Daily Archives: December 16, 2023

THINGS THAT GO BUMP IN THE UNIVERSE: How Astronomers Decode Cosmic Chaos, by C. Rene James

There is one particular pulsar, a type of quick-spinning dead star, that holds the current record for the fastest rotation of any celestial body in the known universe 716 times per second. By contrast, the blade of a Vitamix can turn around 333 times every second, but a blender is small enough to sit on a countertop, and a pulsar is a city-size ball of neutrons that floats in space and contains the mass of half a million Earths.

One can read numbers like this and think, Oh, thats interesting, writes the astronomer C. Rene James in her new book, Things That Go Bump in the Universe. One can also feel that grasping the reality is impossible. But, she says, You should still try.

Pulsars may seem unfathomable, but they are worth studying both for their own sake they are among the weirdest things in the cosmos and for the insight they can offer. They can help us measure the distance between suns and advance our knowledge of nuclear physics. A pulsar like the record-setting PSR J1748-2446ad, which James usefully renames Zippy, is a key tool in the relatively new field of transient astronomy: the study of fast, short-lived, violent phenomena in what we otherwise perceive as a mostly empty and unblinking universe.

The James Webb Space Telescope and its siblings have revealed fascinating portraits of a cosmos spangled with stars, clouds of dust, filaments of gas and the whirling arms of galaxies. Things That Go Bump in the Universe introduces several of the most unusual cosmic characters in these realms, including the extremely abundant and ghostly particles known as neutrinos, which seemingly interact with nothing after they are born, whether they arise in horrifically violent stellar death throes or in the natural decay of the potassium in bananas. We also meet black widow pulsars (over eons they consume their binary-star companions) and see black holes merge. One such collision 1.2 billion years ago made space-time around the Earth shudder in 2015.

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Book Review: Things That Go Bump in the Universe, by C. Rene James - The New York Times

Astronomers have discovered 25 stars in two satellite galaxies of the Milky Way that have had their hydrogen-rich outer layers stripped away by a binary companion, leaving them as exposed helium stars. The hydrogen-stripped stars represent the progenitors of a special type of supernova an explosion that occurs when massive stars die and birth black holes or neutron stars and fill in a glaring hole in our understanding of some of the universe's most powerful events.

When massive stars die in bright supernova explosions, they often outshine the combined light of every star in the galaxy around them. Some of these events lack evidence of hydrogen, so it follows that they must begin with stars that also lack hydrogen in their outer layers. Until now, evidence of these hydrogen-stripped stars has largely eluded scientists.

This is the first time a population of these hydrogen-stripped stars has ever been discovered.

"We've known for a decade or two that almost all massive stars are actually in binary systems, and one in three is close enough to undergo this process where the hydrogen envelope should be removed by the gravitational influence of the other star," Maria Drout, an assistant professor in the Department of Astronomy and Astrophysics at the University of Toronto and co-author of a new study on the stars, told Live Science. "The universe only made sense if these stars existed and were very common. However, only one candidate system was known until we did our study, so it was really a big problem."

With the discovery of these hydrogen-stripped stars in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) two small galaxies that orbit the Milky Way, and the closest galaxies visible to Earth beyond our own the astronomers can finally begin to correct this imbalance, helping to confirm models of stellar evolution. The team's research was published in the Dec. 14 edition of the journal Science.

Hydrogen-stripped stars have been so evasive because the removal of their outer layers leaves them as incredibly hot, exposed stellar cores, Drout said. This means they emit most of their light in the ultraviolet region of the electromagnetic spectrum, beyond the range visible to human eyes.

Ultraviolet light is difficult for ground-based telescopes to observe because it is strongly absorbed by our planet's atmosphere. Ambient dust in the Milky Way absorbs even more of this light, making hydrogen-stripped stars nearly impossible to detect. However, our view of satellite galaxies like the LMC and SMC is much clearer for space telescopes outside Earth's atmosphere.

The team discovered the population of stripped stars in data from the Swift Ultraviolet/Optical Telescope, which has observed millions of stars in the LMC and the SMC from its position in low Earth orbit.

The researchers then confirmed the stars as hot, hydrogen-poor, exposed stellar cores in binary systems using the Magellan Telescopes at Las Campanas Observatory in Chile between 2018 and 2022. While astronomers already knew that massive stars prefer life with a stellar companion, this discovery confirms what that social life looks like as those binary systems age.

Just as the sun will swell up as a red giant star when it runs out of hydrogen in its core in around 5 billion years, massive stars undergo a similar swelling transformation into red supergiant stars when they exhaust the hydrogen in their cores, Drout said.

"If you have two stars that are in a binary and one of them starts to expand, pretty soon, the outer part of that star ends up getting stripped, meaning you can end up with a star with basically no hydrogen left on it," she said. "So we have this process where the binary stars interact and dance with each other and exchange mass and material, and that really affects the rest of their lives dramatically."

While Drout and the team theorize that the 25 newly discovered stars will eventually erupt as hydrogen-poor supernovas, she concedes that astronomers won't be waiting around for this to happen.

"We think we understand what evolutionary stage these stars are in, and they are fusing helium in their cores, meaning they are quite evolved," Drout said. "But that means it will still probably be a million years before these particular stars explode."

When this eventually happens, the team thinks a small sample of the systems they have observed will become something very special. If the supernova creates a neutron star and doesn't push the companion star away, the transfer of matter between the stars could switch. Then, the star that once fed on the now-dead star would begin to lose its hydrogen-rich outer layers to the pull of its new neutron star companion.

This could result in a second hydrogen-poor core-collapse supernova in the binary and thus a system with two neutron stars orbiting each other. As these binary neutron stars spiraled around each other, they would lose angular momentum through the emission of gravitational waves, eventually leading them to merge and send out a flash of light called a kilonova.

To further study these stars and see which are possible kilonova progenitor systems, the team will turn to the Hubble Space Telescope, the Chandra X-ray Observatory, the Magellan Telescopes, and the Anglo-Australian Telescope. Additionally, they will search for hydrogen-stripped stars in other galaxies and within the Milky Way.

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Astronomers discover 25 'stripped stars' that may be a missing link in supernova science - Livescience.com

We are now well into a new era of astronomy, where distant planets (called exoplanets) are being detected at a fast clip. At last count, there have been 5,557 confirmed discoveries of exoplanets and another 10,000 candidates awaiting confirmation. These discoveries have given rise to comparative planetology, a new area of astronomy dedicated to investigating the properties of different worlds, classifying them according to size, mass, (approximate) atmospheric composition, distance from their parent star, and whether they are rocky, gaseous, or some combination of the two.

The main goal is to compare them to Earth and other planets in our Solar System. For example, when astronomers talk about a super-Earth, they mean a rocky planet with a radius somewhat larger than Earths, while a sub-Neptune is a gaseous planet with a radius somewhat smaller than Neptunes. These definitions are operational and the boundaries between planetary classes are not very rigid, but they offer a quick way of classifying what we see.

Exoplanets are planets that orbit other stars in our galaxy (and stars in other galaxies, too, but those are too distant to be detected). An M-type dwarf star (or red dwarf star) is the smallest and coolest star, the most common in the Milky Way. Around three-quarters of the stars in our galaxy are M-type dwarf stars. In comparison, our Sun is a yellow dwarf star, about five times more massive than a red dwarf. Only about 3% of stars are yellow dwarfs like our Sun.

The diversity of planetary systems is absolutely staggering. There is no obvious or common type of planetary system: Some have huge Jupiter-like planets orbiting very near their host stars, while others have planets distributed more evenly, with some resembling our Earth. These seem to be quite rare.

If youre not amazed by what astronomers have discovered about planetary systems, consider the sheer difficulty of discovering distant planets. Finding a planet orbiting another star is much harder than finding a flea in front of a floodlight. To detect them, astronomers capture the ever-so-slight dimming of starlight as a planet passes in front of a star. This is called planetary transit. Imagine measuring the dimming of a floodlight as a flea hops over it. Now, move the floodlight incredibly far away so far as to look like a point source. With this image, you begin to get an idea of how delicate and spectacular the discovery of exoplanets is.

The main motivation, of course, is to figure out how rare or common our planet is. If there are lots of Earth-like planets not just with similar size and composition, but also located at the so-called habitable zone of the star where water, if present on the planets surface, would be liquid then the odds become higher that such worlds could harbor some kind of life. As my Dartmouth colleague Elisabeth Newton reported a few years back while reflecting on her discovery of a young exoplanet orbiting a relatively young star, One of the overall goals of astronomy is understanding the big picture of how we got here, how solar systems and galaxies take shape and why. By finding solar systems that are different from our own especially young ones we can hope to learn why Earth and our own Solar System evolved in the ways that they did.

So, it all boils down to one of the most exciting questions we can ask in science the one kids from ages five to 90 ask across all cultures on our planet: Are we alone in the Universe? Studying other worlds their history, location, and properties allows us to figure out our own history, and how exceptional (or not) it is. We live in this very special time when we can actually begin to answer this question. And it all points to our planet being a rare gem in a Universe that is very hostile to life.

We are still far from knowing whether other worlds harbor life of any kind. Clearly, given that there are so many worlds out there (trillions in our galaxy alone), and that the laws of physics and chemistry are the same across the Universe (this we do know with confidence), the expectation from a large fraction of scientists is: Yes, there should be other worlds with life. Otherwise, as Jodie Fosters character in the movie Contact (based on Carl Sagans homonymous novel) said, [It] seems like an awful waste of space.

But life is not so simple as large numbers. There is a disconnect between the way physical scientists and biologists think about this question. (Of course, there are exceptions in both groups.) Biologists tend to be more careful with such extrapolations, knowing only too well that life is enormously complex. There are many truly mind-boggling steps to go from non-life to the first living creatures, and then on to complex unicellular life and multicellular creatures. Whats more, life doesnt have a plan to get more complex over time; life cares about reproducing efficiently. If species are well-adapted, mutations wont do much. Ultimately, the question of how life did emerge on Earth remains very much open.

What we do know now, and this is extremely important, is that the life history of a planet the details of how it evolved, from its atmosphere to cosmic impacts and seismic activity is imprinted on its creatures. And vice versa: Life changes its host planet in dramatic ways. There is a two-way relationship between a planets history and the kind of life it supports. The planet provides the basic support for life to be possible and life acts back on the planet and changes it. Earth now is a different planet from three billion years ago, when it only had single-celled organisms. Their action changed the planet by dramatically increasing the oxygen levels in the atmosphere. Without that, we wouldnt be here. We can also see this with our own destructive activities, and how they are imprinted on Earth. Human presence has permanently scarred Earth.

Dominant species can change their world, either knowingly or unknowingly. We are living the reality of this fact. Yet, most of us are choosing not to pay attention or change our ways. Alienated from nature, we seem to have forgotten how much our survival depends on it. Bad water + bad air = sick life. Thats the equation everyone should know call it the survival equation. Maybe what we are learning about our planet and its distant cousins will inspire us to rethink how we relate to our world and the creatures we share it with.

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Exoplanet discoveries reveal Earth's profound rarity in the cosmos - Big Think

Frederic Churchs painting of an aurora is reminiscent of the descriptions of an auroral show noted after the Battle of Fredericksburg in Virginia in 1862. Credit: Smithsonian Institution

In the summer of 1863, the U.S. was in the middle of its greatest-ever crisis. A bloody civil war between the Southern Confederacy and the federal government had created hundreds of thousands of casualties, and to many, no end appeared to be in sight. By July of that year, however, things finally seemed to be brightening slightly for the hopes of a united country. Decisive victories for the Union at Gettysburg and Vicksburg gave the first glimmers of foresight that the war would eventually cease and that healing would begin.

Seven weeks after the Battle of Gettysburg, the nations leader, Abraham Lincoln, paid an unusual Washington, D.C., visit. Accompanied by his young private secretary John Hay, Lincoln made an unannounced journey to the U.S. Naval Observatory to indulge his interest in astronomy and to seek a brief reprieve from the war. In those days, the observatory was located at 23rd and E streets, about three blocks north of what is now the Lincoln Memorial site. (This area, called Foggy Bottom due to the frequent haze and fog that rolled off the Potomac, wasnt the best site for a telescope, and eventually the observatory would move.)

On the night of Aug. 22, 1863, the observatory was manned by a young astronomer, Asaph Hall. Fourteen years later, Hall would discover the two moons of Mars, but on that evening, he was an unknown 33-year-old researcher. Lincoln and Hay arrived and introduced themselves as if Lincoln needed to be introduced. The group climbed up a wooden ladder to the dome where the observatorys 9.6-inch refractor was located. There they observed the Moon and the star Arcturus.

In the 1980s, I was privileged to visit the historic site of the Old Naval Observatory, courtesy of Jan Herman, the observatorys former historian and a contributor to Astronomy. Climbing up the same wooden steps Lincoln had used to enter the dome gave me an ethereal feeling of the past, the present, and the universe, all meeting at one point.

Not all participants of the Civil War sought to contemplate the meaning of the cosmos as Abraham Lincoln did, but some viewed certain events as a beacon of hope or demise.

On May 13, 1861, an observer in New South Wales, Australia, found what came to be called the Great Comet of 1861. By midsummer, the comet had moved so that it was visible in the Northern Hemisphere sky and, according to astronomer Horace Tuttle, sported a tail 106 long.

The comet caused a press sensation. The evening spectacle came to be called The War Comet, and the editors of the Brooklyn Daily Eagle posed a question to their readers: What means this visit peace or war? Vanity Fair published a cartoon showing Lt. Gen. Winfield Scott, the senior general of the Union army, as the comets head and a slew of bayonets comprising the tail.

During this time, Charles Johnson, a private in the 9th New York Infantry, wrote in his diary, The comet is now tired of his visit to these regions of space, or disgusted it may be with the appearance of things on this side of the planet, for he is now leaving in seemingly greater haste than he came, with his tail between his legs, for the unknown regions out yonder.

The Great Comet of 1861 faded during the week of the First Battle of Bull Run, leading to vast speculation on that meaning. But comets were not done with the war. In 1862, Tuttle discovered another comet that would rise to significant brightness. Astronomer Lewis Swift had also spotted the comet, which became known as Swift-Tuttle. When that comet faded in September 1862, many attached its significance one way or another to the battle of Antietam, a substantial Union victory. Decades later, astronomers would identify this comet as the source of the Perseid meteor shower.

In December 1862, during the battle of Fredericksburg in Virginia, a different kind of celestial omen made its appearance. After a slow and discouraging lack of progress during the wars first two years, Lincoln assigned Maj. Gen. Ambrose Burnside to command the Army of the Potomac, the principal Union army in the east. Burnside faced Confederate Gen. Robert E. Lee at Fredericksburg and sent repeated frontal attacks into the Rebel works, ending in a Union disaster.

Following the battle, as the cries of wounded filled the icy December air, an aurora appeared in the sky, visible to many thousands of soldiers on both sides. A brilliant aurora illuminated the night and much facilitated the work upon the entrenchments, wrote Confederate Col. Edward Porter Alexander.

The light show was taken as an omen of victory by Southerners, who had inflicted heavy losses on the Yankee troops. And, of course, many Union soldiers saw it as an omen of doom. Citizens in Fredericksburg, in Charlottesville, and all over the region remarked on the unusual aurora. Oh, child, it was a terrible omen, wrote Elizabeth Lyle Saxon in her 1905 reminiscences, quoting an elderly womans words to her. Such lights never burn, save for kings and heroes deaths. A writer for the Richmond Daily Dispatch proposed the crimson columns of light represented the blood of those martyrs who had offered their lives as a sacrifice to their native land.

In the following months, a significant event rocked the command structure of the Confederate Army. The battle of Chancellorsville in May 1863 was yet another huge win for the Confederacy, following the triumph at Fredericksburg. But in the action, the Southern general Thomas J. Stonewall Jackson, was accidentally and mortally wounded by other Confederate troops.

Recently, astronomers have shed some light or rather some moonlight onto why the events of that night led to Jacksons death. As the Sun faded on that fateful day at Chancellorsville, Jackson pressed his men forward. Stonewalls flank attack crushed a portion of the Union force, held by Maj. Gen. Oliver Howards 11th Corps. Jackson rode out under moonlight to the Plank Road, assessing the situation and determining the feasibility of a night attack by the light of the Full Moon. Soldiers in the 18th North Carolina Infantry believed the small group of riders, including Jackson, were Union cavalry and opened fire. Jackson was hit with three bullets, including in his left arm, which had to be amputated later that night. Confederate doctors attempted to transport him to Richmond for follow-up care, but he developed pneumonia and died eight days later.

In 2013, a group led by Don Olson of Texas State University determined that, based on astronomical research and battle maps, Stonewall and his party would have been viewed as a group of dark silhouettes using the light of the Moon, which sat at a low 25 above the horizon, as their guide. Their positions ultimately obscured their identities, resulting in the soldiers mistakenly opening fire.

North of the Mason-Dixon Line, another prominent figure was strongly associated with the night sky.

On the Union side, a well-known astronomer became one of the most prominent general officers in the western theater. Ormsby Mitchel had been born in Kentucky but grew up in Lebanon, Ohio, and was a classmate of Robert E. Lee at West Point. During his career, he helped establish the U.S. Naval Observatory and the Harvard College Observatory. Mitchel also studied the double star Nu () Scorpii and found in 1846 that the fainter of the two stars was also a close double.

After West Point, Mitchel became a professor of mathematics at the military academy, but then returned to Ohio, became a lawyer and engineer, and began a professorship at Cincinnati College. He organized the Cincinnati Astronomical Society and became an early popularizer of the subject. In 1859, Mitchel moved to the Dudley Observatory in New York. But in 1861, as the war rapidly approached, he returned to his military roots at the age of 51.

Commissioned a brigadier general, Mitchel first supervised defenses around Cincinnati and Northern Kentucky. In 1862, he conspired with a Union spy, James J. Andrews, on a plot that would come to be known as the Great Locomotive Chase. Given the nickname Andrews Raiders, they stole the Confederate locomotive The General in northern Georgia, intent on disrupting the important railway between Atlanta and Chattanooga. The plan that Mitchel ordered but did not participate in eventually failed. Many of the raiders were captured and eight were hanged by the Confederacy, including Andrews himself, while others were able to escape. Afterward, 19 of the living and executed men became the first recipients of the Medal of Honor.

Despite the raids failure, Mitchel continued to lead other successful operations throughout the year. By September 1862, he was assigned command of a post in Beaufort, South Carolina, but he contracted yellow fever and died there in October.

The era in which Mitchel lived and the Civil War occurred not only saw a dramatic upheaval of the U.S. but also witnessed the rise of astrophysics. During this time, a field of simple observing and cataloging transformed into understanding the physical nature of what the universe contains.

Out of a maelstrom of chaos eventually came order, a start down the long road to justice and equality, and the beginnings of an understanding of our larger universe.

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The role of astronomy in the American Civil War - Astronomy Magazine

image:

This artist's impression shows how hot, brilliant and high-mass stars evolve. The more massive brighter star expands first, until the outer layers start to strongly feel the gravitational pull of the companion. The companion then starts to suck material from the primary star. When the primary has been stripped from its entire hydrogen-rich envelope it shrinks.

Credit: Navid Marvi, courtesy of the Carnegie Institution for Science

Astronomers at the University of Toronto have discovered a population of massive stars that have been stripped of their hydrogen envelopes by their companions in binary systems. The findings, published today in Science, shed light on the hot helium stars that are believed to be the origins of hydrogen-poor core-collapse supernovae and neutron star mergers.

For over a decade, scientists have theorized that approximately one in three massive stars are stripped of their hydrogen envelope in binary systems. Yet, until now, only one possible candidate had been identified.

This was such a big, glaring hole, says co-lead author Maria Drout, an Assistant Professor in the David A. Dunlap Department of Astronomy & Astrophysics and a Dunlap Institute for Astronomy & Astrophysics Associate at the University of Toronto.

If it turned out that these stars are rare, then our whole theoretical framework for all these different phenomena is wrong, with implications for supernovae, gravitational waves, and the light from distant galaxies, Drout says. This finding shows these stars really do exist.

Going forward, we are going to be able to do much more detailed physics with these stars, Drout says. For example, predictions for how many neutron star mergers we should see are dependent on the properties of these stars, such as how much material comes off ofthem in stellar winds. Now, for the first time, well be able to measure that, whereas people have been extrapolating it before.

Binary stripped stars have been previously evoked to explain why a third of core-collapse supernovae contain much less hydrogen than a typical explosion of a Red Supergiant star. Drout and her colleagues propose that these newly discovered stars will eventually explode as hydrogen-poor supernovae. These star systems are also thought to be necessary to form neutron star mergers, like those that emit gravitational waves detected from Earth by the LIGO experiment.

In fact, the researchers believe that a few objects in their current sample are stripped stars with neutron star or blackhole companions. These objects are at the stage immediately before they become double neutron star or neutron star plus blackhole systems that could eventually merge.

Many stars are part of a cosmic dance with a partner, orbiting each other in a binary system. They're not solitary giants but part of dynamic duos, interacting and influencing each other throughout their lifetimes, says Bethany Ludwig, a PhD student in in the David A. Dunlap Department of Astronomy & Astrophysics at the University Toronto and the third author on this paper. Our work sheds light on these fascinating relationships, revealing a universe that is far more interconnected and active than we previously imagined.

Just as humans are social beings, stars too, especially the massive ones, are rarely alone, Ludwig says.

As stars evolve and expand to become red giants, the hydrogen at the outer edges of one can be stripped by the gravitational pull of its companionleaving a very hot helium core exposed. The process can take tens of thousands, or even hundreds of thousands, of years.

Stripped stars are difficult to find because much of the light they emit is outside of the visible light spectrum and can be obstructed by dust in the universe or outshone by their companion stars.

Drout and her collaborators began their search in 2016. Having studied hydrogen-poor supernovae during her PhD, Drout set out to find the stripped stars thought to be at the heart of them during a NASA Hubble Postdoctoral Fellowship at the Observatories of the Carnegie Institution for Science. She met fellow co-author Ylva Gtberg, now Assistant Professor at the Institute of Science and Technology Austria (ISTA),at a conference, who had recently built new theoretical models of what these stars should look like.

Drout, Gtberg, and their collaborators designed a new survey to look in the ultraviolet part of the spectrum where extremely hot stars emit most of their light. While invisible to the naked eye, ultraviolet light can be detected by specialized instruments and telescopes.

Using data from the Swift Ultra-Violet/Optical Telescope, the researchers collected brightnesses for millions of stars in the Large and Small Magellanic Clouds, two of the closest galaxies to Earth. Ludwig developed the first wide-field UV catalog of the Magellanic Clouds and used UV photometry to detect systems with unusual UV emissions, signaling the possible presence of a stripped star.

They carried out a pilot study of 25 objects, obtaining optical spectroscopy with the Magellan Telescopes at Las Campanas Observatory between 2018 and 2022. They used these observations to demonstrate that the stars were hot, small, hydrogen-poor, and in binary systemsall consistent with their model predictions.

Currently, the researchers are continuing to study the stars identified in this paper and expanding their search to find more. They will be looking both within nearby galaxies and within our own Milky Way with approved programs on the Hubble Space Telescope, the Chandra X-Ray Telescope, the Magellan Telescopes, and the Anglo-Australian Telescope. As part of this publication, all theoretical models and data used to identify these stars have been made public and available to other scientists.

Collaborating institutions include the University of Toronto, the Observatories of the Carnegie Institution for Science, Max-Planck-Institut fr Astrophysik, Anton Pannekoek Institute for Astronomy, Dunlap Institute for Astronomy & Astrophysics, and Steward Observatory.

About the Dunlap Institute for Astronomy & Astrophysics

The Dunlap Institute for Astronomy & Astrophysics in the Faculty of Arts & Science at the University of Toronto is an endowed research institute with over 80 faculty, postdocs, students, and staff, dedicated to innovative technology, groundbreaking research, world-class training, and public engagement.

The research themes of its faculty and Dunlap Fellows span the Universe and include: optical, infrared and radio instrumentation, Dark Energy, large-scale structure, the Cosmic Microwave Background, the interstellar medium, galaxy evolution, cosmic magnetism and time-domain science.

The Dunlap Institute, the David A. Dunlap Department of Astronomy & Astrophysics, and other researchers across the University of Torontos three campuses together comprise the leading concentration of astronomers in Canada, at the leading research university in the country.

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Observational study

Not applicable

An observed population of intermediate mass helium stars that have been stripped in binaries

14-Dec-2023

The authors declare no conflict of interest.

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Astronomers discover first population of binary stripped stars - EurekAlert

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The strange phenomenon, which rarely appears above red sprites that dance over thunderstorms, reveals the presence metals in our atmosphere.

A red sprite appears above a thunderstorm visible from Maunakea in Hawaii. Also present is a blue and white jet, which flows down from the sprite and into the thundercloud. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/A. Smith

High up in the atmosphere, near the boundary of space, a dazzling, fleeting flash of red sometimes briefly appears above a thunderstorm before evaporating away.

These events, which occur far above when lightning strikes in the lower atmosphere, are called sprites. They fall under the umbrella of transient luminous events (TLEs) and only in the past few decades have we been able to observe them. And only since 2019 have we discovered that one out of 100 sprites producers an even more elusive, even more mysterious phenomenon: a greenish glow called a ghost. A new study published today in Nature Communications hints at when and why sprites might form these ghosts.

Read more: Sprites and elves found frolicking in Jupiters skies

TLEs are generated as a result of the intense electrical activity associated with lightning discharges, says study lead author Mara Passas-Varo of the Consejo Superior de Investigaciones Cientficas Instituto de Astrofsica de Andaluca in Granada, Spain. The specific type of TLE that forms depends on factors such as the altitude, the type of lightning discharge, and the characteristics of the atmospheric layers involved.

Not all TLEs are sprites. There are a cornucopia of these events, all a little bit different, and typically named after mythological creatures like elves, gnomes, pixies, and trolls. Its an area of atmospheric research thats still relatively new, and always in need of more data.

Since June 2019, Passas-Varo and her team have been observing lightning storms with an instrument called the Granada Sprite Spectrograph and Polarimeter, or GRASSP. GRASSP examines the light from sprites to determine what elements or molecules in the atmosphere are responsible for the emission. With it, they have recorded at least 2,000 sprites, generating one of the biggest databases of these events in their efforts to look specifically for the ghosts they sometimes create.

To record these rare phenomena, you have to aim the spectrograph at the altitude where the ghost is likely to appear, which becomes a matter of luck combined with expertise,

Passas-Varo says. In almost four years of recording, from more than 2,000 spectra, we have just 42 spectra from the top of a sprite. And from those, she says, only one, which occurred Sept. 21, 2019, was a strong enough signal to study.

Sprites and ghosts occur in the mesosphere, the layer of Earths atmosphere that sits above the stratosphere and extends from about 31 to 53 miles (50 to 85 kilometers) above the ground. The mesosphere is extremely thin, with only about 1/100,000 the atmospheric pressure at sea level. And one of the biggest mysteries surrounding ghosts is what, chemically, causes them. Certain elements likely become charged in the atmosphere during these events, and the researchers wanted to know which ones.

The answer was quite surprising: Its metals, like iron and nickel, and theyre located higher in the atmosphere than the study authors expected to find them.

Thats because while the atmospheric layers above the mesosphere are known to have bits of iron and nickel, likely deposited by meteors as they streak through, these metals had never before been detected in the mesosphere. Passas-Varo says its likely that gravity waves (think ocean-like waves but through the air, not to be confused with gravitational waves) could push the microscopic bits of iron and nickel down to these lower altitudes, where they generate ghosts under the right circumstances.

Now that some ghosts have been caught, Passas-Varo and her colleagues are hatching ideas on how to capture more of them.

The first is to add a green filter to some of their field cameras used to detect lightning. This could help them cross-reference the events with data from the Mesospheric Airglow/Aerosol Tomography and Spectroscopy satellite, which looks for gravity waves in Earths atmosphere. In doing so, they can see whether gravity waves play a role in whether a sprite produces a ghost.

Theyre also considering building a new, GRAASP-like instrument with a different type of lens and slit at the front to take readings. A cylindrical lens funneling light into a vertical slit, Passas-Varo says, will make it easier to image ghosts for further study.

Theres still a lot of work to do, she says. But this study lays the groundwork for future atmospheric ghostbusting and might even unearth some new atmospheric spirits along the way.

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Astronomers capture a green ghost in our atmosphere - Astronomy Magazine

The winter solstice marks the beginning of the winter season in the Northern Hemisphere. Credit: Foundry Co (Pixabay)

Friday, December 15 Asteroid 4 Vesta is skimming just south of several open star clusters near Geminis feet this evening. Just days from reaching opposition later this week, Vesta is currently an easy binocular object at magnitude 6.5. And its also in an easy-to-locate spot, just 12 northwest of Chi2 (2) Orionis.

Once youve found Vesta, all you have to do is slide your field of view some 4 north to land on M35, glowing at magnitude 5.3. This open cluster is roughly 100 million years old and spans about half a degree, making it look best at lower magnifications and with wide-field eyepieces. Higher powers might show a smaller, more concentrated clump of stars to M35s southwest thats magnitude 8.6 NGC 2158, another open cluster. And some 1.6 farther southwest is NGC 2129, a third open cluster that shines at magnitude 6.7. Even if you cant spot NGC 2158, youll likely see the brighter, slightly larger NGC 2129.

Sunrise: 7:15 A.M. Sunset: 4:35 P.M. Moonrise: 10:07 A.M. Moonset: 7:27 P.M. Moon Phase: Waxing crescent (10%) *Times for sunrise, sunset, moonrise, and moonset are given in local time from 40 N 90 W. The Moons illumination is given at 12 P.M. local time from the same location.

Saturday, December 16 The Moon reaches perigee, the closest point to Earth in its orbit, at 1:53 P.M. EST. At that time, Luna sits 228,603 miles (367,901 kilometers) away.

Speaking of the Moon, its light will soon start interfering with observations of Comet 62P/Tsuchinshan 1, so tonight is your best chance to get in a good look for a while. Rising in Leo an hour or two before local midnight, the comet has recently been recorded at magnitude 9, reachable with any telescope under a reasonably dark sky. The best time to observe Tsuchinshan 1 is in the last few hours of darkness before sunrise, when it is highest in the sky. Tsuchinshan 1 currently sits in the midst of the Lions body. To find it, first locate Leos brightest star, Regulus, and scan about 8.5 northeast.

The comet is not far from several great galaxies to observe: NGC 3384, M105, M95, and M96, as well as the Leo Trio of galaxies near the Lions hindquarters. Check out the chart above for the locations of these galaxies relative to Tsuchinshan 1 today.

After this, the Moon will interfere with observing, though deep photography may carry you through for a few more days. And astroimagers may especially want to try for some shots on the 28th, when Tsuchinshan 1 reaches the Leo Trio.

Sunrise: 7:15 A.M. Sunset: 4:36 P.M. Moonrise: 10:47 A.M. Moonset: 8:44 P.M. Moon Phase: Waxing crescent (18%)

Sunday, December 17 The Moon passes 2 south of magnitude 0.9 Saturn at 5 P.M. EST. Its already growing dark on the East Coast, allowing observers there to easily spot the waxing crescent Moon hanging directly beneath the planet in the south. To the pairs lower left, the bright star Fomalhaut in Piscis Austrinus may also begin to peek out from the twilight.

In time zones farther west, observers will see the Moon slowly crawl to Saturns left. Its a great illustration of the way nearer objects appear to move faster against the background sky than those farther away. Luna now sits some 229,056 miles (368,630 km) away; Saturn is 938,850,000 miles (1.5 billion km) from Earth.

By 9 P.M. CST (after the planet has set in the Eastern time zone), the Moon and Saturn sit side by side, now nearly 3 apart. They are low in the west for Midwestern observers.

Through a telescope, Saturns spectacular rings are visible, about 37 from end to end. The planets brightest moon, Titan, sits far to the east, some 2.5 from Saturns center. Several fainter moons stand on the other side of the planet: Dione lies just south of the rings on Saturns western side, while Tethys (closer) and Rhea (farther) are roughly in line with the planets equator farther west. Enceladus possibly too faint for many scopes sits just north of the rings on Saturns western side.

Sunrise: 7:16 A.M. Sunset: 4:36 P.M. Moonrise: 11:20 A.M. Moonset: 10:00 P.M. Moon Phase: Waxing crescent (28%)

Monday, December 18 Canis Major is one of two loyal hunting dogs who follow Orion up into the sky on winter evenings. By about 9:30 P.M. local time, this constellations brightest star, Sirius, stands 15 above the southeastern horizon. This luminary is the brightest star in the sky, and tonight were using it to guide our way toward a colorful target: the open clusterM41.

From Sirius, you need only drop your gaze 4 due south to land on this sparkling star cluster. Under even modest magnifications of 14x, the glittering points of light will begin to show off contrasting colors of blue, orange, yellow, and red. A stars color is generally an indicator of its temperature, as hotter stars appear blue or white, while cooler stars trend toward orange and red. M41 spans roughly 40 and contains about 100 stars, including a bright red giant near the clusters center that shines at 7th magnitude. In truth, this single, aging luminary is some 700 times brighter than our Sun.

Sunrise: 7:17 A.M. Sunset: 4:36 P.M. Moonrise: 11:48 A.M. Moonset: 11:13 P.M. Moon Phase: Waxing crescent (39%)

Tuesday, December 19 The Moon passes 1.3 south of Neptune at 8 A.M. EST; our satellite then reaches First Quarter at 1:39 P.M. EST.

An hour after sunset, the Moon has moved east of Neptune and the two stand high in the south. The distant ice giant is not visible to the naked eye and you will need binoculars or a telescope to spot its magnitude 7.8 glow. The planet lies about 5 due south of Lambda () Piscium, the southeasternmost star in the Circlet of Pisces.

Shift your gaze back up to Lambda, then look 2 to its northeast. You should land on a deep red magnitude 5 star. This is TX Piscium, also cataloged as 19 Piscium and the easternmost star in the Circlet. TX is a variable star known as a carbon star; these are some of the reddest stars in the sky, as carbon in their atmospheres scatters away any blue light they emit.

Sunrise: 7:17 A.M. Sunset: 4:37 P.M. Moonrise: 12:12 P.M. Moonset: Moon Phase: First Quarter

Wednesday, December 20 Jupiters moon Io makes an easy-to-watch transit of the planets face tonight, starting just a few minutes before 10:30 P.M. EST. The gas giant shines brightly in Aries the Ram, making it simple to locate and zoom in on with a telescope to watch.

Io is followed eventually by its shadow, which appears over the cloud tops of the planets eastern limb an hour later (11:30 P.M. EST), just as Io is halfway through its east-to-west journey. The moon finishes its transit just after 12:30 A.M. EST on the 21st (note this is still late on the 20th in time zones farther west), its shadow now roughly centered on the planets prime meridian. Io continues to pull away to the west and the shadow finally disappears around 1:40 A.M. EST (early on the 21st for Eastern and Central time zones; still the 20th for the western half of the country).

You can also see the other three Galilean moons tonight: Ganymede lies alone far to the east, with Europa closer to Jupiters western limb than Callisto on the other side. Plus, Jupiters Great Red Spot makes an appearance, crossing the planets center around 11 P.M. EST. In fact, the storm and Io are roughly moving together, a real treat to see as the hours pass.

Sunrise: 7:18 A.M. Sunset: 4:37 P.M. Moonrise: 12:36 P.M. Moonset: 12:24 A.M. Moon Phase: Waxing gibbous (61%)

Thursday, December 21 Asteroid 4 Vesta reaches opposition today at 2 P.M. EST. The main-belt world is visible all night, roughly from sunset to sunrise, in the constellation Orion.

The winter solstice occurs at 10:27 P.M. EST, bringing the official start of winter to the Northern Hemisphere (and the start of summer in the Southern Hemisphere). On this day, the Sun takes its most southerly path through Northern Hemisphere skies (and, accordingly, its most northerly path through Southern Hemisphere skies).

Many people also think that the winter solstice is the shortest day and longest night in the Northern Hemisphere, but thats not quite true. You can read why, as well as discover some other cool things about the winter solstice, in a past article from former Astronomy senior editor Rich Talcott (now a frequent contributing editor).

In addition to the solstice, today is special for another reason: We are seeing the waxing Moon fully face-on tonight. What does that mean? Over the course of a month, the Moon can appear to nod up and down as it orbits, an effect called libration. Sometimes we see more of its north pole, and sometimes more of its south pole. Today, we are looking directly toward the center of our satellite. In previous days, we were getting a peek at more southerly locales, but now we will start to view more of the northern regions as Luna begins to tilt its face back down, like a person nodding their head down to tuck their chin.

Sunrise: 7:18 A.M. Sunset: 4:38 P.M. Moonrise: 1:00 P.M. Moonset: 1:36 A.M. Moon Phase: Waxing gibbous (72%)

Friday, December 22 The Moon passes 3 north of Jupiter at 9 A.M. EST. Well catch them in the evening sky in next weeks column, so stay tuned.

In other planetary news, Mercury reaches inferior conjunction with the Sun, rendering it invisible to us for now, at 2 P.M. EST. Well start to see it again next month, after the new year.

Today, lets home in on main-belt asteroid 9 Metis, which reaches opposition at 6 P.M. EST. The magnitude 8.4 asteroid lies in far southwestern Gemini, close to that constellations border with Taurus. This region rises shortly after sunset; give it a few hours to climb out of the horizon haze and by 7 or 8 P.M. local time, it should be ripe for observation.

If you have trouble recognizing Gemini by eye, Taurus V-shaped face and Orions three-star Belt are easy signposts. Gemini lies left of Orion and below Taurus. Metis is near the Twins feet, close to the two bright stars Elnath and Alheka, which mark the tips of Taurus horns. But the easiest way to find Metis is to first center on 3rd-magnitude Propus (Eta [] Geminornum). About 2.3 northwest of this star is the 5th-magnitude open cluster M35, which we visited earlier this week.

From M35, continue northwest for 3.3 to arrive at Metis. The asteroid lies just 20 southeast of a 6th-magnitude field star tonight, helping to aid in its identification. If you lock onto that star, you may notice Metis shift ever-so-slowly westward as the hours pass, though the motion is extremely subtle try taking an image at the beginning and at the end of the night and compare the two.

Metis is one of the larger and more massive asteroids in the main belt. Its about 105 miles (170 km) across and is likely a remnant from a much larger parent body that was broken up in a collision.

Sunrise: 7:19 A.M. Sunset: 4:38 P.M. Moonrise: 1:27 P.M. Moonset: 2:46 A.M. Moon Phase: Waxing gibbous (81%)

Sky This Week is brought to you in part by Celestron.

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The Sky This Week from December 15 to 22: Winter begins - Astronomy Magazine

Orion's "selfie" of itself and the Moon. Orion will carry astronauts on several space missions.

Here is a list to help you keep track of many current and scheduled space missions. Weve gathered a selected group of high-profiles ones, listed them below, and linked to official sites where you can get the latest updates and launch dates.

Well update this article periodically when new missions are announced.

Here is the list of missions in alphabetical order:

Mission: This Mars orbiter was launched with the intention of detecting water and ice on the planet, as well as studying its composition.

Agency: NASA

Launch date: April 7, 2001

Updates available here.

Mission: The mission, which name means Sun in Sanskrit, was launched to conduct a comprehensive study of the Sun, sitting at the Lagrange point L1 between the Sun and Earth.

Agency: Indian Space Research Organisation (ISRO)

Launch date: Sept. 2, 2023

Updates available here.

Mission: The orbiter mission was designed to study weather patterns and atmospheric conditions, as well as search for the possibility of lighting and active volcanoes.

Agency: JAXA

Launch date: May 21, 2010

Updates available here.

Mission: This mission will be placed at Lagrange point L2 to study thousands of exoplanets, ranging from rocky planets to gas giants in visible and infrared wavelengths.

Agency: ESA/Ariel Mission Consortium

Expected launch: 2029

Updates available here.

Mission: The mission, featuring a crew of four astronauts, will perform a series of flights maneuvers as well as tests in space to ensure the systems are appropriate to take the Artemis III crew to the Moon.

Agency: NASA

Expected launch: November 2024

Updates available here.

Mission: The mission is expected to take four astronauts to the lunar South Pole for the first time to explore, collect geologic samples, and take images of the regions unique features.

Agency: NASA

Expected launch: 2025

Updates available here.

Mission: BepiColombo, comprised of two orbiters, was designed to study composition, geophysics, atmosphere, magnetosphere and history of Mercury.

Agency: Japan Aerospace Exploration Agency (JAXA)/ESA

Launch date: Oct. 18, 2018

Updates available here.

Mission: With its lander, Vikram, and rover, Pragyan, this mission landed safely on the Moons south pole.

Agency: ISRO

Launch date: July 14, 2023

Updates available here.

Mission: Made up of three spacecrafts, the mission will wait at the Lagrange point L2 before separating to gather 3D images of Comet Interceptor as well as its nucleus and composition.

Agency: ESA

Expected launch: 2029

Updates available here.

Mission: Deep Atmosphere Venus Investigation of Noble Gases, Chemistry, And Imaging (DAVINCI) probe would explore the atmosphere of Venus.

Agency: NASA

Expected Launch: June 2029

Updates available here.

Mission: This dual-quadcopter would explore a variety of locations on Saturns moon, Titan, for possible habitability.

Agency: NASA

Expected launch: 2027

Updates available here.

Mission: The Emirates Mars Mission, named Hope Probe will gather a picture of the Martian atmosphere and its layers. It will also look at the planets loss of hydrogen and oxygen gases into space over the span of one Martian year.

Agency: UAE Space Agency

Launch Date: July 20, 2020

Updates available here.

Mission: The mission is to investigate Venus from its inner core to its upper atmosphere, characterizing the interaction between its atmosphere, surface, and interior.

Agency: ESA

Expected launch: early 2030s

Updates available here.

Mission: The Escape and Plasma Acceleration and Dynamics Explorers (EscaPADE) are a dual-spacecraft mission to study the transfer of solar wind energy and momentum.

Agency: NASA

Expected launch: 2024

Updates available here.

Mission: Europa is expected to explore the moon of Jupiter with the same name during a series of flybys. Its objectives include studying the moons ice shell and ocean, as well as its composition and geology.

Agency: NASA

Expected Launch: Oct. 10, 2024

Updates available here.

Mission: The spacecraft will perform a survey of the target asteroid, Dimorphos and the orbiting moonlet Didymos, after the NASA Dart Mission conducted its asteroid deflection on Sept. 26, 2022.

Agency: ESA

Expected launch: October 2024

Updates available here.

Mission: Jupiter Icy Moons Explorer, or JUICE, was dispatched to study the composition of Jupiter along with its three large, water-logged moons Ganymede, Callisto and Europa.

Agency: European Space Agency (ESA)

Launch date: April 14, 2023

Updates available here.

Mission: Understand origin and evolution of Jupiter and its four largest moons, look for solid planetary core, map magnetic field, measure water and ammonia in deep atmosphere, observe auroras.

Agency: NASA

Launch date: Aug. 5, 2011

Updates available here.

Mission: Known as Danuri, this is a lunar probe expected to carry out the mission of lunar observation while flying at an altitude of 100km over the Moon.

Agency: Korea Aerospace Research Institute (KARI)

Launch date: Aug. 5, 2022

Updates available here.

Mission: Lucy was launched to view trojan asteroids surrounding Jupiter.

Agency: NASA

Launch date: Oct. 16, 2021

Updates available here.

Related: Surprise! NASAs Lucy mission uncovered an asteroid moon that is actually two in one

Mission: The mission began as a way to target areas for future robotic and human exploration on the Moon. After two years, it focused more on studying temperature maps and other scientific data on Earths satellite.

Agency: NASA

Launch date: June 18, 2009

Updates available here.

Mission: The orbiters goal was to complete a map of the Mars atmospheric composition and water on its surface, as well as learning more about one of its moons, Phobos.

Agency: ESA

Launch date: June 2, 2003

Updates available here.

Mission: The mission involves Mars Perseverance Rover working with a lander and orbiter to retrieve samples from Mars and deliver them to Earth.

Agency: NASA/ESA

Expected launch: 2027 (orbiter) and 2028 lander

Updates available here.

Mission: Mars Atmosphere and Volatile Evolution or MAVEN, studies the upper atmosphere of Mars as well as its interaction with the Sun and solar winds.

Agency: NASA

Launch date: Nov. 18, 2013

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Space missions: Present and future voyages | Astronomy.com - Astronomy Magazine