Exomoons: Why study them? What can they teach us about finding life beyond Earth?

Universe Today has had the recent privilege of investigating a multitude of scientific disciplines, including impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, planetary atmospheres, planetary geophysics, cosmochemistry, meteorites, radio astronomy, extremophiles, organic chemistry, black holes, cryovolcanism, planetary protection, dark matter, supernovae, and neutron stars, and how they both individually and collectively contribute to our greater understanding of our place in the universe.

Here, Universe Today discusses the growing field of exomoons with Dr. David Kipping, who is an assistant professor in the Astronomy Department at Columbia University, along with his PhD students, Benjamin Cassese and Daniel Yahalomi, regarding the importance of studying exomoons, the benefits and challenges, potential exomoon candidates, how exomoons can teach us about finding life beyond Earth, and advice for upcoming students who wish to pursue studying exomoons. Therefore, what is the importance of studying exomoons?

Dr. Kipping tells Universe Today, “There’s four reasons to do this: 1) How common are Earth-like worlds? Exomoons may be a significant contributing factor to the cosmic census of habitable bodies; 2) How unique is the Earth-Moon system? The Moon is thought to have played an influential role in the formation and evolution of the Earth, and thus when we detect an Earth-twin we should naturally wonder if it has a Moon twin too.”

Dr. Kipping continues, “3) What are the moon formation channels? In the Solar System, we see at least three pathways, captures (e.g. Triton), impact (e.g. the Moon) and disk formation (e.g. Galilean moons). We would like to understand if there are other methods, and what the details and limitations are of the three methods we know of; 4) When we point HWO [Habitable Worlds Observatory] at an Earth-twin, a Moon-like moon would be unresolvable and thus its light will mix with that of the planet and potentially create false-positive biosignatures. Knowing about moons is vital to our long-term dream of finding life.”

Along with the Earth’s Moon, our solar system consists of more than 200 moons, but only a handful of them are targeted for astrobiology-related research, most notably two of Jupiter’s Galilean moons, Europa and Ganymede, and two of Saturn’s moons, Enceladus and Titan, but all of which have presented significant evidence for possessing interior oceans of liquid water. Along with finding out if the Earth-Moon system is unique, exomoons can teach us if our own solar system is unique given the wide range of moon types, shapes, and sizes, and especially their formation and evolution.

One possible reason for the Earth-Moon uniqueness is due to the tidal forces caused by the two bodies tugging on each other which maintains Earth’s relatively stable axis. As a result, the Earth very slightly wobbles like a spinning top over the course of 26,000 years, meaning its axial tilt only changes by a few degrees during that time, which has allowed our planet to maintain relatively stable climates, enabling life to both survive and thrive. This contrasts to smaller planets like Mars that wobble wildly over the course of hundreds of thousands to millions of years, resulting in large changes in its axial tilt between 15 degrees and 45 degrees, resulting in shifts of its polar caps and drastic climate variations. For context, both Earth’s and Mars’ axial tilts are currently around 25 degrees. But given all the reasons listed by Dr. Kipping, what are some of the benefits and challenges of studying exomoons?

“Some benefits are that finding a moon would automatically tell us more about its host planet,” Cassese tells Universe Today. “For example, we would be able to tell right away that the planet hasn’t gone through any dramatic orbit changes due to scattering with other planets, since that would likely have stripped the moon away. We can also help use the moon’s orbit to measure the mass of the planet, and even of the star, though there are other ways to measure both of those as well.”

“Moons are very difficult to detect and really push the data we receive to their limits,” Yahalomi tells Universe Today. “Therein lies both a challenge and an opportunity. In pursuit of detecting the smallest signals in these datasets, we need to develop new methods and techniques of extremely precise data analysis. I’m working on creating a new analytic framework for studying the gravitational effect that moons have on their host planets. We are working on methods to differentiate between the wobbles caused by moons and neighboring planets in the same stellar system. Without the goal of detecting moons, we would likely not be motivated to develop these statistical techniques, which can then (hopefully) have larger reaching applications.”

As of this writing, NASA has confirmed the existence of 5,678 exoplanets ranging from terrestrial (rocky) worlds to gas giants much larger than Jupiter. in contrast, there have been zero exomoons confirmed to exist anywhere in the cosmos, quite possibly due to the difficulty to detect them, as noted by Yahalomi. Of the 5,678 confirmed exoplanets, 4,193 have been confirmed using the transit method which detects extremely small dips (approximately 1 percent) in starlight when the exoplanet passes in front of, or transits, its parent star.

These dips in starlight are so small that astronomers require several transits to confirm its existence. Therefore, trying to detect exomoons, which could be much smaller than the exoplanet they orbit, is even more difficult. While there are currently no confirmed exomoons, what are some interesting exomoon candidates, including exomoon candidates that these researchers have studied?

“The two candidates we have announced are Kepler-1625 b-i and Kepler 1708 b-I,” Dr. Kipping tells Universe Today. “They both orbit gas giants at relatively wide separations from their star, and both are surprisingly large, 1625b-i is about a Neptune and 1708b-i is a mini-Neptune. In other ways they are quite different, 1708b orbits in a tight Europa-like orbit, seemingly coplanar with the planetary orbit. In contrast, 1625b-i appears inclined and at a much wider orbit, looking more like a captured moon. For 1625b-i, we have a mass thanks to transit timing variations of the primary planet and that lands in agreement with our radius measurement obtained from the dip of the moon in front of the star. For 1708b-i, we only have the dip (just two transits), however the false positive rate is well measured here to be ~1%, giving us dome confidence in the signal.”

As noted, of the more than 200 moons in our solar system, only a handful are currently targets for astrobiology and the search for life beyond Earth. These include two of Jupiter’s moons, Europa and Ganymede, and two of Saturn’s moons, Enceladus and Titan. All four have presented evidence for possessing interior oceans of liquid water, with Titan being the only one with liquid bodies on its surface, although comprised of liquid methane and ethane as opposed to liquid water.

Europa has been previously explored by NASA’s Galileo spacecraft while obtaining incredible images of the moon’s small surface. However, the agency’s Europa Clipper spacecraft, which launches this October, will conduct the most in-depth investigation into Europa’s habitability potential when it arrives in 2030. It will conduct 50 flybys of the small moon, sending back the high-resolutions images of its surface while using its suite of powerful instruments to determine if its interior liquid water ocean can harbor life, as we know it as we don’t know it.

Ganymede has also been studied by NASA’s Galileo spacecraft but the European Space Agency’s JUICE (Jupiter Icy Moons Explorer) spacecraft, which is currently en route to Jupiter with a planned arrival of 2031, hopes to also conduct the most in-depth investigation pertaining to Ganymede’s habitability potential, as well. For Saturn’s moon, Enceladus and Titan, both have been mapped and studied in-depth by NASA’s Cassini spacecraft over the course of its 13-year mission studying Saturn and its many moons.

During this time, Cassini both observed and flew through geysers emanating from Enceladus’ south polar region, indicating a liquid water ocean beneath its icy crust, along with landing a probe on Titan’s surface, revealing rounded boulders possibly formed from flowing liquid methane or ethane. Additionally, evidence has suggested that Titan possesses an interior liquid ocean comprised of water, as opposed to methane and ethane on its surface. Given the habitability potential for these moons, what can exomoons teach us about finding life beyond Earth?

“There are at least two ways moons can affect life elsewhere in the galaxy,” Cassese tells Universe Today. “First, moons can influence and stabilize their host planets [see above]. The other is that moons themselves could be great places for life. Some of the largest liquid water reserves in our solar system exist on moons like Europa, and it’s possible that other moons have similar ingredients that we think are essential for life. If moons are anywhere as near common as planets, the potentially habitable real estate of the galaxy would be much larger than we currently appreciate.”

Yahalomi tells Universe Today, “From what we currently know about planet formation and from our solar system where there are hundreds of moons, there really should be exomoons around many of the exoplanets that we have found. Therefore, if we find that there aren’t exomoons, that would reveal that there is something unique in our solar system and something missing in our understanding of planet formation. As we only know about life on Earth, currently, understanding the larger context of planetary demographics and thus better understanding how common or unique our Solar System truly is, could aid in our understanding of the likeliness of life beyond Earth.”

Like the field of exoplanets, studying exomoons involves a myriad of scientific backgrounds and disciplines to decipher copious amounts of data, including astrophysics, computer science, planetary geology, planetary atmospheres, data science, just to name a few. Additionally, powerful instruments like the aforementioned Habitable Worlds Observatory are required to detect exomoons given their infinitesimally small sizes within the data. It is through this constant collaboration between scientists and use of key instruments that will enable scientists to someday confirm the existence of the first exomoon within the cosmos. Therefore, what advice can the researchers off to upcoming students who wish to pursue studying exomoons?

“It’s a fascinating and rapidly growing area,” Dr. Kipping tells Universe Today. “We are finally in the era where we can detect moons akin to those in the Solar System using JWST. Further, there’s rapidly growing interest in discovering very non-Solar System like moons, such as moons around free-floating planets either using JWST of young systems in Orion (google JUMBOs for example) or using the upcoming Roman telescope with microlensing techniques. We are about to breach the detection threshold in a convincing way.”

How will exomoons help us better understand our place in the universe in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

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What’s Next for the Event Horizon Telescope? Twelve Possible New Targets

Both the Milky Way and a galaxy known as M87 have supermassive black holes at their core. These are the two largest black holes we know about and the Event Horizon Telescope has just captured stunning images of their event horizons. A new paper looks at what we might expect from a next generation EHT and highlights twelve targets that should be top of the list. 

The Event Horizon Telescope (EHT) is an international collaboration that uses a global network of radio telescopes. Connecting multiple telescopes together in a technique known as interferometry enables them all to work together, forming one massive virtual telescope the size of the distance between them. In April 2019, the EHT achieved a historic milestone by capturing the first-ever image of a black hole, located at the centre of the galaxy M87.

The ALMA array in Chile. Once ALMA was added to the Event Horizon Telescope, it increased the EHT’s power by a factor of 10. Image: ALMA (ESO/NAOJ/NRAO), O. Dessibourg

Black holes like that in M87 are most definitely the target of the EHT. They are regions in space with such a strong gravitational forces that nothing, not even light, can escape. They are formed from the remnants of massive stars that collapse under their own gravity, creating an object known as a singularity which has infinite density. Surrounding the singularity is the event horizon, beyond which no information or matter can return and it is this which is of particular interest to EHT.

Several extensions to the array are planned to enhance the quality of images. Doing so will improve its resolution allowing for a larger number of black holes to be studied. Theoretical studies of EHT images of both Sgr A at the centre of our Galaxy and the black hole at the centre of M87 favour models with dynamically significant magnetic fields.

Magnetically arrested disk (MAD) models, which power jet mechanisms, have important implications for the relationship between supermassive black holes and the evolution of its host galaxy. The extensions require new dishes to be added to the infrastructure and many of existing telescopes require upgrades. On completion, simultaneous observations in the frequency range 86-230-345 GHz will be possible, facilitating new studies. 

In the paper authored by Xinyue Alice Zhang from the Center for Astrophysics at the Harvard & Smithsonian and team they report upon their attempt to study the 12 most promising supermassive black hole targets for the EHT. 

The targets were honed in on following an exhaustive analysis which started off with the ETHER database, a list of 3.8 million sources. This was then narrowed down to those with a flux density (signal strength) that allowed mass measurements to be taken optically. A fair chunk of this was done by hand! Further sources with large angular sizes are being constantly added to the database so the number of possible targets will rise in time. 

The target galaxies identified to date include; IC1459, NGC45elliptical94, NGC3998, NGC4261, NGC2663, NGC3894, M84, NGC4552, 3C 317, NGC315, NGC1218 and NGC5077. These are all suitable for future EHT targets but they all exhibit some similarities for example many of them are elliptical galaxies but a few are classed as lenticular galaxies.

Source : Accessing a New Population of Supermassive Black Holes with Extensions to the Event Horizon Telescope

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Neutron Stars: Why study them? What makes them so fascinating?

Over the last several months, Universe Today has explored a plethora of scientific disciplines, including impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, planetary atmospheres, planetary geophysics, cosmochemistry, meteorites, radio astronomy, extremophiles, organic chemistry, black holes, cryovolcanism, planetary protection, dark matter, and supernovae, and how each of these unique disciplines continue to teach is about the cosmos and our place throughout its vastness.

Here, Universe Today discusses the field of neutron stars with Dr. Stuart Shapiro, who is a Professor of Physics and Astronomy and NCSA Senior Research Scientist at the University of Illinois at Urbana-Champaign, regarding the importance of studying neutron stars, the benefits and challenges, the most intriguing aspect about neutron stars he’s studied throughout his career, and any advice he can offer upcoming students who wish to pursue studying neutron stars. Therefore, what is the importance of studying neutron stars?

“Neutron stars are fundamental constituents of the universe,” Dr. Shapiro tells Universe Today. “They are detected throughout our Galaxy as isolated radio pulsars and as X-ray sources accreting gas from normal stars that serve as their binary companions. Neutron stars are also observed in distant galaxies as gravitational wave and gamma-ray emitters during the merger of two neutron stars in a binary system. The interior of neutron stars has the density of an atomic nucleus, some 14 orders of magnitude larger than typical materials on Earth. Such high nuclear densities cannot be reached in a lab on Earth, neutron stars provide an effective lab for studying matter and the laws of physics at extreme densities.”

Animation depicting a rapidly-spinning neutron star, also called a pulsar. (NASA’s Goddard Space Flight Center/Conceptual Image Lab)

The potential existence of neutron stars was first proposed by Fritz Zwicky and Walter Baade in 1933—which was also less than two years after the neutron was officially discovered—at a meeting of the American Physical Society. The goal of these discussions was to ascertain how supernovae were created, but they instead deduced that neutron stars resulted from supernovae, with the original star becoming ultra-dense with neutrons after the explosion.

However, research interest in neutron stars did not occur until several decades later in 1967 due to scientists deducing that they were far too small to be observed with the available technology, and only after neutron stars were found to exhibit large magnetic fields due to their rapid spin rates. Since then, neutron star research has gradually expanded, including using neutron stars to make the first detection of gravitational waves in 2017. Therefore, given their unique characteristics, what are some of the benefits and challenges of studying neutron stars?

Dr. Shapiro tells Universe Today, “We can’t collide neutron stars in an accelerator, as we do for, say, high energy protons and electrons, to study elementary particles. But Nature provides us with neutron star collisions when binary neutron stars collide. We have already detected a couple of collision events when LIGO [Laser Interferometer Gravitational-Wave Observatory] observed the radiated gravitational waves, and more detections are expected in the near future.”

Given their extreme density, this means the size of neutron stars are incredibly small, averaging only 20 kilometers (12 miles) in diameter, or the size of a small city, with a mass of 1.4 times the Sun, meaning one teaspoon of a neutron star weighs approximately one billion tons on Earth. Henceforth, Dr. Shapiro notes these results are extremely difficult to replicate in a laboratory setting. Additionally, their spin rates have been found to be as high as 716 rotations per second, or approximately 0.24 the speed of light if an observer was standing on its surface, with an unconfirmed finding indicating a neutron star exhibiting 1,122 revolutions per second. There are also different types of neutron stars, including pulsars which Dr. Shapiro mentioned, and magnetars which are highly magnetized neutron stars.

Size comparison between a neutron star and Manhattan. (Credit: NASA’s Goddard Space Flight Center)

While neutron stars don’t get as much publicity as other stars, it is currently hypothesized that approximately one billion neutron stars currently exist within the Milky Way Galaxy. This might seem like a large number, except it is estimated there are approximately 100 billion stars in the Milky Galaxy, meaning neutron stars could potentially comprise only one percent of our galaxy’s star population. Therefore, what are some of the most intriguing aspects about neutron stars that Dr. Shapiro has studied throughout his career?

Dr. Shapiro tells Universe Today, “One of the properties my collaborators and I uncovered was the ability of rotation to support neutron stars of higher mass than nonrotating spherical stars. It is well known that nonrotating neutron stars have a maximum mass of a couple of times the mass of the sun, the precise value depending on the equation of state, i.e. the precise nature of the pressure law for nuclear matter that supports the star against gravitational collapse.”

Dr. Shapiro continues, “However, we found that if the star is spinning, then it can support at larger mass. The maximum mass increases by about 20 per cent if it rotates like a rigid body (i.e. uniform rotation) but can increase much more if it rotates differentially, with its spin rate very high at the center and decreasing toward the surface. Stars rotating uniformly above the nonrotating mass limit we called ‘supramassive’, while stars rotating differentially above the supramassive mass limit we called ‘hypermassive’. Supramassive and hypermassive stars are likely formed when binary neutron stars merge, at least until they shed their angular momentum (i.e. Spin) via gravitational radiation and magnetic fields.”

Like black holes or other celestial objects that we rarely observe directly, the study of neutron stars involves a lot of theoretical research where researchers use computer models to simulate their hypotheses and use powerful instruments like LIGO to confirm these hypotheses down the road. Therefore, the study of neutron stars involves several scientific backgrounds, including theoretical astrophysics theory of general relativity, computational astrophysics, computer science, among others. Additionally, one exciting aspect of science is coining new terms, as the terms supramassive and hypermassive were coined by Dr. Shapiro and his colleagues. Therefore, what advice can Dr. Shapiro offer upcoming students who wish to pursue studying neutron stars?

Dr. Shapiro tells Universe Today, “Neutron stars have properties that deal with all four of the fundamental forces of nature: gravitation, electromagnetism, strong and weak particle interactions. To best study neutron stars, one should thus acquire a strong and broad background in physics. Since the equations describing neutron stars in various states are often very complicated, they must be solved numerically on supercomputers. So aspiring students should also acquire a good background in computational physics if they want to work at the cutting edge.”

How will neutron stars teach us about our place in the universe in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

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Supernovae: Why study them? What can they teach us about finding life beyond Earth?

Universe Today has recently investigated a myriad of scientific disciplines, including impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, planetary atmospheres, planetary geophysics, cosmochemistry, meteorites, radio astronomy, extremophiles, organic chemistry, black holes, cryovolcanism, planetary protection, and dark matter, and what they can teach us about how we got here, where we’re going, and whether we might find life elsewhere in the universe.

Here, Universe Today discusses the explosive field of supernovae—plural for supernova—with Dr. Joseph Lyman, who is an assistant professor in the Astronomy and Astrophysics Group at the University of Warwick, regarding the importance of studying supernovae, the benefits and challenges, the most intriguing aspects about supernovae he’s studied throughout his career, what supernovae can teach us about finding life beyond Earth, and any advice he can offer upcoming students who wish to pursue studying supernovae? Therefore, what is the importance of studying supernovae?

“Supernovae really are a window into the universe at its most spectacular,” Dr. Lyman tells Universe Today. “We can’t hope to replicate their immense power with experiments here on Earth, and so they provide an invaluable means of studying what happens to matter under the most extreme conditions as stars explode. These conditions are so extreme that supernovae can create the most exotic objects we know of in the universe: neutron stars and black holes. Studying supernovae is therefore a means to study the production of these mysterious objects.”

Dr. Lyman continues, “Supernovae are also glimpses at our own origins. During these explosions, they release huge amounts of different elements, including oxygen, iron, calcium, into their environments – elements that would otherwise remain locked up in stars. It is the dispersal of such elements by supernovae that puts in motion the building blocks for the formation of planets, and, ultimately, life as we know it.”

The observations of supernovae occurring within our Milky Way Galaxy date back to 185 CE (Common Era) when Chinese astronomers during the Han dynasty observed a bright star that remained in the sky for approximately eight months, after which it faded away. While there has been speculation this observation was a comet despite the object remaining stationary, a 2006 study published in the Chinese Journal of Astronomy and Astrophysics concluded this observation was most likely a supernova after comparing records of the observation with comet observation records during the same time period.

While several more supernovae within our Milky Way Galaxy have been observed since that encounter, the most recent was observed on October 9, 1604, having since been identified as SN 1604. Because of this, astronomers have focused their attention on studying nebulae, which are remnants of supernovae that provide clues into the various elements and minerals that were ejected into space from the explosion, along with the star’s properties before it exploded. So, what are some of the benefits and challenges of studying supernovae?

Dr. Lyman tells Universe Today, “There is a captivating nature to studying an astrophysical phenomenon that is born, and then fades into nothing, right before your eyes. Unlike the unimaginably slow procession of most of the universe, supernova science, and that of other related transients, demands highly reactive modes of working, as astronomers scramble to gather telescopes resources and observations on chance discoveries.”

Dr. Lyman continues, “Studying one-off, dynamic objects is, however, also a huge challenge for these reasons. One can miss important clues on the nature of a supernova simply due to a bit of bad weather at an observatory. Some rare or fortuitous events we discover once per decade, or once per generation – the pressure is really then on to observe all we can about the object during its brief life, since once they’re gone, they’re gone.”

Despite the lack of supernovae observations within our Milky Way Galaxy occurring in the last several hundred years, astronomers have successfully observed countless supernovae flashes in other galaxies. This began in 1933 by the Swiss astronomer, Dr. Fritz Zwicky, who led a team of astronomers at Palomar Observatory in discovering 12 supernovae over a three-year period, with countless other supernovae outside the Milky Way being discovered to the present day. The most recent supernova was observed by NASA’s Hubble Space Telescope in 2018 when it observed an exploding star in the spiral galaxy NGC 2525, which is located approximately 70 million light-years from Earth.

Supernovae are classified into two types: Type I and Type II, with each being broken down into various subtypes based on their appearances or chemical compositions. Additionally, remnants of supernovae can become several types of celestial objects, including nebulae, neutron stars, or black holes, all depending on the size of the original star (progenitor) and the number of metals (metallicity) it was comprised of, as well. Therefore, what are the most intriguing aspects about supernovae that Dr. Lyman has studied throughout his career?

Dr. Lyman tells Universe Today, “A real highlight over the last decade has been the advent of new wide-field sky surveys that are capable now of detecting all manner of supernova types beyond the archetypal classes known about for many decades. The true diverse nature of supernovae, from extremely long-lived and hugely energetic ‘superluminous’ supernovae to fast-and-faint events, is now being revealed. With each new discovery, we are constantly re-evaluating our understanding of how stars evolve and die.”

As noted by Dr, Lyman, supernovae explosions release vast amounts of elements into the cosmos, nearly all of which are found on the Earth in some form or another, including living organisms such as humans. The elements he mentions are oxygen, iron, and calcium, all of which reside within our bodies and are essential for our very survival. Also, depending on the composition of the original star, other elements might include gold, uranium, lead, mercury, tin, silver, and zinc, the last of which is also essential for our survival and the others can be used for industrial purposes around the world. Given how some of these elements are found in our bodies, this falls in line with the famous quote by the American astronomer, Dr. Carl Sagan, who said “we are made of star stuff.” Given these variables, what can supernovae teach us about finding life beyond Earth?

Dr. Lyman tells Universe Today, “Stars that explode as supernovae at the end of their lives are the nuclear fusion reactors of the universe that provide the elements essential for life. Their explosions seed the material used in the next generations of stars and planets. In this sense, supernovae have been crucial to our own existence, and life on Earth. We see supernovae, and the results of the ‘chemical enrichment’ of galaxies throughout the universe. So, in this sense, we already know the conditions needed to create Earth-like planets are not unique to our own position.”

Like all scientific endeavors, the study of supernovae involves a myriad of scientific disciplines, including astronomy, astrophysics, cosmology, nuclear physics, computer science, and chemistry, just to name a few. It is through constant collaboration and teamwork from scientists around the world that enables the study of supernovae to teach us about the formation and evolution of stars throughout the history of the universe and what it means regarding our place in all of it. Therefore, what advice does Dr. Lyman offer upcoming students who wish to pursue studying supernovae?

Dr. Lyman tells Universe Today, “Although we’ve known about supernovae for a century, it remains a very fast-moving research field and, perhaps more so than other astrophysics fields, new students may need to remain open to shifting focus and adapting in their study direction. Upcoming breakthroughs in observational facilities such as the Vera Rubin Observatory, as well as computational work now being able to routinely perform full 3D simulations of supernovae, make for an especially exciting time for the field. I see studying supernovae as a chance to enjoy the serendipity of the universe and see what new explosion it next throws at us to challenge our understanding.”

How will supernovae teach us about our place in the cosmos in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

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Earliest Supermassive Black Holes Were “Shockingly Normal”

The early Universe is a puzzling and—in many ways—still-unknown place. The first billion years of cosmic history saw the explosive creation of stars and the growth of the first galaxies. It’s also a time when the earliest known black holes appeared to grow very massive quickly. Astronomers want to know how they grew and why they feed more like “normal” recent supermassive black holes (SMBH).

Today we see SMBH in galaxies that can have upwards of millions or billions of solar masses sequestered away. Astronomers naturally assumed that it took a long time for such monsters to build up. Like billions of years. So, when JWST observed the most distant quasar J1120+0641, they expected to see an active galactic nucleus as it looked some 770 million years after the Big Bang. That is, they expected a still-growing central supermassive black hole. They were intrigued to find that it had a mass of at least a billion suns.

This image of ULAS J1120+0641, a very distant quasar powered by a black hole, was created from images taken from surveys made by both the Sloan Digital Sky Survey and the UKIRT Infrared Deep Sky Survey. The quasar appears as a faint red dot close to the center. It’s the most distant yet found, seen as it was 770 million years after the Big Bang.

That raised a question: how could such an early SMBH get so big so fast? For something that young, having that much mass says something about its feeding mechanism. Astronomers already know that SMBH existed early in cosmic time. These structures at the hearts of those distant quasars apparently already existed when the Universe was very young—about 5% of its current age.

Theory vs Observation: How Do Supermassive Black Holes Form?

The growth of SMBH in the early Universe is a hot topic these days. The standard idea for a long time was that they grew slowly through mergers and acquisitions during galaxy formation. Since those mergers take a long time—millions of years, at least—it seemed that the black holes would go along for the long, slow ride. And, you can’t speed up black hole growth too much once one forms. As matter swirls into the black hole, it does so through the accretion disk that feeds it. The disk—the active galactic nucleus—is very bright due to the radiation emitted as the matter heats up through friction and magnetic field interactions. The light pressure pushes stuff away. That limits how quickly the black hole can eat. Still, astronomers found these early SMBH sporting 10 billion solar masses when, by conventional wisdom, they should have been less massive.

For J1120+0641, astronomers considered different scenarios for its growth, including a so-called “ultra-effective feeding mode”. That implies early SMBH had some very efficient way of accreting gas and dust and other material. So, astronomers looked at these active galactic nuclei at the hearts of distant quasars in more detail using JWST. It has the MIRI spectrograph that looks at the light from those quasars in great detail. The MIRI spectra of J1120+0641 revealed the presence of a large dust torus (a donut-shaped ring) surrounding the accretion disk of the SMBH. That disk is feeding the SMBH at a very “normal” rate similar to SMBH in the “modern” Universe. The quasar’s broad-line region, where clumps of gas orbit the black hole at speeds near the speed of light look normal, too.

Artist’s interpretation of ULAS J1120+0641, a very distant quasar with a supermassive black hole at its heart. Credit: ESO/M. Kornmesser

In the Final Analysis

By almost all the properties that can be deduced from the spectrum, J1120+0641 turns out to be feeding no differently than quasars at later times. So, what does that mean for theories of SMBH formation in the early Universe? According to Sarah Bosman, who headed up the team that used JWST to study this and other quasars, the observations rule out fast feeding and other explanations for why the SMBH is so massive. “Overall, the new observations only add to the mystery: early quasars were shockingly normal. No matter in which wavelengths we observe them, quasars are nearly identical at all epochs of the Universe,” she said.

If you extrapolate these observations to other ideas about early SMBH, it means the process of black hole growth was pretty much set early in cosmic history. They didn’t start as stellar-mass black holes that got big. Instead, they formed from the collapse of very massive early clouds of gas to become massive primordial seeds. From there, not only did they feed from their accretion disks, but probably did grow even more massive through those mergers and acquisitions. Thanks to JWST, however, astronomers now know that the early feeding mechanisms were already in place very early in cosmic time. Now they just need to figure out when the primordial seeds of SMBH first appeared in the infant Universe.

For More Information

A Black Hole of Inexplicable Mass
A Mature Quasar at Cosmic Dawn Revealed by JWST Rest-frame Infrared Spectroscopy
First rest-frame Infrared Spectrum of a Z > 7 Quasar: JWST/MRS Observations of J1120+0641

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Asteroid Samples Were Once Part of a Wetter World

Nine months have passed since NASA’s OSIRIS-REx returned its samples of asteroid Bennu to Earth. The samples are some of the Solar System’s primordial, pristine materials. They’ve made their way into scientists’ hands, and their work is uncovering some surprises.

Some of the material in the samples indicates that Bennu had a watery past.

NASA chose Bennu for the OSIRIS-REx sampling mission for several reasons. First, it’s a near-Earth asteroid (NEA), so it’s relatively close to Earth. It’s also not very large at about 500 meters in diameter and rotates slowly enough to allow for a safe sampling procedure.

But the overarching reason was probably its composition. It’s a B-type asteroid, a subtype of carbonaceous asteroids, which means it contains organic molecules. Finding organic molecules throughout the Solar System is one way of tracing its origin and formation.

Returning samples to Earth is the best and most complete way to study asteroids. Asteroid fragments that fall to Earth are scientifically valuable. But much of their lighter material simply burns up when entering Earth’s atmosphere, leaving a huge crater in our understanding.

Space missions always seem to surprise us somehow. If they didn’t, there’d be less impetus to send them. In this case, the sample contains chemicals that OSIRIS-REx didn’t spot when it was studying Bennu.

“Bennu potentially could have once been part of a wetter world.”

Dante Lauretta, Principal Investigator, OSIRIS-REx mission

New research in the journal Meteoritics and Planetary Science presents these findings. It’s titled “Asteroid (101955) Bennu in the laboratory: Properties of the sample collected by OSIRIS-REx.” The co-lead author is Dante S. Lauretta, the principal investigator for the OSIRIS-REx mission and the Regents Professor of Planetary Sciences at the University of Arizona Lunar and Planetary Laboratory. The paper is an overview of the sample and serves as a catalogue from which researchers can request sample material for their research.

“Finally having the opportunity to delve into the OSIRIS-REx sample from Bennu after all these years is incredibly exciting,” Lauretta said in a press release. “This breakthrough not only answers longstanding questions about the early solar system but also opens new avenues of inquiry into the formation of Earth as a habitable planet. The insights outlined in our overview paper have sparked further curiosity, driving our eagerness to explore deeper.”

This image shows OSIRIS-REx’s Bennu sample poured from the TAGSAM into eight trays. Image Credit: NASA/UoA/LPL

“We describe the delivery and initial allocation of this asteroid sample and introduce its bulk physical, chemical, and mineralogical properties from early analyses,” the authors write in their paper. The 120-gram sample dates back billions of years. It’s pristine, meaning it hasn’t melted and resolidified since it was formed.

The astromaterials curation team at NASA’s Johnson Space Center used the Advanced Imaging and Visualization of Astromaterials (AIVA) procedure to document the condition of the sample and the sampling equipment. This was done while the sample was still inside its glovebox, which is highly reflective for this purpose. This is a meticulous process involving hundreds of images stacked together.

Overall, the sample is dark. But there are brighter materials interspersed in it. “Some stones appear mottled by brighter material that occurs as veins and crusts,” the authors write. The largest piece is about 3.5 cm long, but much of it is dust. Stones with hummocky morphologies have the lowest densities, and mottled stones have the highest densities.

“Some of the high-reflectance phases have a hexagonal crystal habit, whereas others appear as clusters of small spheres, platelets, and dodecahedral forms,” the authors write. The collection also contains some individual pieces that are highly reflective.

Overall, the material is grouped into three categories:

• Hummocky material with uneven surfaces. Their surfaces feature rounded mounds and depressions reminiscent of cauliflower. This material is generally dark but has some microscopic, brighter material.
• Angular particles that have been fractured and have sharper edges. They have hexagonal and polygonal shapes and have some layering. They’re generally dark, but some faces have a metallic lustre and specular reflections. They also have some highly reflective inclusions like the hummocky material.
• Mottled particles that are mostly darker but have layers of reflective material. The reflective material fills in small cracks in the darker material and also occurs as bright, individual flakes.

The three sub-types of material in the Bennu sample are hummocky, angular, and mottled. Image Credit: Lauretta et al. 2024.

Representative samples were also analyzed at other institutions in the US using different instruments including a plasma mass spectrometer, an infrared spectrometer, and an X-ray computer tomographer. These examinations revealed other information, like particle densities and elemental abundances. In particular, it contains isotopic information for hydrogen, carbon, nitrogen, and oxygen. It also compares these abundances to those of other asteroids.

But what jumps out from this initial analysis is the sample’s serpentine and other clay minerals. Their presence is similar to what’s found on Earth’s mid-ocean ridges, where Earth’s mantle encounters water.

Earth’s mid-ocean ridges are where seafloor spreading takes place. Rising hot rock meets the oceans, driving the serpentinization process. Image Credit: By 37ophiuchi BrucePL – Based on diagram File: Mittelozeanischer Ruecken – Schema.png. I translated it from German to English and revised the outlines of rock units. CC BY-SA 4.0, https://ift.tt/Knk8rS5

On Earth, contact between mantle material and ocean water also creates clays and other minerals like carbonates, iron oxides, and iron sulphides. These were also found in the Bennu sample.

But one finding stands out among the rest: water-soluble phosphates. These compounds are found throughout Earth’s biosphere and are an important component of biochemistry.

JAXA’s Hayabusa 2 mission found a similar phosphate in its sample from asteroid Ryugu. But the phosphate from Bennu is different. Unlike any other asteroid sample, it has no inclusions and different-sized grains. The magnesium sodium phosphate in the Bennu sample suggests a watery past.

This image shows reflective phosphate in one of the rocks in the Bennu sample. The presence of phosphates suggests a watery past. Image Credit: Lauretta et al. 2024.

“The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” Lauretta said. “Bennu potentially could have once been part of a wetter world. Although, this hypothesis requires further investigation.”

In their paper, the authors outline several hypotheses for Bennu’s past. One of them states that “… the dominant lithologies on Bennu’s surface have mineralogical, petrological, and compositional properties closely resembling those of the most aqueously altered carbonaceous chondrites.”

The Bennu sample also shows that the asteroid is chemically primitive, meaning it has remained largely unchanged since its formation. The rocks have not melted and resolidified since their initial creation. The asteroid’s elemental properties also mirror that of the Sun.

“The sample we returned is the largest reservoir of unaltered asteroid material on Earth right now,” Lauretta said.

This figure from the research shows a reflected light image (a) and a UV fluorescence image (b) of a part of the Bennu sample. The UV fluorescence microscopy image shows the distribution of carbonates and phosphates (blue fluorescence) and organic nanoglobules (yellow fluorescence). Image Credit: Lauretta et al. 2024.

The initial research also shows that Bennu is rich in carbon and nitrogen, critical clues to the asteroid’s origins. These chemicals also play a role in the appearance of life, adding to the intrigue.

“These findings underscore the importance of collecting and studying material from asteroids like Bennu – especially low-density material that would typically burn up upon entering Earth’s atmosphere,” said Lauretta. “This material holds the key to unraveling the intricate processes of solar system formation and the prebiotic chemistry that could have contributed to life emerging on Earth.”

Harold Connolly is a co-author of the study and the mission sample scientist who leads the Sample Analysis Team. He’s also a professor at Rowan University in Glassboro, New Jersey, and a visiting research scientist at UArizona. “The Bennu samples are tantalizingly beautiful extraterrestrial rocks,” Connolly said. “Each week, analysis by the OSIRIS-REx Sample Analysis Team provides new and sometimes surprising findings that are helping place important constraints on the origin and evolution of Earthlike planets.”

And this is really just the beginning. With these evaluations in hand and the sample catalogued, research scientists around the world will request samples for their own research.

Further secrets will be revealed.

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Seeing Both Sides of the Sun at the Same Time

As everybody who saw May’s spectacular auroral displays knows, the Sun is in its most active period in 11 years. The active region sunspot group that unleased the giant X-class flare rotated around the Sun, away from our direct view. But, that isn’t keeping the Solar Orbiter from spotting what’s happening with it and other active regions as they travel around on the Sun.

This European Space Agency solar satellite continuously observed the region as it transited the solar far side. The onboard x-ray instrument (STIX) watched in real time as that sunspot group (dubbed AR3664) belched out another massive flare on May 20th. That outburst is currently the record-holder for strongest flare of the current solar cycle. If it was aimed toward Earth, we’d have seen fantastic auroral displays again. However, the flare could have posed a huge threat to our satellites, communications services, and even astronauts in orbit.

Observing the Whole Sun

Scientists were, until relatively recently, limited to a view of one side of the Sun at the same time, from both Earth-based and space-based observatories and missions. That point of view limits how much information we can get about solar activities. Thanks to the Solar Observer, however, that view is changing and scientists take advantage of its position in space to see the far side of the Sun. It watches from an eccentric orbit that takes it as close as 60 solar radii to the Sun. That’s even closer than the orbit of Mercury. It makes this close approach every half-year.

Solar Orbiter’s view of the sunspot group AR3664 vs. Earth-centric view of the Sun. Courtesy: ESA & NASA/Solar Orbiter/EUI

The Solar Orbiter has returned the closest-ever images of our star, measures the solar wind, and studies the solar polar regions. “Solar Orbiter’s position, in combination with other missions watching the Sun from Earth’s side, gives us a 360-degree view of the Sun for an extended period of time. This will only happen three more times in the future of Solar Orbiter, so we are in a unique situation to observe active regions on the far side that will then rotate into Earth’s view,” said ESA Solar Orbiter Project Scientist Daniel Müller.

Solar Orbiter’s Mission to Observe the Sun

Data from Solar Orbiter allow scientists to understand solar activity and provide improved space weather forecasts. Solar physicists use the term “space weather” as a catch-all for the kinds of geomagnetic storms caused by solar outbursts. Usually, these occur in the form of X-class flares and coronal mass ejections. They happen more frequently during solar maximum—the most active time of the Sun’s 11-year cycle of sunspots. That heightened activity poses a real threat to Earth and human technologies on and off planet.

In the case of sunspot group AR3664, measurements from Solar Orbiter, in conjunction with Mars Express and the BepiColumbo spacecraft showed that it was still very active as it transited around the Sun. The May 20th outburst, for example, turned out to be an estimated class of X12. “This makes it the strongest flare yet of the current solar cycle, and in the top ten flares since 1996,” said ESA research fellow Laura Hayes.

A simulation of charged particles moving out from the Sun through the inner solar system after the outburst of May 27th, 2024. Courtesy: EUHFORIA/J. Pomoell

The Sun continued to be active even as it rotated around toward Earth and erupted again on May 27th. According to Müller, Earth dodged a bullet because the storm bypassed us. “If this flare and coronal mass ejection had been directed towards Earth, it would have caused another major geomagnetic storm for sure. But even like this, it resulted in a strong radio blackout over North America.”

Tracking An Active Sunspot Region

The same pesky sunspot region continues to be active as the Sun rotates and brings it around again and again and spacecraft capture evidence of its eruptions. The May 20th outburst also sent a shower of fast-moving ions and electrons across space. Solar Orbiter’s energetic particle detector measured them, and BepiColumbo and Mars Express were affected. The energetic particles hit memory storage on both spacecraft. That caused numerous errors during spacecraft operations. Interestingly, the memory problems also provided an alternate way to detect space weather events.

The offending sunspot group was also associated with a huge coronal mass ejection, which the Orbiter’s magnetometer measured almost immediately. This outburst was so massive that the Solar and Heliospheric Observatory (SOHO) captured a view from its Lagrange point orbit. It did it again on June 11th, emitting yet another X-class flare. It’s probably only a matter of time before it aims one at Earth again.

The May 27th coronal mass ejection from the Sun as seen by the SOHO and Solar Dynamics Observatories. Courtesy: SOHO (ESA & NASA), NASA/SDO/AIA, JHelioviewer/D. Müller

Solar Missions and Space Weather

Thanks to observations from Solar Orbiter and other spacecraft such as the Parker Solar Probe, scientists should be on the watch for outbursts and issue warnings in time for satellite operators, space agencies, and others to prepare. Solar Orbiter’s views of the entire Sun are just the start of complete real-time solar observations. There’s another mission, called Vigil, being designed to monitor the Sun and improve space weather predictions. It won’t launch until at least 2031 and will do its work from an L5 position in space.

“Adding Vigil’s data to our space weather services can give us forecasts up to 4–5 days earlier for certain space weather effects and provides more detail than ever before. Such early warnings give astronauts time to take shelter, and operators of satellites, power grids and telecommunication systems time to take protective measures,” said Giuseppe Mandorlo, Vigil Project Manager at ESA.

For More Information

Can’t Stop, Won’t Stop: Solar Orbiter Shows the Sun Raging On
Solar Orbiter Mission

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Could A Mound of Dust and Rock Protect Astronauts from Deadly Radiation?

Protecting the astronauts of the Artemis program is one of NASA’s highest priorities. The agency intends to have a long-term presence on the Moon, which means long-term exposure to dangerous radiation levels. As part of the development of the Artemis program, NASA also set limits to the radiation exposure that astronauts can suffer. Other hazards abound on the lunar surface, including a potential micrometeoroid strike, which could cause catastrophic damage to mission equipment or personnel. NASA built a team to design and develop a “Lunar Safe Haven” to protect from these hazards. Their working paper was released in 2022 but still stands as NASA’s best approach to long-term living on the lunar surface.

The two hazards mentioned above provided the primary impetus for the design, but there are some nuances to them—in particular, radiation. Astronauts will experience two main types of hazardous radiation on the lunar surface: cosmic rays and solar eruptions. 

Cosmic rays are the more insidious of the two. They have a high energy range, so a shielding material that might work well for higher-energy particles might not do so for lower-energy ones. Moreover, some high-energy particles can interact with shielding, causing even more damaging radiation further down its path. Essentially, this increases the radiation risk inside the shielding compared to outside. The order in which the radiative particles are dealt with is one of the critical design considerations for dealing with this dangerous phenomenon. 

Lunar regolith can be hard to deal with, as Fraser discusses with Dr. Kevin Cannon.

However, solar particle events (SPEs) are the more overtly dangerous of the two types of radiation. While rare, they can cause acute radiation sickness. Current astronauts must shelter in place inside a protected chamber on the ISS when these happen, and building something equivalent on the surface of the Moon is a necessity to ensure that astronauts don’t simply die of acute radiation poisoning within the first six months of arrival.

With the problems to solve firmly in hand, the design team moved on to other considerations—like what the habitat inside the LSH would actually look like and how it would be built. Consideration of the habitat shape focused on one primary distinction—should the habitat be horizontal or vertical? The answer is vertical based on modeling the risk of radiation and micrometeoroid strikes.

So, how do you build a structure around a vertical habitat on the Moon? You employ robots and remotely operated construction equipment. Other groups at NASA had been working on solutions like the Lightweight Surface Manipulation System (LSMS), essentially a large crane that can be constructed in lunar gravity, and the Lunar Attachment Node for Construction and Excavation (LANCE) – a bulldozer module designed to attach to the front of NASA’s Chariot exploration vehicle. Utilizing these ideas and other construction ideas, it’s possible to construct a protective dome of lunar regolith around a long-term habitat for the Artemis missions. 

Fraser overviews the Artemis mission that LSH will attempt to help.

Such a protective habitat has significant advantages over digging one into the ground, which requires moving a massive amount of regolith or utilizing lava tubes with indeterminate structural integrity. But that means the LSH must have an above-ground design. The team developed two separate design ideas – a parabolic arch and a “Round Cake” design using polyethylene. The first is self-explanatory, but the second looks more like a typical cylinder with the radiation and micrometeoroid-blocking polyethylene stored in “beans” at the top of the structure. This could be made of waste materials from the mission, such as discarded food packaging.

Each design has advantages and disadvantages, and the team didn’t pick a final one as part of the paper. However, they did come up with a five-phase development process, from preparing the site in advance to living in interconnected habitats surrounded by regolith and protective shielding. Depending on the amount of automation involved and some real luck, those development phases could take anywhere from a few years to a few decades. 

It remains to be seen if this system will be adopted as an official part of the Artemis program. But it serves a need of critical importance to humanity’s long-term existence on the Moon. If that is indeed NASA’s goal for the end of the 2030s, it would be good to consider how to start making the LSH a reality.

Learn More:
Wok et al. – Design Analysis for Lunar Safe Haven Concepts
Moses & Grande – Lunar Safe Haven Seedling Study
UT – What Could We Build With Lunar Regolith?
UT – There are Four Ways to Build with Regolith on the Moon

Lead Image:
Artist’s depiction of the Parabolic Arc LSH in cutaway.
Credit – Wok et al.

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Cepheid Variables are the Bedrock of the Cosmic Distance Ladder. Astronomers are Trying to Understand them Better

One of the most fundamental questions astronomers ask about an object is “What’s its distance?” For very faraway objects, they use classical Cepheid variable stars as “distance rulers”. Astronomers call these pulsating stars “standard candles”. Now there’s a whole team of them precisely clocking their speeds along our line of sight.

What makes a classical Cepheid a “standard candle” in the darkness of the Universe? It’s that pulsation. Not only does a Cepheid grow larger in a regular rhythm, but its brightness changes over predictable periods of time. In the early 1900s, astronomer Henrietta Leavitt studied thousands of these stars. She found something pretty interesting: there’s a strong relationship between a Cepheid’s luminosity and its pulsation period. And that’s a useful relationship.

When you compare a Cepheid’s luminosity to its pulsation period, you can derive the star’s distance. This relationship appears to be true for all known Cepheids. That’s why they’re considered an important part of the cosmic distance ladder. They’re the main benchmark for scaling the huge distances between galaxies and galaxy clusters.

Types of Cepheids

There are different “flavors” of Cepheids. The “classical” ones have pulsation periods ranging from a few days to a few months. They’re all more massive than the Sun and can be up to a hundred thousand times more luminous. Their radii can change pretty drastically during a cycle—some grow by millions of kilometers and then shrink. Type II Cepheids have pulsation periods between 1 and 50 days and are usually very old, low-mass stars. There are other types, including anomalous Cepheids with very short periods. Scientists also know about double-mode Cepheids with “heartbeats” that pulsate in two or more modes.

Some pretty well-known stars are Cepheid variables. For example, Polaris—the well-known “North Star” is one, as is RR Puppis, Delta Cephei, and Eta Aquilae—all visible from Earth. Why these stars pulsate is still being studied but here’s a very basic look at their process. The core of the star produces heat which heats the outer layers. They expand, and then cool. Radiation is escaping, which makes the star appear brighter. The cooler gas contracts under gravity and makes the star look smaller and cooler. Of course, the devil is in the details, which is why astronomers want to know more about the processes these stars undergo.

Polaris A (Pole Star) with its two stellar companions, Polaris Ab and Polaris B. Polaris itself is a Cepheid type variable star. Artists impression. Credit: NASA

However, it turns out Cepheids are not exactly easy to study. For one thing, it’s tough to measure their pulsations and radial velocities accurately. In addition, some have companion stars and the presence of a nearby star complicates any measurements. For another thing, different instruments and measuring methods give slightly different results, which doesn’t help astronomers understand those stars any better.

Precision Measurements of Cepheid Variables

Measuring the intricacies of Cepheid pulsations requires spectroscopic techniques that can measure light from stars and break it down into its component wavelengths. That reveals a lot of data about a star, including its chemical makeup, temperature, and motions in space.

Calibrated Period-luminosity Relationship for Cepheid variables. Courtesy Spitzer Space Telescope/IPAC.

A worldwide consortium of astronomers led by Richard I. Anderson at Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL) is measuring specific properties of classical and other Cepheids using two high-resolution spectrographs. One is called HERMES on La Palma in the northern hemisphere and the other is CORALIE in Chile. They both detected tiny shifts in the light of target Cepheids. Those shifts gave valuable information about the motions of the stars.

“Tracing Cepheid pulsations with high-definition velocimetry gives us insights into the structure of these stars and how they evolve,” he said. “In particular, measurements of the speed at which the stars expand and contract along the line of sight—so-called radial velocities—provide a crucial counterpart to precise brightness measurements from space. However, there has been an urgent need for high-quality radial velocities because they are expensive to collect and because few instruments are capable of collecting them.”

VELOCE is on the Job

The team’s measurement project is called the VELOCE Project—short for VELOcities of CEpheids. It’s 12-year-long collaboration among astronomers and astrophysicists. Anderson began the VELOCE project during his Ph.D work at the University of Geneva, continued it as a postdoc in the US and Germany, and has now completed it at EPFL.

According to Ph.D student Giordano Viviani, the data from the project are already enabling new discoveries about Cepheids. “The wonderful precision and long-term stability of the measurements have enabled interesting new insights into how Cepheids pulsate,” Viviani said. “The pulsations lead to changes in the line-of-sight velocity of up to 70 km/s, or about 250,000 km/h. We have measured these variations with a typical precision of 130 km/h (37 m/s), and in some cases as good as 7 km/h (2 m/s), which is roughly the speed of a fast walking human.”

Uncovering New Details about these Pulsating Stars

The VELOCE project’s precision measurements also revealed some strange facts about these stars. For example, there’s an interesting phenomenon called the Hertzsprung Progression. It describes double-peaked bumps in a Cepheid’s pulsations. Astronomers aren’t quite sure yet why these bumps occur. But, they could give some insight into the structure of Cepheid variables, particularly the so-called “classical” ones.

Other Cepheids show very complex variability, and changes in their radial velocities are not always consistent with predicted periods, according to postdoctoral researcher Henryka Netzel. “This suggests that there are more intricate processes occurring within these stars, such as interactions between different layers of the star, or additional (non-radial) pulsation signals that may present an opportunity to determine the structure of Cepheid stars by asteroseismology,” Netzel said.

As part of their study, the team also measured 77 Cepheids that are part of binary systems. One in three Cepheids “lives” in a binary system, and often those unseen companions are detectable by velocity measurements. Characterizing the different “flavors” of Cepheids and the intricacies of their pulsations has larger implications than determining their radial velocities and bumps in their periods, according to Anderson. “Understanding the nature and physics of Cepheids is important because they tell us about how stars evolve in general, and because we rely on them for determining distances and the expansion rate of the Universe,” Anderson said, noting that VELOCE is also providing a valuable “cross-check” with Gaia measurements. It’s on track to conduct a large-scale survey of Cepheid radial velocity measurements.

Cross-checking with Gaia

Additionally, VELOCE provides the best available cross-checks for similar, but less precise, measurements from the ESA mission Gaia. That spacecraft is on track to conduct the largest survey of Cepheid radial velocity measurements. Data from that mission provides a growing three-dimensional map of millions of stars in the Milky Way and beyond. It not only charts their positions but also their motions (including radial velocity), as well as temperatures and compositions. Combined with high-precision data from VELOCE about Cepheids, astronomers should soon be able to get a handle on stellar and galactic evolutionary history.

For More Information

High-precision Measurements Challenge the Understanding of Cepheids
VELOcities of CEpheids (VELOCE)

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