In this illustration, the Dragonfly helicopter drone is descending to the surface of Titan. Image: NASA
The only thing cooler than sending a helicopter drone to explore Titan is sending a nuclear powered one to do the job. Called the “Dragonfly” spacecraft, this helicopter drone mission has been selected as one of two finalists for NASA’s robotic exploration missions planned for the mid 2020’s. NASA selected the Dragonfly mission from 12 proposals they were considering under their New Horizons program.
Titan is Saturn’s largest moon, and is a primary target in the search for life in our Solar System. Titan has liquid hydrocarbon lakes on its surface, a carbon-rich chemistry, and sub-surface oceans. Titan also cycles methane the way Earth cycles water.
This true-color image of Titan, taken by the Cassini spacecraft, shows the moon’s thick, hazy atmosphere. Image: By NASA – http://photojournal.jpl.nasa.gov/catalog/PIA14602, Public Domain, https://commons.wikimedia.org/w/index.php?curid=44822294
Dragonfly would fulfill its mission by hopping around on the surface of Titan. Once an initial landing site is selected on Titan, Dragonfly will land there with the assistance of a ‘chute. Dragonfly will spend periods of time on the ground, where it will charge its batteries with its radioisotope thermoelectric generator. Once charged, it would then fly for hours at time, travelling tens of kilometers during each flight. Titan’s dense atmosphere and low gravity (compared to Earth) allows for this type of mission.
During these individual flights, potential landing sites would be identified for further scientific work. Dragonfly will return to its initial landing site, and only visit other sites once they have been verified as safe.
Dragonfly is being developed at the Johns Hopkins Applied Physics Laboratory (JHAPL.) It has a preliminary design weight of 450 kg. It’s a double quad-copter design, with four sets of dual rotors.
“Titan is a fascinating ocean world,” said APL’s Elizabeth Turtle, principal investigator for Dragonfly. “It’s the only moon in the solar system with a dense atmosphere, weather, clouds, rain, and liquid lakes and seas—and those liquids are ethane and methane. There’s so much amazing science and discovery to be done on Titan, and the entire Dragonfly team and our partners are thrilled to begin the next phase of concept development.”
The science objectives of the Dragonfly mission center around prebiotic organic chemistry and habitability on Titan. It will likely have four instruments:
Being chosen as a finalist has the team behind Dragonfly excited for the project. “This brings us one step closer to launching a bold and very exciting space exploration mission to Titan,” said APL Director Ralph Semmel. “We are grateful for the opportunity to further develop our New Frontiers proposals and excited about the impact these NASA missions will have for the world.”
Exploring Titan holds a daunting set of challenges. But as we’ve seen in recent years, NASA and its partners have the capability to meet those challenges. The JHAPL team behind Dragonfly also designed and built the New Horizons mission to Pluto and the Kuiper Belt object 2014 MU69. Their track record of success has everyone excited about the Dragonfly mission.
The Dragonfly mission, and the other finalist—the Comet Astrobiology Exploration Sample Return being developed by Cornell University and the Goddard Space Flight Center—will each receive funding through the end of 2018 to work on the concepts. In the Spring of 2019, NASA will select one of them and will fund its continued development.
Dragonfly is part of NASA’s New Frontiers program. New Frontiers missions are planetary science missions with a cap of approximately $850 million. New Frontiers missions include the Juno mission to Jupiter, the Osiris-REx asteroid sample-return missions, and the aforementioned New Horizons mission to Pluto.
Artist's impression of a hypothetical planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Credit: ESO
At a distance of 4.37 light-years from Earth, Alpha Centauri is the nearest star system to our own. For generations, scientists and speculative thinkers have pondered whether it might have a planetary system like our own Sun, and whether or not life may also exist there. Unfortunately, recent efforts to locate extra-solar planets in this star system have failed, with potential detections later shown to be the result of artifacts in the data.
In response to these failed efforts, several more ambitious projects are being developed to find exoplanets around Alpha Centauri. These include direct-imaging space telescopes like Project Blue and the interstellar mission known as Breakthrough Starshot. But according to a new study led by researchers from Yale University, existing data can be used to determine the probability of planets in this system (and even which kind).
The study which detailed their findings recently appeared in The Astronomical Journal under the title “Planet Detectability in the Alpha Centauri System“. The study was led by Lily Zhao, a graduate student from Yale University and a fellow with the National Science Foundation (NSF), and was co-authored by Debora Fischer, John Brewer and Matt Giguere of Yale and Bárbara Rojas-Ayala of the Universidad Andrés Bello in Chile.
Artist’s impression of what the surface might look like on a planet orbiting Alpha Centauri system. Credit: Michael S. Helfenbein
For the sake of their study, Zhao and her team considered why efforts to locate planets within the the closest star system to our own have so far failed. This is surprising when one considers how, statistically speaking, Alpha Centauri is very likely to have a system if its own. As Prof. Fischer indicated in a recent Yale News press release:
“The universe has told us the most common types of planets are small planets, and our study shows these are exactly the ones that are most likely to be orbiting Alpha Centauri A and B… Because Alpha Centauri is so close, it is our first stop outside our solar system. There’s almost certain to be small, rocky planets around Alpha Centauri A and B.”
In addition to being a professor of astronomy at Yale University, Debora Fischer is also one of the leaders of the Yale Exoplanets Group. As an expert in her field, Fischer has devoted decades of her life to researching exoplanets and searching for Earth analogues beyond our Solar System. With partial funding provided by NASA and the National Science Foundation, the team relied on existing data collected by some of the latest exoplanet-hunting instruments.
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
Using ten years of data collected by these instruments, Zhao and her colleagues then set up a grid system for the Alpha Centauri system. Rather than looking for signs of planets that did exist, they used the data to rule out what types of planets could not exist there. As Zhao told Universe Today via email:
“This study was special in that it used existing data of the Alpha Centauri system not to find planets, but to characterize what planets could not exist. By doing so, it returned more information about the system as a whole and provides guidance for future observations of this uniquely charismatic system.
In addition, the team analyzed the chemical composition of the stars in the Alpha Centauri system to learn more about the kinds of material that would be available to form planets. Based on the different values obtained by observations campaigns conducted by different telescopes on Alpha Centauri’s three stars (Alpha, Beta and Proxima), they were able to place constraints on what kinds of planets could exist there.
“We found that existing data rules out planets in the habitable zone above 53 Earth masses for alpha Centauri A, 8.4 Earth masses for Alpha Centauri B, and 0.47 Earth masses for Proxima Centauri,” said Zhao. “As for the chemical compositions, we found that the ratios of Carbon/Oxygen and Magnesium/Silicon for Alpha Centauri A and B are quite similar to that of the Sun.”
Artist’s impression of how the surface of a planet orbiting a red dwarf star may appear. Credit: M. Weiss/CfA
Basically, the results of their study effectively ruled out the possibility of any Jupiter-sized gas giants in the Alpha Centauri system. For Alpha Centauri A, they further found that planets that were less than 50 Earth masses could exist, while Alpha Centauri B might have planets smaller than 8 Earth masses. For Proxima Centauri, which we know to have at least one Earth-like planet, they determined that there might more that are less than half of Earth’s mass.
In addition to offering hope for exoplanet-hunters, this study carries with it some rather interesting implications for planetary habitability. Basically, the presence of rocky planets in the system is encouraging; but with no gas giants, a key ingredient in ensuring that planets remain habitable could be missing.
“[N]ot only could there still be habitable, Earth-mass planets around our closest stellar neighbors, but there also aren’t any gas giants that could endanger the survival of these potentially habitable, rocky planets,” said Zhao. “Furthermore, if these planets do exist, they are likely to have similar compositions to our very own Earth given the similarity in Alpha Cen A/B and our beloved Sun.”
At present, there are no instruments that have been able to confirm the existence of any exoplanets in Alpha Centauri. But as Zhao indicated, her and her teammates are optimistic that future surveys will have the necessary sensitivity to do it:
“[T]his very month has seen the commissioning of several next-generation instruments promising the precision necessary to discover these possible planets in the near future, and this analysis has shown that it is for sure worth it to keep looking!”
The ESO’s Paranal Observatory, located in the Atacama Desert of Chile. Credit: ESO
“These instruments are promising a precision of down to 10-30 cm/s and should be able to detect many more smaller, and further away planets – such as habitable planets around the Centauri stars,” said Zhao. “The field of view of these two instruments are slightly different (ESPRESSO has the southern hemisphere, where Alpha Centauri is, while EXPRES covers the northern hemisphere, for instance where the Kepler and many of the K2 fields are).”
With new instruments at their disposal, and methods like the one Zhao and her team developed, the closest star system to Earth is sure to become a veritable treasure trove for astronomers and exoplanet-hunters in the coming years. And anything we find there will surely become targets for direct studies by groups like Project Blue and Breakthrough Starshot. If ET resides next door, we’re sure to hear about it soon!
A new study by an international team of scientists considers whether Mars and Earth formed farther away from the Sun than previously thought. Credit: NASA/JPL-Caltech/USGS
In recent years, astronomers have been looking to refine our understanding of how the Solar System formed. On the one hand, you have the traditional Nebular Hypothesis which argues that the Sun, the planets, and all other objects in the Solar System formed from nebulous material billions of years ago. However, astronomers traditionally assumed that the planets formed in their current orbits, which has since come to be questioned.
This has come to be challenged by theories like the Grand Tack model. This theory states that Jupiter migrated from its original orbit after it formed, which had a big impact on the inner Solar System. And in a more recent study, an international team of scientists have taken things a step further, proposing that Mars actually formed in what is today the Asteroid Belt and migrated closer to the Sun over time.
Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration
For the sake of their study, the team addressed one of the most glaring issues with traditional models of Solar System formation. This is the assumption that Mars, Earth and Venus formed closely together and that Mars migrated outward to its current orbit. In addition, the theory holds that Mars – roughly 53% as large as Earths and only 15% as massive – is essentially a planetary embryo that never became a full, rocky planet.
However, this has contradicted by bulk elemental and isotopic studies performed on Martian meteorites, which have noted key differences in composition between Mars and Earth. As Brasser and his team indicated in their study:
“This suggests that Mars formed outside of the terrestrial feeding zone during primary accretion. It is therefore probable that Mars always remained significantly farther from the Sun than Earth; its growth was stunted early and its mass remained relatively low.”
To test this hypothesis, the team conducted dynamical simulations that were consistent with the Grand Tack model. In these simulations, Jupiter moved a large concentration of mass towards the Sun at it migrated towards the inner Solar System, which had a profound influence on the formation and orbital characteristics of the terrestrial planets (Mercury, Venus, Earth and Mars).
The theory also holds that this migration pulled material away from Mars, thus accounting for the compositional differences and the planet’s smaller size and mass relative to Venus and Earth. What they found was that in a small percentage of their simulations, Mars formed farther from the Sun and that Jupiter’s gravitational pull pushed Mars into its current orbit.
The Grand Tack model (top) compared to the traditional theories about how the Inner Solar System formed. Credit: Sean Raymond/planetplanet.net
From this, the team concluded that either scientists lack the necessary mechanisms to explain Mars’ formation, or that of all the possibilities, this statistically rare scenario is indeed the correct one. As Stephen Mojzsis – a geological sciences professor at the University of Colorado and a co-author on the study – indicated in a recent interview with Astrobiology Magazine, the fact that the scenario is rare does not make it any less plausible:
“Given enough time, we can expect these events. For example, you’ll eventually get double sixes if you roll the dice enough times. The probability is 1/36 or roughly the same as we get for our simulations of Mars’ formation.”
In truth, a 2% probability (which is what they obtained from the simulations) is hardly poor odds when considered in cosmological terms. And when one considers that such a possibility would allow for the key differences between Mars and its terrestrial cousins (i.e. Earth and Venus), this slim probability appears rather possible. However, the idea that Mars migrated inward during the course of its history also carries with it some serious implications.
For starters, the researchers were pressed to explain how Mars could have possessed a thicker, warmer atmosphere that would have allowed for liquid water to exist on the surface. If Mars actually formed in the modern-day Asteroid Belt, it would have been subject to far less solar flux, and surface temperatures would have been significantly lower than if it had formed in its present-day location.
Scientists were able to gauge the rate of water loss on Mars by measuring the ratio of water and HDO from today and 4.3 billion years ago. Credit: Kevin Gill
However, as they go to indicate, if Mars had enough carbon-dioxide in its early atmosphere, then it is possible that impacts during the Late Heavy Bombardment could have allowed for intermittent periods where liquid water could exist on the surface. Or as they explain it:
“Unless, as our model shows, an intrinsically volatile-rich Mars possessed a strong and sustainable greenhouse atmosphere, its average surface temperature was unremittingly below 0 °C. Such a cold surface environment would have been regularly affected by early impact bombardments that both restarted a moribund hydrological cycle, and provided a haven for possible early life in the martian crust.”
Basically, while Mars would have been subject to less in the way of solar energy during its early lifespan, its possible it could have still been warm enough to support liquid water on its surface. And as Mojzsis stated in a paper he co-authored last year, the many bombardments it received (as attested to by its many craters) would have been enough to melt surface ice, thicken the atmosphere, and trigger a periodic hydrological cycle.
Another interesting thing about this study is how it predicts that Venus likely has a bulk composition (including its oxygen isotopes) that is similar to that of the Earth-Moon system. According to their simulations, this is due to the fact that Venus and Earth always shared the same building blocks, whereas Earth and Mars did not. These findings were consistent with recent ground-based infrared observations of Venus and its atmosphere.
Artist’s impression of the joint NASA-Roscosmos Venera-D mission concept, which wold include a Venus orbiter and a lander designed to survive on Venus’ surface for a few hours. Credit: NASA/JPL-Caltech
But of course, no definitive conclusions can be drawn about that until samples of Venus’ crust can be obtained. This could be accomplished if and when the proposed Venera-Dolgozhivuschaya (Venera-D) mission – a joint NASA/Roscomos plan to send a orbiter and lander to Venus – is launched in the coming decade. In the meantime, there are other outstanding issues in the Grand Tack model and Nebular Hypothesis that need to be addressed.
According to Mojzsis, these include how the gas/ice giants of the Solar System could have formed in their current locations. The idea that they formed in their current orbits beyond the Asteroid Belt seems inconsistent with models of the early Solar System, which show that there was not enough of the necessary material that far from the Sun. An alternative is that they formed closer to the Sun and also migrated outward.
As Mojzsis explained, this possibility is bolstered by recent studies of extra-solar planetary systems, where gas giants have been found to orbit very close to their stars (i.e. “Hot Jupiters”) and farther away:
“We understand from direct observations via the Kepler Space Telescope and earlier studies that giant planet migration is a normal feature of planetary systems. Giant planet formation induces migration, and migration is all about gravity, and these worlds affected each other’s orbits early on.”
If there’s one benefit to being able to look farther out into the Universe, its the way it has allowed astronomers to come up with better and more complete theories of how the Solar System came to be. And as our exploration of the Solar System continues to grow, we are sure to learn many things that will help advance our understanding of other star systems as well.
Artist's impression of vessels floating near GJ436 its exoplanet, which orbits its star from pole to pole. Credit: University of Geneva/Denis Bajram
When we think of other planetary systems, we tend to think that they will operate by the same basic rules as our own. In the Solar System, the planets orbit close to the equatorial plane of the Sun – meaning around its equator. The Sun’s rotational axis, the direction of its poles based to its rotation, is also the same as most of the planets’ (the exception being Uranus, which rotates on its side).
But if the study of extra-solar planets has taught us anything, it is that the Universe is full of possibilities. Consider the star known as GJ436, a red dwarf located about 33 light-years from Earth. For years, astronomers have known that this star has a planet that behaves very much like a comet. But according to a recent study led by astronomers from the University of Geneva (UNIGE), this planet also has a very peculiar orbit.
Artist’s concept of the Neptune-sized planet Gliese 436b, surrounded by an envelop of hydrogen gas. Credit: NASA/ESA/STScI/G. Bacon
GJ436 has already been the source of much scientific interest, thanks in part to the discovery that its only confirmed exoplanet has a gaseous envelop similar a comet. This exoplanet, known as GJ436b, was first observed in 2004 using radial velocity measurements taken by the Keck Observatory. In 2007, GJ436b became the first Neptune-sized planet known to be orbiting very closely to its star (aka. a “Hot Neptune”).
And in 2015, GJ436 b made headlines again when scientists reported that its atmosphere was evaporating, resulting in a giant cloud around the planet and a long, trailing tale. This cloud was found to be the result of hydrogen in the planet’s atmosphere evaporating, thanks to the extreme radiation coming from its star. This never-before-seen phenomena essentially means that GJ436 b looks like a comet.
Another interesting fact about this planet is its orbital inclination, which astronomers have puzzled over for the past 10 years. Unlike the planets of the Solar System – whose orbits are largely circular – GJ436b follows a very eccentric, elliptical path. And as the research team indicated in their study, the planet also doesn’t orbit along the star’s equatorial plane, but passes almost above the its poles.
As Vincent Bourrier – a researcher at the Department of Astronomy of the UNIGE Faculty of Science, a member of the European Research Council project FOUR ACES, and the lead author of the study – explained in a UNIGE press release:
“This planet is under enormous tidal forces because it is incredibly close to its star, barely 3% of the Earth-Sun distance. The star is a red dwarf whose lifespan is very long, the tidal forces it induces should have since circularized the orbit of the planet, but this is not the case!”
Artist’s impression of JG436b, a hot Neptune located about 33 light years from Earth. Credit: Courtesy Space Telescope Science Institute
This was an especially interesting find for many reasons. On the one hand, it is the first instance where a planet was found to have a polar orbit. On the other, studying how planets orbit around a star is a great way to learn more about how that system formed and evolved. For instance, if a planet has been disturbed by the passage of a nearby star, or is being influenced by the presence of other massive planets, that will be apparent from its orbit.
As Christophe Lovis, a UNIGE researcher and co-author of the study, explained:
“Even if we have already seen misaligned planetary orbits, we do not necessarily understand their origin, especially since here it is the first time we measure the architecture of a planetary system around a red dwarf.”
Hervé Beust, an astronomer from the University of Grenobles Alpes, was responsible for doing the orbital calculations on GJ436b. As he indicated, the likeliest explanation for GJ436b’s orbit is the existence of a more massive and more distant planet in the system. While this planet is not currently known, this could be the first indication that GJ436 is a multi-planet system.
“If that is true, then our calculations indicate that not only would the planet not move along a circle around the star, as we’ve known for 10 years, but it should also be on a highly inclined orbit,” he said. “That’s exactly what we just measured!”
Artist impression of what GJ436b might look like. Credit: NASA
Another interesting takeaway from this study was the prediction that the planet has not always orbited so closely to its star. Based on their calculations, the team hypothesizes that the GJ436b may have migrated over time to become a “evaporating planet” that it is today. Here too, the existence of an as-yet-undetected companion is believed to be the most likely cause.
As with all exoplanet studies, these findings have implications for our understanding of the Solar System as well. Looking ahead, the team hopes to conduct further studies of this system in the hopes of determining if there is an elusive planetary companion to be found. These surveys will likely benefit from the deployment of next-generation missions, particularly the James Webb Space Telescope (JWST).
As Bourier indicated, “Our next goal is to identify the mysterious planet that has upset this planetary system.” Locating it will be yet another indirect way in which astronomers discover exoplanets – determining the presence of other planets based on orbital inclination of already discovered ones. The orbital inclination method, perhaps?
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
We record the Weekly Space Hangout every Wednesday at 5:00 pm Pacific / 8:00 pm Eastern. You can watch us live on Universe Today, or the Weekly Space Hangout YouTube page – Please subscribe!
Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar object, named 1I/2017 U1 (aka. ‘Oumuamua). After originally hypothesizing that it was a comet, observations performed by the European Southern Observatory (ESO) and other astronomers indicated that it was likely a strange-looking asteroid measuring about 400 meters (1312 ft) long.
Since that time, multiple surveys have been conducted to determine the true nature of this asteroid, which have included studies of its composition to Breakthrough Listen‘s proposal to listen to it for signs of radio transmissions. And according to the latest findings, it seems that ‘Oumuamua may actually be more icy than previously thought (thus indicated that it is a comet) and is not an alien spacecraft as some had hoped.
‘Oumuamua, as imaged by the William Herschel Telescope on October 29th, 2017. Credit: Queen’s University Belfast/William Herschel Telescope
As they indicate in their study, the team relied on information from the ESO’s Very Large Telescope in Chile and the William Herschel Telescope in La Palma. Using these instruments, they were able to obtain spectra from sunlight reflected off of ‘Oumuamua within 48 hours of the discovery. This revealed vital information about the composition of the object, and pointed towards it being icy rather than rocky. As Fitzsimmons explained in op-ed piece in The Conversation:
“Our data revealed its surface was red in visible light but appeared more neutral or grey in infra-red light. Previous laboratory experiments have shown this is the kind of reading you’d expect from a surface made of comet ices and dust that had been exposed to interstellar space for millions or billions of years. High-energy particles called cosmic rays dry out the surface by removing the ices. These particles also drive chemical reactions in the remaining material to form a crust of chemically organic (carbon-based) compounds.”
These findings not only addressed a long-standing question about ‘Oumuamua true nature, it also addresses the mystery of why the object did not experience outgassing as it neared our Sun. Typically, comets experience sublimation as they get closer to a star, which results in the formation of a gaseous envelope (aka. “halo”). The presence of an outer layer of carbon-rich material would explain why this didn’t happen ‘Oumuamua.
They further conclude that the red layer of material could be the result of its interstellar journey. As Fitzsommons explained, “another study using the Gemini North telescope in Hawaii showed its color is similar to some ‘trans-Neptunian objects’ orbiting in the outskirts of our solar system, whose surfaces may have been similarly transformed.” This red coloring is due to the presence of tholins, which form when organic molecules like methane are exposed to ultra-violet radiation.
Similarly, another enduring mystery about this object was resolved thanks to the recent efforts of Breakthrough Listen. As part of Breakthrough Initiatives’ attempts to explore the Universe and search for signs of Extra-Terrestrial Intelligence (ETI), this project recently conducted a survey of ‘Oumuamua to determine if there were any signs of radio communications coming from it.
While previous studies had all indicated that the object was natural in origin, this survey was more about validating the sophisticated instruments that Listen relies upon. The observation campaign began on Wednesday, December 13th, at 3:00 pm EST (12:00 PST) using the Robert C. Byrd Greenbank Radio Telescope, the world’s premiere single-dish radio telescope located in West Virginia.
The observations period was divided into four “epochs” (based on the object’s rotational period), the first of which ran from 3:45 pm to 9:45 pm ET (12:45 pm to 6:45 pm PST) on Dec 13th, and last for ten hours. During this time, the observation team monitored ‘Oumuamua across four radio bands, ranging from the 1 to 12 GHz bands. In addition to calibrating the instrument, the survey accumulated 90 terabytes of raw data over after observing ‘Oumuamua itself for two hours.
“It is great to see data pouring in from observations of this novel and interesting source. Our team is excited to see what additional observations and analyses will reveal”.
So far, no signals have been detected, but the analysis is far from complete. This is being conducted by Listen’s “turboSETI” pipeline, which combs the data for narrow bandwidth signals that are drifting in frequency. This consists of filtering out interference signals from human sources, then matching the rate at which signals drift relative to the expected drift caused by ‘Oumuamua’s own motion.
In so doing, the software attempts to identify any signals that might be coming from ‘Oumuamua itself. So far, data from the S-band receiver (frequencies ranging from 1.7 to 2.6 GHz) has been processed, and analysis of the remaining three bands – which corresponds to receivers L, X, and C is ongoing. But at the moment, the results seem to indicate that ‘Oumuamua is indeed a natural object – and an interstellar comet to boot.
This is certainly bad news for those who were hoping that ‘Oumuamua might be a massive cylinder-shaped generation ship or some alien space probe sent to communicate with the whales! I guess first contact – and hence, proof we are NOT alone in the Universe – is something we’ll have to wait a little longer for.
Artist's illustration of two merging neutron stars. The narrow beams represent the gamma-ray burst while the rippling spacetime grid indicates the isotropic gravitational waves that characterize the merger. Swirling clouds of material ejected from the merging stars are a possible source of the light that was seen at lower energies. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet
Shortly thereafter, scientists at LIGO, Advanced Virgo, and the Fermi Gamma-ray Space Telescope were able to determine where in the sky the neutron star merger occurred. While many studies have focused on the by-products of this merger, a new study by researchers from Trinity University, the University of Texas at Austin and Eureka Scientific, has chosen to focus on the remnant, which they claim is likely a black hole.
For the sake of their study, which recently appeared online under the title “GW170817 Most Likely Made a Black Hole“, the team consulted data from the Chandra X-ray Observatory to examine what resulted of the supernova merger. This data was obtained during Director’s Discretionary Time observations that were made on December 3rd and 6th, 2017, some 108 days after the merger.
This data showed a light-curve increase in the X-ray band which was compatible to the radio flux increase that was reported by a previous study conducted by the same team. These combined results suggest that radio and X-ray emissions were being produced at the same source, and that the rising light-curve that followed the merger was likely due to an increase in accelerated charged particles in the external shock – the region where an outflow of gas interacts with the interstellar medium.
As they indicate in their study, this could either be explained as the result of a more massive neutron star being formed from the merger, or a black hole:
“The merger of two neutron stars with mass 1.48 ± 0.12 M and 1.26 ± 0.1 M — where the merged object has a mass of 2.74 +0.04-0.01 M… could result in either a neutron star or a black hole. There might also be a debris disk that gets accreted onto the central object over a period of time, and which could be source of keV X-rays.”
The team also ruled out various possibilities of what could account for this rise in X-ray luminosity. Basically, they concluded that the X-ray photons were not coming from a debris disk, which would have been left over from the merger of the two neutron stars. They also deduced that they would not be produced by a relativistic jet spewing from the remnant, since the flux would be much lower after 102 days.
Collisions of neutron stars produce powerful gamma-ray bursts – and heavy elements like gold. Credit: Dana Berry, SkyWorks Digital, Inc.
All of this indicated that the remnant was more likely to be a black hole than a hyper-massive neutron star. As they explained:
“We show next that if the merged object were a hyper-massive neutron star endowed with a strong magnetic field, then the X-ray luminosity associated with the dipole radiation would be larger than the observed luminosity 10 days after the event, but much smaller than the observed flux at t ~ 100 days. This argues against the formation of a hyper-massive neutron star in this merger.”
Last, but not least, they considered the X-ray and radio emissions that were present roughly 100 days after the merger. These, they claim, are best explained by continued emissions coming from the merger-induced shock (and the not remnant itself) since these emissions would continue to propagate in the interstellar medium around the remnant. Combined with early X-ray data, this all points towards GW170817 now being a black hole.
The first-ever detection of gravitational waves signaled the dawn of a new era in astronomical research. Since that time, observatories like LIGO, Advanced Virgo, and GEO 600 have also benefited from information-sharing and new studies that have indicated that mergers are more common than previously thought, and that gravity waves could be used to probe the interior of supernovae.
With this latest study, scientists have learned that they are not only able to detect the waves caused by black hole mergers, but even the creation thereof. At the same time, it shows how the study of the Universe is growing. Not only is astronomy advancing to the point where we are able to study more and more of the visible Universe, but the invisible Universe as well.
In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle
With every passing year, more and more extra-solar planets are discovered. To make matters more interesting, improvements in methodology and technology are allowing for the discovery of more planets within individual systems. Consider the recent announcement of a seven-planet system around the red dwarf star known as TRAPPIST-1. At the time, this discovery established the record for most exoplanets orbiting a single star.
Well move over TRAPPIST-1! Thanks to the Kepler Space Telescope and machine learning, a team from Google AI and the Harvard-Smithsonian Center of Astrophysics (CfA) recently discovered an eighth planet in the distant star system of Kepler-90. Known as Kepler -90i, the discovery of this planet was made possible thanks to Google algorithms that detected evidence of a weak transit signal in the Kepler mission data.
Welcome, come in to the 540th Carnival of Space! The Carnival is a community of space science and astronomy writers and bloggers, who submit their best work each week for your benefit. So now, on to this week’s stories! Continue reading “Carnival of Space #540”
Our journey through interesting science fiction, this time we talk about speculative fiction dealing with materials science, nanotechnology and 3D printing. It’s a staple in Star Trek, but what other stories deal with it?
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
