From Northwestern University via Science Alert (AU): “The Most Common Stars in Our Galaxy May Be More Habitable Than We Thought”

From Northwestern University

via

Science Alert (AU)

17 JANUARY 2021
EVAN GOUGH

Our Sun’s solar flare, 2 October 2014. Credit: NASA/SDO.

NASA/SDO.

Red dwarf stars are the most common kind of star in our neighbourhood, and probably in the Milky Way. Because of that, many of the Earth-like and potentially life-supporting exoplanets we’ve detected are in orbit around red dwarfs. The problem is that red dwarfs can exhibit intense flaring behaviour, much more energetic than our relatively placid Sun.

So what does that mean for the potential of those exoplanets to actually support life?

Most life on Earth, and likely on other worlds, relies on stellar energy to survive. The Sun has been the engine for life on Earth since the first cells reproduced. But sometimes, like all stars, the Sun acts up and emits flares.

Sometimes it emits extremely energetic flares. The powerful magnetic energy in the Sun’s atmosphere becomes unstable, and an enormous amount of energy is released. If it’s released towards Earth, it can cause problems. It can lead to disruptions in radio communications and even blackouts.

But in terms of flaring activity, the Sun is relatively weak compared to some other stars. Some stars, especially red dwarfs, can flare frequently and violently. A team of researchers studied how flaring activity affects the atmosphere and potential for life on Earth-like planets orbiting low-mass stars, including M-type stars, K-type stars, and G-type stars.

Art of a flaring red dwarf star, orbited by an exoplanet. Credit: NASA/ESA/G. Bacon/STScI.

NASA/ESA Hubble Telescope.

The new study is called Persistence of flare-driven atmospheric chemistry on rocky habitable zone worlds. The lead author is Howard Chen, a PhD student at Northwestern University. The paper is published in the journal Nature Astronomy.

“Our Sun is more of a gentle giant,” said Allison Youngblood, an astronomer at the University of Colorado at Boulder and co-author of the study.

“It’s older and not as active as younger and smaller stars. Earth also has a strong magnetic field, which deflects the Sun’s damaging winds.”

That helps explain why Earth is positively rippling with life as Carl Sagan described our planet. But for planets orbiting low-mass stars like red dwarfs (M-dwarfs) the situation is much different.

We know that solar flares and associated coronal mass ejections can be very damaging to the prospects of life on unprotected exoplanets. The authors write in their introduction that “[s]tellar activity – which includes stellar flares, coronal mass ejections (CMEs) and stellar proton events (SPEs) – has a profound influence on a planet’s habitability, primarily via its effect on atmospheric ozone.”

A single flare here and there over time doesn’t have much effect. But many red dwarfs exhibit more frequent and prolonged flaring.

“We compared the atmospheric chemistry of planets experiencing frequent flares with planets experiencing no flares. The long-term atmospheric chemistry is very different,” said Northwestern’s Howard Chen, the study’s first author, in a press release.

“Continuous flares actually drive a planet’s atmospheric composition into a new chemical equilibrium.”

One of the things the team looked at was ozone, and the effect flares have on it. Here on Earth, our ozone layer helps protects us from the Sun’s UV radiation. But extreme flaring activity on red dwarfs can destroy ozone in the atmosphere of planets orbiting close to it.

When ozone levels drop, a planet is less protected from UV radiation coming from its star. Powerful UV radiation can diminish the possibility of life.

How could stars help us detect life on other planets?

In their study, the team used models to help understand flaring and its effects on exoplanet atmospheres. They used flaring data from NASA’s TESS (Transiting Exoplanet Survey Satellite) and long-term exoplanet climate data from other studies.

NASA/MIT TESS replaced Kepler in search for exoplanets.

They found some cases where ozone persisted, despite flaring.

“We’ve found that stellar flares might not preclude the existence of life,” added Daniel Horton, the study’s senior author. “In some cases, flaring doesn’t erode all of the atmospheric ozone. Surface life might still have a fighting chance.”

This figure from the study shows global-mean vertical profiles of atmospheric species on a simulated planet around a Sun-like G-type star. From left to right are the mixing ratios for ozone, nitrous oxide, nitric acid, and water vapour.Credit: Chen et al, Nature Astronomy, 2020.

Planets that can support life, at least potentially, can be in a tough spot. They must be close enough to their stars to prevent their water from freezing, but not too close or they’re too hot. But this dance with proximity can expose them to the powerful flares.

Red dwarfs are smaller and cooler than our Sun, so that means the habitable zone for any planets orbiting them is smaller and much closer to the star than Earth is to the Sun. That not only exposes them to flares but leads to planets being tidally locked to their stars.

The combination of flaring and tidal-locking can be bad for life’s prospects. Earth’s rotation generates its protective magnetosphere, but tidally-locked planets can’t generate one and are largely unprotected from stellar UV radiation.

“We studied planets orbiting within the habitable zones of M and K dwarf stars – the most common stars in the universe,” Horton said.

“Habitable zones around these stars are narrower because the stars are smaller and less powerful than stars like our Sun. On the flip side, M and K dwarf stars are thought to have more frequent flaring activity than our Sun, and their tidally locked planets are unlikely to have magnetic fields helping deflect their stellar winds.”

This figure from the study shows how repeated stellar flaring can alter the atmospheric gases in a simulated Earth-like planet around a Sun-like star. Credit: Chen et al, 2020.

There’s a more positive side to this study as well. The team found that flaring activity can actually help the search for life.

The flares can make it easier to detect some gases which are biomarkers. In this case, they found energy from flaring can highlight the presence of gases like nitric acid, nitrous dioxide, and nitrous oxide, which can all be indicators of living processes.

This figure from the study shows how repeated stellar flaring can affect the atmospheric chemistry on a modelled Earth-like planet around a K-type star. Note the raised levels of detectable NO, a potential bio-marker. Credit: Chen et al, 2020.

“Space weather events are typically viewed as a detriment to habitability,” Chen said.

“But our study quantitatively showed that some space weather can actually help us detect signatures of important gases that might signify biological processes.”

But only some. In other cases, their work showed that flaring can destroy potential biosignatures from anoxic life.

“Although we report the 3D effects of stellar flares on oxidizing atmospheres, strong flares could have other unexpected impacts on atmospheres with reducing conditions. For instance, hydrogen oxide species derived from stellar flares could destroy key anoxic biosignatures such as methane, dimethyl sulfide and carbonyl sulfide, thereby suppressing their spectroscopic features,” the authors report.

Can There Be Life On Planets Around Red Dwarf Stars?

Another interesting result of this study concerns exoplanet magnetospheres. They find that hyperflares may help reveal the nature and extent of magnetospheres.

“More speculatively, proton events during hyperflares may reveal the existence of planetary-scale magnetic fields by highlighting particular regions of the planet. By identifying nitrogen- or hydrogen oxide-emitting flux fingerprints during magnetic storms and/or auroral precipitation events, one may be able to determine the geometric extent of exoplanetary magnetospheres.”

Hyperflares might help us understand the extent of exoplanet magnetospheres by identifying the extent of nitrogen oxide flux fingerprints. Credit: Chen et al, 2020.

Other recent research has suggested that exoplanets subjected to flaring, especially around red dwarf stars, are not great locations to search for life. The flaring activity is too detrimental. But this study shows that there’s more complexity to the situation.

Overall it shows that flaring could help us detect biosignatures in some cases. It also shows that while flaring can disrupt exoplanet atmospheres, in many cases they return to normal. It’s also a fact that low-mass stars live much longer than stars like our Sun, meaning there’s more time for life to develop on their planets.

This new work highlights how complicated the search for life is, and how many variables are involved. And it contains at least one surprise. Whereas flaring has been largely considered detrimental to exoplanet habitability, the fact that it may help detect biosignatures means there’s more going on than expected.

This research required cooperation from scientists across many disciplines. It relied on climate scientists, astronomers, observers and theorists, and of course, exoplanet scientists.

“This project was a result of fantastic collective team effort,” said Eric T. Wolf, a planetary scientist at CU Boulder and a co-author of the study.

“Our work highlights the benefits of interdisciplinary efforts when investigating conditions on extrasolar planets.”

See the full article here .

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South Campus

Northwestern is recognized nationally and internationally for its educational programs.

On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

From Japan Advanced Institute of Science and Technology (北陸先端科学技術大学院大学: hokuriku sentan kagaku gijutsu daigakuin daigaku) (JP) via phys.org: “Shapeshifting crystals- Varying stability in different forms of gallium selenide monolayers”

From Japan Advanced Institute of Science and Technology (北陸先端科学技術大学院大学: hokuriku sentan kagaku gijutsu daigakuin daigaku) (JP)

via

phys.org

The P and AP phases of a GaSe monolayer. Credit: Japan Advanced Institute of Science and Technology

The gallium selenide monolayer has been recently discovered to have an alternative crystal structure and has diverse potential applications in electronics. Understanding its properties is crucial to understand its functions. Now, scientists from the Japan Advanced Institute of Science and Technology and the University of Tokyo have explored its structural stability, electronic states and transformation of crystal phases.

Solid materials comprise a symmetric arrangement of atoms that confer properties like conductivity, strength and durability. Changes in size can change this arrangement, thereby changing the overall properties of the material. For instance, the electrical, chemical, optical and mechanical properties of certain materials can change as we move towards the nanoscale. Science now lets us study the differences in properties across various dimensions right from monolayer (atomic) level.

Gallium selenide (GaSe) is a layered metal-chalcogenide, which is known to have polytypes, which differ in their stacking sequence of layers, but not a polymorph, which has a different atomic arrangement inside the layer. GaSe has sparked a great deal of interest in areas of physical and chemical research, owing to its potential use in photoconduction, far-infrared conversion and optical applications. Conventionally, a GaSe monolayer is composed of gallium (Ga) and selenium (Se) atoms bonded covalently, with the Se atoms projecting outwards, forming a trigonal prism-like structure called the P phase. Part of the same research group had earlier reported a novel crystal phase of GaSe using transmission electron microscopy in Surface and Interface Analysis, wherein the Se atoms are arranged in a trigonal antiprismatic manner to the Ga atoms, referred to as AP phase, with a symmetry different from the conventional P phase (see Picture 1). Because of the novelty of this monolayer structure, very little is known about how it does its shape shifting. Moreover, how do variations in the intralayer structure of such compounds affect stability?

To answer this, Mr. Hirokazu Nitta and Prof. Yukiko Yamada-Takamura from the Japan Advanced Institute of Science and Technology (JAIST) explored the structural stability and electronic states of phases of GaSe monolayer using first-principles calculations, in their latest study in Physical Review B.

Hirokazu Nitta says, “We have found out through first-principles calculations that this new phase is metastable, and stability against the ground-state conventional phase reverses upon applying tensile strain, which we think is strongly related to the fact that we saw this phase formed only at the film-substrate interface.”

To compare the structural stability of the P and AP phases of GaSe, the researchers first calculated the total energy at different in-plane lattice constants, which represent the size of a unit cell in the crystal, given that its structure comprises a lattice, an organized meshwork of atoms. The lowest energy that corresponds to the most stable state was computed and at this state, the P phase, was found to be more stable than the AP phase.

Then, to investigate if the AP and P phases can transform into each other, they determined the energy barriers that the material needs to cross to change, and additionally performed molecular dynamics calculations using a supercomputer (see Picture 2). They found the energy barrier for phase transition of P-phase and AP-phase GaSe monolayers is large likely due to the need of breaking and making new bonds, which prohibits direct transition from P to AP phase. The calculations also revealed that the relative stability of P-phase and AP-phase GaSe monolayers can be reversed by applying tensile strain, or a stretching-type force.

Highlighting the importance and future prospects of their study, Prof. Yamada-Takamura says, “Layered chalcogenides are interesting 2-D materials after graphene, having wide variety and especially bandgap. We have just found out a new polymorph (not polytype) of a layered monochalcogenide. Its physical as well as chemical properties are yet to be discovered.”

Together, the findings of this study describe the electronic structure of a less-known structure of GaSe that can provide insights into the behavior of similar epitaxially grown monolayers, revealing yet another secret about the unknown family members of GaSe and related monochalcogenides.

See the full article here.

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Please help promote STEM in your local schools.

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Japan Advanced Institute of Science and Technology: JAIST (北陸先端科学技術大学院大学: hokuriku sentan kagaku gijutsu daigakuin daigaku) is a postgraduate university in Japan, established in 1990.

JAIST was established in the centre of Ishikawa Science Park (ISP). It is to the south of Kanazawa City. JAIST has programs of advanced research and development in science and technology. This university has several satellite campuses: Shinagawa Campus in Shinagawa, Tokyo (relocated from its earlier Tamachi Campus in Minato, Tokyo), open course in Information Technology and Management of Technology (MOT), and satellite lectures in Kanazawa City and Toyama City.

In The 21st Century Center Of Excellence Program, JSPS granted two programs to JAIST. One program is the “Technology　Creation based on Knowledge Science” (知識科学に基づく科学技術の創造と実践, chishiki kagaku ni motoduku kagaku-gijyutsu no sōzō to jissen) (2003), and the other program is “Verifiable and Evolvable E-Society” (検証進化可能電子社会, kenshō shinka kanō denshi shakai) (2004).

From University of Michigan, Caltech and UCLA via Science Alert (AU):”Our Solar System Is Going to Totally Disintegrate Sooner Than We Thought”

From University of Michigan

and

Caltech

and

UCLA

via

Science Alert (AU)

29 NOVEMBER 2020
MICHELLE STARR

Milky Way Credits: NASA/JPL-Caltech /ESO R. Hurt. The bar is visible in this image.

A white dwarf star after ejecting its mass to form a planetary nebula. Credit: ESO/P. Weilbacher/AIP.

Although the ground beneath our feet feels solid and reassuring (most of the time), nothing in this Universe lasts forever.

One day, our Sun will die, ejecting a large proportion of its mass before its core shrinks down into a white dwarf, gradually leaking heat until it’s nothing more than a cold, dark, dead lump of rock, a thousand trillion years later.

But the rest of the Solar System will be long gone by then. According to new simulations, it will take just 100 billion years for any remaining planets to skedaddle off across the galaxy, leaving the dying Sun far behind.

Astronomers and physicists have been trying to puzzle out the ultimate fate of the Solar System for at least hundreds of years.

“Understanding the long-term dynamical stability of the solar system constitutes one of the oldest pursuits of astrophysics, tracing back to Newton himself, who speculated that mutual interactions between planets would eventually drive the system unstable,” wrote astronomers Jon Zink of the University of California, Los Angeles, Konstantin Batygin of Caltech and Fred Adams of the University of Michigan in The Astronomical Journal.

But that’s a lot trickier than it might seem. The greater the number of bodies that are involved in a dynamical system, interacting with each other, the more complicated that system grows and the harder it is to predict. This is called the N-body problem.

Because of this complexity, it’s impossible to make deterministic predictions of the orbits of Solar System objects past certain timescales. Beyond about five to 10 million years, certainty flies right out the window.

But, if we can figure out what’s going to happen to our Solar System, that will tell us something about how the Universe might evolve, on timescales far longer than its current age of 13.8 billion years.

In 1999, astronomers predicted [Science] that the Solar System would slowly fall apart over a period of at least a billion billion – that’s 10^18, or a quintillion – years. That’s how long it would take, they calculated, for orbital resonances from Jupiter and Saturn to decouple Uranus.

According to Zink’s team, though, this calculation left out some important influences that could disrupt the Solar System sooner.

Firstly, there’s the Sun.

In about 5 billion years, as it dies, the Sun will swell up into a red giant, engulfing Mercury, Venus and Earth. Then it will eject nearly half its mass, blown away into space on stellar winds; the remaining white dwarf will be around just 54 percent of the current solar mass.

This mass loss will loosen the Sun’s gravitational grip on the remaining planets, Mars and the outer gas and ice giants, Jupiter, Saturn, Uranus, and Neptune.

Secondly, as the Solar System orbits the galactic centre, other stars ought to come close enough to perturb the planets’ orbits, around once every 23 million years.

“By accounting for stellar mass loss and the inflation of the outer planet orbits, these encounters will become more influential,” the researchers wrote.

“Given enough time, some of these flybys will come close enough to disassociate – or destabilise – the remaining planets.”

With these additional influences accounted for in their calculations, the team ran 10 N-body simulations for the outer planets (leaving out Mars to save on computation costs, since its influence should be negligible), using the powerful Shared Hoffman2 Cluster.

Hoffman2 Cluster. Credit: UCLA.

These simulations were split into two phases: up to the end of the Sun’s mass loss, and the phase that comes after.

Although 10 simulations isn’t a strong statistical sample, the team found that a similar scenario played out each time.

After the Sun completes its evolution into a white dwarf, the outer planets have a larger orbit, but still remain relatively stable. Jupiter and Saturn, however, become captured in a stable 5:2 resonance – for every five times Jupiter orbits the Sun, Saturn orbits twice (that eventual resonance has been proposed many times, not least by Isaac Newton himself).

These expanded orbits, as well as characteristics of the planetary resonance, makes the system more susceptible to perturbations by passing stars.

After 30 billion years, such stellar perturbations jangle those stable orbits into chaotic ones, resulting in rapid planet loss. All but one planet escape their orbits, fleeing off into the galaxy as rogue planets.

That last, lonely planet sticks around for another 50 billion years, but its fate is sealed. Eventually, it, too, is knocked loose by the gravitational influence of passing stars. Ultimately, by 100 billion years after the Sun turns into a white dwarf, the Solar System is no more.

That’s a significantly shorter timeframe than that proposed in 1999. And, the researchers carefully note, it’s contingent on current observations of the local galactic environment, and stellar flyby estimates, both of which may change. So it’s by no means engraved in stone.

Even if estimates of the timeline of the Solar System’s demise do change, however, it’s still many billions of years away. The likelihood of humanity surviving long enough to see it is slim.

Sleep tight!

See the full article here .

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For nearly 100 years, UCLA has been a pioneer, persevering through impossibility, turning the futile into the attainable.

We doubt the critics, reject the status quo and see opportunity in dissatisfaction. Our campus, faculty and students are driven by optimism. It is not naïve; it is essential. And it has fueled every accomplishment, allowing us to redefine what’s possible, time after time.

This can-do perspective has brought us 12 Nobel Prizes, 12 Rhodes Scholarships, more NCAA titles than any university and more Olympic medals than most nations. Our faculty and alumni helped create the Internet and pioneered reverse osmosis. And more than 100 companies have been created based on technology developed at UCLA.

The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

Caltech campus

The University of Michigan (U-M, UM, UMich, or U of M), frequently referred to simply as Michigan, is a public research university located in Ann Arbor, Michigan, United States. Originally, founded in 1817 in Detroit as the Catholepistemiad, or University of Michigania, 20 years before the Michigan Territory officially became a state, the University of Michigan is the state’s oldest university. The university moved to Ann Arbor in 1837 onto 40 acres (16 ha) of what is now known as Central Campus. Since its establishment in Ann Arbor, the university campus has expanded to include more than 584 major buildings with a combined area of more than 34 million gross square feet (781 acres or 3.16 km²), and has two satellite campuses located in Flint and Dearborn. The University was one of the founding members of the Association of American Universities.

Considered one of the foremost research universities in the United States,[7] the university has very high research activity and its comprehensive graduate program offers doctoral degrees in the humanities, social sciences, and STEM fields (Science, Technology, Engineering and Mathematics) as well as professional degrees in business, medicine, law, pharmacy, nursing, social work and dentistry. Michigan’s body of living alumni (as of 2012) comprises more than 500,000. Besides academic life, Michigan’s athletic teams compete in Division I of the NCAA and are collectively known as the Wolverines. They are members of the Big Ten Conference.

From Science Alert: “Something’s Making Dead Stars Mysteriously Hot, And We’re Running Out of Explanations”

From Science Alert (AU)

24 NOVEMBER 2020
MICHELLE STARR

White dwarf stars in globular cluster NGC 6397. (NASA, ESA, and H. Richer/University of British Columbia)

When stars like the Sun reach the end of their lives, the object that remains is a white dwarf. This is the star’s shrunken, naked core, no longer capable of nuclear fusion. It shines, but only with residual heat, slowly cooling over billions of years until it’s completely cold and dark.

But not all white dwarfs cool the same way. Last year, astronomers found a certain type of massive white dwarf stars cool more slowly than others, as though they have an additional source of heat. But figuring out what that heat source could be is proving tricky.

We know now, thanks to new research, one thing that it isn’t: the sedimentation, or inward sinking, of a neutron-rich stable isotope of neon deep in the stars’ interiors.

Most stars in the Milky Way galaxy – those below about eight times the mass of the Sun – are destined to become white dwarf stars.

Stars of this mass, having run out of hydrogen and helium to fuse, have insufficient pressure to ignite the carbon that remains. They eject their outer material, and the core contracts into a sphere about the size of the Earth.

This Earth-sized sphere, consisting mainly of carbon and oxygen, is incredibly dense, the most massive up to around 1.4 times the mass of the Sun.

Only something called electron degeneracy pressure, an outward pressure generated by the inability of electrons with the same spin to occupy the same state, prevents the core from complete collapse.

Because they are so dense, with such a small surface area, they take a very long time to lose heat. Once the core of a white dwarf has stopped contracting, it can exceed temperatures of around 100,000 Kelvin (around 100,000 degrees Celsius and 180,000 degrees Fahrenheit).

Astronomers think that not enough time has passed since the beginning of the Universe for a white dwarf to have cooled completely.

But the so-called Q-branch white dwarf stars, which constitute around 6 percent of massive white dwarfs, cool even slower than that. According to a 2019 paper [The Astrophysical Journal] led by astronomer Sihao Cheng of Johns Hopkins University, this small fraction of white dwarfs demonstrate a cooling delay of about 8 billion years, compared to other white dwarfs.

Although the rate of sedimentation from single crystals is likely too slow to produce the observed heating, 22Ne clustering could potentially speed up the process. Even this, however, the team found unlikely.

In the simulations, they found that microcrystals of 22Ne in a liquid of carbon and oxygen at the ratios found in white dwarfs are always unstable.

There are only two options – either the mixture is so hot that the crystal melts and the neon dissolves into the liquid, or the whole mixture freezes.There’s no middle point.

Even when the mixture is below the melting point of neon, but above the melting point of carbon and oxygen, the neon dissolves.

The team then used phase diagrams, a graph showing the physical states of a substance under a range of temperatures and pressures, to work out how much neon would be required in the mixture for neon to separate and stabilise.

Typically, carbon-oxygen white dwarfs have around 2 percent neon. In order for neon to be stable, this mixture would need to contain at least 30 percent neon.

Now a team of astronomers led by Matt Caplan of Illinois State University have tested that hypothesis with molecular dynamics simulations and phase diagrams.

According to their findings, that’s just not possible.

Although the rate of sedimentation from single crystals is likely too slow to produce the observed heating, 22Ne clustering could potentially speed up the process. Even this, however, the team found unlikely.

In the simulations, they found that microcrystals of 22Ne in a liquid of carbon and oxygen at the ratios found in white dwarfs are always unstable.

There are only two options – either the mixture is so hot that the crystal melts and the neon dissolves into the liquid, or the whole mixture freezes.There’s no middle point.

Even when the mixture is below the melting point of neon, but above the melting point of carbon and oxygen, the neon dissolves.

The team then used phase diagrams, a graph showing the physical states of a substance under a range of temperatures and pressures, to work out how much neon would be required in the mixture for neon to separate and stabilise.

Typically, carbon-oxygen white dwarfs have around 2 percent neon. In order for neon to be stable, this mixture would need to contain at least 30 percent neon.

“In summary,” the researchers wrote in their paper, “we find that there are no conditions where a 22Ne-enriched cluster is stable in a carbon-oxygen white dwarf, and therefore enhanced diffusion of 22Ne cannot explain the Q branch.”

This suggests that these Q-branch white dwarf stars may have a peculiar composition to explain the additional heating.

If the stars were just a little bit richer in neon – around 6 percent – single particle sedimentation, rather than cluster sedimentation, could generate heat. Sodium and magnesium would be poor candidates; like neon, they don’t separate to form solids in relatively small quantities.

Iron-group elements, however, look a little more promising. Iron separates in a carbon-oxygen mixture, and as little as 0.1 percent can produce notable heating.

If some astrophysical process could enrich iron in Q-branch white dwarfs to 1 percent, that would be sufficient to delay cooling by several billion years, the researchers said.

“Thus, this work motivates including iron in white dwarf cooling models,” they wrote. “This will require new phase diagrams of iron and a survey with molecular dynamics of the clustering and the characteristic sizes of iron clusters, which will be the subject of future work.”

The research has been published in The Astrophysical Journal Letters.

See the full article here .

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From Science Alert: “The First Star in Our Galaxy Caught Sending Out Fast Radio Bursts Is Doing It Again”

From Science Alert (AU)

22 OCTOBER 2020
MICHELLE STARR

Artist’s impression of a magnetar. Credit: Sophia Dagnello, NRAO/AUI/NSF.

A little dead star that dazzled us earlier this year is not done with its shenanigans.

Magnetar SGR 1935+2154, which in April emitted the first known fast radio burst from inside the Milky Way, has flared up once more, giving astronomers yet another chance to solve more than one major cosmic mystery.

On 8 October 2020, the CHIME/FRB collaboration detected SGR 1935+2154 emitting three millisecond radio bursts in three seconds.

CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia (CA), the University of Toronto (CA), McGill University (CA), Yale and the National Research Council in British Columbia (CA), at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, CA Altitude 545 m (1,788 ft).

Following up on the CHIME/FRB detection, the FAST radio telescope found something else – a pulsed radio emission consistent with the magnetar’s spin period.

“It’s really exciting to see SGR 1935+2154 back again, and I’m optimistic that as we study these bursts more carefully, it will help us better understand the potential relationship between magnetars and fast radio bursts,” astronomer Deborah Good of the University of British Columbia in Canada, and member of the CHIME/FRB, told ScienceAlert.

The detections, reported in The Astronomer’s Telegram, are currently undergoing analysis.

Before April of this year, fast radio bursts (FRBs) had only ever been detected coming from outside the galaxy, usually from sources millions of light-years away. The first one was discovered in 2007, and ever since, astronomers have been trying to figure out what causes them.

As the name implies, FRBs are bursts of extremely powerful radio waves detected in the sky, some discharging more energy than hundreds of millions of Suns. They last mere milliseconds.

Because most fast radio burst sources seem to flare once and haven’t been detected repeating, they’re extremely unpredictable. In addition, the ones we’ve detected usually come from so far away, our telescopes are unable to pick out individual stars. Both of these characteristics make FRBs challenging to track down either to an exact source galaxy, or a known cause.

But SGR 1935+2154 is only around 30,000 light-years away. On 28 April 2020, it spat out a powerful millisecond-duration burst, which has since been named FRB 200428 in keeping with fast radio burst naming conventions.

Once the power of the signal was corrected for distance, FRB 200428 was found to be not quite as powerful as extragalactic fast radio bursts – but everything else about it fit the profile.

“If the same signal came from a nearby galaxy, like one of the nearby typical FRB galaxies, it would look like an FRB to us,” astronomer Shrinivas Kulkarni of Caltech told ScienceAlert in May. “Something like this has never been seen before.”

We don’t know much about the three new bursts yet. Because scientists are still working on the data, it’s possible that some early conclusions are likely to change, Good told ScienceAlert. But we can already tell that they are both like and unlike FRB 200428.

They are a little less powerful again, but they are all still incredibly strong, and all just milliseconds long. “Although less bright than the detection earlier this year, these are still very bright bursts which we’d see if they were extragalactic,” Good said.

“One of the most interesting aspects of this detection is that our three bursts seem to have occurred within one rotation period. The magnetar is known to rotate once every ~3.24 seconds, but our first and second bursts were separated by 0.954 seconds, and the second and third were separated by 1.949 seconds. That’s a bit unusual, and I think it’s something that we’ll be looking into further going forward.”

That could reveal something new and useful about magnetar behaviour, because – let’s face it – they are pretty weird.

Magnetars – of which we have only confirmed 24 to date – are a type of neutron star; that’s the collapsed core of a dead star not massive enough to turn into a black hole. Neutron stars are small and dense, about 20 kilometres (12 miles) in diameter, with a maximum mass of about two Suns. But magnetars add something else to the mix: a shockingly powerful magnetic field.

These jaw-dropping fields are around a quadrillion times more powerful than Earth’s magnetic field, and a thousand times more powerful than that of a normal neutron star. And we still don’t fully understand how they got that way.

But we do know that magnetars undergo periods of activity. As gravity tries to keep the star together – an inward force – the magnetic field, pulling outward, is so powerful, it distorts the star’s shape. This leads to ongoing tension which occasionally produces gargantuan starquakes and giant magnetar flares.

SGR 1935+2154 has been undergoing such activity, suggesting a link between magnetar tantrums and at least some FRBs.

Obviously, astronomers have found the source of the first intra-galactic FRB to be of intense interest. When CHIME/FRB reported their detection, other astronomers went to have a look at the star, including a team led by Zhu Weiwei of the National Astronomical Observatories of China who had access to FAST, the largest single-aperture radio telescope in the world.

FAST [Five-hundred-meter Aperture Spherical Telescope] radio telescope, with phased arrays from CSIRO engineers Australia located in the Dawodang depression in Pingtang County, Guizhou Province, South China.

And they found something interesting, also reported in The Astronomer’s Telegram – pulsed radio emission. These radio pulses were nowhere near as strong as the bursts, but they’re extremely rare: If validated, SGR 1935+2154 will only be the sixth magnetar with pulsed radio emission. And the pulse period was found to be 3.24781 seconds – almost exactly the star’s spin period.

This is curious, because so far, astronomers have struggled to find a link between magnetars and radio pulsars. Pulsars are another type of neutron star; they have a more normal magnetic field, but they pulse in radio waves as they spin, and astronomers have long tried to figure out how the two types of stars are related.

Earlier this year, Australian astronomers identified a magnetar that was behaving like a radio pulsar – a possible “missing link” between the two, and evidence that at least some magnetars could evolve into pulsars. SGR 1935+2154 could be another piece of the puzzle.

“Based on these results and the increasing bursting activities, we speculate that the magnetar may be in the process of turning into an active radio pulsar,” Weiwei’s team wrote.

What an absolutely bloody fascinating little star this is turning out to be.

See the full article here .

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From University of Maryland via Science Alert: “Astronomers Detect Eerie Glow Still Radiating From Neutron Star Collision Years Later”

From University of Maryland

via

Science Alert

Artist’s impression of GW170817. (ESO/L. Calçada/M. Kornmesser.)

12 OCTOBER 2020
MICHELLE STARR

It’s now been over three years since history was made with the first-ever detection of colliding neutron stars. From 130 million light-years away, astronomers watched a brilliant flash of gamma-radiation, heralded by rippling gravitational waves, as the two dead stars came together.

Since then, astronomers have been keeping a careful eye on the corner of space in which the collision occurred, to see what happens in the aftermath of such a violent event. And, surprisingly, they found it still continued to glow in the X-ray spectrum long after models predicted such glowing would cease.

“We are entering a new phase in our understanding of neutron stars,” said astronomer Eleonora Troja of the University of Maryland.

“We really don’t know what to expect from this point forward, because all our models were predicting no X-rays and we were surprised to see them 1,000 days after the collision event was detected. It may take years to find out the answer to what is going on, but our research opens the door to many possibilities.”

The collision event, named GW170817, was first detected on 17 August 2017 as gravitational waves emanating from a section of sky in the constellation of Hydra, thanks to the LIGO-Virgo gravitational wave detectors.

From GW170817 Press Release.

MIT /Caltech Advanced aLigo .

Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA.

Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA.

VIRGO Gravitational Wave interferometer, near Pisa, Italy.

VIRGO Gravitational Wave interferometer, near Pisa, Italy.

Then, just 1.7 seconds later, two space-based observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory, picked up an intense gamma-ray burst – the brightest and most energetic events in the Universe – from the same area of sky.

NASA/Fermi LAT.

NASA/Fermi Gamma Ray Space Telescope.

ESA/Integral.

Nine days later, astronomers picked up a glow spanning the electromagnetic spectrum from radio waves to X-rays. This was something new, never seen following a gamma-ray burst. Previously, all gamma-ray bursts had completely faded within a few minutes, while this glow defied our understanding of the gamma-ray burst aftermath.

This new afterglow emission was interpreted as the result of a relativistic jet [The Astrophysical Journal Letters] – that is, a jet moving at a significant percentage of the speed of light – from the kilonova explosion. As this jet expands into space, it generates its own shockwave, which emits light across the spectrum, from radio waves to X-rays.

The afterglow continued to grow in brightness, peaking at 160 days and then rapidly fading away – but the X-radiation lingered. It was last detected in March of this year by the Chandra X-ray Observatory, two and a half years after the first detection of the collision; in subsequent observations in May using the Australian Telescope Compact Array, the glow was below the detection threshold.

NASA/Chandra X-ray Telescope

Australian Telescope Compact Array, an array of six 22-m antennas, at the Paul Wild Observatory, 25 km west of the town of Narrabri in rural New South Wales.

Troja and her team have mapped the X-ray glow, and found that the prolonged emission is still consistent with a relativistic jet, but are not quite sure what enabled it to continue this long after the collision.

Given that GW170817 is the first event of its kind that we’ve been able to observe, it’s likely there are things we don’t understand about how gamma-ray bursts and neutron star collisions happen.

“Having a collision so close to us that it’s visible opens a window into the whole process that we rarely have access to,” Troja said. “It may be there are physical processes we have not included in our models because they’re not relevant in the earlier stages that we are more familiar with, when the jets form.”

It’s also possible that it’s not the jet itself that caused the extended emission, but an expanding cloud of gas from the kilonova that followed behind it, creating its own shockwave. If multiple shockwaves take place at different times and behave differently, that could explain the differences in how the different wavelengths faded.

Or the X-rays could have been prolonged by what the researchers called “continued energy injection by a long-lived central engine” – that whatever was left behind by the collision continued to emit X-radiation.

We don’t currently have enough data to work out which of these scenarios caused the continued glow, but some things are clear. Firstly, we don’t fully understand neutron star mergers. Something is missing from our models, and only continued observations and analysis will help figure out what that is.

Secondly, since this glow has only been identified in relation to a neutron star collision, it could be a signature we can use to identify other neutron star collisions that we may have missed. It’s characteristics could be used to look for similar emission in X-ray data archives to uncover these missed events.

More observations of the GW170817 patch of sky will commence in December of this year, and astronomers are not sure what they are going to find. Either way, it will help constrain our understanding of the event.

“This may be the last breath of an historical source or the beginning of a new story, in which the signal brightens up again in the future and may remain visible for decades or even centuries,” Troja said. “Whatever happens, this event is changing what we know about neutron star mergers and rewriting our models.”

The research is due to appear in the Monthly Notices of the Royal Astronomical Society, and is available on arXiv [A thousand days after the merger: continued X-ray emission from GW170817]

See the full article here .

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Driven by the pursuit of excellence, the University of Maryland has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

From KU Leuven BE via Science Alert: “We Now Know How Dying Stars Carve Out Mesmerising Mandalas of Stardust”

From KU Leuven BE

via

Science Alert

18 SEPTEMBER 2020
MICHELLE STARR

Planetary nebula NGC 2392. (NASA, ESA, Andrew Fruchter/STScI, and the ERO team/STScI + ST-ECF.)

The last gasps of dying stars are some of the most beautiful objects in the galaxy.

They’re called planetary nebulae, clouds of stellar material ejected out into space as a red giant star enters the last stage of its life. The dying star shucks off its outer layers, which are illuminated from within by the hot, exposed core.

These clouds are complex, and gorgeous, with mandala-like waves, strange discs, even bilobed jets akin to wings. The stunning complexity and variety of these shapes seems at odds with the uniform shape of their precursor stars.

“The Sun – which will ultimately become a red giant – is as round as a billiard ball, so we wondered: how can such a star produce all these different shapes?” said astronomer Leen Decin of KU Leuven in Belgium.

Now, through a detailed collection of observations and hydrodynamical simulations, scientists have discovered how planetary nebulae might get their shapes: through gravitational interactions with binary star companions, and large planets like Jupiter that survive the violent deaths of their host stars.

Initially, the team wasn’t looking at planetary nebulae at all. The focus of their studies was a slightly earlier life stage called the asymptotic giant branch (AGB).

This is when the red giant is in the last stages of evolution before the planetary nebula phase, and powerful winds from the star are blowing out into the space around it, scattering gas and dust.

Red giants are the old age of a particular kind of star, less than about eight times the mass of the Sun. It’s how the Sun is going to end its life, puffing up to engulf Mercury, Venus and maybe even Earth, before its core collapses into a tiny white dwarf gleaming brightly with residual heat.

So, how these stars die is very interesting to astronomers. And yet Decin’s international team found that a detailed database of observational data on the winds of AGB stars has not been compiled. So they set about creating one.

“The lack of such detailed observational data caused us to initially assume that the stellar winds have an overall spherical geometry, much like the stars they surround,” said astronomer Carl Gottlieb of the Harvard-Smithsonian Center for Astrophysics.

“Our new observational data shapes a much different story of individual stars, how they live, and how they die. We now have an unprecedented view of how stars like our Sun will evolve during the last stages of their evolution.”

(L. Decin, ESO/ALMA)

Using the Atacama Large Millimeter/submillimeter Array in Chile, the team took observations of a sample of AGB stars.

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

In those data, they noticed a range of structures – including arcs, shells, bipolar structures, clumps, spirals, doughnut shapes, and rotating discs.

Since the radially outflowing winds were smooth, the team quickly ascertained that something in the immediate vicinity of the star could be causing the structures in the material – like a small binary companion or giant planet, too faint to be seen, but whose gravitational tugging could be affecting the material.

Sure enough, when they modelled the effect of a companion on these outflows, the team found that each type of structure they observed could be created by the presence of a secondary object. The mass of that object, its distance from the star, and the eccentricity of its orbit can all play a role in the variety of the structures produced in the stellar wind.

“Just like a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind,” Decin said.

“All of our observations can be explained by the fact that the stars have a companion.”

All the shapes bore strong similarities to the complex structures and shapes seen in planetary nebulae, suggesting the structures in the two stages have the same formation mechanism. And there are wide-ranging implications for our understanding of stellar evolution.

“Our findings change a lot,” Decin said. “Since the complexity of stellar winds was not accounted for in the past, any previous mass-loss rate estimate of old stars could be wrong by up to a factor of 10.”

The discovery also strongly hints at what might happen when the Sun dies. Our Sun, of course, does not have a binary companion (which is also a bit of a mystery in its own right).

But the Solar System does have two planets massive enough to potentially influence its outflows. Those are Jupiter and Saturn, the gas giants, whose mass is already large enough to tug the Sun around in a tiny wobbly circle.

They’ll be far beyond the Sun’s reach when our star becomes a red giant, and recent discoveries suggest that giant planets can indeed survive their stars’ deaths – maybe not for long, but long enough to make some waves (or arcs or shells).

The team’s calculations predict that Jupiter, and maybe Saturn, will be able to carve some relatively weak spirals in the Sun’s AGB wind.

The team is now conducting further research to find out what else their discovery might change for our understanding of the deaths of stars.

The research has been published in Science.

See the full article here.

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KU Leuven is a research university in the Dutch-speaking city of Leuven in Flanders, Belgium. It conducts teaching, research, and services in the natural sciences, engineering, humanities, medicine, law, business, and social sciences.

The university’s full name is Katholieke Universiteit Leuven, officially Katholieke Universiteit te Leuven, which translates in English as Catholic University of Leuven. It is however not translated in official communications, like its similarly-named French-language sister university Université catholique de Louvain (UCLouvain).

In addition to its main campus in Leuven, it has satellite campuses in Kortrijk, Antwerp, Ghent, Bruges, Ostend, Geel, Diepenbeek, Aalst, Sint-Katelijne-Waver, and in Belgium’s capital Brussels. KU Leuven is the largest university in Belgium and the Low Countries. In 2017–18, more than 58,000 students were enrolled. Its primary language of instruction is Dutch, although several programs are taught in English, particularly graduate degrees.

KU Leuven consistently ranks among the top 100 universities in the world by major ranking tables. As of 2020, it ranks 45th in the Times Higher Education rankings, 80th according QS World University Rankings, 85th according to the Shanghai Academic Ranking of World Universities. For four consecutive years starting in 2016, Thomson Reuters ranked KU Leuven as Europe’s most innovative university, with its researchers having filed more patents than any other university in Europe; its patents are also the most cited by external academics.

Although Catholic in heritage, KU Leuven operates independently from the Church. Due to its historic roots to the old University of Leuven, it is considered the oldest extant Catholic university. KU Leuven is open to students from different faiths or life-stances.

From Arizona State University via Science Alert: “Myriad Exoplanets in Our Galaxy Could Be Made of Diamond And Rock”

From Arizona State University

via

Science Alert

14 SEPTEMBER 2020
MICHELLE STARR

(Shim/ASU/Vecteezy)

Here in the Solar System, we have quite an interesting variety of planets, but they are limited by the composition of our Sun. Since the planets, moons, asteroids and other bodies are made out of what was left over after the Sun was finished forming, their chemistry is thought to be related to our host.

But not all stars are made out of the same stuff as our Sun, which means that out there in the wide expanses of our galaxy, we can expect to find exoplanets wildly different from the offering in our little Solar System.

For example, stars that are rich in carbon compared to our Sun – with more carbon than oxygen – could have exoplanets that are made primarily of diamond, with a little bit of silica, if the conditions are just right. And now, in a lab, scientists have squished and heated silicon carbide to find out what those conditions could be.

“These exoplanets are unlike anything in our Solar System,” said geophysicist Harrison Allen-Sutter of Arizona State University’s School of Earth and Space Exploration.

The idea that stars with a higher carbon-to-oxygen ratio than the Sun might produce diamond planets first emerged with the discovery of 55 Cancri e [The Astrophysical Journal Letters], a super-Earth exoplanet orbiting a star thought to be rich in carbon 41 light-years away.

It was later discovered that this star wasn’t as carbon-rich as previously thought [The Astronomical Journal], which put paid to that idea – at least as far as 55 Cancri e is concerned.

But between 12 and 17 percent of planetary systems could be located around carbon-rich stars – and with thousands of exoplanet-hosting stars identified to date, the diamond planet seems a distinct possibility.

Scientists have already explored and confirmed the idea that such planets are likely to be composed primarily of carbides, compounds of carbon and other elements. If such a planet was rich in silicon carbide, the researchers hypothesised, and if water was present to oxidise the silicon carbide and convert it into silicon and carbon, then with sufficient heat and pressure, the carbon could become diamond.

In order to confirm their hypothesis, they turned to a diamond anvil cell, a device used to squeeze small samples of material to very high pressures.

They took minute samples of silicon carbide and immersed them in water. Then, the samples were placed in the diamond anvil cell, which squeezed them to pressures up to 50 gigapascals – about half a million times Earth’s atmospheric pressure at sea level. After the samples had been squeezed, the team heated them with lasers.

In all, they conducted 18 runs of the experiment – and they found that, just as they had predicted, at high heat and high pressure, their silicon carbide samples reacted with water to convert into silica and diamond.

Thus, the researchers concluded that at temperatures of up to 2,500 Kelvin, and pressures up to 50 gigapascals, in the presence of water, silicon carbide planets could become oxidised, and have their interior compositions dominated by silica and diamond.

If we could identify these planets – perhaps by their density profiles, and the composition of their stars – we could therefore rule them out as planets that could host life.

Their interiors, the researchers said, would be too hard for geological activity, and their composition would make their atmospheres inhospitable to life as we know it.

“This is one additional step in helping us understand and characterise our ever-increasing and improving observations of exoplanets,” Allen-Sutter said.

“The more we learn, the better we’ll be able to interpret new data from upcoming future missions like the James Webb Space Telescope and the Nancy Grace Roman Space Telescope to understand the worlds beyond on our own Solar System.”

The research has been published in The Planetary Science Journal.

See the full article here .

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ASU is the largest public university by enrollment in the United States. 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. 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.

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. ASU also offers international academic program partnerships in Mexico, Europe and China. ASU is accredited as a single institution by The Higher Learning Commission.

From Science Alert: “Space Could Be Littered With Eerie Transparent Stars Made Entirely of Bosons”

From Science Alert

9 SEPTEMBER 2020
MICHELLE STARR

L-R: A non-rotating black hole; a rotating black hole; a boson star as they’d appear to the EHT. (Olivares et al., MNRAS, 2020)

Last year, the astronomical community achieved an absolute wonder. For the very first time, the world collectively laid eyes on an actual image of the shadow of a black hole.

Messier 87*, The first image of a black hole. This is the supermassive black hole at the center of the galaxy Messier 87. Image via JPL/ Event Horizon Telescope Collaboration.

It was the culmination of years of work, a magnificent achievement in both human collaboration and technical ingenuity.

Event Horizon Telescope Array

Arizona Radio Observatory at Kitt Peak, AZ USA, U Arizona Steward Observatory at altitude 2,096 m (6,877 ft).

Arizona Radio Observatory.

ESO/MPIfR APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft).

ESO APEX.

Combined Array for Research in Millimeter-wave Astronomy (CARMA), in the Inyo Mountains to the east of the Owens Valley Radio Observatory, at a site called Cedar Flat, Altitude 1,222 m (4,009 ft), relocated to Owens Valley Radio Observatory, Altitude 1,222 m (4,009 ft).

CARMA.

NAOJ Atacama Submillimeter Telescope Experiment (ASTE) deployed to its site on Pampa La Bola, near Cerro Chajnantor and the Llano de Chajnantor, Observatory in northern Chile, Altitude 4,800 m (15,700 ft).

NAOJ Atacama Submillimeter Telescope Experiment (ASTE).

Caltech Submillimeter Observatory on Mauna Kea, Hawaii, USA, Altitude 4,205 m (13,796 ft).

Caltech Submillimeter Observatory.

NSF CfA Greenland telescope.

Greenland Telescope.

IRAM 30m Radio telescope, on Pico Veleta in the Spanish Sierra Nevada,, Altitude 2,850 m (9,350 ft).

Institut de Radioastronomie Millimetrique (IRAM) 30m.

IRAM NOEMA in the French Alps on the wide and isolated Plateau de Bure at an elevation of 2550 meters, the telescope currently consists of ten antennas, each 15 meters in diameter.interferometer, Located in the French Alpes on the wide and isolated Plateau de Bure at an elevation of 2550 meters.

IRAM NOEMA, France.

East Asia Observatory James Clerk Maxwell Telescope, Mauna Kea, Hawaii, USA,4,207 m (13,802 ft).

James Clerk Maxwell Telescope.

The University of Massachusetts Amherst and Mexico’s Instituto Nacional de Astrofísica, Óptica y Electrónica
Large Millimeter Telescope Alfonso Serrano, Mexico, at an altitude of 4850 meters on top of the Sierra Negra.

Large Millimeter Telescope Alfonso Serrano.

CfA Submillimeter Array Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft).

Submillimeter Array Hawaii SAO.

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

ESO/NRAO/NAOJ ALMA Array.

South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.

South Pole Telescope SPTPOL.

Future Array/Telescopes

Caltech Owens Valley Radio Observatory, located near Big Pine, California (US) in Owens Valley, Altitude1,222 m (4,009 ft).

Caltech Owens Valley Radio Observatory.

And, like the best scientific breakthroughs, it opened a whole new world of enquiry. For a team led by astrophysicist Hector Olivares from Radboud University in the Netherlands and Goethe University in Germany, that enquiry was: how do we know M87* is a black hole?

“While the image is consistent with our expectations on what a black hole would look like, it is important to be sure that what we are seeing is really what we think,” Olivares told ScienceAlert.

“Similarly to black holes, boson stars are predicted by general relativity and are able to grow to millions of solar masses and reach a very high compactness. The fact that they share these features with supermassive black holes led some authors to propose that some of the supermassive compact objects located at the center of galaxies could actually be boson stars.”

So, in a new paper, Olivares and his team have calculated what a boson star might look like to one of our telescopes, and how that would differ from a direct image of an accreting black hole.

Boson stars are among the strangest theoretical objects out there. They’re not much like conventional stars, except that they’re a glob of matter. But where stars are primarily made up of particles called fermions – protons, neutrons, electrons, the stuff that forms more substantial parts of our Universe – boson stars would be made up entirely of… bosons.

These particles – including photons, gluons and the famous Higgs boson – don’t follow the same physical rules as fermions.

Fermions are subject to the Pauli exclusion principle, which means you can’t have two identical particles occupying the same space. Bosons, however, can be superimposed; when they come together, they act like one big particle or matter wave. We know this, because it’s been done in a lab, producing what we call a Bose-Einstein condensate.

In the case of boson stars, the particles can be squeezed into a space which can be described with distinct values, or points on a scale. Given the right kind of bosons in the right arrangements, this ‘scalar field’ could fall into a relatively stable arrangement.

That’s the theory, at least. Not that anybody has seen one in action. Bosons with the mass required to form such a structure, let alone one with the mass of a supermassive black hole, are yet to be spotted.

If we could identify a boson star, we would have effectively located this elusive particle.

“In order to form a structure as large as the SMBH candidates, the mass of the boson needs to be extremely small (less than 10-17 electronvolts),” Olivares said.

“Spin-0 bosons with similar or smaller masses appear in several cosmological models and string theories, and have been proposed as dark matter candidates under different names (scalar field dark matter, ultra-light axions, fuzzy dark matter, quantum wave dark matter). Such hypothetical particles would be extremely difficult to detect, but the observation of an object looking like a boson star would point to their existence.”

Boson stars do not fuse nuclei, and they would not emit any radiation. They’d just sit there in space, being invisible. Much like black holes.

Unlike black holes, however, boson stars would be transparent – they lack an absorbing surface that would stop photons, nor do they have an event horizon. Photons can escape boson stars, although their path may be bent a little by the gravity.

But some boson stars may be surrounded by a rotating ring of plasma – a lot like the accretion disc that surrounds a black hole. And it would look fairly similar, like a glowing doughnut with a dark region inside.

So, Olivares and his team performed simulations of the dynamics of these plasma rings, and compared them to what we might expect to see of a black hole.

“The plasma configuration that we use is not set up ‘by hand’ (under reasonable assumptions), but results from a simulation of plasma dynamics. This allows the plasma to evolve in time and to form structures as it would in nature,” Olivares explained.

“In this way we could relate the size of the dark region in the boson star images (which mimics a black hole shadow) to the radius where a plasma instability stops operating. In turn, this means that the size of the dark region is not arbitrary – it will depend on the properties of the boson star space-time – and also allows us to predict its size for other boson stars that we have not simulated.”

They found that the boson star’s shadow would be significantly smaller than the shadow of a black hole of similar mass. Thus, the team ruled out M87* as a boson star – the object’s mass has been inferred from the rotation velocity of the gas around it, and the shadow is too big to be produced by a boson star of that mass.

But the team also took into account the technical capabilities and limitations of the Event Horizon Telescope which delivered that first black hole image; they deliberately set about visualising their results as they thought boson stars might look as imaged by the EHT.

This means their results can be compared to future EHT observations, to determine if what we’re looking at is indeed a supermassive black hole.

If it were not, that would be a very big deal. It wouldn’t mean that supermassive black holes don’t exist – the range of masses for black holes is way too broad for boson stars. But it would hint that boson stars are real, and in turn that would have huge implications, for everything from the inflation of the early Universe to the search for dark matter.

“It would mean that cosmological scalar fields exist and play an important role in the formation of structures in the Universe,” Olivares told ScienceAlert.

“The growth of supermassive black holes is still not understood very well, and if it turns out that at least some of the candidates are actually boson stars, we would need to think of different formation mechanisms involving scalar fields.”

The research was published in July in the MNRAS.

See the full article here.

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From Curtin University AU via Science Alert: “Across 10 Million Stars Not a Single Whisper of Alien Technology”

From Curtin University AU

via

Science Alert

8 SEPTEMBER 2020
MICHELLE STARR

The Vela supernova remnant. (Harel Boren/PBase, CC BY-SA 4.0).

In a comprehensive search of a patch of the Southern sky, not even a hint of alien technology has been detected at low radio frequencies.

Across at least 10 million stars that populate the Vela region – the deepest and widest survey for extraterrestrial intelligence yet – the Murchison Widefield Array (MWA) in Australia found none of the technosignatures that might be expected within its range.

Dipole antennas of the Murchison Widefield Array (MWA) radio telescope in Mid West Western Australia. Credit: Dragonfly Media.

SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO).

However, astronomers Chenoa Tremblay and Steven Tingay from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) say their results aren’t disappointing at all.

Instead, the research shows how easy it is to conduct the search for extraterrestrial intelligence (SETI) almost incidentally, while obtaining other astrophysical observations.

SETI is really quite tricky. We don’t really know what kind of technology an alien civilisation could develop, so we base it on what we know – our own technology, and theories. In the case of the MWA, that means radio signals in frequencies similar to FM radio.

Here on Earth, very low frequency radio can “leak” out through the ionosphere – it’s been picked up by our own space probes, as heard in the above audio, recorded by a NASA Polar spacecraft in 1996. More recently, these VLF emissions have been found to be creating a giant bubble around our planet.

If aliens are also producing such signals, and if those signals are powerful enough, researchers believe that we might be able to detect them. However, if we could, it’s not with the MWA, and not in the vicinity of the Vela constellation.

“The MWA is a unique telescope, with an extraordinarily wide field-of-view that allows us to observe millions of stars simultaneously,” Tremblay said.

“We observed the sky around the constellation of Vela for 17 hours, looking more than 100 times broader and deeper than ever before. With this dataset, we found no technosignatures – no sign of intelligent life.”

The constellation of Vela may only seem like a small patch of sky when you’re standing down here looking up, but it’s a lot busier than it appears. It contains the Vela supernova remnant – that’s what Tremblay has been studying, looking specifically at the chemical composition of the cloud in low frequencies.

And the region studied has at least 10 million stars at a variety of distances, a little slice of the Milky Way galaxy, which overall has an estimated number of stars somewhere between 100 and 400 billion (or possibly even higher, depending on whom you ask).

Therefore, it’s not really a huge surprise that no signals were detected.

“As Douglas Adams noted in The Hitchhiker’s Guide to the Galaxy, ‘space is big, really big’,” Tingay said.

See the full article here .

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Curtin University (formerly known as Curtin University of Technology and Western Australian Institute of Technology) is an Australian public research university based in Bentley and Perth, Western Australia. The university is named after the 14th Prime Minister of Australia, John Curtin, and is the largest university in Western Australia, with over 58,000 students (as of 2016).

Curtin was conferred university status after legislation was passed by the Parliament of Western Australia in 1986. Since then, the university has been expanding its presence and has campuses in Singapore, Malaysia, Dubai and Mauritius. It has ties with 90 exchange universities in 20 countries. The University comprises five main faculties with over 95 specialists centres. The University formerly had a Sydney campus between 2005 & 2016. On 17 September 2015, Curtin University Council made a decision to close its Sydney campus by early 2017.

Curtin University is a member of Australian Technology Network (ATN), and is active in research in a range of academic and practical fields, including Resources and Energy (e.g., petroleum gas), Information and Communication, Health, Ageing and Well-being (Public Health), Communities and Changing Environments, Growth and Prosperity and Creative Writing.

It is the only Western Australian university to produce a PhD recipient of the AINSE gold medal, which is the highest recognition for PhD-level research excellence in Australia and New Zealand.

Curtin has become active in research and partnerships overseas, particularly in mainland China. It is involved in a number of business, management, and research projects, particularly in supercomputing, where the university participates in a tri-continental array with nodes in Perth, Beijing, and Edinburgh. Western Australia has become an important exporter of minerals, petroleum and natural gas. The Chinese Premier Wen Jiabao visited the Woodside-funded hydrocarbon research facility during his visit to Australia in 2005.