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Showing posts with label Space & Astrophysics. Show all posts
Showing posts with label Space & Astrophysics. Show all posts

Wednesday, 1 April 2020

Early Mars Had Multiple Water Sources, New Study Shows

An analysis of two Martian meteorites — Northwest Africa (NWA) 7034 and Allan Hills (ALH) 84001 — shows that Mars likely received water from at least two vastly different sources early in its history; the variability implies that Mars, unlike Earth and the Moon, never had a global ocean of magma.

A close view of the surface of Mars. What lies below continues to intrigue.

“These two different sources of water in Mars’ interior might be telling us something about the kinds of objects that were available to coalesce into the inner, rocky planets,” said Dr. Jessica Barnes, a researcher at NASA’s Johnson Space Center and the Lunar and Planetary Laboratory at the University of Arizona.

“Two distinct planetesimals with vastly different water contents could have collided and never fully mixed. This context is also important for understanding the past habitability and astrobiology of Mars.”

Dr. Barnes and colleagues were able to piece together Mars’ water history by looking for clues in two isotopes of hydrogen: light hydrogen and deuterium.

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The researchers analyzed samples they knew were originated from the Martian crust: NWA 7034 (also known as the Black Beauty meteorite) and ALH 84001 meteorites.

Black Beauty was especially helpful because it’s a mashup of surface material from many different points in Mars’ history.

“This allowed us to form an idea of what Mars’ crust looked like over several billions of years,” Dr. Barnes said.

The isotopic ratios of the meteorite samples fell about midway between the value for Earth rocks and Mars’ atmosphere.

When the team’s findings were compared with previous studies, including results from NASA’s Curiosity rover, it seems that this was the case for most of Mars’ 4 billion-plus-year history.



“We thought, ok this is interesting, but also kind of weird. How do we explain this dichotomy where the Martian atmosphere is being fractionated, but the crust is basically staying the same over geological time?” Dr. Barnes said.

The scientists also grappled with trying to explain why the crust seemed so different from the Martian mantle, the rock later which lies below.

“If you try and explain this fairly constant isotopic ratio of Mars’ crust, you really can’t use the atmosphere to do that. But we know how crusts are formed. They’re formed from molten material from the interior that solidifies on the surface,” Dr. Barnes said.

“The prevailing hypothesis before we started this work was that the interior of Mars was more Earthlike and unfractionated, and so the variability in hydrogen isotope ratios within Martian samples was due to either terrestrial contamination or atmospheric implantation as it made its way off Mars.”

Illustration showing the present-day hydrogen reservoirs in and on Mars. The mass fractions (pie chart) of Martian water are based on the mass of water in the bulk crust (C), the mantle (M) and the combined inventory (A) of the atmosphere and polar ice deposits (PID). The mantle mass fraction is the combination of depleted shergottites (DS) and enriched shergottites (ES). Image credit: Barnes et al, doi: 10.1038/s41561-020-0552-y.

The idea that Mars’ interior was Earthlike in composition came from one study of a Martian meteorite thought to have originated from the mantle — the interior between the planet’s core and its surface crust.

“However, Martian meteorites basically plot all over the place, and so trying to figure out what these samples are actually telling us about water in the mantle of Mars has historically been a challenge,” Dr. Barnes said.

“The fact that our data for the crust was so different prompted us to go back through the scientific literature and scrutinize the data.”

The study authors found that two geochemically different types of Martian volcanic rocks — enriched shergottites and depleted shergottites — contain water with different hydrogen isotope ratios.

Enriched shergottites contain more deuterium than the depleted shergottites, which are more Earth-like, they found.



“It turns out that if you mix different proportions of hydrogen from these two kinds of shergottites, you can get the crustal value,” Dr. Barnes said.

“We think that the shergottites are recording the signatures of two different hydrogen — and by extension, water — reservoirs within Mars. The stark difference hints to them that more than one source might have contributed water to Mars and that Mars did not have a global magma ocean.”


Bibliography:

Multiple early-formed water reservoirs in the interior of Mars

Jessica J. Barnes, Francis M. McCubbin, Alison R. Santos, James M. D. Day, Jeremy W. Boyce, Susanne P. Schwenzer, Ulrich Ott, Ian A. Franchi, Scott Messenger, Mahesh Anand & Carl B. Agee

Nat. Geosci. (2020).

https://doi.org/10.1038/s41561-020-0552-y

Friday, 13 March 2020

ESO Telescope detected Exoplanet Where It Rains Iron


Commissioned in 1998 in the Atacama Desert in Chile, the VLT has made it possible to make numerous discoveries thanks to all of the scientific instruments that compose it. In particular, it has ESPRESSO, a spectrograph which makes it possible to search for planets similar to Earth, but whose capacities have in fact been revealed to be much broader. Indeed, thanks to him, a team of astrophysicists was able to study a giant ultra-hot exoplanet on which it literally rains liquid iron.

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Researchers using ESO's Very Large Telescope (VLT) have observed an extreme planet where they suspect it rains iron. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400 degrees Celsius, high enough to vaporise metals. Strong winds carry iron vapour to the cooler night side where it condenses into iron droplets.

"One could say that this planet gets rainy in the evening, except it rains iron," says David Ehrenreich, a professor at the University of Geneva in Switzerland. He led a study, published today in the journal Nature, of this exotic exoplanet. Known as WASP-76b, it is located some 640 light-years away in the constellation of Pisces.



On day side and on night side with different atmospheric properties

This strange phenomenon happens because the 'iron rain' planet only ever shows one face, its day side, to its parent star, its cooler night side remaining in perpetual darkness. Like the Moon on its orbit around the Earth, WASP-76b is 'tidally locked': it takes as long to rotate around its axis as it does to go around the star.

Video showing the evolution of the WASP-76b exoplanet on its orbit:


On its day side, it receives thousands of times more radiation from its parent star than the Earth does from the Sun. It's so hot that molecules separate into atoms, and metals like iron evaporate into the atmosphere. The extreme temperature difference between the day and night sides results in vigorous winds that bring the iron vapour from the ultra-hot day side to the cooler night side, where temperatures decrease to around 1500 degrees Celsius.

Condensation and fallout of iron as precipitation

Not only does WASP-76b have different day-night temperatures, it also has distinct day-night chemistry, according to the new study. Using the new ESPRESSO instrument on ESO's VLT in the Chilean Atacama Desert, the astronomers identified for the first time chemical variations on an ultra-hot gas giant planet. They detected a strong signature of iron vapour at the evening border that separates the planet's day side from its night side. "Surprisingly, however, we do not see the iron vapour in the morning," says Ehrenreich. The reason, he says, is that "it is raining iron on the night side of this extreme exoplanet."

"The observations show that iron vapour is abundant in the atmosphere of the hot day side of WASP-76b," adds Marรญa Rosa Zapatero Osorio, an astrophysicist at the Centre for Astrobiology in Madrid, Spain, and the chair of the ESPRESSO science team. "A fraction of this iron is injected into the night side owing to the planet's rotation and atmospheric winds. There, the iron encounters much cooler environments, condenses and rains down."

This result was obtained from the very first science observations done with ESPRESSO, in September 2018, by the scientific consortium who built the instrument: a team from Portugal, Italy, Switzerland, Spain and ESO.

ESPRESSO -- the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations -- was originally designed to hunt for Earth-like planets around Sun-like stars. However, it has proven to be much more versatile. "We soon realised that the remarkable collecting power of the VLT and the extreme stability of ESPRESSO made it a prime machine to study exoplanet atmospheres," says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile.



"What we have now is a whole new way to trace the climate of the most extreme exoplanets," concludes Ehrenreich.


Bibliography:

Nightside condensation of iron in an ultrahot giant exoplanet.

Ehrenreich, D., Lovis, C., Allart, R. et al.

Nature, 2020;

DOI: 10.1038/s41586-020-2107-1

Friday, 21 February 2020

Special gravitational waves could explain the mystery of the existence of the Universe


According to the standard cosmological model, at the time of the Big Bang, matter and antimatter are created in identical proportions. They should therefore have annihilated themselves, leaving an empty universe. However, today, it is a universe composed mainly of matter that we observe. This defect in antimatter is called matter-antimatter asymmetry and constitutes one of the most active research themes in particle physics. Several hypotheses have been put forward: one of them suggests that neutrinos played a key role in this mechanism. And recently, physicists have proposed a way to test this hypothesis.

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The neutrino hypothesis suggests that about a million years after the Big Bang, the Universe has cooled and undergone a phase transition. This phase change caused the neutrinos to decay into more matter than antimatter, implying a violation of CP symmetry.

But according to Jeff Dror, lead author of the new study and postdoctoral researcher at the University of California at Berkeley, there is no simple way to probe this theory and understand if this process actually happened in the Universe. primitive. The results of the study were published in the journal Physical Review Letters.



A phase transition at the origin of the creation of cosmic strings

But Dror and his team, through theoretical models and calculations, found a way to see this phase transition. They proposed that the change would have created extremely long and thin strands of energy called cosmic cords , which are still present in the Universe today.

According to the authors, the phase transition at the origin of the matter-antimatter asymmetry would also have created particular structures called cosmic cords which, today, would be at the origin of detectable gravitational waves. Credits: R. Hurt / Caltech-JPL, NASA, and ESA Credit: Kavli IPMU

Cosmic cords are topological defects. Topological defects are hypothetical structures presumed stable which would have formed in the first moments of the Universe.

Theories implying the formation of topological defects predict that they would have appeared at the end of the inflationary period. More precisely, topological defects are deemed to have formed during the various phase transitions of the primitive universe.

In the Standard Model, these phase transitions are accompanied by different spontaneous symmetry breaks. The cosmic cords therefore appeared when, at the end of the inflationary period, cylindrical and axial symmetries were broken.

These are one-dimensional topological defects of linear form. The number of cosmic strings in the universe cannot be determined with certainty, however, Kibble's calculations indicate that there would be approximately one cosmic cord per Hubble volume, i.e., one cosmic cord every 10^31 cubic light years .

Cosmic strings: potential sources of gravitational waves

Dror and his team suggest that these cosmic cords are very likely to be the source of gravitational waves. The strongest gravitational waves occur when a supernova emerges; when two massive stars rotate around one another; or when two black holes merge. But the potential gravitational waves caused by cosmic cords would be much weaker than those detected so far.

Frequency and amplitude at which gravitational waves produced by cosmic strings can be detected. The detection sensitivities of current and future instruments are also indicated. Credits: Jeff A. Dror et al. 2020

However, when the team modeled this hypothetical phase transition under various temperature conditions that could have occurred during this phase transition, they made an encouraging discovery: In all cases, cosmic strings would create gravitational waves that would be detectable by future observatories, such as NASA's Laser Interferometer Space Antenna (LISA), the European Space Agency's proposed Big Bang Observer and the Japan Aerospace Exploration Agency's Deci-hertz Interferometer Gravitational wave Observatory (DECIGO).

"If these strings are produced at sufficiently high energy scales, they will indeed produce gravitational waves that can be detected by planned observatories," concludes Tanmay Vachaspati, a theoretical physicist at Arizona State University




Bibliography:

Testing the Seesaw Mechanism and Leptogenesis with Gravitational Waves

Jeff A. Dror, Takashi Hiramatsu, Kazunori Kohri, Hitoshi Murayama, and Graham White

Phys. Rev. Lett. 124, 041804

DOI:https://doi.org/10.1103/PhysRevLett.124.041804

Thursday, 20 February 2020

For the first time oxygen has been detected in another galaxy


Although it is ubiquitous on Earth, molecular oxygen (also called oxygen) is not so easy to find outside of our planet. By just two times, astrophysicists have detected them outside the Solar System. But recently, their instruments have identified traces of O2 even further, more than 500 million light years from Earth, outside the Milky Way. This important discovery, the first detection of dioxygen outside our galaxy , should help astrophysicists better understand the complex molecular dynamics of galactic regions.

Oxygen is the third most abundant element in the Universe, behind hydrogen and helium. Thus, its chemistry and its abundance in interstellar clouds are important for understanding the role of molecular gas in galaxies.

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Astronomers have searched for oxygen again and again, using millimetre astronomy, which detects the radio wavelengths emitted by molecules; and spectroscopy, which analyses the spectrum to look for wavelengths absorbed or emitted by specific molecules.

But these searches have turned up a puzzling lack of oxygen molecules. Which means "a comprehensive picture of oxygen chemistry in different interstellar environments is still missing," wrote a team of astronomers led by Junzhi Wang of the Chinese Academy of Sciences in a new paper.




Release of dioxygen into space: the molecular shock hypothesis

One place where molecular oxygen has already been detected is the Orion Nebula, it's been hypothesised that out in space, oxygen is bound up with hydrogen in the form of water ice that is clinging to dust grains.

But the Orion nebula is a stellar nursery, and it's possible that the intense radiation from very hot young stars shocks the water ice into sublimation and splits the molecules, releasing the oxygen. Astrophysicists then turned to the Markarian 231 galaxy.

In 2011, data from the Herschel satellite showed the presence of molecular oxygen in the Orion nebula. Credits: ESA

Markarian 231 is special. It is located 561 million light years away and contains a quasar. It is an extremely bright galactic nucleus with an active supermassive black hole in the center. These are the brightest objects in the Universe, and Markarian 231 contains the closest quasar to Earth. In fact, astronomers believe that Markarian 231 could have two active supermassive black holes in its center, swirling around each other.


Galactic molecular oxygen: potential interactions between molecular fluxes and molecular clouds

An active galactic nucleus induces molecular fluxes, producing such continuous shocks, which could release oxygen from the water in molecular clouds. Molecular fluxes from Markarian 231 are particularly rapid, so Wang and his colleagues went there to get oxygen. Using the 30-meter IRAM radio telescope in Spain, they made observations of the galaxy for four days, over several wavelengths.

Dioxygen spectrum in the Markarian 231 galaxy, established thanks to observations from the IRAM telescope for 4 days. Credits: Junzhi Wang et al. 2020

In those data, they found the spectral signature of oxygen, in line with the shock hypothesis.

"With deep observations toward Markarian 231 using the IRAM 30 meter telescope and NOEMA, we detected [molecular oxygen] emission in [an] external galaxy for the first time," the researchers wrote in their paper.

"The detected O2 emission is located in regions about 10 kpc (32,615 light-years) away from the center of Markarian 231 and may be caused by the interaction between the active galactic nucleus-driven molecular outflow and the outer disc molecular clouds."

The team's measurements revealed that the abundance of oxygen compared to hydrogen was around 100 times higher than that found in the Orion nebula, so the galaxy could be undergoing a more intense version of the same molecule-splitting process.

As Markarian is a starburst galaxy, undergoing furious star formation, this could be possible. Just one region in the galaxy is forming new stars at a rate of over 100 solar masses a year. The Milky Way, by contrast, is pretty quiet, with a star formation rate of around 1 to two solar masses.

Better understand the complex dynamics of galactic oxygen

On the other hand, these results could also mean that more observations need to be made to confirm the detection of oxygen. If the results are valid, the phenomenon could be used to better understand both molecular oxygen in galaxies and the molecular flow of an active galactic nucleus.



"This first detection of extragalactic molecular oxygen provides an ideal tool to study active galactic nucleus-driven molecular outflows on dynamic timescales of tens of megayears," they wrote.

"O2 may be a significant coolant for molecular gas in such regions affected by active galactic nucleus-driven outflows." conclude the authors.


Bibliography:

Molecular Oxygen in the Nearest QSO Mrk 231

Junzhi Wang, Di Li, Paul F. Goldsmith, Zhi-Yu Zhang, Yu Gao, Yong Shi8, Shanghuo Li, Min Fang, Juan Li, and Jiangshui Zhang

Published 2020 January 30

The Astrophysical Journal, Volume 889, Number 2

Tuesday, 11 February 2020

Physicists proposed a theory to get rid of Dark Energy



The Dark Energy theory, which would explain the acceleration and expansion of the Universe, has seen its number of followers drop dramatically.
The drop in popularity is no accident: All attempts to find any basis in reality for Dark Energy have so far failed.

Until the end of the last century, scientists believed that space is filled with ordinary matter — stars, planets, asteroids, comets and highly rarefied intergalactic gas. But, if this is so, then accelerated expansion is contrary to the law of gravity, which says that bodies are attracted to each other. Gravitational forces tend to slow down the expansion of the universe, but cannot accelerate it.

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But then the telescopes improved and measurements began to indicate that very distant stars and galaxies would be moving away from us at  faster rate - which indicates that the Universe is not just expanding, but expanding with acceleration.

“And then the idea was born that the Universe is filled for the most part not with ordinary matter, but with some “dark energy,” which has special properties. No one knows what is it and how it works, so it named “Dark Energy” as something unknown. And 70% of the Universe consists of this Energy.” contextualizes Professor Artyom Astashenok, from Immanuel Kant University, in Russia.

As the observational results to support this theory do not appear, Astashenok and his colleague Alexander Tepliakov went to look for explanations for the acceleration and expansion of the Universe that can work without having to appeal to Dark Energy or any other unknown entity.



And they found something that makes sense, just adding an idea that is not entirely foreign to physicists either: the proposal that the Universe has "edges".

Frontiers of the Universe

In their article, the pair presents a mathematically solid model of the Universe in which there is an additional repulsion capable of explaining the acceleration of expansion, and in which there is no contradiction between the fact that the expansion of the Universe is accelerating and the law of gravitation. universal.

Professor Astashenok himself explains the new theory:  “The so-called Casimir effect (named after the Dutch physicist Hendrik Casimir), which consists in the fact that two metal plates placed in a vacuum are attracted to each other, has long been known. It would seem that this cannot be, because there is nothing in the vacuum. But in fact, according to quantum theory, particles constantly appear and disappear there, and as a result of their interaction with plates, which indicate certain boundaries of space (which is extremely important), a very small attraction occurs. And there is an idea according to this, approximately the same thing happens in space. Only this leads, on the contrary, to additional repulsion, which accelerates the expansion of the Universe. That is, there is essentially no “Dark Energy,” but there is a manifestation of the boundaries of the Universe. This, of course, does not mean that it ends somewhere, but some kind of complex topology can take place. You can draw an analogy with the Earth. After all, it also has no boundaries, but it is finite. The difference between the Earth and the Universe is that in the first case we are dealing with two-dimensional space, and in the second — with three-dimensional.”



This is not the first time that an attempt has been made to create a way to dispense with dark energy , and it probably will not be the last.

After all, a whole generation of scientists graduated from this theory, the scientific community gave it the highest honor - the Nobel Prize in Physics - and millionaire projects are underway, which means that not everyone is willing to abandon the idea of ​​finding evidence of the so famous unknown energy.


Bibliography:

Article: Some models of holographic dark energy on the Randall-Sundrum brane and observational data

Authors: Artem V. Astashenok, Alexander S. Tepliakov

Magazine: International Journal of Modern Physics D

DOI: 10.1142 / S0218271819501761

Hawking radiation: researchers finally think they know how to detect and confirm it



In 1974, the physicist Stephen Hawking, while working on the thermodynamics of black holes , highlighted a theoretical process taking place on the edge of the event horizon: the radiation of Hawking . In the environment of a black hole , the gravitational field is so intense that it separates the pairs of particle-antiparticle resulting from the quantum fluctuations of the vacuum, one particle being absorbed and the other re-emitted. Possessing the electromagnetic characteristic of black body radiation, this radiation is still entirely theoretical. However, the gravitational data from the GW170817 event could contain indications of its presence.

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The existence of this radiation would mean that black holes evaporate slowly, resolving the information paradox. But, just like gravitational waves until just a few years ago, it is too weak to be detected by our current instruments.

However, two cosmologists have recently shown that gravitational waves could contain echoes of Hawking radiation. the study was published in the Journal of Cosmology and Astroparticle Physics.



Echoes of Hawking radiation in gravitational waves

The analogs of black holes developed in the laboratory seem to suggest that the Hawking radiation is real . But gravitational waves could play a role in the process. Because if Hawking's radiation is real, there should be a quantum “blur” around the outside of the event horizon of a black hole. And this “quantum fog” should produce an echo in the generated gravitational waves.

Spatiotemporal representation of the echoes of the gravitational waves of a membrane on the stretched horizon, following the gravitational collapse coming from a fusion of binary neutron stars . Credits: Jahed Abedi and Niayesh Afshordi

“Scientists have not been able to determine experimentally whether a material escapes from black holes until the very recent detection of gravitational waves. If the quantum blur responsible for the Hawking radiation exists around the black holes, the gravitational waves could bounce on it, which would create smaller gravitational wave signals after the main gravitational collision event, similar to repeated echoes.” Says Niayesh Ashfordi, astrophysicist at the University of Waterloo.

Potential echo cues to take with caution

This is what Afshordi and his colleague, the cosmologist Jahed Abedi of the Max Planck Institute for Gravitational Physics in Germany, think they could have detected in the gravitational data. Their results, they say, correspond to simulated echoes predicted by fuzzy black hole models emitting Hawking radiation. But there are some precautions to take.

Representation of the amplitude-frequency of the first echo peak 1 second after the fusion of the two Hawkings radiation stars (GW170817). The blue area between 63 Hz and 92 Hz is the frequency range in which an echo peak was most likely to occur. Credits: Jahed Abedi and Niayesh Afshordi

For one thing, an analysis last year of the gravitational wave data from GW150914 found no evidence of Hawking radiation. Additionally, another study from last year included a concerted analysis of all gravitational wave signals collected to date, looking for evidence of gravitational wave echoes and, by extension, Hawking radiation. The authors found no statistically significant evidence of echoes.



But it is quite possible, in fact, that our instruments are still not sensitive enough to detect Hawking radiation. And Afshordi recognizes that the signal detected by the team could in reality simply be a spurious noise in the data. The way to find out would be to look for similar signals in other gravitational wave data sets.


Bibliography:

Echoes from the Abyss: A highly spinning black hole remnant for the binary neutron star merger GW170817

Jahed Abedi, Niayesh Afshordi

arXiv:1803.10454v3

Sunday, 9 February 2020

Relativistic drag predicted by Einstein is confirmed

Artistic representation of the "reference drag": two stars orbiting each other twisting space and time

A century after it was theorized, astronomers detected the effects of the Lense-Thirring precession - a drag effect of relativistic references - on the movement of a binary star system, composed of a white dwarf and a pulsar.

Vivek Krishnan and colleagues from four countries analyzed twenty years of observational data from the binary to finally confirm this prediction, made by Einstein's general theory of relativity.

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When a massive object spins, general relativity predicts that it pulls space-time around it, a phenomenon known as frame drag.

This phenomenon causes the precession of the orbital movement of gravitationally coupled objects, such as the two bodies of a binary system - precession is the change in the axis of rotation of an object induced by another star, a very subtle gyroscopic effect, but one that can be imagined like a clumsy top that threatens to fall.



Although the trail of references has already been detected by artificial satellite experiments in the Earth's gravitational field, in these cases the effect is tremendously small and difficult to measure. More massive objects, such as white dwarfs or neutron stars, offer a better opportunity to observe the phenomenon under much more intense gravitational fields.

Artistic representation of a rapidly rotating neutron star and a white dwarf dragging the fabric of space-time around its orbit.

Precession

Vivek Krishnan and his colleagues observed PSR J1141-6545, a young pulsar spinning rapidly in a tight orbit around a huge white dwarf.
The pulsar is located 10,000 to 25,000 light-years from Earth in the constellation Musca (the fly), which is near the famous Southern Cross constellation.

A pulsar is a fast-spinning neutron star that emits radio waves along its magnetic poles. (Neutron stars are corpses of stars that died in catastrophic explosions known as supernovas; the gravity of these remnants is powerful enough to crush protons together with electrons to form neutrons.)

PSR J1141-6545 circles a white dwarf with a mass about the same as the sun's. White dwarfs are the superdense Earth-size cores of dead stars that are left behind after average-size stars have exhausted their fuel and shed their outer layers. Our sun will end up as a white dwarf one day, as will more than 90% of all stars in our galaxy.

The pulsar orbits the white dwarf in a tight, fast orbit less than 5 hours long, hurtling through space at about 620,000 mph (1 million km/h), with a maximum separation between the stars barely larger than the size of our sun,

They measured the arrival times of the pulses - a pulsar flashes as if it were a cosmic beacon - with an accuracy of 100 microseconds, over a period of almost twenty years, which allowed them to identify a long-term deviation in orbital parameters.



After eliminating other possible causes of this orbital drift, the team concluded that it is the result of the Lense-Thirring precession (Josef Lense [1890-1985] and Hans Thirring [1888-1976]) due to the rapid rotation of the white dwarf's companion.

These results confirm the prediction of general relativity and allowed the authors to improve the accuracy of the calculations of the speed of rotation of the white dwarf.


Bibliography:

Article: Lense-Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system

Authors: Vivek Venkatraman Krishnan, M. Bailes, W. van Straten, N.Wex, PCC Freire, EF Keane, TM Tauris, PA Rosado, NDR Bhat, C. Flynn, A. Jameson, S. Osowski

Magazine: Science

Vol .: 367, Issue 6477 pp. 577-580

DOI: 10.1126 / science.aax7007

Friday, 7 February 2020

SpaceX launches its online space launch reservation service. Prices start at a million dollars…


SpaceX has launched a new online booking tool. The service, already announced last year by the company, plans to mainly operate the most successful launcher so far, the Falcon 9. The prices for the “space carpooling” services that SpaceX offers on its website start at 1 million dollars for payloads up to 200 kg, with an additional cost of 10,000 dollars per additional kg.

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The selection tool asks to specify the desired orbit (synchronous with the Sun, low Earth or polar) as well as the minimum date of preparation (ie the closest at which the payload can be ready). The first dates proposed are in June 2020. The total mass of the load must then be entered in order to obtain an estimate of the cost.



We then access a series of screens where it is possible to add a 15 or 24 inch port if necessary (which largely depends on the volume and mass), as well as to choose the specific rocket on which one wishes to book the flight (from scheduled missions to come).

Home screen of the online booking tool. Credits: SpaceX

Other options include accessories such as port adapters to meet the standard dimensions used by SpaceX, as well as a separation system provided by SpaceX, with on-site fueling options if the spacecraft being dispatched has its own propulsion system. Insurance covering a maximum value of $ 2 million is also offered.

Credits: SpaceX


An instant booking tool

It is important to note that this is not just a simple lead generation form. In fact, once all the options have been selected and it is confirmed that you are not subject to any action or restriction on international arms trafficking (ITAR) imposed by the United States government, the system requests a number credit card to instantly deposit $ 5,000 as a deposit. The rest of the payment can then be made in three installments, after confirmation of the acceptance of your request by SpaceX.

A user guide, which provides more details on the program, including technical requirements, details on environmental testing, legal considerations and much more, is also available online.

Credits: SpaceX

Credits: SpaceX

This reservation system clearly shows how SpaceX is revolutionizing the space sector, in particular by making it more accessible to private companies. Indeed, it becomes almost as easy (as long as you have the necessary funds) to send an object into orbit aboard a reusable rocket as it is to reserve a car. To test the tool (or to book a real launch…), it's Here.



Reservation Link

Tuesday, 4 February 2020

The formation and dynamics of the ice cap of the South Pole of Mars finally explained



Although it has been studied for decades, the red planet still contains mysteries. For many years, a particular structure has caught the attention of planetologists, its origin remaining a mystery: an ice cap, composed of ice water and CO2, covering the South Pole of Mars. Recently, a team of NASA astrophysicists, using simulations, was able to confirm the generally advanced hypothesis to explain the formation and dynamics of this ice structure.

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The main assumption  is that these layers stacked on top of each other during variations in the tilt of the axis of Mars during its orbit around the Sun, and new simulations published in the journal confirm this idea. The ice cap in question is about a kilometer deep and is believed to contain as much CO2 as the Martian atmosphere today, and a combination of factors has produced this unusual layer pattern.



“Usually when you run a model, you don't expect the results to match as closely as you observe. But the thickness of the layers, determined by the model, perfectly matches the radar measurements of satellites in orbit,” explains Peter Buhler, planetologist at NASA's Jet Propulsion Laboratory.

Structural graph of the ice cap of the South Pole of Mars. Credits: PB Buhler et al. 2020

CO2 ice stabilized thanks to the dynamics of Mars

What makes the South Pole ice cap so strange is that it really shouldn't be there - water ice is more thermally stable and darker than CO2 ice, so planetologists would expect that the CO2 ice is destabilized when it is trapped under the water ice.

CO2 ice cycle on the ice cap of the South Pole of Mars. The dynamics of this ice are subject to climatic and atmospheric variations on the planet. Credits: PB Buhler et al. 2020

According to the new model, three factors prevented this from happening: the changing tilt of Mars as it orbits the Sun, the differences in how these two types of ice reflect sunlight, and the change in atmospheric pressure. which occurs when the CO2 ice turns to gas.

Oscillations of the obliquity of Mars responsible for the CO2 ice cap

The "oscillations" of Mars on its axis of rotation would change the amount of sunlight reaching the South Pole, forming CO2 ice during certain periods and sublimating it (by passing it from a solid to a gas) during other periods.

During periods of ice formation, water ice would be trapped alongside the CO2. As sublimation occurs, this more stable ice would remain behind, forming the layers now present at the South Pole of Mars.

(A and D): Graphs showing the variations in mass of CO2 as a function of the variations in obliquity of Mars. (E) Image showing the structure of the ice cap of the South Pole of Mars with comparison between the observations and the authors' model. Credits: PB Buhler et al. 2020

Over time, climate change on the red planet has not resulted in a systematic sublimation of CO2, piling up successive layers of CO2 ice and water ice. Models show that this process changes atmospheric pressure - between a quarter and twice the level it is today - just as Leighton and Murray predicted in the 1960s.

This has been going on for around 510,000 years, suggest the authors - since the last period of extreme solar illumination, when all of the CO2 had been sublimated in the Martian atmosphere. " Our determination of the history of the large pressure fluctuations of Mars is fundamental to understanding the evolution of the planet's climate, including the history of the stability and habitability of liquid water near the surface  " Buhler concludes.




Bibliography:

Coevolution of Mars’s atmosphere and massive south polar CO2 ice deposit

P. B. Buhler, A. P. Ingersoll, S. Piqueux, B. L. Ehlmann & P. O. Hayne

Nature Astronomy (2019)

https://doi.org/10.1038/s41550-019-0976-8

Saturday, 1 February 2020

In a binary system, a rapidly rotating white dwarf carries space-time with it



From black holes to gravitational waves to the effects of gravitational lenses, Albert Einstein's theory of general relativity has made many predictions that have been validated experimentally over time. However, some of these predictions are less known than others. This is the case of the Lense-Thirring effect, which describes a phenomenon of space-time training around very dense objects in very fast rotation. Launched in 2004, NASA's Gravity Probe B satellite made it possible to confirm this phenomenon experimentally in 2011. And recently, astrophysicists have once again been able to confirm the Lense-Thirring effect around a white dwarf as part of a binary system.

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In everyday life, this phenomenon is both undetectable and inconsequential, because the effect is ridiculously small. Detecting the spacetime entrainment caused by Earth's rotation requires satellites such as the $ 750 million Gravity probe B and detecting angular changes in gyroscopes equivalent to one degree every 100 '000 years approximately.



Fortunately, the Universe contains many natural gravitational laboratories where physicists can observe Einstein's predictions in detail. This new study, published in the journal Science , reveals evidence of the Lense-Thirring effect on a much more noticeable scale, using a radio telescope and a unique pair of compact stars rotating around each other. on the other at dizzying speeds.

A white dwarf and a pulsar to confirm the Lense-Thirring effect

The movement of these stars would have made astronomers perplexed at Newton's time, because they move in a distorted space-time, and require the general theory of relativity of Einstein to explain their trajectories. One of his least known predictions of this theory is that rotating bodies carry with them space-time. The faster an object turns and the more massive it is, the more powerful the drive.

White dwarfs are a great place to study this process. They are similar in size to Earth but hundreds of thousands of times more massive. They can also rotate very quickly, up to one revolution per minute. The training caused by such a white dwarf would be about 100 million times more powerful than that of Earth.

Illustration showing the Lense-Thirring effect as part of a white-pulsar dwarf binary system. Credits: Mark Myers / OzGrav ARC Center of Excellence

Twenty years ago, the CSIRO's Parkes radio telescope discovered a unique star pair made up of a white dwarf (the size of Earth but about 300,000 times more massive) and a radio-pulsar. Pulsars are made up of closely related neutrons , which makes them incredibly dense. In addition, they spin much faster than white dwarfs: 150 revolutions / minute for the pulsar studied by the authors.

PSR J1141-6545: an ideal gravitational laboratory for studying general relativity

This means that, 150 times per minute, a beam of radio waves emitted by this pulsar scans our point of observation here on Earth. Astrophysicists can use it to map the trajectory of the pulsar as it orbits the white dwarf, timing when its pulse arrives at the telescope, and knowing the speed of light. This method revealed that the two stars orbit each other in less than 5 hours.

This pair, officially called PSR J1141-6545, is an ideal gravitational laboratory. Since 2001, researchers have used Parkes several times a year to map the orbit of this system, which has a multitude of gravitational effects.



Although PSR J1141-6545 is several hundred quadrillion kilometers (one quadrillion represents a million billion), the data shows that the pulsar rotates 2.54 times per second, and that its orbit varies in space. This means that the plane of its orbit is not fixed, but rotates slowly.

Binary system: the companion star accelerates the rotation of the white dwarf

When pairs of stars are born, the most massive one dies first, often creating a white dwarf. Before the second star dies, it transfers matter to its white dwarf companion. A disc forms when this material falls towards the white dwarf, and over tens of thousands of years, it accelerates the latter, until it makes a complete revolution every few minutes.

Many binary systems involve a giant star and a white dwarf, the latter accreting matter from the former. This accretion leads to an acceleration of the rotation of the white dwarf. Credit: Pearson Ed

In rare cases like this, the second star can then explode as a supernova, leaving behind a pulsar. The rapidly spinning white dwarf carries space-time with it, rocking the pulsar's orbital plane as it moves. This inclination is what astrophysicists have observed through the mapping of the orbit of the pulsar.


Bibliography:

Lense–Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system

V. Venkatraman Krishnan, M. Bailes, W. van Straten, N. Wex, P. C. C. Freire, E. F. Keane, T. M. Tauris, P. A. Rosado, N. D. R. Bhat, C. Flynn, A. Jameson1, S. Osล‚owski

Science  31 Jan 2020:

Vol. 367, Issue 6477, pp. 577-580

DOI: 10.1126/science.aax7007

Thursday, 30 January 2020

Discover these spectacular images of the Sun with the highest resolution ever

The highest resolution image of the Sun’s surface ever taken. | NSO / AURA / NSF

A new telescope specially designed to study the Sun has released its first images, and they are breathtaking. They show the surface of the Sun like never before, revealing the extraordinary details of its surface, convection granules the size of Texas as well as tiny magnetic characteristics (like lines of magnetic field which extend in space).

The telescope that provided these images is the National Science Foundation's Daniel K. Inouye Solar Telescope, located in Haleakalฤ (Maui), Hawaii.

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His future observations will provide a much broader insight into the wild dynamics of the solar surface and how it affects the Earth. " This is literally the greatest advance in mankind's ability to study the Sun from the ground, since the time of Galilee, " said astronomer Jeff Kuhn of the Institute of Astronomy in Mฤno, from the University of Hawaii.

These moving spots that you can see in the video below, are called granules . These are the tops of the convection cells in the solar plasma, with hot plasma rising in the middle, then falling down at the edges when it moves outwards and cools. Each granule is extremely large: up to 1600 km in diameter. In comparison, the US state of Texas is approximately 1,270 kilometers long.


Study magnetic fields to understand more about solar dynamics

These images are of course extraordinary, but scientists are particularly interested in the magnetic fields, twisted and tangled by the plasma, which can cause powerful solar storms, capable of interrupting the electrical networks here on Earth (although such consequences are rare).

However, less powerful solar storms can still impact communication and navigation systems and generate magnificent auroras. But today our understanding and ability to predict space weather is still extremely limited. As a result, scientists hope that this telescope will help them better understand solar phenomena.

" On Earth, we can predict if it will rain almost anywhere in the world in a very precise way, but this is not the case with space weather, " said Matt Mountain of the Association of Universities for research in astronomy, which manages the solar telescope. " What we need is to understand the physics behind space weather, and it starts with the Sun, which the Inouye solar telescope will study in the coming decades, " he said. added.

This is none other than the highest resolution snapshot of the Sun's surface ever taken. Credits: NSO / AURA / NSF

Thanks to its many advanced instruments (some of which are not yet operational), the telescope will be able to measure and characterize magnetic fields precisely, like never before.

These measurements could then teach us more about solar storms and how to detect them before they happen: at the moment, we only get to know about 48 minutes in advance. Scientists hope that improving our understanding of the behavior of magnetic fields, leading to a solar storm, could increase this time to 48 hours.

"It all depends on the magnetic field, " said Thomas Rimmele, director of the Inouye solar telescope. " To unravel the greatest mysteries of the Sun, we must not only be able to clearly see these tiny structures located 150 million kilometers away, but also to measure very precisely the strength and direction of the magnetic field near the surface and to trace its extension in the crown, the outside atmosphere of the Sun, to a million degrees, "he added.

The largest square on the surface of the sun is the entire image taken by the telescope. The enlarged (an area of ​​the first square) is a zoom making 7000 kilometers along its length. The small box in the zoom represents approximately the size of Texas. Finally, the tiny point which is almost invisible, is about the size of Manhattan. Credits: NSO / NSF / AURA

In the coming months, additional instruments will reinforce the already phenomenal power of the telescope.

There will be the near infrared cryogenic spectropolarimeter (CryoNIRSP), which is designed to take measurements of the solar magnetic field beyond the visible solar disk, in the crown. And also the near infrared limited diffraction spectropolarimeter (DL-NIRSP), which will study magnetic fields and their polarization with high spectral and spatial resolution.



“These first images are just the start! Said astronomer David Boboltz of the National Science Foundation's Astronomical Sciences Division." The Inouye solar telescope will collect more information about our Sun during the first 5 years of its life than all the solar data collected since Galileo pointed a telescope to the sun in 1612," he added. . The telescope is expected to be fully completed by June 2020.




Bibliography:

https://nsf.gov/news/news_summ.jsp?cntn_id=299908&org=NSF&from=news

Tuesday, 28 January 2020

A giant star devoured his companion and caused one of the brightest supernovas of all time



When a sufficiently massive star reaches the end of its life, it produces one of the most cataclysmic events in the Universe: a supernova. The light and energy released are such that the event often overshadows all the surrounding objects. However, there is an even more intense phenomenon: hypernovas (or superluminous supernovas). This is what astrophysicists observed in the constellation of Perseus 14 years ago, during the event called SN 2006gy. And recently, they proposed a hypothesis explaining the origin of the phenomenon.

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In September 2006, “a” star 50 billion times brighter than the Sun, and in the process of exploding, located 240 million light years away in the constellation of Perseus, began to shine intensely. For 70 days, the explosion became more and more brilliant, eclipsing its original galaxy by being tens or even hundreds of times more powerful than a typical supernova. At the time, this super bright supernova (also known as a hypernova) was the brightest star explosion ever detected.

What was special about this record explosion (officially named SN 2006gy)? Nobody knew. But now, more than a decade later, astrophysicists may finally have an idea. In a new study published in the journal Science , the researchers re-analyzed the mysterious emission lines emanating from the explosion about a year after its peak.

The SN 2006gy event observed by the Hubble space telescope. Credits: Hubble

A hypernova involving a binary stellar system

The team discovered large amounts of iron in the emissions, which they said could only be the result of the interaction of the supernova with a preexisting layer of stellar material ejected hundreds of years earlier. Where does all this ejected stellar material come from? A likely scenario is that the SN 2006gy event did not start with one star, but with two.

“No one had tried to compare the spectra of neutral iron, that is to say the iron that all the electrons kept, with the unidentified emission lines of SN 2006gy, because iron is normally ionized. We tried it out and saw with enthusiasm how, line after line, the lines were aligned with the observed spectrum,” explains Anders Jerkstrand, of the University of Stockholm.

Many binary systems involve a giant star and a white dwarf. In the SN 2006gy scenario, the white dwarf accelerated matter from the giant companion star while spiraling towards it after being caught in the expansion of its gaseous envelope. Credit: Pearson Ed

"A candidate scenario to explain this is the evolution of a binary progenitor system, in which a white dwarf spirals towards a giant or supergiant companion star" explain the researchers.

Collisions between binary stars (two stars orbiting each other) are rare, occurring once every 10,000 years or so in the Milky Way. When the stars collide, they can eject into the surrounding space a gaseous envelope of stellar material when the two stellar nuclei slowly merge.

The progenitor of SN 2006gy was, according to the new model, a double star composed of a white dwarf the same size as Earth and a massive star rich in hydrogen as large as our Solar System, in close orbit. As the hydrogen-rich star has expanded its envelope, which occurs when nuclear reactions are triggered in the later stages of evolution, the white dwarf has been caught in the envelope and has spiraled towards the center of the companion.


A supernova amplified by the previous collision of the two stars

When it reached the center, the unstable white dwarf exploded and a so-called type Ia supernova was born. This supernova then collided with the ejected envelope, which is projected during the spiral descent of the white dwarf, and this gigantic collision gave birth to the light of SN 2006gy.

Artist's impression showing what the SN 2006gy hypernova could have looked like. Credits: NASA / CXC / M.Weiss

If such a collision had occurred between 10 and 200 years before the supernova was detected, the two stars could have released a gaseous envelope that lingered around the system when the stars merged over the next century. When the fusion finally ended with an explosion of type Ia supernova, the gaseous envelope could have amplified the brightness of the explosion to the staggering levels that astronomers observed, and also produced the appropriate iron emission lines. .

This explanation is, for the moment, purely mathematical, astrophysicists having never seen two binary stars merge. A new clue could come from a nearby star system called Eta Carinae.

Located about 7,500 light years from Earth, Eta Carinae is a pair of giant stars that have exploded slowly over the past few hundred years, gradually lighting up to become the brightest star system in the Milky Way. Researchers believe that stars could end up in hypernova in the next 1000 years.




Bibliography:

A type Ia supernova at the heart of superluminous transient SN 2006gy

Anders Jerkstrand, Keiichi Maeda, Koji S. Kawabata

Science  24 Jan 2020

Vol. 367, Issue 6476, pp. 415-418

DOI: 10.1126/science.aaw1469

Thursday, 23 January 2020

ESA launches the first prototype oxygen extraction plant from the lunar regolith

๐Ÿ“ท | ESA

NASA's Artemis mission will mark the return of humans to the moon since the last Apollo mission in 1972. But bringing astronauts to lunar soil is not the ultimate goal of space agencies. Some plans aim to install real permanent lunar bases in order to carry out scientific experiments and test different engineering techniques. One of the essential resources to manage to maintain these inhabited bases is oxygen. Even if the Moon does not have an atmosphere, the regolith that lines its surface contains a lot of oxygen. And to test the technique of extracting oxygen from the regolith, ESA will host the first large-scale prototype factory using this process.

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Last year, researchers published an article on how to extract oxygen from a lunar dust simulator (regolith); now the first prototype oxygen plant will attempt this extraction on a larger scale. If it works, the technology could provide humans with important resources that will aid future lunar missions, and perhaps even allow long-term bases and colonies on the Moon.



“ Having our own facility allows us to focus on producing oxygen, measuring it with a mass spectrometer when it is extracted from the regolith simulator. Being able to acquire oxygen from the resources found on the Moon would obviously be extremely useful for future lunar colonists, both for breathing and for the local production of rocket fuel "explains the chemist Beth Lomax of the University of Glasgow , in Scotland.

Oxygen is the main resource necessary for the establishment of permanent manned lunar bases. Geochemists have developed a way to extract the oxygen contained in the regolith. Credits: ESA

Extract the oxygen from the regolith by electrolysis into molten salt

The installation, located at the European Space Research and Technology Center of the European Space Agency in the Netherlands, will use the technique developed by Lomax and his colleagues. Geochemists know, on the basis of samples of the lunar regolith, that oxygen is really very abundant in this material. Between 40 and 45% of the regolith by weight is oxygen.

Using an exact copy of the lunar regolith made on Earth, called a simulator of the lunar regolith, attempts have been made in the past to figure out how to extract oxygen, with poor results - too complicated, too weak, or destructive of the regolith. The Lomax team has remedied this by using a technique called “molten salt electrolysis”.

The electrolysis in molten salt of the regolith extracts oxygen while producing usable metal residues. Credits: Lomax et al., Planetary and Space Science, 2019

First, the regolith is placed in a mesh basket. Calcium chloride - the electrolyte - is added and the mixture is heated to about 950 degrees Celsius, a temperature that does not melt the material. Then an electric current is applied. This extracts oxygen and migrates the salt to an anode, where it can be easily removed. This technique extracts up to 96% of the oxygen from the regolith; as a bonus, the remaining material from this process is a mixture of metal alloys.

Use materials left over from electrolysis

" This is another useful avenue of research, to see what are the most useful alloys that could be produced from these, and for what type of applications could they be used." Could they be 3D printed directly, for example, or would they require refinement? The precise combination of metals will depend on where, on the Moon, the regolith is mined - there would be significant regional differences, "said Alexandre Meurisse of the European Space Agency.



The current configuration of the system is based on commercial deoxidation plants, where oxygen is only a useless by-product which is discharged. However, as the facility evolves, a means of storing oxygen will be included. The end goal, of course, is to develop a system that could work on the Moon, using a real lunar regolith, not a simulator.


Bibliography:

ESA opens oxygen plant – making air out of moondust

17/01/2020

http://www.esa.int/Enabling_Support/Space_Engineering_Technology/ESA_opens_oxygen_plant_making_air_out_of_moondust


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