their environment (SN Online: 12/6/17).

That gas often organizes itself into a disk that spirals into the black hole, with friction heating the disk to white-hot temperatures that create a brilliant glow visible across billions of light-years. These black holes feeding on gas are called quasars. The faster a quasar eats, the brighter its disk glows.

But the glow from that gas also limits the black hole’s growth: The bright disk’s photons push away fresh material. That sets a physical limit on how fast black holes of a given mass can grow. Astronomers express how fast a black hole is eating with a term called the Eddington ratio, measuring the black hole’s actual brightness in relation to the brightness it would have if it were eating as fast as it possibly could.

Finicky feeders

Astronomers have measured Eddington ratios for only about 20 supermassive black holes in the early universe. Most seem to be eating at the limit, in contrast to quasars in the present-day universe that feed at about a tenth that speed. Those furious feeding rates still seem to defy the black holes’ supermassive size: A 100-solar-mass black hole accreting at the limit should take about 800 million years to reach a billion solar masses, even taking into account that it would eat faster as it grew. And that 800 million years doesn’t include the time it took the initial black hole seed to form.

But physicist Myungshin Im of Seoul National University in South Korea and colleagues worried that previous observations were missing pickier eaters because fast eaters are brighter and easier to spot. If some early massive black holes were lazy eaters, their super sizes become even more puzzling — and may rule out some theories for how they grew.

So the team deliberately sought out dimmer distant quasars in a September 2015 observing run at the Las Campanas Observatory in Chile.

The researchers found IMS J2204+0112 [ApJ Submitted on 8 Feb 2018], a billion-solar-mass black hole eating at a tenth of its speed limit and hailing from when the universe was about 940 million years old. But at its feeding rate, the black hole shouldn’t have fully matured until the universe was 8 billion years old, the team reported on arXiv.org February 9.

“We show for the first time that quasars with low Eddington ratio exist in the early universe,” Im says.

IMS J2204+0112 is the dimmest slow-eating quasar spotted yet, but it’s not alone. Physicist Chiara Mazzucchelli of the Max Planck Institute for Astronomy in Germany and colleagues reported 11 fussy supermassive black holes that existed when the universe was less than 800 million years old, in The Astrophysical Journal last November.

On average, those quasars weigh in at around 1.62 billion solar masses but eat at about 40 percent of the speed limit, the team reported. Strangely, the largest black hole in that group, HSC J1205-0000, had the lowest feeding rate: The black hole is 4.7 billion solar masses yet eats at only 6 percent of its limit.

It was strange enough to find supermassive black holes with gluttonous appetites in the early universe, but these picky eaters are even harder to explain.

Astronomers hope peering farther back in time will help find the “seed” black holes that may grow into behemoths. If some black holes started out huge, from 10,000 to a million solar masses, they could grow even larger either by merging with each other or accreting at the Eddington limit.

“If you start with such a very massive seed, you have a jump-start,” says astrophysicist Avi Loeb of Harvard University. “Then you don’t need as much time to grow to a billion solar masses.”

But theorists have been trying for 15 years to figure out how such huge black holes could form in the first place. One idea is that massive gas clouds or supermassive stars collapsed directly into a massive black hole.

Supermassive seeds

More recent work suggests it wouldn’t be that simple. Theoretical studies show it’s hard to prevent those gas clouds from fragmenting to form a cluster of small stars, rather than collapsing into one large star, says physicist Dominik Schleicher of the University of Concepción in Chile.

In the May 2018 Monthly Notices of the Royal Astronomical Society, Schleicher and colleagues show that such clusters also could create massive black hole seeds, as newly formed stars accrete gas left over in the cluster. Such stars could swell to 100 to 1,000 times the radius of the sun. Their inflated sizes and close proximity to one another would make these stars collide, triggering a domino effect that eventually collects all the stars in the cluster into a single supermassive star 10,000 times the mass of the sun. That supermassive star could then collapse to form a relatively massive seed black hole.

The other possibility is that early supermassive black holes simply broke the Eddington limit. They may have gone through periods of eating more quickly than was thought possible and grew to near-supermassive proportions before calming down.

Loeb points out that there are situations in the present-day universe where black holes eat faster than the Eddington limit, such as when they rip apart and devour a star (SN: 4/1/17, p. 5). There are also situations where radiation can be trapped near the surface of the black hole, preventing it from pushing material away. “In that case you can feed the black hole as fast as you want,” Loeb says.

In a December 2017 study in the Astrophysical Journal Letters, she and her colleagues ran computer simulations showing that some environments can boost a black hole’s growth, allowing the black hole to consume a continuous stream of gas.

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The rich get richer

Simulations show that a small black hole seed will never grow fast enough to become supermassive before the universe is a billion years old. But a black hole that was born large will grow faster and faster.

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Still, only black holes born with masses at least 10,000 times that of the sun can grow to a billion solar masses within a billion years. But the most massive seeds are more likely to be born in a gas-rich environment.

“The environment around and the birth conditions for these black holes actually puts them on a track either for rapid growth spurts, or for rather slow growth,” Natarajan says. “The massive black hole seeds are the ones that won the birth lottery and got the best start in life.”

Ultimately, astronomers will need to see even farther back in time [The Astrophysical Journal] if they hope to find supermassive seeds. The James Webb Space Telescope, due to launch in 2019, should be able to detect quasars and stars at 400 million or 500 million years after the Big Bang. And a future gravitational wave observatory called LISA will aim to detect supermassive black holes across cosmic history.

NASA/ESA/CSA Webb Telescope annotated

ESA/NASA eLISA space based, the future of gravitational wave research

“The only way to discriminate between these models is going back in time,” Natarajan says.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “Superconductors may shed light on the black hole information paradox”

ScienceNews

March 9, 2018
Emily Conover

Scientists are trying to understand what happens to information that falls into a black hole.

MIRROR, MIRROR When black holes evaporate, where does the trapped information go? One potential explanation, that the black hole reflects the information instead of trapping it, has parallels with the behavior of materials that conduct electricity without resistance. NASA Goddard Space Flight Center.

Insights into a black hole paradox may come from a down-to-Earth source.

Superconductors, materials through which electrons can move freely without resistance, may share some of the physics of black holes, physicist Sreenath Kizhakkumpurath Manikandan of the University of Rochester in New York reported March 7 at a meeting of the American Physical Society. The analogy between the two objects could help scientists understand what happens to information that gets swallowed up in a black hole’s abyss.

When a black hole gobbles up particles, information about the particles’ properties is seemingly trapped inside. According to quantum mechanics, such information cannot be destroyed. Physicist Stephen Hawking determined in 1974 that black holes slowly evaporate over time, emitting what’s known as Hawking radiation before eventually disappearing. That fact implies a conundrum known as the black hole information paradox (SN: 5/31/14, p. 16): When the black hole evaporates, where does the information go?

One possible solution, proposed in 2007 by physicists Patrick Hayden of Stanford University and John Preskill of Caltech, is that the black hole could act like a mirror, with information about infalling particles being reflected outward, imprinted in the Hawking radiation. Now, Manikandan and physicist Andrew Jordan, also of the University of Rochester, report that a process that occurs at the interface between a metal and a superconductor is analogous to the proposed black hole mirror [Physical Review D].

The effect, known as Andreev reflection, occurs when electrons traveling through a metal meet a superconductor. The incoming electron carries a quantum property known as spin, similar to the spinning of a top. The direction of that spin is a kind of quantum information. When the incoming electron meets the superconductor, it pairs up with another electron in the material to form a duo known as a Cooper pair. Those pairings allow electrons to glide easily through the material, facilitating its superconductivity. As the original electron picks up its partner, it also leaves behind a sort of electron alter ego reflecting its information back into the metal. That reflected entity is referred to as a “hole,” a disturbance in a material that occurs when an electron is missing. That hole moves through the metal as if it were a particle, carrying the information contained in the original particle’s spin.

Likewise, if black holes act like information mirrors, as Hayden and Preskill suggested, a particle falling into a black hole would be followed by an antiparticle coming out — a partner with the opposite electric charge — which would carry the information contained in the spin of the original particle. Manikandan and Jordan showed that the two processes were mathematically equivalent.

It’s still not clear whether the black hole mirror is the correct solution to the paradox, but the analogy suggests experiments with superconductors could clarify what happens to the information, Jordan says. “That’s something you can’t ever do with black holes: You can’t do those detailed experiments because they’re off in the middle of some galaxy somewhere.”

The theory is “intriguing,” says physicist Justin Dressel of Chapman University in Orange, Calif. Such comparisons are useful in allowing scientists to take insights from one area and apply them elsewhere. But additional work is necessary to determine how strong an analogy this is, Dressel says. “You may find with further inspection the details are different.”

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “50 years ago, pulsars burst onto the scene”

ScienceNews

March 8, 2018
Emily Conover

Excerpt from the March 16, 1968 issue of Science News

LIKE CLOCKWORK Scientists reported the first discovery of a pulsar 50 years ago. The rapidly rotating neutron stars emit beams of radiation (illustrated), which sweep past Earth at regular intervals. NASA’s Goddard Space Flight Center.

The strangest signals reaching Earth

The search for neutron stars has intensified because of a relatively small area, low in the northern midnight sky, from which the strangest radio signals yet received on Earth are being detected. If the signals come from a star, the source broadcasting the radio waves is very likely the first neutron star ever detected. — Science News, March 16, 1968

Susan Jocelyn Bell

Update

That first known neutron star’s odd pulsating signature earned it the name “pulsar.” The finding garnered a Nobel Prize just six years after its 1968 announcement — although one of the pulsar’s discoverers, astrophysicist Dame Jocelyn Bell Burnell, was famously excluded.

Dame Susan Jocelyn Bell Burnell 2009

Since then, astronomers have found thousands of these blinking collapsed stars, which have confirmed Einstein’s theory of gravity and have been proposed as a kind of GPS for spacecraft.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “The quest to identify the nature of the neutrino’s alter ego is heating up”

ScienceNews

February 26, 2018
Emily Conover

Physicists are trying to see if the particle’s matter and antimatter versions are the same.

ANTIMATTER MYSTERY Physicists suspect that the neutrino may be its own antiparticle. Experiments such as GERDA (shown) are attempting to determine whether that hunch is correct by searching for a rare type of nuclear decay. K. Freund/GERDA collaboration

Galaxies, stars, planets and life, all are formed from one essential substance: matter.

But the abundance of matter is one of the biggest unsolved mysteries of physics. The Big Bang, 13.8 billion years ago, spawned equal amounts of matter and its bizarro twin, antimatter. Matter and antimatter partners annihilate when they meet, so an even-stephen universe would have ended up full of energy — and nothing else. Somehow, the balance tipped toward matter in the early universe.

A beguiling subatomic particle called a neutrino may reveal how that happened. If neutrinos are their own antiparticles — meaning that the neutrino’s matter and antimatter versions are the same thing — the lightweight particle might point to an explanation for the universe’s glut of matter.

So scientists are hustling to find evidence of a hypothetical kind of nuclear decay that can occur only if neutrinos and antineutrinos are one and the same. Four experiments have recently published results showing no hint of the process, known as neutrinoless double beta decay (SN: 7/6/02, p. 10). But another attempt, set to begin soon, may have a fighting chance of detecting this decay, if it occurs. Meanwhile, planning is under way for a new generation of experiments that will make even more sensitive measurements.

“Right now, we’re standing on the brink of what potentially could be a really big discovery,” says Janet Conrad, a neutrino physicist at MIT not involved with the experiments.

A league of its own

Each matter particle has an antiparticle, a partner with the opposite electric charge. Electrons have positrons as partners; protons have antiprotons. But it’s unclear how this pattern applies to neutrinos, which have no electric charge.

Rather than having distinct matter and antimatter varieties, neutrinos might be the lone example of a theorized class of particle dubbed a Majorana fermion (SN: 8/19/17, p. 8), which are their own antiparticles. “No other particle that we know of could have this property; the neutrino is the only one,” says neutrino physicist Jason Detwiler of the University of Washington in Seattle, who is a member of the KamLAND-Zen and Majorana Demonstrator neutrinoless double beta decay experiments.

Neutrinoless double beta decay is a variation on standard beta decay, a relatively common radioactive process that occurs naturally on Earth. In beta decay, a neutron within an atom’s nucleus converts into a proton, releasing an electron and an antineutrino. The element thereby transforms into another one further along the periodic table.

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Beta decays

The standard type of beta decay (left) occurs when a neutron in an atom’s nucleus converts into a proton and releases an electron (blue, e-) and an antineutrino (red). For certain species of atoms, two such decays can happen at once (middle). If the neutrino is its own antiparticle, those double beta decays could also occur without any emitted antineutrinos (right).

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In certain isotopes of particular elements — species of atoms characterized by a given number of protons and neutrons — two beta decays can occur simultaneously, emitting two electrons and two antineutrinos. Although double beta decay is exceedingly rare, it has been detected. If the neutrino is its own antiparticle, a neutrino-free version of this decay might also occur: In a rarity atop a rarity, the antineutrino emitted in one of the two simultaneous beta decays might be reabsorbed by the other, resulting in no escaping antineutrinos.

Such a process “creates asymmetry between matter and antimatter,” says physicist Giorgio Gratta of Stanford University, who works on the EXO-200 neutrinoless double beta decay experiment.

SLAC EXO-200 Enriched Xenon Observatory near Carlsbad, New Mexico

In typical beta decay, one matter particle emitted — the electron — balances out the antimatter particle — the antineutrino. But in neutrinoless double beta decay, two electrons are emitted with no corresponding antimatter particles. Early in the universe, other processes might also have behaved in a similarly asymmetric way.

On the hunt

To spot the unusual decay, scientists are building experiments filled with carefully selected isotopes of certain elements and monitoring the material for electrons of a particular energy, which would be released in the neutrinoless decay.

If any experiment observes this process, “it would be a huge deal,” says particle physicist Yury Kolomensky of the University of California, Berkeley, a member of the CUORE neutrinoless double beta decay experiment. “It is a Nobel Prize‒level discovery.”

CUORE experiment UC Berkeley, experiment at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS), a search for neutrinoless double beta decay

Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

Unfortunately, the latest results won’t be garnering any Nobels. In a paper accepted in Physical Review Letters, the GERDA experiment spotted no signs of the decay. Located in the Gran Sasso underground lab in Italy, GERDA looks for the decay of the isotope germanium-76. (The number indicates the quantity of protons and neutrons in the atom’s nucleus.) Since there were no signs of the decay, if the process occurs it must be extremely rare, the scientists concluded, and its half-life must be long — more than 80 trillion trillion years.

Three other experiments have also recently come up empty. The Majorana Demonstrator experiment, located at the Sanford Underground Research Facility in Lead, S.D., which also looks for the decay in germanium, reported no evidence of neutrinoless double beta decay in a paper accepted in Physical Review Letters.

U Washington Majorana Demonstrator Experiment at SURF

Meanwhile, EXO-200, located in the Waste Isolation Pilot Plant, underground in a salt deposit near Carlsbad, N.M., reported no signs of the decay in xenon-136 in a paper published in the Feb. 16 Physical Review Letters.

Likewise, no evidence for the decay materialized in the CUORE experiment, in results reported in a paper accepted in Physical Review Letters. Composed of crystals containing tellurium-130, CUORE is also located in the Gran Sasso underground lab.

The most sensitive search thus far comes from the KamLAND-Zen neutrinoless double beta decay experiment located in a mine in Hida, Japan, which found a half-life longer than 100 trillion trillion years for the neutrinoless double beta decay of xenon-136.

KamLAND at the Kamioka Observatory in located in a mine in Hida, Japan

That result means that, if neutrinos are their own antiparticles, their mass has to be less than about 0.061 to 0.165 electron volts depending on theoretical assumptions, the KamLAND-Zen collaboration reported in a 2016 paper in Physical Review Letters. (An electron volt is particle physicists’ unit of energy and mass. For comparison, an electron has a much larger mass of half a million electron volts.)

Neutrinos, which come in three different varieties and have three different masses, are extremely light, but exactly how tiny those masses are is not known. Mass measured by neutrinoless double beta decay experiments is an effective mass, a kind of weighted average of the three neutrino masses. The smaller that mass, the lower the rate of the neutrinoless decays (and therefore the longer the half-life), and the harder the decays are to find.

KamLAND-Zen looks for decays of xenon-136 dissolved in a tank of liquid. Now, KamLAND-Zen is embarking on a new incarnation of the experiment, using about twice as much xenon, which will reach down to even smaller masses, and even rarer decays. Finding neutrinoless double beta decay may be more likely below about 0.05 electron volts, where neutrino mass has been predicted to lie if the particles are their own antiparticles.

Supersizing the search

KamLAND-Zen’s new experiment is only a start. Decades of additional work may be necessary before scientists clinch the case for or against neutrinos being their own antiparticles. But, says KamLAND-Zen member Lindley Winslow, a physicist at MIT, “sometimes nature is very kind to you.” The experiment could begin taking data as early as this spring, says Winslow, who is also a member of CUORE.

To keep searching, experiments must get bigger, while remaining extremely clean, free from any dust or contamination that could harbor radioactive isotopes. “What we are searching for is a decay that is very, very, very rare,” says GERDA collaborator Riccardo Brugnera, a physicist at the University of Padua in Italy. Anything that could mimic the decay could easily swamp the real thing, making the experiment less sensitive. Too many of those mimics, known as background, could limit the ability to see the decays, or to prove that they don’t occur.

In a 2017 paper in Nature, the GERDA experiment deemed itself essentially free from background — a first among such experiments. Reaching that milestone is good news for the future of these experiments. Scientists from GERDA and the Majorana Demonstrator are preparing to team up on a bigger and better experiment, called LEGEND, and many other teams are also planning scaled-up versions of their current detectors.

Antimatter whodunit

If scientists conclude that neutrinos are their own antiparticles, that fact could reveal why antimatter is so scarce. It could also explain why neutrinos are vastly lighter than other particles. “You can kill multiple problems with one stone,” Conrad says.

Theoretical physicists suggest that if neutrinos are their own antiparticles, undetected heavier neutrinos might be paired up with the lighter neutrinos that we observe. In what’s known as the seesaw mechanism, the bulky neutrino would act like a big kid on a seesaw, weighing down one end and lifting the lighter neutrinos to give them a smaller mass. At the same time, the heavy neutrinos — theorized to have existed at the high energies present in the young universe — could have given the infant cosmos its early preference for matter.

Discovering that neutrinos are their own antiparticles wouldn’t clinch the seesaw scenario. But it would provide a strong hint that neutrinos are essential to explaining where the antimatter went. And that’s a question physicists would love to answer.

“The biggest mystery in the universe is who stole all the antimatter. There’s no bigger theft that has occurred than that,” Conrad says.

Citations

J.B. Albert et al. Search for neutrinoless double-beta decay with the upgraded EXO-200 detector. Physical Review Letters. Vol. 120, February 16, 2018, p. 072701. doi: 10.1103/PhysRevLett.120.072701.

C.E. Aalseth et al. Search for zero-neutrino double beta decay in 76Ge with the Majorana demonstrator. Physical Review Letters, in press, 2018.

M. Agostini et al. Improved limit on neutrinoless double beta decay of 76Ge from GERDA Phase II. Physical Review Letters, in press, 2018.

CUORE Collaboration. First results from CUORE: a search for lepton number violation via 0νββ decay of 130Te. Physical Review Letters, in press, 2018.

KamLAND-Zen Collaboration. Search for majorana neutrinos near the inverted mass hierarchy region with KamLAND-Zen. Physical Review Letters. Vol. 117, August 19, 2017, p. 082503. doi:10.1103/PhysRevLett.117.082503.

The GERDA Collaboration. Background-free search for neutrinoless double-β decay of 76Ge with GERDA. Nature. Vol. 544, April 6, 2017, p. 47. doi:10.1038/nature21717.

See the full article here .

Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

Please help promote STEM in your local schools.

Stem Education Coalition

From ScienceNews: “Two-way communication is possible with a single quantum particle”

ScienceNews

February 23, 2018
Emily Conover

Studies show two people can simultaneously swap information using only one photon

DOUBLE DUTY Thanks to the phenomenon of quantum superposition, a single particle of light can send information in two directions at once, scientists report.

Communication is a two-way street. Thanks to quantum mechanics, that adage applies even if you’ve got only one particle to transmit messages with.

Using a single photon, or particle of light, two people can simultaneously send information to one another, scientists report in a new pair of papers. The feat relies on a quirk of quantum mechanics — superposition, the phenomenon through which particles can effectively occupy two places at once.

Sending information via quantum particles is a popular research subject, thanks to the promise of unhackable quantum communication (SN: 12/23/17, p. 27). The new studies specify a previously unidentified twist on that type of technique. “Sometimes you overlook a cool idea, and then it’s just literally right in front of your nose,” says University of Vienna experimental physicist Philip Walther.

Theoretical physicists Flavio Del Santo of the University of Vienna and Borivoje Dakić from the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences describe the theory behind the procedure in the Feb. 9 Physical Review Letters. Walther, Del Santo, Dakić and colleagues follow up with a demonstration of the technique in a paper posted at arXiv.org on February 14.

Imagine that two people, Alice and Bob, are stationed some distance apart. In standard classical physics, Alice and Bob would each require their own photon to send each other messages simultaneously, with each light particle transmitting a single bit, 0 or 1.

But if Alice and Bob possess a photon that is in a superposition — simultaneously located near Alice and near Bob — both of them can manipulate that photon to encode a 0 or 1, and then send it back to the other. How each manipulates the photon determines which of the two receives the photon in the end. If Alice and Bob put in the same bit — both 0s or both 1s — Alice receives the photon. If their bits don’t match, Bob gets it. Since Alice knows whether she sent a 0 or a 1, she immediately knows whether Bob encoded a 0 or 1, and vice versa.

To show that such communication is possible, Walther and colleagues sent single photons through an arrangement of mirrors and other optical devices. The setup put the photon in a superposition, sending it simultaneously to two stations that represented Alice and Bob.

By changing the phase of the light’s electromagnetic wave — shifting where the troughs and peaks of the wave fell — the researchers encoded the photon with a 0 or 1 at each station. Then, at each station, the photon — still in limbo between Alice and Bob — was sent to the opposite station. Along the way, the photon interacted with itself, interfering like water ripples combining to amplify their strength or cancel out. That interference determined whether the final photon was detected at Alice’s station or Bob’s.

“It’s a very nice idea,” says physicist Giulio Chiribella of the University of Oxford, who was not involved with the research. “This is another way in which quantum mechanics catches us off guard.”

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