Researchers Measure The Inner Structure Of Distant Suns From Their Pulsations

At first glance, it would seem to be impossible to look inside a star. An international team of astronomers, under the leadership of Earl Bellinger and Saskia Hekker of the Max Planck Institute for Solar System Research in Göttingen, has, for the first time, determined the deep inner structure of two stars based on their oscillations.

Our Sun, and most other stars, experience pulsations that spread through the star’s interior as sound waves. The frequencies of these waves are imprinted on the light of the star, and can be later seen by astronomers here on Earth. Similar to how seismologists decipher the inner structure of our planet by analyzing earthquakes, astronomers determine the properties of stars from their pulsations—a field called asteroseismology. Now, for the first time, a detailed analysis of these pulsations has enabled Earl Bellinger, Saskia Hekker and their colleagues to measure the internal structure of two distant stars.

The two stars they analyzed are part of the 16 Cygni system (known as 16 Cyg A and 16 Cyg B) and both are very similar to our own sun. “Due to their small distance of only 70 light years, these stars are relatively bright and thus ideally suited for our analysis,” says lead author Earl Bellinger. “Previously, it was only possible to make models of the stars’ interiors. Now we can measure them.”

To make a model of a star’s interior, astrophysicists vary stellar evolution models until one of them fits to the observed frequency spectrum. However, the pulsations of the theoretical models often differ from those of the stars, most likely due to some stellar physics still being unknown.

Bellinger and Hekker therefore decided to use the inverse method. Here, they derived the local properties of the stellar interior from the observed frequencies. This method depends less on theoretical assumptions, but it requires excellent measurement data quality and is mathematically challenging.

Using the inverse method, the researchers looked more than 500,000 km deep into the stars—and found that the speed of sound in the central regions is greater than predicted by the models. “In the case of 16 Cyg B, these differences can be explained by correcting what we thought to be the mass and the size of the star,” says Bellinger. In the case of 16 Cyg A, however, the cause of the discrepancies could not be identified.

It is possible that as-yet unknown physical phenomena are not sufficiently taken into account by the current evolutionary models. “Elements that were created in the early phases of the star’s evolution may have been transported from the core of the star to its outer layers,” explains Bellinger. “This would change the internal stratification of the star, which then affects how it oscillates.”

This first structural analysis of the two stars will be followed by more. “Ten to 20 additional stars suitable for such an analysis can be found in the data from the Kepler Space Telescope,” says Saskia Hekker, who leads the Stellar Ages and Galactic Evolution (SAGE) Research Group at the Max Planck Institute in Göttingen. In the future, NASA’s TESS mission (Transiting Exoplanet Survey Satellite) and the PLATO (Planetary Transits and Oscillation of Stars) space telescope planned by the European Space Agency (ESA) will collect even more data for this research field.

The inverse method delivers new insights that will help to improve our understanding of the physics that happens in stars. This will lead to better stellar models, which will then improve our ability to predict the future evolution of the sun and other stars in our galaxy.

Tabby’s Star: Alien Megastructure Not The Cause Of Dimming Of The ‘Most Mysterious Star In The Universe’

A team of more than 200 researchers, including Penn State Department of Astronomy and Astrophysics Assistant Professor Jason Wright and led by Louisiana State University’s Tabetha Boyajian, is one step closer to solving the mystery behind the “most mysterious star in the universe.” KIC 8462852, or “Tabby’s Star,” nicknamed after Boyajian, is otherwise an ordinary star, about 50 percent bigger and 1,000 degrees hotter than the Sun, and about than 1,000 light years away. However, it has been inexplicably dimming and brightening sporadically like no other. Several theories abound to explain the star’s unusual light patterns, including that an alien megastructure is orbiting the star.

The mystery of Tabby’s Star is so compelling that more than 1,700 people donated over $100,000 through a Kickstarter campaign in support of dedicated ground-based telescope time to observe and gather more data on the star through a network of telescopes around the world. As a result, a body of data collected by Boyajian and colleagues in partnership with the Las Cumbres Observatory is now available in a new paper in The Astrophysical Journal Letters.

“We were hoping that once we finally caught a dip happening in real time we could see if the dips were the same depth at all wavelengths. If they were nearly the same, this would suggest that the cause was something opaque, like an orbiting disk, planet, or star, or even large structures in space” said Wright, who is a co-author of the paper, titled “The First Post-Kepler Brightness Dips of KIC 8462852.” Instead, the team found that the star got much dimmer at some wavelengths than at others.

“Dust is most likely the reason why the star’s light appears to dim and brighten. The new data shows that different colors of light are being blocked at different intensities. Therefore, whatever is passing between us and the star is not opaque, as would be expected from a planet or alien megastructure,” Boyajian said.

The scientists closely observed the star through the Las Cumbres Observatory from March 2016 to December 2017. Beginning in May 2017 there were four distinct episodes when the star’s light dipped. Supporters from the crowdfunding campaign nominated and voted to name these episodes. The first two dips were named Elsie and Celeste. The last two were named after ancient lost cities — Scotland’s Scara Brae and Cambodia’s Angkor. The authors write that in many ways what is happening with the star is like these lost cities.

“They’re ancient; we are watching things that happened more than 1,000 years ago,” the authors wrote. “They’re almost certainly caused by something ordinary, at least on a cosmic scale. And yet that makes them more interesting, not less. But most of all, they’re mysterious.”

The method in which this star is being studied — by gathering and analyzing a flood of data from a single target — signals a new era of astronomy. Citizen scientists sifting through massive amounts of data from the NASA Kepler mission were the ones to detect the star’s unusual behavior in the first place. The main objective of the Kepler mission was to find planets, which it does by detecting the periodic dimming made from a planet moving in front of a star, and hence blocking out a tiny bit of starlight. The online citizen science group Planet Hunters was established so that volunteers could help to classify light curves from the Kepler mission and to search for such planets.

“If it wasn’t for people with an unbiased look on our universe, this unusual star would have been overlooked,” Boyajian said. “Again, without the public support for this dedicated observing run, we would not have this large amount of data.”

Now there are more answers to be found. “This latest research rules out alien megastructures, but it raises the plausibility of other phenomena being behind the dimming,” Wright said. “There are models involving circumstellar material — like exocomets, which were Boyajian’s team’s original hypothesis — which seem to be consistent with the data we have.” Wright also points out that “some astronomers favor the idea that nothing is blocking the star — that it just gets dimmer on its own — and this also is consistent with this summer’s data.”

Boyajian said, “It’s exciting. I am so appreciative of all of the people who have contributed to this in the past year — the citizen scientists and professional astronomers. It’s quite humbling to have all of these people contributing in various ways to help figure it out.”

Meteorite Analysis Shows Reduced Salt Is Key In Earth’s New Recipe

Scientists have found the halogen levels in the meteorites that formed the Earth billions of years ago are much lower than previously thought.

The research was carried out by international team of researchers, led by the Universities of Manchester and Oxford, and has recently been published in Nature.

Halogens such as Chlorine, Bromine and Iodine, form naturally occurring salts which are essential for most life forms — but too much can prohibit life. When previously comparing halogen levels in meteorites that formed the planet, the Earth should have unhealthy levels of salt.

Many theories have been put forward to explain the mystery of why, instead, Earth salt concentrations are ‘just right’. The answer turns out to be quite simple — previous estimates meteorites were just too high.

Using a new analytical technique, the team looked at different kinds of chondrite meteorites, a type of primitive meteorite approximately 4.6 billion years old.

Dr Patricia Clay, lead author of the study from the University of Manchester’s School of Earth and Environmental Sciences (SEES), said: ‘These kinds of meteorites are remnants of the solar nebula, a molecular cloud made up of interstellar dust and hydrogen gas that predates our Solar System. Studying them provides important clues for our understanding of the origin and age of the Solar System.’

How the Earth acquired its volatile elements has long interested scientists. To answer the question the team re-examined one of the largest collection of meteorites assembled for this type of study.

They found that previous estimates of halogen levels in meteorites were too high, but the technique used by the team helped them avoid contaminated sources.

Dr Clay explains: “No single model of Earth formation using the old meteorite measurements could easily account for the halogens we see today. Some of these models needed catastrophic planetary wide removal of halogens without affecting related elements — which just didn’t make sense.”

Professor Ray Burgess, co-author and also from The University of Manchester, added: “The new simplified model we have developed is a big step forward in understanding how key ingredients essential for life were brought to our planet, including water that probably helped distribute the halogens between the planetary interior and surface.”

The results were a huge surprise, and time after time each meteorite measured was found to have halogen levels far lower than previously thought, and remarkably consistent between different types of meteorites.

Professor Chris Ballentine, co-author from the University of Oxford and who designed the study, added: “Another big surprise of the study was just how uniform the halogen content of very different meteorites actually is — this is an incredibly important picture into the processes that formed the meteorites themselves — but also means that whatever meteorites formed the earth the halogen ingredients for Earth’s recipe remains the same.”

Researchers Present List Of Comet 67P/Churyumov-Gerasimenko Ingredients

The dust that comet 67P/Churyumov-Gerasimenko emits into space consists to about one half of organic molecules. The dust belongs to the most pristine and carbon-rich material known in our solar system and has hardly changed since its birth. These results of the COSIMA team are published today in the journal Monthly Notices of the Royal Astronomical Society. COSIMA is an instrument onboard the Rosetta spacecraft, which investigated comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. In their current study, the involved researchers including scientists from the Max Planck Institute for Solar System Research (MPS) analyze as comprehensively as ever before, what chemical elements constitute cometary dust.

When a comet traveling along it highly elliptical orbit approaches the Sun, it becomes active: frozen gases evaporate, dragging tiny dust grains into space. Capturing and examining these grains provides the opportunity to trace the “building materials” of the comet itself. So far, only few space missions have succeeded in this endeavor. These include ESA’s Rosetta mission. Unlike their predecessors, for their current study the Rosetta researchers were able to collect and analyze dust particles of various sizes over a period of approximately two years. In comparison, earlier missions, such as Giotto’s Flyby of comet 1P/Halley or Stardust, which even returned cometary dust from comet 81P/Wild 2 back to Earth, provided only a snapshot. In the case of the space probe Stardust, which raced past its comet in 2004, the dust had changed significantly during capture, so that a quantitative analysis was only possible to a limited extent.

In the course of the Rosetta mission, COSIMA collected more than 35000 dust grains. The smallest of them measured only 0.01 millimeters in diameter, the largest about one millimeter. The instrument makes it possible to first observe the individual dust grains with a microscope. In a second step, these grains are bombarded with a high-energy beam of indium ions. The secondary ions emitted in this way can then be “weighed” and analyzed in the COSIMA mass spectrometer. For the current study, the researchers limited themselves to 30 dust grains with properties that ensured a meaningful analysis. Their selection includes dust grains from all phases of the Rosetta mission and of all sizes.

“Our analyzes show that the composition of all these grains is very similar,” MPS researcher Dr. Martin Hilchenbach, Principal Investigator of the COSIMA team, describes the results. The scientists conclude that the comet’s dust consists of the same “ingredients” as the comet’s nucleus and thus can be examined in its place.

As the study shows, organic molecules are among those ingredients at the top of the list. These account for about 45 percent of the weight of the solid cometary material. “Rosetta’s comet thus belongs to the most carbon-rich bodies we know in the solar system,” says MPS scientist and COSIMA team member Dr. Oliver Stenzel. The other part of the total weight, about 55 percent, is provided by mineral substances, mainly silicates. It is striking that they are almost exclusively non-hydrated minerals i.e. missing water compounds.

“Of course, Rosetta’s comet contains water like any other comet, too,” says Hilchenbach. “But because comets have spent most of their time at the icy rim of the solar system, it has almost always been frozen and could not react with the minerals.” The researchers therefore regard the lack of hydrated minerals in the comet’s dust as an indication that 67P contains very pristine material.

This conclusion is supported by the ratio of certain elements such as carbon to silicon. With more than 5, this value is very close to the Sun’s value, which is thought to reflect the ratio found in the early solar system.
The current findings also touch on our ideas of how life on Earth came about. In a previous publication, the COSIMA team was able to show that the carbon found in Rosetta’s comet is mainly in the form of large, organic macromolecules. Together with the current study, it becomes clear that these compounds make up a large part of the cometary material. Thus, if comets indeed supplied the early Earth with organic matter, as many researchers assume, it would probably have been mainly in the form of such macromolecules.

M– USE Probes Uncharted Depths Of Hubble Ultra Deep Field

The M– USE HUDF Survey team, led by Roland Bacon of the Centre de recherche astrophysique de Lyon (CNRS/Université Claude Bernard Lyon 1/ENS de Lyon), France, used M– USE (Multi Unit Spectroscopic Explorer/ to observe the Hubble Ultra Deep Field (heic0406/, a much-studied patch of the southern constellation of Fornax (The Furnace). This resulted in the deepest spectroscopic observations ever made; precise spectroscopic information was measured for 1600 galaxies, ten times as many galaxies as has been painstakingly obtained in this field over the last decade by ground-based telescopes.

The original HUDF images were pioneering deep-field observations with the NASA/ESA Hubble Space Telescope published in 2004. They probed more deeply than ever before and revealed a menagerie of galaxies dating back to less than a billion years after the Big Bang. The area was subsequently observed many times by Hubble and other telescopes, resulting in the deepest view of the Universe to date. Now, despite the depth of the Hubble observations, M– USE has — among many other results — revealed 72 galaxies never seen before in this very tiny area of the sky.

Roland Bacon takes up the story: “M– USE can do something that Hubble can’t — it splits up the light from every point in the image into its component colours to create a spectrum. This allows us to measure the distance, colours and other properties of all the galaxies we can see — including some that are invisible to Hubble itself.”

The M– USE data provides a new view of dim, very distant galaxies, seen near the beginning of the Universe about 13 billion years ago. It has detected galaxies 100 times fainter than in previous surveys, adding to an already richly observed field and deepening our understanding of galaxies across the ages.

The survey unearthed 72 candidate galaxies known as Lyman-alpha emitters that shine only in Lyman-alpha light. Current understanding of star formation cannot fully explain these galaxies, which just seem to shine brightly in this one colour. Because M– USE disperses the light into its component colours these objects become apparent, but they remain invisible in deep direct images such as those from Hubble.

“M– USE has the unique ability to extract information about some of the earliest galaxies in the Universe — even in a part of the sky that is already very well studied,” explains Jarle Brinchmann, lead author of one of the papers describing results from this survey, from the University of Leiden in the Netherlands and the Institute of Astrophysics and Space Sciences at CAUP in Porto, Portugal. “We learn things about these galaxies that is only possible with spectroscopy, such as chemical content and internal motions — not galaxy by galaxy but all at once for all the galaxies!”

Another major finding of this study was the systematic detection of luminous hydrogen halos around galaxies in the early Universe, giving astronomers a new and promising way to study how material flows in and out of early galaxies.

Many other potential applications of this dataset are explored in the series of papers, and they include studying the role of faint galaxies during cosmic reionisation (starting just 380,000 years after the Big Bang), galaxy merger rates when the Universe was young, galactic winds, star formation as well as mapping the motions of stars in the early Universe.

“Remarkably, these data were all taken without the use of M– USE’s recent Adaptive Optics Facility upgrade. The activation of the AOF after a decade of intensive work by ESO’s astronomers and engineers promises yet more revolutionary data in the future,” concludes Roland Bacon.

Astronomers Reveal Nearby Stars That Are Among The Oldest In Our Galaxy

Astronomers have discovered some of the oldest stars in our Milky Way galaxy by determining their locations and velocities, according to a study led by scientists at Georgia State University.

Just like humans, stars have a life span: birth, youth, adulthood, senior and death. This study focused on old or “senior citizen” stars, also known as cool subdwarfs, that are much older and cooler in temperature than the sun.

The Milky Way is nearly 14 billion years old, and its oldest stars developed in the early stage of the galaxy’s formation, making them about six to nine billion years old. They’re found in the halo, a roughly spherical component of the galaxy that formed first, in which old stars move in orbits that are highly elongated and tilted. Younger stars in the Milky Way rotate together along the galaxy’s disc in roughly circular orbits, much like horses on a merry-go-round.

In this study, published in the November 2017 edition of The Astronomical Journal, astronomers conducted a census of our solar neighborhood to identify how many young, adult and old stars are present. They targeted stars out to a distance of 200 light years, which is relatively nearby considering the galaxy is more than 100,000 light years across. A light year is how far light can travel in one year. This is farther than the traditional horizon for the region of space that is referred to as “the solar neighborhood,” which is about 80 light years in radius.

“The reason my horizon is more distant is that there are not a lot of senior citizens (old stars) in our solar neighborhood,” said Dr. Wei-Chun Jao, lead author of the study and research scientist in the Department of Physics and Astronomy at Georgia State. “There are plenty of adult stars in our solar neighborhood, but there’s not a lot of senior citizens, so we have to reach farther away in the galaxy to find them.”

The astronomers first observed the stars over many years with the 0.9 meter telescope at the United State’s Cerro Tololo Inter-American Observatory in the foothills of the Chilean Andes. They used a technique called astrometry to measure the stars’ positions and were able to determine the stars’ motions across the sky, their distances and whether or not each star had a hidden companion orbiting it.

The team’s work increased the known population of old stars in our solar neighborhood by 25 percent. Among the new subdwarfs, the researchers discovered two old binary stars, even though older stars are typically found to be alone, rather than in pairs.

“I identified two new possible double stars, called binaries,” Jao said. “It’s rare for senior citizens to have companions. Old folks tend to live by themselves. I then used NASA’s Hubble Space Telescope to detect both stars in one of the binaries and measured the separation between them, which will allow us to measure their masses.”

Jao also outlined two methods to identify these rare old stars. One method uses stars’ locations on a fundamental map of stellar astronomy known as the Hertzsprung-Russell (H-R) diagram. This is a classic technique that places the old stars below the sequence of dwarf stars such as the sun on the H-R diagram, hence the name “subdwarfs.”

The authors then took a careful look at one particular characteristic of known subdwarf stars — how fast they move across the sky.

“Every star moves across the sky,” Jao said. “They don’t stay still. They move in three dimensions, with a few stars moving directly toward or away from us, but most moving tangentially across the sky. In my research, I’ve found that if a star has a tangential velocity faster than 200 kilometers per second, it has to be old. So, based on their movements in our galaxy, I can evaluate whether a star is an old subdwarf or not. In general, the older a star is, the faster it moves.”

They applied the tangential velocity cutoff and compared stars in the subdwarf region of the H-R diagram to other existing star databases to identify an additional 29 previously unidentified old star candidates.

In 2018, results from the European Space Agency’s Gaia mission, which is measuring accurate positions and distances for millions of stars in the Milky Way, will make finding older stars much easier for astronomers. Determining the distance of stars is now very labor intensive and requires a lot of telescope time and patience. Because the Gaia mission will provide a much larger sample size, Jao says the limited sample of subdwarfs will grow, and the rarest of these rare stars — binary subdwarfs — will be revealed.

Finding old stars could also lead to the discovery of new planets, Jao said.

“Maybe we can find some ancient civilizations around these old stars,” Jao said. “Maybe these stars have some planets around them that we don’t know about.”

Hubble Sees Nearby Asteroids Photobombing Distant Galaxies

Like rude relatives who jump in front your vacation snapshots of landscapes, some of our solar system’s asteroids have photobombed deep images of the universe taken by NASA’s Hubble Space Telescope. These asteroids reside, on average, only about 160 million miles from Earth-right around the corner in astronomical terms. Yet they’ve horned their way into this picture of thousands of galaxies scattered across space and time at inconceivably farther distances.

This Hubble photo of a random patch of sky is part of a survey called Frontier Fields. The colorful image contains thousands of galaxies, including massive yellowish ellipticals and majestic blue spirals. Much smaller, fragmentary blue galaxies are sprinkled throughout the field. The reddest objects are most likely the farthest galaxies, whose light has been stretched into the red part of the spectrum by the expansion of space.

Intruding across the picture are asteroid trails that appear as curved or S-shaped streaks. Rather than leaving one long trail, the asteroids appear in multiple Hubble exposures that have been combined into one image. Of the 20 total asteroid sightings for this field, seven are unique objects. Of these seven asteroids, only two were earlier identified. The others were too faint to be seen previously.

The trails look curved due to an observational effect called parallax. As Hubble orbits around Earth, an asteroid will appear to move along an arc with respect to the vastly more distant background stars and galaxies.

This parallax effect is somewhat similar to the effect you see from a moving car, in which trees by the side of the road appear to be passing by much more rapidly than background objects at much larger distances. The motion of Earth around the Sun, and the motion of the asteroids along their orbits, are other contributing factors to the apparent skewing of asteroid paths.

All the asteroids were found manually, the majority by “blinking” consecutive exposures to capture apparent asteroid motion. Astronomers found a unique asteroid for every 10 to 20 hours of exposure time.

The Frontier Fields program is a collaboration among NASA’s Great Observatories and other telescopes to study six massive galaxy clusters and their effects. Using a different camera, pointing in a slightly different direction, Hubble photographed six so-called “parallel fields” at the same time it photographed the massive galaxy clusters. This maximized Hubble’s observational efficiency in doing deep space exposures. These parallel fields are similar in depth to the famous Hubble Deep Field, and include galaxies about four-billion times fainter than can be seen by the human eye.

This picture is of the parallel field for the galaxy cluster Abell 370. It was assembled from images taken in visible and infrared light. The field’s position on the sky is near the ecliptic, the plane of our solar system. This is the zone in which most asteroids reside, which is why Hubble astronomers saw so many crossings. Hubble deep-sky observations taken along a line-of-sight near the plane of our solar system commonly record asteroid trails.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.