BLOGS

An illustration of a black hole and its event horizon. (Image credit: Nicholas Forder/Future Publishing)

Topics: Astronomy, Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

"Small" black holes are estimated to make up 1% of the universe's matter.

Scientists have estimated the number of "small" black holes in the universe. And no surprise: It's a lot.

This number might seem impossible to calculate; after all, spotting black holes is not exactly the simplest task. Because there are as pitch-black as the space they lurk in, the light swallowing cosmic goliaths can be detected only under the most extraordinary circumstances — like when they're bending the light around them, snacking on the unfortunate gases and stars that stray too close, or spiraling toward enormous collisions that unleash gravitational waves.

But that hasn't stopped scientists from finding some ingenious ways to guess the number. Using a new method, outlined Jan. 12 in The Astrophysical Journal, a team of astrophysicists has produced a fresh estimate for the number of stellar-mass black holes — those with masses 5 to 10 times that of the sun — in the universe.

And it's astonishing: 40,000,000,000,000,000,000, or 40 quintillions, stellar-mass black holes populate the observable universe, making up approximately 1% of all normal matter, according to the new estimate.

So how did the scientists arrive at that number? By tracking the evolution of stars in our universe they estimated how often the stars — either on their own or paired into binary systems — would transform into black holes, said first author Alex Sicilia, an astrophysicist at the International School of Advanced Studies (SISSA) in Trieste, Italy.

40 quintillion stellar-mass black holes are lurking in the universe, a new study finds, Ben Turner, Space.com

Image: Artist’s impression of a Dyson sphere under construction. Credit: Steve Bowers.

Topics: Astronomy, Astrophysics, Dyson Sphere, SETI

Although the so-called Dysonian SETI has been much in the air in recent times, its origins date back to the birth of SETI itself. It was in 1960 – the same year that Frank Drake used the National Radio Astronomy Observatory in Green Bank, West Virginia to study Epsilon Eridani and Tau Ceti – that Freeman Dyson proposed the Dyson sphere. In fiction, Olaf Stapledon had considered such structures in his novel Star Maker in 1937. As Macy Huston and Jason Wright (both at Penn State) remind us in a recent paper, Dyson’s idea of energy-gathering structures around an entire star evolved toward numerous satellites around the star rather than a (likely unstable) single spherical shell.

We can’t put the brakes on what a highly advanced technological civilization might do, so both solid sphere and ‘swarm’ models can be searched for, and indeed have been, for in SETI terms we’re looking for infrared waste heat. And if we stick with Dyson (often a good idea!), we would be looking for structures orbiting in a zone where temperatures would range in the 200-300 K range, which translates into searching at about 10 microns, the wavelength of choice. But Huston and Wright introduce a new factor, the irradiation from the interior of the sphere onto the surface of the star.

This is intriguing because it extends our notions of Dyson spheres well beyond the habitable zone as we consider just what an advanced civilization might do with them. It also offers up the possibility of new observables. So just how does such a Dyson sphere return light back to a star, affecting its structure and evolution? If we can determine that, we will have a better way to predict these potential observables. As we adjust the variables in the model, we can also ponder the purposes of such engineering.

Think of irradiation as Dyson shell ‘feedback.’ We immediately run into the interesting fact that adding energy to a star causes it to expand and cool. The authors explain this by noting that total stellar energy is a sum of thermal and gravitational energies. Let’s go straight to the paper on this. In the clip below, E_* refers to the star’s total energy, with E_therm being thermal energy:

When energy is added to a star (E_∗ increases), gravitational energy increases and thermal energy decreases, so we see the star expand and cool both overall (because E_therm is lower) and on its surface (because being larger at the same or a lower luminosity its effective temperature must drop). A larger star should also result in less pressure on a cooler core, so we also expect its luminosity to decrease.

Dyson Sphere ‘Feedback’: A Clue to New Observables? Paul Gilster, Centauri Dreams

Evolutionary and Observational Consequences of Dyson Sphere Feedback, Macy Huston, Jason Wright, Astrophysical Journal

Artist’s impression of an exomoon (left) orbiting a giant planet around a distant star. Credit: Helena Valenzuela Widerström

Topics: Astronomy, Astrophysics, Exomoon, Exoplanets

And then there were two—maybe. Astronomers say they have found a second plausible candidate for a moon beyond our solar system, an exomoon, orbiting a world nearly 6,000 light-years from Earth. Called Kepler-1708 b-i, the moon appears to be a gas-dominated object, slightly smaller than Neptune, orbiting a Jupiter-sized planet around a sunlike star—an unusual but not wholly unprecedented planet-moon configuration. The findings appear in Nature Astronomy. Confirming or refuting the result may not be immediately possible, but given the expected abundance of moons in our galaxy and beyond, it could further herald the tentative beginnings of an exciting new era of extrasolar astronomy—one focused not on alien planets but on the natural satellites that orbit them and the possibilities of life therein.

There are more than 200 moons in our solar system, and they have an impressive array of variations. Saturn’s moon Titan possesses a thick atmosphere and frigid hydrocarbon seas on its surface, possibly an analog of early Earth. Icy moons such as Jupiter’s Europa are frozen balls that hide subsurface oceans, and they may be prime habitats for life to arise. Others still, such as our own moon, are apparently barren wastelands but could have water ice in their shadowed craters and maze-like networks of tunnels running underground. An important shared trait among these worlds, however, is their mere existence: six of the eight major planets of our solar system have moons. Logic would suggest the same should be true elsewhere. “Moons are common,” says Jessie Christiansen of the California Institute of Technology. “In our solar system, almost everything has a moon. I am very confident that moons are everywhere in the galaxy.”

Astronomers Have Found Another Possible ‘Exomoon’ beyond Our Solar System, Jonathan O'Callaghan, Scientific American

Credit: Pete Saloutos/Getty Images

Topics: Astronomy, Astrophysics, Comets, Philosophy, Science Fiction

On a recent morning, in Lower Manhattan, 20 scientists, including me, gathered for a private screening of the new film Don’t Look Up, followed by lunch with the film’s director, Adam McKay.

The film’s plot is simple. An astronomy graduate student, Kate Dibiasky (Jennifer Lawrence), and her professor, Randall Mindy (Leonardo DiCaprio), discover a new comet and realize that it will strike the Earth in six months. It is about nine kilometers across, like the one that wiped out the dinosaurs 66 million years ago. The astronomers try to alert the president, played by Meryl Streep, to their impending doom.

“Let’s just sit tight and assess,” she says, and an outrageous, but believable comedy ensues, in which the astronomers wrangle an article in a major newspaper and are mocked on morning TV, with one giddy host asking about aliens and hoping that the comet will kill his ex-spouse.

At last, mainstream Hollywood is taking on the gargantuan task of combatting the rampant denial of scientific research and facts. Funny, yet deadly serious, Don’t Look Up is one of the most important recent contributions to popularizing science. It has the appeal, through an all-star cast and wicked comedy, to reach audiences that have different or fewer experiences with science.

Don’t Look Up isn’t a movie about climate change, but one about planetary defense from errant rocks in space. It handles that real and serious issue effectively and accurately. The true power of this film, though, is in its ferocious, unrelenting lampooning of science deniers.

After the screening, in that basement theater in SoHo, McKay said: “This film is for you, the scientists. We want you to know that some of us do hear you and do want to help fight science denialism.”

Hollywood Can Take On Science Denial: Don’t Look Up Is a Great Example, Rebecca Oppenheimer, curator, and professor of astrophysics at the American Museum of Natural History/Scientific American

Topics: Astrobiology, Astronomy, Astrophysics, Carl Sagan, James Webb Space Telescope, SETI

The relief was as deep as the stakes were high. At 7:20 A.M. (ET), the rocket carrying the largest, most ambitious space telescope in history cleared the launchpad in French Guiana, and the members of mission control at the Space Telescope Science Institute in Baltimore roared their elation.

The suspense was not quite over. Half an hour postlaunch, the telescope still needed to decouple from its host rocket, after which it had to deploy solar panels to partly power its journey. Only after that first deployment proved successful, said a NASA spokesperson in a statement to Scientific American, would “we know we have a mission.”

Astronomers have more riding on the rocket than the James Webb Space Telescope (JWST). Also at risk is the viability of NASA’s vast space-science portfolio, if not the future of astronomy itself. As the successor to the Hubble Space Telescope (HST), JWST is one of those once-in-a-generation scientific projects that can strain the patience of government benefactors, as well as the responsible agency’s credibility, but also define a field for decades to come—and possibly redefine it forever.

The telescope that would become JWST was already under discussion even before HST launched in April 1990. By orbiting Earth, HST would have a line of sight free of the optical distortions endemic to our planet’s atmosphere. It would therefore be able to see farther across the universe (and, given that the speed of light is finite, farther back in time) than any terrestrial telescope.

The James Webb Space Telescope Has Launched: Now Comes the Hard Part, Richard Panek, Scientific American

Artist's impression of a neutron-star merger (Courtesy: NASA)

Topics: Astronomy, Astrophysics, Chemistry, Materials Science, Neutron Stars

The amounts of heavy elements such as gold created when black holes merge with neutron stars have been calculated and compared with the amounts expected when pairs of neutron stars merge. The calculations were done by Hsin-Yu Chen and Salvatore Vitale at the Massachusetts Institute of Technology and Francois Foucart at the University of New Hampshire using advanced simulations and gravitational-wave observations made by the LIGO–Virgo collaboration. Their results suggest that merging pairs of neutron stars are likely to be responsible for more heavy elements in the universe than mergers of black holes with neutron stars.

Today, astrophysicists have an incomplete understanding of how elements heavier than iron are made. In this nucleosynthesis process, lighter nuclei must be able to capture neutrons from their surroundings. Astrophysicists believe this can happen in two ways, each producing about half of the heavy elements in the universe. These are the slow process (s-process) that occurs in large stars and the rapid process (r-process), which is believed to occur in extreme conditions such as the explosion of a star in a supernova. However, exactly where the r-process can take place is hotly debated.

One event that could support the r-process is the merger of a pair of neutron stars, which can result in a huge explosion called a kilonova. Indeed, such an event was seen by LIGO–Virgo in 2017, and simultaneous observations using light-based telescopes suggest that heavy elements were created in that event.

Merging neutron stars create more gold than collisions involving black holes, Sam Jarman, Physics World

The pulsar J0030 appears to have two to three hotspots on its southern hemisphere only – finding astronomers didn’t expect.
NASA’s Goddard Space Flight Center/CI Lab (animation on the page link below)

Topics: Astronomy, Astrophysics, NASA, Neutron Stars, Pulsars

NASA’s NICER instrument reveals that neutron stars are not as simple as we thought.

Pulsars are the lighthouses of the universe. These tiny, compact objects are neutron stars — the remnants of once-massive stars — that spin rapidly, beaming radiation into space. Now, for the first time, astronomers have mapped the surface of a 16-mile-wide pulsar in exquisite detail. The discovery calls into question astronomers’ textbook depiction of pulsar appearance and opens the door to learning more about these extreme objects.

The Neutron star Interior Composition Explorer, or NICER, searches for X-rays from extreme astronomical objects such as pulsars from its perch on the exterior of the International Space Station. Researchers used NICER to observe the pulsar J0030+0451, or J0030 for short, which is located 1,100 light-years away in the constellation Pisces, in a series of papers published in The Astrophysical Journal Letters. Two teams, one led by researchers at the University of Amsterdam and the other by researchers at the University of Maryland, used X-ray light from J0030 to map the pulsar’s surface and calculate its mass. Both teams arrived at a conclusion that was unexpected.

A New Picture

What the teams found presented a different picture: J0030 has two or three hotspots, all of which are located in the southern hemisphere. The researchers at the University of Amsterdam believe the pulsar has one small, circular spot and one thin, crescent-shaped spot spinning around its lower latitudes. The University of Maryland team discovered that the X-rays could be coming from two oval spots in the star’s southern hemisphere, as well as one cooler spot near the star’s south pole.

Neither result is the simple picture astronomers expected, indicating that the pulsar’s magnetic field, which causes the hotspots, is likely even more complex than originally assumed. While the result certainly leaves astronomers wondering, “It tells us NICER is on the right path to help us answer an enduring question in astrophysics: What form does matter take in the ultra-dense cores of neutron stars?” NICER science lead and study co-author Zaven Arzoumanian said in a press release.

Astronomers Map a Neutron Star’s Surface for the First Time, Ignat, I Love the Universe

Hot and humid The surface of a Hycean planet as interpreted by an artist. (Courtesy: Amanda Smith, University of Cambridge).

Topics: Astronomy, Astrophysics, Astrobiology, Exoplanets, Space Exploration

Hot, ocean-covered exoplanets with hydrogen-rich atmospheres could harbor life and may be more common than planets that are Earth-like in size, temperature, and atmospheric composition. According to astronomers at the University of Cambridge, UK, this newly defined class of exoplanets could boost the search for life elsewhere in the universe by broadening the search criteria and redefining which biosignatures are important.

Astronomers define the habitable or “Goldilocks” zone as the region where an exoplanet is neither too close nor too far from its host star to have liquid water on its surface – water being the perfect solvent for many forms of life. Previous studies of planetary habitability have focused primarily on searching for Earth-like exoplanets and evidence that they could harbor the kind of chemistry found in life on Earth. However, it has so far proven difficult to detect atmospheric signatures from Earth-like planets orbiting Sun-like stars.

Potentially habitable mini-Neptunes

Larger exoplanets are easier to detect than smaller, Earth-sized ones, and exoplanets around 1.6‒4 times bigger than the Earth, with masses of up to 15 Earth masses and temperatures that in some cases exceed 2000 K, are relatively common. These planets are known as mini-Neptune's as they are similar to the ice giant planets in our solar system.

Previous studies suggested that the high pressures and temperatures beneath these planets’ hydrogen-rich atmospheres were incompatible with life. However, based on their analysis of an exoplanet called K2-18b, exoplanet scientist Nikku Madhusudhan and colleagues at Cambridge say that life could, in fact, exist on a subset of mini-Neptunes that meet specific criteria.

This subset, which the researchers dub “Hycean” (hydrogen + ocean) planets, consists of planets that have radii up to 2.6 times larger than Earth’s and are capable of harboring vast oceans under atmospheres dominated by molecular hydrogen and water vapor. Such oceans could cover the whole planet and reach depths greater than the Earth’s oceans, and the researchers say that the conditions within them could be compatible with some forms of Earth-based microbial life. Hycean planets tidally locked with their host star could also exhibit habitable conditions on their permanent night side.

Astronomers define new class of potentially habitable ocean worlds, Chaneil James, Physics World

A global view of Ganymede, based on data gathered by NASA’s Voyager 1, Voyager 2, and Galileo spacecraft. Credit: USGS Astrogeology Science Center, Wheaton, NASA and JPL-Caltech

Topics: Astronomy, Astrophysics, NASA, Planetary Science, Space Exploration

Ganymede, get ready for your close-up.

No probe has gotten a good view of Jupiter’s largest moon since 2000 when NASA’s Galileo spacecraft swung past the strange world, which is the largest moon in the whole solar system. But on Monday (June 7),  at 1:35 p.m. EDT (1735 GMT), NASA’s Juno spacecraft will skim just 645 miles (1,038 kilometers) above Ganymede’s surface, gathering a host of observations as it does so.

“Juno carries a suite of sensitive instruments capable of seeing Ganymede in ways never before possible," principal investigator Scott Bolton, a space scientist at the Southwest Research Institute in San Antonio, said in a NASA statement. “By flying so close, we will bring the exploration of Ganymede into the 21st century.”

Ganymede is a fascinating world for scientists. Despite its status as a moon, it’s larger than the tiny planet Mercury and is the only moon to sport a magnetic field, a bubble of charged particles dubbed a magnetosphere. Until now, the only spacecraft to get a good look at Ganymede were NASA’s twin Voyager probes in 1979 and the Galileo spacecraft, which flew past the moon in 2000.

NASA’s Juno Set for Close Encounter with Jupiter’s Moon Ganymede, Meghan Bartels, SPACE.com, Scientific American

The first coronal mass ejection, or CME, observed by the Solar Orbiter Heliospheric Imager (SoloHI) appears as a sudden gust of white (the dense front from the CME) that expands into the solar wind. This video uses different images, created by subtracting the pixels of the previous image from the current image to highlight changes. The missing spot in the image on the far right is an overexposed area where light from the spacecraft solar array is reflected into SoloHI’s view. The little black and white boxes that blip into view are telemetry blocks – an artifact from compressing the image and sending it back down to Earth.
Credits: ESA & NASA/Solar Orbiter/SoloHI team/NRL

Topics: Astronomy, Astrophysics, ESA, Heliophysics, NASA

For the new Sun-watching spacecraft, the first solar eruption is always special.

On February 12, 2021, a little more than a year from its launch, the European Space Agency, and NASA’s Solar Orbiter caught sight of this coronal mass ejection or CME. This view is from the mission’s SoloHI instrument — short for Solar Orbiter Heliospheric Imager — which watches the solar wind, dust, and cosmic rays that fill the space between the Sun and the planets.

It's a brief, grainy view: Solar Orbiter’s remote sensing won’t enter full science mode until November. SoloHI used one of its four detectors at less than 15% of its normal cadence to reduce the amount of data acquired. Still, a keen eye can spot the sudden blast of particles, the CME, escaping the Sun, which is off-camera to the upper right. The CME starts about halfway through the video as a bright burst – the dense leading edge of the CME – and drifts off-screen to the left.

For SoloHI, catching this CME was a happy accident. At the time the eruption reached the spacecraft, Solar Orbiter had just passed behind the Sun from Earth’s perspective and was coming back around the other side. When the mission was being planned, the team wasn’t expecting to be able to record any data during that time.

A New Space Instrument Captures Its First Solar Eruption, Miles Hatfield, NASA

Topics: Astronomy, Astrophysics, Cosmology

Physicists have spent centuries grappling with an inconvenient truth about nature: Faced with three stars on a collision course, astronomers could measure their locations and velocities in nanometers and milliseconds and it wouldn’t be enough to predict the stars’ fates. 

But the cosmos frequently brings together trios of stars and black holes. If astrophysicists hope to fully understand regions where heavenly bodies mingle in throngs, they must confront the “three-body problem.” 

While the result of a single three-body event is unknowable, researchers are discovering how to predict the range of outcomes of large groups of three-body interactions. In recent years, various groups have figured out how to make statistical forecasts of hypothetical three-body matchups: For instance, if Earth tangled with Mars and Mercury thousands of times, how often would Mars get ejected? Now, a fresh perspective developed by physicist Barak Kol simplifies the probabilistic “three-body problem,” by looking at it from an abstract new perspective. The result achieves some of the most accurate predictions yet. 

Physicists Edge Closer to Taming the Three-Body Problem, Charlie Wood, Scientific American

Astronomers searched for candidate antimatter stars among nearly 6000 gamma-ray sources. After eliminating known objects and sources that lacked the spectral signature of an antistar, 14 possibles remained. (Courtesy: Simon Dupourqué/IRAP)

Topics: Astronomy, Astrophysics, Cosmology, High Energy Physics

Fourteen possible antimatter stars (“antistars”) have been flagged up by astronomers searching for the origin of puzzling amounts of antihelium nuclei detected coming from deep space by the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station.

Three astronomers at the University of Toulouse – Simon Dupourqué, Luigi Tibaldo, and Peter von Ballmoos – found the possible antistars in archive gamma-ray data from NASA’s Fermi Gamma-ray Space Telescope. While antistars are highly speculative, if they are real, then they may be revealed by their production of weak gamma-ray emission peaking at 70 MeV, when particles of normal matter from the interstellar medium fall onto them and are annihilated.

Antihelium-4 was created for the first time in 2011, in particle collisions at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory. At the time, scientists stated that if antihelium-4 were detected coming from space, then it would definitely have to come from the fusion process inside an antistar.

However, when it was announced in 2018 that AMS-02 had tentatively detected eight antihelium nuclei in cosmic rays – six of antihelium-3 and two of antihelium-4 – those unconfirmed detections were initially attributed to cosmic rays colliding with molecules in the interstellar medium and producing the antimatter in the process.

Subsequent analysis by scientists including Vivian Poulin, now at the University of Montpellier, cast doubt on the cosmic-ray origin since the greater the number of nucleons (protons and neutrons) that an antimatter nucleus has, the more difficult it is to form from cosmic ray collisions. Poulin’s group calculated that antihelium-3 is created by cosmic rays at a rate 50 times less than that detected by the AMS, while antihelium-4 is formed at a rate 10⁵ times less.

The mystery of matter and antimatter

The focus has therefore turned back to what at first may seem an improbable explanation – stars made purely from antimatter. According to theory, matter and antimatter should have been created in equal amounts in the Big Bang, and subsequently, all annihilated leaving a universe full of radiation and no matter. Yet since we live in a matter-dominated universe, more matter than antimatter must have been created in the Big Bang – a mystery that physicists have grappled with for decades.

“Most scientists have been persuaded for decades now that the universe is essentially free of antimatter apart from small traces produced in collisions of normal matter,” says Tibaldo.

The possible existence of antistars threatens to turn this on its head. “The definitive discovery of antihelium would be absolutely fundamental,” says Dupourqué.

Are antimatter stars firing bullets of antihelium at Earth? Physics World, published in Physical Review D

Topics: Astrobiology, Astronomy, Cosmology, SETI

I would extend his theme to cover something that comes naturally to us all, which I’ll call Pseudo-exceptionalism—the unearned conviction that we are exceptional, superior to others because we were born...us.

We simply assume that we’re kinder, more honest, more realistic, more wholesome than those around us. After all, we’re married to ourselves for life, so we make accommodations: We cut ourselves slack. We’re fast to forgive ourselves. When challenged, we’re much better at making our case than our opponent’s. We spot injustices to ourselves far faster than we spot our injustices to others.</em>

Why Some People (Maybe Even Us) Think They're So Special
… and what to do about it. Jeremy E. Sherman Ph.D., MPP, Psychology Today

It is presumptuous to assume that we are worthy of special attention from advanced species in the Milky Way. We may be a phenomenon as uninteresting to them as ants are to us; after all, when we’re walking down the sidewalk we rarely if ever examine every ant along our path.

Our sun formed at the tail end of the star formation history of the universe. Most stars are billions of years older than ours. So much older, in fact, that many sunlike stars have already consumed their nuclear fuel and cooled off to a compact Earth-size remnant known as a white dwarf. We also learned recently that of order half of all sunlike stars host an Earth-size planet in their habitable zone, allowing for liquid water and for the chemistry of life.

Since the dice of life were rolled in billions of other locations within the Milky Way under similar conditions to those on Earth, life as we know it is likely common. If that is indeed the case, some intelligent species may well be billions of years ahead of us in their technological development. When weighing the risks involved in interactions with less-developed cultures such as ours, these advanced civilizations may choose to refrain from contact. The silence implied by Fermi's paradox (“Where is everybody?”) may mean that we are not the most attention-worthy cookies in the jar.

Why Do We Assume Extraterrestrials Might Want to Visit Us? Avi Loeb, Scientific American

Topics: Astrobiology, Astronomy, Astrophysics, SETI

Cultural references: The post title refers to NC A&T Alumni, and Civil Rights icon Reverend Jesse Jackson's appearance on Saturday Night Live, and the Wow! signal. Personal note: This signal appeared on the same day my granddaughter was born.

<p>On April 29, 2019, the Parkes Radio Telescope in Australia began listing to the radio signals from the Sun’s nearest neighbor, Proxima Centauri, just over 4 lightyears away. The telescope was looking for evidence of solar flares and so listened for 30 minutes before retraining on a distant quasar to recalibrate and then pointing back.

In total, the telescope gathered 26 hours of data. But when astronomers analyzed it in more detail, they noticed something odd — a single pure tone at a frequency of 982.02 MHz that appeared five times in the data.

The signal was first reported last year in The Guardian, a British newspaper. The article raised the possibility that the signal may be evidence of an advanced civilization on Proxima Centauri, a red dwarf star that is known to have an Earth-sized planet orbiting in its habitable zone.

But researchers have consistently played down this possibility saying that, at the very least, the signal must be observed again before any conclusions can be drawn. Indeed, the signal has not been seen again, despite various searches.

Now Amir Siraj and Abraham Loeb from Harvard University in Cambridge, Massachusetts, have calculated the likelihood that the signal came from a Proxima Centauri-based civilization, even without another observation. They say the odds are so low as to effectively rule out the possibility — provided the assumptions they make in their calculations are valid.</p>

Why The Recent Signal That Appeared to Come From Proxima Centauri Almost Certainly Didn't, Physics arXiv Blog, Discovery Magazine

The stone circle of Nabta Playa marks the summer solstice, a time that coincided with the arrival of monsoon rains in the Sahara Desert thousands of years ago. (Credit: Wikimedia Commons)

Topics: African Studies, Astronomy, Astrophysics, Diversity in Science

For thousands of years, ancient societies all around the world erected massive stone circles, aligning them with the sun and stars to mark the seasons. These early calendars foretold the coming of spring, summer, fall, and winter, helping civilizations track when to plant and harvest crops. They also served as ceremonial sites, both for celebration and sacrifice.

These megaliths — large, prehistoric monuments made of stone — may seem mysterious in our modern era, when many people lack a connection with, or even view of, the stars. Some even hold them up as supernatural or divined by aliens. But many ancient societies kept time by tracking which constellations rose at sunset, like reading a giant, celestial clock. And others pinpointed the sun’s location in the sky on the summer and winter solstice, the longest and shortest days of the year, or the spring and fall equinox.

Europe alone holds some 35,000 megaliths, including many astronomically-aligned stone circles, as well as tombs (or cromlechs) and other standing stones. These structures were mostly built between 6,500 and 4,500 years ago, largely along the Atlantic and Mediterranean coasts.

The most famous of these sites is Stonehenge, a monument in England that’s thought to be around 5,000 years old. Though still old, at that age, Stonehenge may have been one of the youngest such stone structures to be built in Europe.

The chronology and extreme similarities between these widespread European sites lead some researchers to think the regional tradition of constructing megaliths first emerged along the coast of France. It was then passed across the region, eventually reaching Great Britain.

But even these primitive sites are at least centuries younger than the world’s oldest known stone circle: Nabta Playa.

Located in Africa, Nabta Playa stands some 700 miles south of the Great Pyramid of Giza in Egypt. It was built more than 7,000 years ago, making Nabta Playa the oldest stone circle in the world — and possibly Earth’s oldest astronomical observatory. It was constructed by a cattle worshiping cult of nomadic people to mark the summer solstice and the arrival of the monsoons.

“Here is human beings’ first attempt to make some serious connection with the heavens," says J. McKim Malville, a professor emeritus at the University of Colorado and archeoastronomy expert.

Nabta Playa: The World's First Astronomical Site Was Built in Africa and Is Older Than Stonehenge, Eric Betz, Discover Magazine

Topics: Astronomy, Astrophysics, Comets, Space Exploration

Invisible structures generated by gravitational interactions in the Solar System have created a "space superhighway" network, astronomers have discovered.

These channels enable the fast travel of objects through space and could be harnessed for our own space exploration purposes, as well as the study of comets and asteroids.

By applying analyses to both observational and simulation data, a team of researchers led by Nataša Todorović of Belgrade Astronomical Observatory in Serbia observed that these superhighways consist of a series of connected arches inside these invisible structures, called space manifolds - and each planet generates its own manifolds, together creating what the researchers have called "a true celestial autobahn."

This network can transport objects from Jupiter to Neptune in a matter of decades, rather than the much longer timescales, on the order of hundreds of thousands to millions of years, normally found in the Solar System.

Finding hidden structures in space isn't always easy, but looking at the way things move around can provide helpful clues. In particular, comets and asteroids.

There are several groups of rocky bodies at different distances from the Sun. There's the Jupiter-family comets (JFCs), those with orbits of less than 20 years, that don't go farther than Jupiter's orbital paths.

Centaurs are icy chunks of rocks that hang out between Jupiter and Neptune. And the trans-Neptunian objects (TNOs) are those in the far reaches of the Solar System, with orbits larger than that of Neptune.

Astronomers Just Found Cosmic 'Superhighways' For Fast Travel Through The Solar System, Michelle Starr (no kidding), Science Alert

The first direct image of two exoplanets orbiting a Sun-like star, seen here, was captured by the SPHERE instrument on the ESO’s Very Large Telescope. The system is called TYC 8998-760-1 and is located some 300 light-years from Earth.

Topics: Astronomy, Astrophysics, Exoplanets

In another exoplanetary first, the European Southern Observatory's Very Large Telescope (VLT) in Chile's Atacama Desert has captured an image of two worlds orbiting a younger version of the Sun. The system, called TYC 8998-760-1, is located roughly 300 light-years away in the southern constellation Musca. And although it hides two gas giants orbiting a Sun-like star, we don’t have anything quite like these worlds in our own solar system.

The inner planet lies about 160 astronomical units from its host star (where one astronomical unit, or AU, is the average Earth-Sun distance) and is some 14 times the mass of Jupiter. With that amount of heft, the gas giant skirts the border between planet and brown dwarf, which is a type of almost-star. The more distant planet is located about 320 AU from its star and weighs in at about six Jupiter masses.

Two exoplanets seen dancing around Sun-like star for the first time, Mark Zastrow, Astronomy.com

Red-giant spotter: artist’s impression of the Kepler space telescope in Earth orbit. (Courtesy: NASA)

Topics: Astronomy, Astrophysics, Solar Physics

Some red-giant stars are rotating much faster than previously thought, according to a study led by Patrick Gaulme at Germany’s Max Planck Institute for Solar System Research. Using NASA’s Kepler space telescope, the astronomers found that about 8% of the red giants they observed are rotating fast enough to display starspots. The team reckons that the elderly stars acquire their rapid rotation by following one of three distinct routes in their evolution.

In main sequence stars like the Sun, the complex interplay that occurs between stellar rotation and the motions of plasma creates incredibly lively magnetic fields. When this magnetic activity is particularly strong, upwelling plumes of plasma in a star’s convective outer layers can be blocked, producing dark patches on its surface. To an observer on Earth, these starspots cause a periodic variation in the star’s brightness as it rotates, bringing the spots in and out of our field of view.

Until recently, starspots were not thought to be present on red giant surfaces. Since these older stars expand rapidly as they move out of the main sequence, while maintaining their angular momentum, previous theories had predicted that they must rotate more slowly than main sequence stars. Slower rotation should reduce magnetic activity, preventing starspots from forming.

Starspot study sheds light on why some red giants spin faster than others, Sam Jarman, Physics World

Comet NEOWISE over Mount Hood on July 11, 2020. Credit: Kevin Morefield Getty Images

Topics: Astronomy, Astrophysics, Comets

Comet NEOWISE has been entertaining space enthusiasts across the Northern Hemisphere. Although its official name is C/2020 F3, the comet has been dubbed NEOWISE after the Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) space telescope that first noticed it earlier this year. This “icy snowball” with a gassy tail made its closest approach to the sun on July 3 and is now heading back from whence it came: the far reaches of the outer solar system. Its long, looping orbit around our star ensures that after passing closest to Earth on July 22, Comet NEOWISE will not return for some 6,800 years.

Even though the comet is now bright enough to observe with unaided eyes, inexperienced stargazers might have trouble knowing when and where to look. Scientific American spoke to Jackie Faherty, an astronomer at the American Museum of Natural History in New York City, for observing tips and a better appreciation of why comets are so special.

How does one prepare to watch Comet NEOWISE with the naked eye?

Find the darkest possible swath of sky and make sure your eyes are adjusted so that you give yourself the best possible opportunity to see faint objects. It means: don’t just walk outside after staring at lights or screens and expect to see [the comet] really well. You need 15 minutes or so to adjust your eyes, so that your pupils are adjusted, and they’re used to seeing fainter things. It’s the same as walking into a dark room, and everybody knows that [you] can’t see [things] first—and then, all of a sudden, you start seeing things. You need to do the same thing when you walk outside. And use the Comet NEOWISE app developed by astrophysicist Hanno Rein of University of Toronto Scarborough to see exactly where it is, so that you know what direction you need to look. And then the key would be to find yourself a place that is the darkest possible, that [has] no lights.

The Best Way to Watch Comet NEOWISE, Wherever You Are, Karen Kwon, Scientific American

This artist’s concept shows a hypothetical planet covered in water around the binary star system of Kepler-35A and B. The composition of such water worlds has fascinated astronomers and astrophysicists for years. (Image by NASA/JPL-Caltech.)

Topics: Astronomy, Astrobiology, Astrophysics, Cosmology, Exoplanets

Out beyond our solar system, visible only as the smallest dot in space with even the most powerful telescopes, other worlds exist. Many of these worlds, astronomers have discovered, may be much larger than Earth and completely covered in water — basically ocean planets with no protruding land masses. What kind of life could develop on such a world? Could a habitat like this even support life?

A team of researchers led by Arizona State University (ASU) recently set out to investigate those questions. And since they couldn’t travel to distant exoplanets to take samples, they decided to recreate the conditions of those water worlds in the laboratory. In this case, that laboratory was the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility at the DOE’s Argonne National Laboratory.

What they found — recently published in Proceedings of the National Academy of Sciences — was a new transitional phase between silica and water, indicating that the boundary between water and rock on these exoplanets is not as solid as it is here on Earth. This pivotal discovery could change the way astronomers and astrophysicists have been modeling these exoplanets, and inform the way we think about life evolving on them.

Dan Shim, associate professor at ASU, led this new research. Shim leads ASU’s Lab for Earth and Planetary Materials and has long been fascinated by the geological and ecological makeup of these distant worlds. That composition, he said, is nothing like any planet in our solar system — these planets may have more than 50% water or ice atop their rock layers, and those rock layers would have to exist at very high temperatures and under crushing pressure.

Beneath the surface of our galaxy’s water worlds, Andre Salles, Argonne National Laboratory