Ultra-Hot Gas Around Remnants Of Sun-Like Stars

Solving a decades-old mystery, an international team of astronomers have discovered an extremely hot magnetosphere around a white dwarf, a remnant of a star like our Sun. The work was led by Dr Nicole Reindl, Research Fellow of the Royal Commission 1851, based at the University of Leicester, and is published today (7 November) in the journal Monthly Notices of the Royal Astronomical Society.

White dwarfs are the final stage in the lives of stars like our Sun. At the end of their lives, these stars eject their outer atmospheres, leaving behind a hot, compact and dense core that cools over billions of years. The temperature on their surfaces is typically around 100,000 degrees Celsius (in comparison the surface of the Sun is 5500 degrees).

Some white dwarfs though challenge scientists, as they show evidence for highly ionised metals. In astronomy ‘metals’ describe every element heavier than helium, and high ionisation here means that all but one of the outer electrons usually in their atoms have been stripped away. That process needs a temperature of 1 million degrees Celsius, so far higher than the surface of even the hottest white dwarf stars.

Reindl’s team used the 3.5-metre Calar Alto telescope in Spain to discover and observe a white dwarf in the direction of the constellation of Triangulum, catalogued as GALEXJ014636.8+323615, located 1200 light years from the Sun. Analysing the light from the white dwarf with a technique known as spectroscopy, where the light is dispersed into its constituent colours, revealed the signatures of highly ionised metals. Intriguingly these varied over a period of six hours — the same time it takes for the white dwarf to rotate.

Reindl and her team conclude that the magnetic field around the star — the magnetosphere — traps material flowing from its surface. Shocks within the magnetosphere heat the material dramatically, stripping almost all the electrons from the metal atoms.

“It’s like a doughnut made up of ultra-hot material that surrounds the already very hot star” explains Reindl.

“The axis of the magnetic field of the white dwarf is tilted from its rotational axis. This means that the amount of shock-heated material we see varies as the star rotates.

‘After decades of finding more and more of these obscure stars without having a clue where these highly ionised metals come from,” she continues, “our shock-heated magnetosphere model finally explains their origin.”

Magnetospheres are found around other types of stars, but this is the first report of one around a white dwarf. The discovery might have far-reaching consequences. “We simply didn’t take this into account,” admits Reindl. “Ignoring their magnetospheres could mean measurements of other basic properties of white dwarfs are wrong, like their temperatures and masses.”

It may be that a quarter of white dwarfs go through a stage of trapping and super-heating material. Reindl and her team now plan to model them in detail and to extend their research by studying more of these fascinating objects.

Scientists Theorize New Origin Story For Earth’s Water

Earth’s water may have originated from both asteroidal material and gas left over from the formation of the Sun, according to new research. The new finding could give scientists important insights about the development of other planets and their potential to support life.

In a new study in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union, researchers propose a new theory to address the long-standing mystery of where Earth’s water came from and how it got here.

The new study challenges widely-accepted ideas about hydrogen in Earth’s water by suggesting the element partially came from clouds of dust and gas remaining after the Sun’s formation, called the solar nebula.

To identify sources of water on Earth, scientists have searched for sources of hydrogen rather than oxygen, because the latter component of water is much more abundant in the solar system.

Many scientists have historically supported a theory that all of Earth’s water came from asteroids because of similarities between ocean water and water found on asteroids. The ratio of deuterium, a heavier hydrogen isotope, to normal hydrogen serves as a unique chemical signature of water sources. In the case of Earth’s oceans, the deuterium-to-hydrogen ratio is close to what is found in asteroids.

But the ocean may not be telling the entire story of Earth’s hydrogen, according to the study’s authors.

“It’s a bit of a blind spot in the community,” said Steven Desch, a professor of astrophysics in the School of Earth and Space Exploration at Arizona State University in Tempe, Arizona and co-author of the new study, led by Peter Buseck, Regents’ Professor in the School of Earth and Space Exploration and School of Molecular Sciences at Arizona State University. “When people measure the [deuterium-to-hydrogen] ratio in ocean water and they see that it is pretty close to what we see in asteroids, it was always easy to believe it all came from asteroids.”

More recent research suggests hydrogen in Earth’s oceans does not represent hydrogen throughout the entire planet, the study’s authors said. Samples of hydrogen from deep inside the Earth, close to the boundary between the core and mantle, have notably less deuterium, indicating this hydrogen may not have come from asteroids. Noble gases helium and neon, with isotopic signatures inherited from the solar nebula, have also been found in the Earth’s mantle.

In the new study, researchers developed a new theoretical model of Earth’s formation to explain these differences between hydrogen in Earth’s oceans and at the core-mantle boundary as well as the presence of noble gases deep inside the planet.

Modeling Earth’s beginning

According to their new model, several billion years ago, large waterlogged asteroids began developing into planets while the solar nebula still swirled around the Sun. These asteroids, known as planetary embryos, collided and grew rapidly. Eventually, a collision introduced enough energy to melt the surface of the largest embryo into an ocean of magma. This largest embryo would eventually become Earth.

Gases from the solar nebula, including hydrogen and noble gases, were drawn in by the large, magma-covered embryo to form an early atmosphere. Nebular hydrogen, which contains less deuterium and is lighter than asteroidal hydrogen, dissolved into the molten iron of the magma ocean.

Through a process called isotopic fractionation, hydrogen was pulled towards the young Earth’s center. Hydrogen, which is attracted to iron, was delivered to the core by the metal, while much of the heavier isotope, deuterium, remained in the magma which eventually cooled and became the mantle, according to the study’s authors. Impacts from smaller embryos and other objects then continued to add water and overall mass until Earth reached its final size.

This new model would leave Earth with noble gases deep inside its mantle and a lower deuterium-to-hydrogen ratio in its core than in its mantle and oceans.

The authors used the model to estimate how much hydrogen came from each source. They concluded most was asteroidal in origin, but some of Earth’s water did come from the solar nebula.

“For every 100 molecules of Earth’s water, there are one or two coming from solar nebula,” said Jun Wu, assistant research professor in the School of Molecular Sciences and School of Earth and Space Exploration at Arizona State University and lead author of the study.

An insightful model

The study also offers scientists new perspectives about the development of other planets and their potential to support life, the authors said. Earth-like planets in other solar systems may not all have access to asteroids loaded with water. The new study suggests these exoplanets could have obtained water through their system’s own solar nebula.

“This model suggests that the inevitable formation of water would likely occur on any sufficiently large rocky exoplanets in extrasolar systems,” Wu said. “I think this is very exciting.”

Anat Shahar, a geochemist at the Carnegie Institution for Science, who was not involved with the study, noted the hydrogen fractionation factor, which describes how the deuterium-to-hydrogen ratio changes when the element dissolves in iron, is currently unknown and difficult to measure. For the new study, this property of hydrogen had to be estimated.

The new model, which fits in well with current research, could be tested once experiments reveal the hydrogen fractionation factor, Shahar said.

“This paper is a very creative alternative to what is an old problem,” Shahar said. “The authors have done a good job of estimating what these different fractionation factors would be without having the experiments.”

Astronomers Find Pairs Of Black Holes At The Centers Of Merging Galaxies

For the first time, a team of astronomers has observed several pairs of galaxies in the final stages of merging together into single, larger galaxies. Peering through thick walls of gas and dust surrounding the merging galaxies’ messy cores, the research team captured pairs of supermassive black holes — each of which once occupied the center of one of the two original smaller galaxies — drawing closer together before they coalescence into one giant black hole.

Led by University of Maryland alumnus Michael Koss (M.S. ’07, Ph.D. ’11, astronomy), a research scientist at Eureka Scientific, Inc., with contributions from UMD astronomers, the team surveyed hundreds of nearby galaxies using imagery from the W.M. Keck Observatory in Hawaii and NASA’s Hubble Space Telescope. The Hubble observations represent more than 20 years’ worth of images from the telescope’s lengthy archive. The team described their findings in a research paper published on November 8, 2018, in the journal Nature.

“Seeing the pairs of merging galaxy nuclei associated with these huge black holes so close together was pretty amazing,” Koss said. “In our study, we see two galaxy nuclei right when the images were taken. You can’t argue with it; it’s a very ‘clean’ result, which doesn’t rely on interpretation.”

The high-resolution images also provide a close-up preview of a phenomenon that astronomers suspect was more common in the early universe, when galaxy mergers were more frequent. When the black holes finally do collide, they will unleash powerful energy in the form of gravitational waves — ripples in space-time recently detected for the first time by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors.

The images also presage what will likely happen in a few billion years, when our Milky Way galaxy merges with the neighboring Andromeda galaxy. Both galaxies host supermassive black holes at their center, which will eventually smash together and merge into one larger black hole.

The team was inspired by a Hubble image of two interacting galaxies collectively called NGC 6240, which later served as a prototype for the study. The team first searched for visually obscured, active black holes by sifting through 10 years’ worth of X-ray data from the Burst Alert Telescope (BAT) aboard NASA’s Neil Gehrels Swift Observatory.

“The advantage to using Swift’s BAT is that it observes high-energy, ‘hard’ X-rays,” said study co-author Richard Mushotzky, a professor of astronomy at UMD and a fellow of the Joint Space-Science Institute (JSI). “These X-rays penetrate through the thick clouds of dust and gas that surround active galaxies, allowing the BAT to see things that are literally invisible in other wavelengths.”

The researchers then combed through the Hubble archive, zeroing in on the merging galaxies they spotted in the X-ray data. They then used the Keck telescope’s super-sharp, near-infrared vision to observe a larger sample of the X-ray-producing black holes not found in the Hubble archive.

The team targeted galaxies located an average of 330 million light-years from Earth — relatively close by in cosmic terms. Many of the galaxies are similar in size to the Milky Way and Andromeda galaxies. In total, the team analyzed 96 galaxies observed with the Keck telescope and 385 galaxies from the Hubble archive.

Their results suggest that more than 17 percent of these galaxies host a pair of black holes at their center, which are locked in the late stages of spiraling ever closer together before merging into a single, ultra-massive black hole. The researchers were surprised to find such a high fraction of late-stage mergers, because most simulations suggest that black hole pairs spend very little time in this phase.

To check their results, the researchers compared the survey galaxies with a control group of 176 other galaxies from the Hubble archive that lack actively growing black holes. In this group, only about one percent of the surveyed galaxies were suspected to host pairs of black holes in the later stages of merging together.

This last step helped the researchers confirm that the luminous galactic cores found in their census of dusty interacting galaxies are indeed a signature of rapidly-growing black hole pairs headed for a collision. According to the researchers, this finding is consistent with theoretical predictions, but until now, had not been verified by direct observations.

“People had conducted studies to look for these close interacting black holes before, but what really enabled this particular study were the X-rays that can break through the cocoon of dust,” explained Koss. “We also looked a bit farther in the universe so that we could survey a larger volume of space, giving us a greater chance of finding more luminous, rapidly-growing black holes.”

It is not easy to find galactic nuclei so close together. Most prior observations of merging galaxies have caught the coalescing black holes at earlier stages, when they were about 10 times farther away. The late stage of the merger process is so elusive because the interacting galaxies are encased in dense dust and gas, requiring very high-resolution observations that can see through the clouds and pinpoint the two merging nuclei.

“Computer simulations of galaxy smashups show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that’s what we have found in our survey,” said Laura Blecha, an assistant professor of physics at the University of Florida and a co-author of the study. Blecha was a JSI Prize Postdoctoral Fellow in the UMD Department of Astronomy prior to joining UF’s faculty in 2017. “The fact that black holes grow faster and faster as mergers progress tells us galaxy encounters are really important for our understanding of how these objects got to be so monstrously big.”

Future infrared telescopes such as NASA’s highly anticipated James Webb Space Telescope (JWST), slated for launch in 2021, will provide an even better view of mergers in dusty, heavily obscured galaxies. For nearby black hole pairs, JWST should also be capable of measuring the masses, growth rates and other physical parameters for each black hole.

“There might be other objects that we missed. Even with Hubble, many nearby galaxies at low redshift cannot be resolved — the two nuclei just merge into one,” said study co-author Sylvain Veilleux, a professor of astronomy at UMD and a JSI Fellow. “With JWST’s higher angular resolution and sensitivity to the infrared, which can pass through the dusty cores of these galaxies, searches for these nearby objects should be easy to do. Also with JWST, we will be able to push toward larger distances, to see objects at higher redshift. With these observations, we can begin to explore the fraction of objects that are merging in the youngest, most distant regions of the universe — which should be fairly frequent.”

Astronomers Discover The Giant That Shaped The Early Days Of Our Milky Way

Some ten billion years ago, the Milky Way merged with a large galaxy. The stars from this partner, named Gaia-Enceladus, make up most of the Milky Way’s halo and also shaped its thick disk, giving it its inflated form. A description of this mega-merger, discovered by an international team led by University of Groningen astronomer Amina Helmi, is now published in the scientific journal Nature.

Large galaxies like our Milky Way are the result of mergers of smaller galaxies. An outstanding question is whether a galaxy like the Milky Way is the product of many small mergers or of a few large ones. The University of Groningen’s Professor of Astronomy, Amina Helmi, has spent most of her career looking for ‘fossils’ in our Milky Way which might offer some hints as to its evolution. She uses the chemical composition, the position and the trajectory of stars in the halo to deduce their history and thereby to identify the mergers which created the early Milky Way.

The recent second data release from the Gaia satellite mission last April provided Professor Helmi with data on around 1.7 billion stars. Helmi has been involved in the development of the Gaia mission for some twenty years and was part of the data validation team on the second data release. She has now used the data to look for traces of mergers in the halo: “We expected stars from fused satellites in the halo. What we didn’t expect to find was that most halo stars actually have a shared origin in one very large merger.”

This is indeed what she found. The chemical signature of many halo stars was clearly different from the ‘native’ Milky Way stars. “And they are a fairly homogenous group, which indicates they share a common origin.” By plotting both trajectory and chemical signature, the ‘invaders’ stood out clearly. Helmi: “The youngest stars from Gaia-Enceladus are actually younger than the native Milky Way stars in what is now the thick disk region. This means that the progenitor of this thick disk was already present when the fusion happened, and Gaia-Enceladus, because of its large size, shook it and puffed it up.”

In a previous paper, Helmi had already described a huge ‘blob’ of stars sharing a common origin. Now, she shows that stars from this blob in the halo are the debris from the merging of the Milky Way with a galaxy which was slightly more massive than the Small Magellanic Cloud, some ten billion years ago. The galaxy is called Gaia-Enceladus, after the Giant Enceladus who in Greek mythology was born of Gaia (the Earth goddess) and Uranus (the Sky god).

The data on kinematics, chemistry, age and spatial distribution from the native Milky Way stars and the remnants of Gaia-Enceladus reminded Helmi of simulations performed by a former PhD student, some ten years ago. His simulations of the merging of a large disc-shaped galaxy with the young Milky Way produced a distribution of stars from both objects, which is totally in line with the Gaia data. “It was amazing to look at the new Gaia data and realize that I had seen it before!,” says the astronomer.

Comet Tails Blowing In The Solar Wind

Engineers and scientists gathered around a screen in an operations room at the Naval Research Laboratory in Washington, D.C., eager to lay their eyes on the first data from NASA’s STEREO spacecraft. It was January 2007, and the twin STEREO satellites — short for Solar and Terrestrial Relations Observatory — which had launched just months before, were opening their instruments’ eyes for the first time. First up: STEREO-B. The screen blinked, but instead of the vast starfield they expected, a pearly white, feathery smear — like an angel’s wing — filled the frame. For a few panicky minutes, NRL astrophysicist Karl Battams worried something was wrong with the telescope. Then, he realized this bright object wasn’t a defect, but an apparition, and these were the first satellite images of Comet McNaught. Later that day, STEREO-A would return similar observations.

Comet C/2006 P1 — also known as Comet McNaught, named for astronomer Robert McNaught, who discovered it in August 2006 — was one of the brightest comets visible from Earth in the past 50 years. Throughout January 2007, the comet fanned across the Southern Hemisphere’s sky, so bright it was visible to the naked eye even during the day. McNaught belongs to a rarefied group of comets, dubbed the Great Comets and known for their exceptional brightness. Setting McNaught apart further still from its peers, however, was its highly structured tail, composed of many distinct dust bands called striae, or striations, that stretched more than 100 million miles behind the comet, longer than the distance between Earth and the Sun. One month later, in February 2007, an ESA (European Space Agency) and NASA spacecraft called Ulysses would encounter the comet’s long tail.

“McNaught was a huge deal when it came because it was so ridiculously bright and beautiful in the sky,” Battams said. “It had these striae — dusty fingers that extended across a huge expanse of the sky. Structurally, it’s one of the most beautiful comets we’ve seen for decades.”

How exactly the tail broke up in this manner, scientists didn’t know. It called to mind reports of another storied comet from long ago: the Great Comet of 1744, which was said to have dramatically fanned out in six tails over the horizon, a phenomenon astronomers then couldn’t explain. By untangling the mystery of McNaught’s tail, scientists hoped to learn something new about the nature of comets — and solve two cosmic mysteries in one.

A key difference between studying comets in 1744 and 2007 is, of course, our ability to do so from space. In addition to STEREO’s serendipitous sighting, another mission, ESA/NASA’s SOHO — the Solar and Heliospheric Observatory — made regular observations as McNaught flew by the Sun. Researchers hoped these images might contain their answers.

Now, years later, Oliver Price, a planetary science Ph.D. student at University College London’s Mullard Space Science Laboratory in the United Kingdom, has developed a new image-processing technique to mine through the wealth of data. Price’s findings — summarized in a recently published Icarus paper — offer the first observations of striations forming, and an unexpected revelation about the Sun’s effect on comet dust.

Comets are cosmic crumbs of frozen gas, rock and dust left over from the formation of our solar system 4.6 billion years ago — and so they may contain important clues about our solar system’s early history. Those clues are unlocked, as if from a time capsule, every time a comet’s elliptical orbit brings it close to the Sun. Intense heat vaporizes the frozen gases and releases the dust within, which streams behind the comet, forming two distinct tails: an ion tail carried by the solar wind — the constant flow of charged particles from the Sun — and a dust tail.

Understanding how dust behaves in the tail — how it fragments and clumps together — can teach scientists a great deal about similar processes that formed dust into asteroids, moons and even planets all those billions of years ago. Appearing as one of the biggest and most structurally complex comets in recent history, McNaught was a particularly good subject for this type of study. Its brightness and high dust production made it much easier to resolve the evolution of fine structures in its dust tail.

Price began his study focusing on something the scientists couldn’t explain. “My supervisor and I noticed weird goings-on in the images of these striations, a disruption in the otherwise clean lines,” he said. “I set out to investigate what might have happened to create this weird effect.”

The rift seemed to be located at the heliospheric current sheet, a boundary where the magnetic orientation, or polarity, of the electrified solar wind changes directions. This puzzled scientists because while they have long known a comet’s ion tail is affected by the solar wind, they had never seen the solar wind impact dust tails before.

Dust in McNaught’s tail — roughly the size of cigarette smoke — is too heavy, the scientists thought, for the solar wind to push around. On the other hand, an ion tail’s miniscule, electrically charged ions and electrons easily sail along the solar wind. But it was difficult to tell exactly what was going on with McNaught’s dust, and where, because at roughly 60 miles per second, the comet was rapidly traveling in and out of STEREO and SOHO’s view.

“We got really good data sets with this comet, but they were from different cameras on different spacecraft, which are all in different places,” Price said. “I was looking for a way to bring it all together to get a complete picture of what’s happening in the tail.”

His solution was a novel image-processing technique that compiles all the data from different spacecraft using a simulation of the tail, where the location of each tiny speck of dust is mapped by solar conditions and physical characteristics like its size and age, or how long it’d been since it’d flown off the head, or coma, of the comet. The end result is what Price dubbed a temporal map, which layers information from all the images taken at any given moment, allowing him to follow the dust’s movements.

The temporal maps meant Price could watch the striations form over time. His videos, which cover the span of two weeks, are the first to track the formation and evolution of these structures, showing how dust fragments topple off the comet head and collapse into long striations.

But the researchers were most excited to find that Price’s maps made it easier to explain the strange effect that drew their attention to the data in the first place. Indeed, the current sheet was the culprit behind the disruptions in the dust tail, breaking up each striation’s smooth, distinct lines. For the two days it took the full length of the comet to traverse the current sheet, whenever dust encountered the changing magnetic conditions there, it was jolted out of position, as if crossing some cosmic speed bump.

“It’s like the striation’s feathers are ruffled when it crosses the current sheet,” University College London planetary scientist Geraint Jones said. “If you picture a wing with lots of feathers, as the wing crosses the sheet, lighter ends of the feathers get bent out of shape. For us, this is strong evidence that the dust is electrically charged, and that the solar wind is affecting the motion of that dust.”

Scientists have long known the solar wind affects charged dust; missions like Galileo Cassini, and Ulysses watched it move electrically charged dust through the space near Jupiter and Saturn. But it was a surprise for them to see the solar wind affect larger dust grains like those in McNaught’s tail — about 100 times bigger than the dust seen ejected from around Jupiter and Saturn — because they’re that much heavier for the solar wind to push around.

With this study, scientists gain new insights into long-held mysteries. The work sheds light on the nature of striated comet tails from the past and provides a crucial lens for studying other comets in the future. But it also opens a new line of questioning: What role did the Sun have in our solar system’s formation and early history?

“Now that we see the solar wind changed the position of dust grains in McNaught’s tail, we can ask: Could it have been the case that early on in the solar system’s history, the solar wind played a role in organizing ancient dust as well?” Jones said.

Thirty Years In The Life Of Supernova 1987A

Since it first appeared in the southern night sky on February 24th 1987, Supernova 1987A has been one of the most studied objects in the history of astronomy.

The supernova was the cataclysmic death of a blue supergiant star, some 168,000 light-years from Earth, in the Large Magellanic Cloud, a satellite galaxy of our own Milky Way Galaxy. It was the brightest supernova to appear in our skies since Kepler’s Supernova in 1604 and the first since the invention of the telescope.

The brilliant new star was first spotted by two astronomers working at the Las Campanas Observatory in northern Chile the night of the 24th: the University of Toronto’s Ian Shelton, and a telescope operator at the observatory, Oscar Duhalde.

Now, Yvette Cendes, a graduate student with the University of Toronto and the Leiden Observatory, has created a time-lapse showing the aftermath of the supernova over a 25-year period, from 1992 to 2017. The images show the shockwave expanding outward and slamming into debris that ringed the original star before its demise.

In an accompanying paper, published in the Astrophysical Journal on October 31st, Cendes and her colleagues add to the evidence that the expanding remnant is shaped — not like a ring like those of Saturn’s — but like a donut, a form known as a torus.

They also confirm that the shockwave has now picked up some one thousand kilometres per second in speed. The acceleration has occurred because the expanding torus has punched through the ring of debris.

Orionids 2018 Meteor Shower Peaking Overnight Tonight

The Orionids meteor shower will peak overnight from Sunday, Oct. 21 to Monday, Oct. 22. The meteor shower, which will produce between 15 to 20 meteors per hour, is best seen between 2-5 a.m. The origin of the Orionids shower comes from Halley’s comet as it returns to our inner solar system.

Peaking during mid-October, the Orionids are considered one of the most beautiful showers of the year. Its meteors are fast, traveling at about 148,000 mph and leaving glowing “trains” – incandescent bits of debris in the wake of the meteor – which last for several seconds to minutes, according to NASA.

The shower’s radiant – or the point in the sky from which the Orionids appear to come from – is the constellation Orion but NASA said don’t limit your viewing to only that area. The Orionids should be visible throughout the night sky.

If you miss the Orionids, don’t fret. The Leonids meteor shower will peak on Nov. 17.