Scientists Devise New Method to Locate Dark Matter Axions

Recently, the Department of Energy’s Pacific Northwest National Laboratory (PNNL) researchers, helped shed light on the possible existence of dark matter – called “dark” because it is invisible to today’s telescopes – that may be responsible for gravitational effects that can be detected but not explained by the matter we can observe.

PNNL scientists apply their expertise in physics, chemistry, materials science and engineering to advance our understanding of nuclear and particle physics. Their research delves deep into questions about the universe and its origin, its unseen building blocks, and how the forces within it work together.

The existence of dark matter and its resulting gravitational effects would help to explain how galaxies formed. Scientists are convinced that dark matter far outweighs observable matter in the universe, but there is still much they do not know.

Theories predict that dark matter is composed of fundamental sub-atomic particles that have yet to be discovered, including one dubbed the “axion.” Last month, a large international collaboration of scientists announced the creation of an ultra-sensitive device that can “hear” the telltale signs of dark matter axions while tuning out the electromagnetic “noise” that makes them difficult to detect.

In this project, PNNL used its state-of-the-art microwave engineering and modeling expertise to help design a highly sensitive microwave receiver that “listens” for and identifies the weak axion signal. This same capability underpins the millimeter-wave security scanners used to screen passengers at airports.

In a different collaboration, PNNL is involved in another of the world’s most sensitive dark matter experiments. This one will search for a different class of theorized dark matter particles called weakly interacting massive particles, or WIMPs. Rather than “listening” for these particles, this project seeks to measure WIMP dark matter with a highly sensitive radiation detector.

PNNL researchers are helping to design this detector, which must be made of materials with ultra-low levels of naturally occurring radioactivity so as not to interfere with the measurements they seek.

Unusual Laser Emission From The Ant Nebula

An international team of astronomers have discovered an unusual laser emission that suggests the presence of a double star system hidden at the heart of the “spectacular” Ant Nebula.

The extremely rare phenomenon is connected to the death of a star and was discovered in observations made by European Space Agency’s (ESA) Herschel space observatory.

When low- to middleweight stars like our Sun approach the end of their lives they eventually become dense, white dwarf stars. In the process, they cast off their outer layers of gas and dust into space, creating a kaleidoscope of intricate patterns known as a planetary nebula. Our Sun is expected to one day form such a planetary nebula.

A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. The Ant Nebula earns its nickname from the twin lobes that resemble the head and body of an ant.

The recent Herschel observations have shown that the dramatic demise of the central star in the core of the Ant Nebula is even more theatrical than implied by its colourful appearance in visible images — such as those taken by the NASA/ESA Hubble Space Telescope.

The new data shows that the Ant Nebula also beams intense laser emission from its core. Lasers are well-known down on earth in everyday life, from special visual effects in music concerts to health care and communications. In space, laser emission is detected at very different wavelengths and only under certain conditions. Only a few of these infrared space lasers are known.

By coincidence, astronomer Donald Menzel who first observed and classified this particular planetary nebula in the 1920s (it is officially known as Menzel 3 after him) was also one of the first to suggest that in certain conditions natural ‘light amplification by stimulated emission of radiation’ — from which the acronym ‘laser’ derives — could occur in nebulae in space. This was well before the discovery of lasers in laboratories.

Dr Isabel Aleman, lead author of a paper describing the new results, said “We detected a very rare type of emission called hydrogen recombination laser emission, which is only produced in a narrow range of physical conditions.

“Such emission has only been identified in a handful of objects before and it is a happy coincidence that we detected the kind of emission that Menzel suggested, in one of the planetary nebulae that he discovered.”

This kind of laser emission needs very dense gas close to the star. Comparison of the observations with models found that the density of the gas emitting the lasers is around ten thousand times denser than the gas seen in typical planetary nebulae and in the lobes of the Ant Nebula itself.

Normally, the region close to the dead star — close in this case being about the distance of Saturn from the Sun — is quite empty, because its material is ejected outwards. Any lingering gas would soon fall back onto it.

Co-author Prof Albert Zijlstra, from the Jodrell Bank Centre for Astrophysics at University of Manchester, added: “The only way to keep such dense gas close to the star is if it is orbiting around it in a disc. In this nebula, we have actually observed a dense disc in the very centre that is seen approximately edge-on. This orientation helps to amplify the laser signal.

“The disc suggests there is a binary companion, because it is hard to get the ejected gas to go into orbit unless a companion star deflects it in the right direction. The laser gives us a unique way to probe the disc around the dying star, deep inside the planetary nebula.”

Astronomers have not yet seen the expected second star, hidden in the heart of the Ant nebula.

Göran Pilbratt, ESA’s Herschel project scientist, added: “It is a nice conclusion that it took the Herschel mission to connect together Menzel’s two discoveries from almost a century ago.”

The paper’s publication coincides with the first UNESCO International Day of Light, and celebrates the anniversary of the first successful operation of the laser in 1960 by physicist and engineer, Theodore Maiman.

Orbital Variations Can Trigger ‘Snowball’ States In Habitable Zones Around Sunlike Stars

Aspects of an otherwise Earthlike planet’s tilt and orbital dynamics can severely affect its potential habitability — even triggering abrupt “snowball states” where oceans freeze and surface life is impossible, according to new research from astronomers at the University of Washington.

The research indicates that locating a planet in its host star’s “habitable zone” — that swath of space just right to allow liquid water on an orbiting rocky planet’s surface — isn’t always enough evidence to judge potential habitability.

Russell Deitrick, lead author of a paper to be published in the Astronomical Journal, said he and co-authors set out to learn, through computer modeling, how two features — a planet’s obliquity or its orbital eccentricity — might affect its potential for life. They limited their study to planets orbiting in the habitable zones of “G dwarf” stars, or those like the sun.

A planet’s obliquity is its tilt relative to the orbital axis, which controls a planet’s seasons; orbital eccentricity is the shape, and how circular or elliptical — oval — the orbit is. With elliptical orbits, the distance to the host star changes as the planet comes closer to, then travels away from, its host star.

Deitrick, who did the work while with the UW, is now a post-doctoral researcher at the University of Bern. His UW co-authors are atmospheric sciences professor Cecilia Bitz, astronomy professors Rory Barnes, Victoria Meadows and Thomas Quinn and graduate student David Fleming, with help from undergraduate researcher Caitlyn Wilhelm.

The Earth hosts life successfully enough as it circles the sun at an axial tilt of about 23.5 degrees, wiggling only a very little over the millennia. But, Deitrick and co-authors asked in their modeling, what if those wiggles were greater on an Earthlike planet orbiting a similar star?

Previous research indicated that a more severe axial tilt, or a tilting orbit, for a planet in a sunlike star’s habitable zone — given the same distance from its star — would make a world warmer. So Deitrick and team were surprised to find, through their modeling, that the opposite reaction appears true.

“We found that planets in the habitable zone could abruptly enter ‘snowball’ states if the eccentricity or the semi-major axis variations — changes in the distance between a planet and star over an orbit — were large or if the planet’s obliquity increased beyond 35 degrees,” Deitrick said.

The new study helps sort out conflicting ideas proposed in the past. It used a sophisticated treatment of ice sheet growth and retreat in the planetary modeling, which is a significant improvement over several previous studies, co-author Barnes said.

“While past investigations found that high obliquity and obliquity variations tended to warm planets, using this new approach, the team finds that large obliquity variations are more likely to freeze the planetary surface,” he said. “Only a fraction of the time can the obliquity cycles increase habitable planet temperatures.”

Barnes said Deitrick “has essentially shown that ice ages on exoplanets can be much more severe than on Earth, that orbital dynamics can be a major driver of habitability and that the habitable zone is insufficient to characterize a planet’s habitability.” The research also indicates, he added, “that the Earth may be a relatively calm planet, climate-wise.”

This kind of modeling can help astronomers decide which planets are worthy of precious telescope time, Deitrick said: “If we have a planet that looks like it might be Earth-like, for example, but modeling shows that its orbit and obliquity oscillate like crazy, another planet might be better for follow-up” with telescopes of the future.”

The main takeaway of the research, he added, is that “We shouldn’t neglect orbital dynamics in habitability studies.”

Black Hole And Stellar Winds Form Giant Butterfly, Shut Down Star Formation In Galaxy

Researchers at the University of Colorado Boulder have completed an unprecedented “dissection” of twin galaxies in the final stages of merging.

The new study, led by CU Boulder research associate Francisco Müller-Sánchez, explores a galaxy called NGC 6240. While most galaxies in the universe hold only one supermassive black hole at their center, NGC 6240 contains two — and they’re circling each other in the last steps before crashing together.

The research reveals how gases ejected by those spiraling black holes, in combination with gases ejected by stars in the galaxy, may have begun to power down NGC 6240’s production of new stars. Müller-Sánchez’s team also shows how these “winds” have helped to create the galaxy’s most tell-tale feature: a massive cloud of gas in the shape of a butterfly.

“We dissected the butterfly,” said Müller-Sánchez of CU Boulder’s Department of Astrophysical and Planetary Sciences (APS). “This is the first galaxy in which we can see both the wind from the two supermassive black holes and the outflow of low ionization gas from star formation at the same time.”

The team zeroed in on NGC 6240, in part, because galaxies with two supermassive black holes at their centers are relatively rare. Some experts also suspect that those twin hearts have given rise to the galaxy’s unusual appearance. Unlike the Milky Way, which forms a relatively tidy disk, bubbles and jets of gas shoot off from NGC 6240, extending more than 30,000 light years into space and resembling a butterfly in flight.

“Galaxies with a single supermassive black hole never show such a phenomenal structure,” Müller-Sánchez said.

In research that will be published April 18 in Nature, the team discovered that two different forces have given rise to the nebula. The butterfly’s northwest corner, for example, is the product of stellar winds, or gases that stars emit through various processes. The northeast corner, on the other hand, is dominated by a single cone of gas that was ejected by the pair of black holes — the result of those black holes gobbling up large amounts of galactic dust and gas during their merger.

Those two winds combined evict about 100 times the mass of Earth’s sun in gases from the galaxy every year. That’s a “very large number, comparable to the rate at which the galaxy is creating stars in the nuclear region,” Müller-Sánchez said.

Such an outflow can have big implications for the galaxy itself. He explained that when two galaxies merge, they begin a feverish burst of new star formation. Black hole and stellar winds, however, can slow down that process by clearing away the gases that make up fresh stars — much like how a gust of wind can blow away the pile of leaves you just raked.

“NGC 6240 is in a unique phase of its evolution,” said Julie Comerford, an assistant professor in APS at CU Boulder and a co-author of the new study. “It is forming stars intensely now, so it needs the extra strong kick of two winds to slow down that star formation and evolve into a less active galaxy.”

340,000 Stars’ DNA Interrogated In Search For Sun’s Lost Siblings

An Australian-led group of astronomers working with European collaborators has revealed the “DNA” of more than 340,000 stars in the Milky Way, which should help them find the siblings of the Sun, now scattered across the sky.

This is a major announcement from an ambitious Galactic Archaeology survey, called GALAH, launched in late 2013 as part of a quest to uncover the formulation and evolution of galaxies. When complete, GALAH will investigate more than a million stars.

The GALAH survey used the HERMES spectrograph at the Australian Astronomical Observatory’s (AAO) 3.9-metre Anglo-Australian Telescope near Coonabarabran, NSW, to collect spectra for the 340,000 stars.

The GALAH Survey today makes its first major public data release.

The ‘DNA’ collected traces the ancestry of stars, showing astronomers how the Universe went from having only hydrogen and helium — just after the Big Bang — to being filled today with all the elements we have here on Earth that are necessary for life.

“No other survey has been able to measure as many elements for as many stars as GALAH,” said Dr Gayandhi De Silva, of the University of Sydney and AAO, the HERMES instrument scientist who oversaw the groups working on today’s major data release.

“This data will enable such discoveries as the original star clusters of the Galaxy, including the Sun’s birth cluster and solar siblings — there is no other dataset like this ever collected anywhere else in the world,” Dr De Silva said.

Dr. Sarah Martell from the UNSW Sydney, who leads GALAH survey observations, explained that the Sun, like all stars, was born in a group or cluster of thousands of stars.

“Every star in that cluster will have the same chemical composition, or DNA — these clusters are quickly pulled apart by our Milky Way Galaxy and are now scattered across the sky,” Dr Martell said.

“The GALAH team’s aim is to make DNA matches between stars to find their long-lost sisters and brothers.”

For each star, this DNA is the amount they contain of each of nearly two dozen chemical elements such as oxygen, aluminium, and iron.

Unfortunately, astronomers cannot collect the DNA of a star with a mouth swab but instead use the starlight, with a technique called spectroscopy.

The light from the star is collected by the telescope and then passed through an instrument called a spectrograph, which splits the light into detailed rainbows, or spectra.

Associate Professor Daniel Zucker, from Macquarie University and the AAO, said astronomers measured the locations and sizes of dark lines in the spectra to work out the amount of each element in a star.

“Each chemical element leaves a unique pattern of dark bands at specific wavelengths in these spectra, like fingerprints,” he said.

Dr Jeffrey Simpson of the AAO said it takes about an hour to collect enough photons of light for each star, but “Thankfully, we can observe 360 stars at the same time using fibre optics,” he added.

The GALAH team has spent more than 280 nights at the telescope since 2014 to collect all the data.

The GALAH survey is the brainchild of Professor Joss Bland-Hawthorn from the University of Sydney and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and Professor Ken Freeman of the Australian National University (ANU). It was conceived more than a decade ago as a way to unravel the history of our Milky Way galaxy; the HERMES instrument was designed and built by the AAO specifically for the GALAH survey.

Measuring the abundance of each chemical in so many stars is an enormous challenge. To do this, GALAH has developed sophisticated analysis techniques.

PhD student Sven Buder of the Max Planck Institute for Astronomy, Germany, who is lead author of the scientific article describing the GALAH data release, is part of the analysis effort of the project, working with PhD student Ly Duong and Professor Martin Asplund of ANU and ASTRO 3D.

Mr. Buder said: “We train [our computer code] The Cannon to recognize patterns in the spectra of a subset of stars that we have analysed very carefully, and then use The Cannon’s machine learning algorithms to determine the amount of each element for all of the 340,000 stars.” Ms. Duong noted that “The Cannon is named for Annie Jump Cannon, a pioneering American astronomer who classified the spectra of around 340,000 stars by eye over several decades a century ago — our code analyses that many stars in far greater detail in less than a day.”

The GALAH survey’s data release is timed to coincide with the huge release of data on 25 April from the European Gaia satellite, which has mapped more than 1.6 billion stars in the Milky Way — making it by far the biggest and most accurate atlas of the night sky to date.

In combination with velocities from GALAH, Gaia data will give not just the positions and distances of the stars, but also their motions within the Galaxy.

Professor Tomaz Zwitter (University of Ljubljana, Slovenia) said today’s results from the GALAH survey would be crucial to interpreting the results from Gaia: “The accuracy of the velocities that we are achieving with GALAH is unprecedented for such a large survey.”

Dr Sanjib Sharma from the University of Sydney concluded: “For the first time we’ll be able to get a detailed understanding of the history of the Galaxy.”

The ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) is a $40m Research Centre of Excellence funded by the Australian Research Council (ARC) and six collaborating Australian universities — The Australian National University, The University of Sydney, The University of Melbourne, Swinburne University of Technology, The University of Western Australia and Curtin University.

Martian Moons Model Indicates Formation Following Large Impact

Southwest Research Institute scientists posit a violent birth of the tiny Martian moons Phobos and Deimos, but on a much smaller scale than the giant impact thought to have resulted in the Earth-Moon system. Their work shows that an impact between proto-Mars and a dwarf-planet-sized object likely produced the two moons, as detailed in a paper published today in Science Advances.

The origin of the Red Planet’s small moons has been debated for decades. The question is whether the bodies were asteroids captured intact by Mars gravity or whether the tiny satellites formed from an equatorial disk of debris, as is most consistent with their nearly circular and co-planar orbits. The production of a disk by an impact with Mars seemed promising, but prior models of this process were limited by low numerical resolution and overly simplified modeling techniques.

“Ours is the first self-consistent model to identify the type of impact needed to lead to the formation of Mars’ two small moons,” said lead author Dr. Robin Canup, an associate vice president in the SwRI Space Science and Engineering Division. Canup is one of the leading scientists using large-scale hydrodynamical simulations to model planet-scale collisions, including the prevailing Earth-Moon formation model.

“A key result of the new work is the size of the impactor; we find that a large impactor — similar in size to the largest asteroids Vesta and Ceres — is needed, rather than a giant impactor,” Canup said. “The model also predicts that the two moons are derived primarily from material originating in Mars, so their bulk compositions should be similar to that of Mars for most elements. However, heating of the ejecta and the low escape velocity from Mars suggests that water vapor would have been lost, implying that the moons will be dry if they formed by impact.”

The new Mars model invokes a much smaller impactor than considered previously. Our Moon may have formed when a Mars-sized object crashed into the nascent Earth 4.5 billion years ago, and the resulting debris coalesced into the Earth-Moon system. The Earth’s diameter is about 8,000 miles, while Mars’ diameter is just over 4,200 miles. The Moon is just over 2,100 miles in diameter, about one-fourth the size of Earth.

While they formed in the same timeframe, Deimos and Phobos are very small, with diameters of only 7.5 miles and 14 miles respectively, and orbit very close to Mars. The proposed Phobos-Deimos forming impactor would be between the size of the asteroid Vesta, which has a diameter of 326 miles, and the dwarf planet Ceres, which is 587 miles wide.

“We used state-of-the-art models to show that a Vesta-to-Ceres-sized impactor can produce a disk consistent with the formation of Mars’ small moons,” said the paper’s second author, Dr. Julien Salmon, an SwRI research scientist. “The outer portions of the disk accumulate into Phobos and Deimos, while the inner portions of the disk accumulate into larger moons that eventually spiral inward and are assimilated into Mars. Larger impacts advocated in prior works produce massive disks and more massive inner moons that prevent the survival of tiny moons like Phobos and Deimos.”

These findings are important for the Japan Aerospace Exploration Agency (JAXA) Mars Moons eXploration (MMX) mission, which is planned to launch in 2024 and will include a NASA-provided instrument. The MMX spacecraft will visit the two Martian moons, land on the surface of Phobos and collect a surface sample to be returned to Earth in 2029.

“A primary objective of the MMX mission is to determine the origin of Mars’ moons, and having a model that predicts what the moons compositions would be if they formed by impact provides a key constraint for achieving that goal,” Canup said.

Deep inside Perseus A – A Telescope Larger Than The Earth Makes A Sharp Image Of The Formation Of Black Hole Jets In The Core Of A Radio Galaxy

An international team of researchers has imaged newly forming jets of plasma from a massive black hole with unprecedented accuracy. Radio images made with a combination of telescopes in space and on the ground resolve the jet structure merely a couple of hundred black hole radii or 12 light days from its launching site.

At the centres of all massive galaxies are black holes weighing as much as several billion times the mass of our sun. It has been known for long that some of these massive black holes eject spectacular plasma jets at a near speed-of-light that can extend far beyond the confines of their host galaxy. But how these jets form in the first place has been a long-standing mystery. One of the main difficulties in studying them has been astronomers’ inability to image the structure of the jets driven by the black hole close enough to their launching site so that direct comparison to theoretical and computational models of jet formation would be possible.

Now an international team of researchers from eight different countries has made ultra-high angular resolution images of the black hole jet at the centre of the giant galaxy NGC 1275, also known as radio source Perseus A or 3C 84. The researchers were able to resolve the jet structure ten times closer to the black hole in NGC 1275 than what has been possible before with ground-based instruments, revealing unprecedented details of the jet formation region.

“The results were surprising. It turned out that the observed width of the jet was significantly wider than what was expected in the currently favoured models where the jet is launched from the black hole’s ergosphere — an area of space right next to a spinning black hole where space itself is dragged to a circling motion around the hole,” explains Professor Gabriele Giovannini from Italian National Institute for Astrophysics, the lead author of the paper published in Nature Astronomy.

“This may imply that at least the outer part of the jet is launched from the accretion disk surrounding the black hole. Our result does not yet falsify the current models where the jets are launched from the ergosphere, but we hope it will give the theorists an insight into the jet structure close to the launching site and clues about how to develop the models,” adds Dr. Tuomas Savolainen from Aalto University in Finland, head of the RadioAstron observing program which produced the images.

Another result from the study is that the jet structure in NGC 1275 significantly differs from the jet in the very nearby galaxy Messier 87, which is the only other jet whose structure has been imaged equally close to the black hole. Researchers think that this is due to the difference in the age of these two jets. “The jet in NGC 1275 was re-started just over a decade ago and is currently still forming, which provides a unique opportunity to follow the very early growth of a black hole jet. Continuing these observations will be very important,” explains a co-author of the paper, Dr. Masanori Nakamura from Academia Sinica in Taiwan.

“This study of the innermost region of NGC 1275 continues our investigations of Active Galactic Nuclei at the highest possible resolution. As the distance to that galaxy is only 70 Megaparsec or 230 million light years, we are able to examine the jet structure with an unprecedented accuracy of only a few hundred black hole radii or 12 light days,” concludes Professor Anton Zensus, director at the Max Planck Institute for Radio Astronomy in Bonn, Germany and head of its VLBI research department, a co-author of the paper.

One radio telescope in space — dozens on the ground

The significant improvement in the sharpness of the jet images was made possible by the Earth-to-Space Interferometer RadioAstron, which consists of a 10-metre orbiting radio telescope and a collection of about two dozen of the world’s largest ground-based radio telescopes. When the signals of individual telescopes are combined using the interference of radio waves, this array of telescopes has the angular resolution equivalent to a radio telescope of 350,000 km in diameter — almost the distance between the Earth and Moon. This makes RadioAstron the highest angular resolution instrument in the history of astronomy. The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the State Space Corporation ROSCOSMOS, in collaboration with partner organizations in Russia and other countries.

“We at the RadioAstron mission are truly happy that the unique combination of the Russian-made space radio telescope and the huge international ground array of the largest radio telescopes has allowed to study this young relativistic jet in the immediate vicinity of the supermassive black hole,” comments the RadioAstron Project Scientist, Professor Yuri Kovalev from the Lebedev Institute in Moscow.