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

Tuesday, 19 November 2019

NASA confirms the presence of water vapor on the surface of Europa


The fourth largest natural satellite of Jupiter and sixth largest in the Solar System, Europa has been of interest to planetologists for many years. About forty years ago, the Voyager program provided the first detailed picture of the veined surface of the icy moon. In the last decades, the data collected on Europa has made it a priority target for space agencies in the search for life. And recently, planetologists have confirmed the presence of water vapor in Europe.

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What makes this moon so attractive is the possibility that it has all the ingredients necessary for life. Planetologists have evidence that one of these ingredients, liquid water, is present under the icy surface and can sometimes burst into space in the form of gigantic geysers. But so far no one has been able to confirm the presence of water in these plumes by directly detecting the water molecule.

Europa: water vapor and a potential ocean of liquid water

Now, an international research team led by NASA's Goddard Space Flight Center has directly detected water vapor for the first time over the surface of Europa. The team did this detection by surveying Europa through one of the largest telescopes in the world in Hawaii.

By confirming the presence of water vapor over Europa, planetologists can better understand the inner workings of the moon. For example, it helps to support the idea that there is an ocean of liquid water, perhaps twice as large as the Earth's, beneath the thick ice shell of that moon. Some astrophysicists suspect that another source of water for the plumes could be shallow reservoirs of melted water ice.

Although planetologists have still not surveyed the interior of Europe, the predominant hypothesis suggests the existence of an ocean of liquid water beneath its frozen surface. Credits: NASA

" The essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur) and energy sources, two of the three requirements of life, are present throughout the Solar System. But the third - liquid water - is a little hard to find beyond the Earth, "said Lucas Paganini, NASA's planetologist. " Although the scientists have not yet detected the liquid water directly, we have found the second best thing: water in the form of steam ."

First direct detection of water molecules over Europa

In Nature Astronomy , Paganini and his team said they detected enough water ejected from Europa (at a rate of 2360 kilograms per second) to fill an Olympic pool in minutes. However, the authors also discovered that water appears too rarely, at least in sufficient quantity, to be detected from Earth.

" For me, the interest of this work is not only the first direct detection of water over Europa, but also its absence within the limits of our detection method, " says Paganini.

Indeed, Paganini's team detected the weak but distinct signal of water vapor during 17 nights of observation between 2016 and 2017. Looking at the moon from WM Keck observatory at the top of Mauna Kea volcano in Hawaii, researchers have seen water molecules on the main hemisphere of Europa. (Europa, like the Earth's moon, is gravitationally locked on its host planet, so the main hemisphere is always oriented in the direction of the orbit, while the secondary hemisphere is always in the opposite direction).

Differentiate terrestrial water vapor from that of Europa: models in reinforcement

For this, the researchers used a Keck observatory spectrometer, which measures the chemical composition of planetary atmospheres by means of the infrared light they emit or absorb. Molecules such as water emit specific frequencies of infrared light when they interact with solar radiation.

When interacting with solar radiation, water molecules emit specific infrared frequencies. Credits: Michael Lentz / NASA Goddard

Detecting water vapor on other worlds is a challenge. Existing spacecraft have limited capabilities to detect it, and scientists using ground-based telescopes must take into account the distortion effects of the Earth's atmosphere.

To minimize this effect, Paganini's team used complex mathematical and computer modeling to simulate the conditions of the Earth's atmosphere, in order to differentiate between atmospheric water from Earth and Europa from the atmosphere. data returned by the Keck spectrograph.

We conducted rigorous safety checks to eliminate potential contaminants in ground observations, " said Avi Mandell, a planetologist on the Paganini team. " But in the end, we will have to get closer to Europa to see what is really happening ."

Structure of Europa: study it in detail thanks to the Europa Clipper mission

Scientists will soon be able to get close enough to Europa to resolve their outstanding questions about the internal and external functioning of this possibly habitable world. The next mission, Europa Clipper, which is scheduled for launch in the mid-2020s, will complete half a century of scientific discoveries that began with a modest photo.

When it arrives in Europa, the Clipper orbiter will carry out a detailed study of the surface, the deep interior, the weak atmosphere, the submarine ocean and possibly even smaller active vents. Clipper will try to take images of all the plumes and sample the molecules he will find in the atmosphere to study with his mass spectrometers. He will also look for a site from which a future lander could collect a sample.

In this video, NASA returns in detail on the detection of water vapor in Europa:



Bibliography:

Article: A measurement of water vapour amid a largely quiescent environment on Europa

authors: L. Paganini, G. L. Villanueva, L. Roth, A. M. Mandell, T. A. Hurford, K. D. Retherford & M. J. Mumma

Nature Astronomy

Source

Sunday, 17 November 2019

Another mystery on Mars: Oxygen appears and disappears without explanation



With the mystery of Mars methane still unresolved , the space robot Curiosity brought scientists a new puzzle: Martian oxygen.

The information came by measuring the seasonal levels of all gases in the atmosphere directly above the surface of the Gale Crater, where Curiosity is located. The result is disconcerting.

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On Mars, oxygen, the gas most creatures on Earth use to breathe, behaves in a way that scientists have so far failed to explain through any known chemical process.

Over the course of three Martian years (nearly six years of Earth), a Curiosity instrument called SAM ( Sample Analysis at Mars ) inhaled the air of the Gale Crater and analyzed its composition.

The results confirmed the composition of the Martian surface atmosphere: 95% by volume of carbon dioxide (CO2), 2.6% of molecular nitrogen (N2), 1.9% of argon (Ar), 0.16% of molecular oxygen. (O 2), and 0.06% carbon monoxide (CO).

Measurements also revealed how molecules in Martian air blend and circulate with changes in air pressure throughout the year. These changes are induced when CO2 gas freezes at the poles in winter, lowering air pressure across the planet after air redistribution to maintain pressure balance. When CO2 evaporates in spring and summer and mixes on Mars, the air pressure increases.

The oxygen mystery of Mars

In this environment, data show that nitrogen and argon follow a predictable seasonal pattern, with their concentration increasing and decreasing over the year relative to the amount of CO2 in the air.

Scientists expected oxygen to keep pace, but that is not the case. Instead, the amount of oxygen in the air rises throughout spring and summer by up to 30 percent, and then returns to the levels predicted by known autumn chemistry. This pattern repeats each spring, although the amount of oxygen added to the atmosphere varies, implying that something is producing oxygen and then taking it away.

"The first time we saw this, we were racking our brains," said Sushil Atreya, professor of climate and space science at the University of Michigan.

The team set out to look for possible explanations, first considering the possibility that CO2 or water (H2O) molecules could release oxygen when they separate into the atmosphere, leading to a brief rise in oxygen. But that would consume five times more water than there is in the atmosphere of Mars, and CO2 decomposes too slowly to generate it in such a short time. What about decreasing oxygen? Couldn't solar radiation break oxygen molecules into two atoms, which would then leak into space? No, the scientists concluded, as it would take at least 10 years for oxygen to disappear through this process.

"We are struggling to explain this," said Melissa Trainer, planetary scientist at NASA's Goddard Space Flight Center. "The fact that oxygen behavior doesn't repeat perfectly every season makes us think it's not a problem that has to do with atmospheric dynamics. It has to be a chemical source and a sinkhole that we can't yet explain."

The amount of oxygen in the air increases throughout spring and summer by up to 30 percent, and then returns to the levels predicted by known autumn chemistry

Methane and oxygen, biological and abiotic

The history of oxygen is curiously similar to the methane mystery of Mars. Methane is constantly in the air inside the Gale Crater in such small quantities (0.00000004% on average) that it almost goes unnoticed by the most sensitive instruments ever sent to Mars. Although methane increases and decreases seasonally, it increases abundantly by about 60% in the summer months for unexplained reasons - in fact, methane also fires randomly and dramatically, but no one has yet any idea why.

With the new oxygen discoveries at hand, the NASA team wonders if a chemistry similar to the one that is generating the natural seasonal variations of methane can also explain the variations in oxygen - the two gases even float together, but only occasionally.

"We are beginning to see this tantalizing correlation between methane and oxygen for much of the year on Mars," said Atreya. "I think there's something there. I don't have the answers yet. No one has."

Oxygen and methane can be produced biologically (from microbes, for example) and abiotically (from water and rock-related chemicals). Scientists are considering all options, although we have no convincing evidence of biological activity on Mars.

The Curiosity robot has no instruments that can definitely tell whether the source of methane or oxygen on Mars is biological or geological. With current data, nonbiological explanations are more likely.

Bibliography:

Article: Seasonal variations in atmospheric composition as measured in Gale Crater, Mars

Authors: Melissa G. Trainer, Michael H. Wong, Timothy H. McConnochie, Heather B. Franz, Sushil K. Atreya, Pamela G. Conrad, Franck Lefèvre , Paul R. Mahaffy, Charles A. Malespin, Heidi LK Manning, Javier Martín-Torres, Germán M. Martínez, Christopher P. McKay, Rafael Navarro-González, Alvaro Vicente-Retortillo, Christopher R. Webster, Maria-Paz Zorzano

Magazine : Journal of Geophysical Research: Planets

DOI: 10.1029 / 2019JE006175  

Thursday, 14 November 2019

The Japanese space probe Hayabusa-2 returns to Earth with samples of an asteroid


Yesterday, the Japanese space probe Hayabusa-2 left its orbit around a distant asteroid and is now heading for the Earth after an exemplary mission. The latter will yield important samples, which could help scientists solve some of the mysteries about the origins of the Solar System.

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For the spacecraft, the long return journey began Wednesday, Nov. 13, 2019, and is expected to reach Earth "by the end of 2020," said Japan Aerospace Exploration Agency (JAXA).

"  We hope that Hayabusa-2 will provide us with new scientific knowledge, " said project director Yuichi Tsuda. The probe will bring back to Earth "carbon and organic matter", which will provide data on "how matter is dispersed in the solar system, why it exists on the asteroid and how it is related to the Earth", Tsuda added.

Below: The images taken by the Hayabusa-2 probe as it leaves the orbit of the asteroid are also displayed in the control room. This is a camera that continues to take scientifically valid photographs, but this time, the pictures were taken for the pleasure of all.



The mission of the Japanese space probe (the size of a large fridge) took her to some 300 million kilometers from the Earth, where she was able to analyze and explore the asteroid Ryugu, whose name means "Palace of Dragon "in Japanese. A name referring to a castle at the bottom of the ocean, in an ancient fable.

In April 2019, the Hayabusa-2 space probe launched an "impactor" on the asteroid in order to "stir" materials that had never been exposed to the atmosphere. The probe was then able to collect dust samples from the surface of the asteroid and never exposed to space vacuum so far. A first !

Scientists hope this will provide clues to the nature of the Solar System at birth, about 4.6 billion years ago. " I feel half-sad and half-determined, so we can do our best to bring the probe home. Ryugu has been at the heart of our daily lives for a year and a half ...  "said Tsuda.

The surface of the asteroid Ryugu, photographed in detail by the Hayabusa-2 probe at 64 and 67 meters altitude. Credits: JAXA

Now, the Hayabusa-2 space probe has begun its return to planet Earth. It will be released permanently from the gravity of the asteroid on November 18, and can start at full speed its main engines at the beginning of December.

Tsuda said the six-year mission, whose total cost is around 30 billion yen (about $ 278 million), had exceeded expectations at the scientific level, but he also admitted that his team had to deal with many technical problems. It took three and a half years for the probe to get to the asteroid, but the return trip should be much shorter because now the Earth and the Ryugu asteroid are much closer (because of their respective current positions).

The Hayabusa-2 probe is expected to deposit the collected samples in the southern Australian desert, but "JAXA is negotiating the details of this part of the mission with the Australian government," Tsuda said.

Note that this probe succeeds the first JAXA asteroid explorer, Hayabusa (which means "hawk" in Japanese). The first probe was sent back to Earth with dust samples of a small asteroid in 2010, despite several setbacks during its epic seven-year odyssey, and was hailed as a scientific triumph.

According to the current plan, Hayabusa-2 will continue its journey into space after depositing its capsule containing the samples on Earth, and could even " perform a new exploration of asteroid, " said spokesman JAXA Keiichi Murakami. "  The team has just started to study what could be done (after the probe has deposited the capsule), but there are no concrete plans for a new destination,  " Tsuda said.

Source

We finally know more about what would have preceded the Big Bang


In the framework of the "pre-Big Bang" model, implying that the Big Bang is preceded by a first inflation, scientists theorize that the universe was formed in two stages. It would first spread rapidly from a dense mass of matter, then entered a phase of expansion more progressive but very energetic, commonly called "Big Bang". However, the way in which these two stages are related has long been misunderstood by researchers. As part of a new study of this period of the Universe and involving this initial theory, physicists finally think they have solved this mystery remained unanswered for decades, and suggest a way to explain the connection between these two eras primitive.

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During the first primitive period, the Universe would have gone from a small dense mass of matter to nearly a half-million times (x 10 48 ) its size in less than a trillionth of a second (10 -12 s) . In the context of the pre-Big Bang model, this period of rapid inflation was followed by a more gradual but violent expansion phase, the Big Bang.

During the Big Bang, a "ball" of extremely hot matter composed of fundamental particles (protons, neutrons and electrons ) then developed and cooled to form the first atoms, stars and galaxies .

The standard Big Bang theory , which also describes cosmic inflation, remains the most widely supported explanation for the beginnings of our universe. However, scientists are still puzzled as to how these completely different expansion periods are nested.

To solve this mystery, a team of researchers from Kenyon College, the Massachusetts Institute of Technology (MIT) and the University of Leiden in the Netherlands, simulated the critical transition between cosmic inflation and the Big Bang as part of a pre-Big Bang model; a period called "reheat".

" The post-inflation warm-up period defines the conditions of the Big Bang and, in a sense, places the 'Bang' in the Big Bang,  " David Kaiser, a professor of physics at MIT , said in a statement . " It's a time of transfer, when hell is unleashed and the matter behaves in a complex way  ."

The history of the universe (standard model of the Big Bang). Above, inflation, which generates two types of waves: gravitational waves and density waves. Below, the radius of the visible Universe, from the Big Bang (t0), then the inflation (white / yellow), the formation of the protons, the beginning of the nuclear fusion, the end of the nuclear fusion (3 minutes), up to the 13.8 billion years that the Universe has today. Credits: DrBogdan / Yinweichen / Wikimedia

When the Universe developed into a "fraction of a second" during cosmic inflation, all existing matter spread out in all directions, leaving in space an empty, cold place, devoid of "soup." primordial "(dense and hot cluster of particles) necessary to start the Big Bang. During the warm-up period, it is thought that the energy that propelled inflation broke down into particles, said Rachel Nguyen, PhD student in physics at the University of Illinois and lead author of the study.

Once these particles are produced, they bounce off and bump into each other, transferring inertia and energy,  " Nguyen said. " And this is what thermises and warms the universe to define the initial conditions of the Big Bang  ".

In their model, Nguyen and his colleagues simulated the behavior of an exotic form of matter called inflaton. Scientists believe that the scalar field of this material, which is similar in nature to that of the Higgs boson, is responsible for creating the energy field that has led to cosmic inflation.

Their model showed that, under proper conditions, the hypothetical scalar field energy could be efficiently redistributed to create the diversity of particles needed to warm the primitive Universe. The results of the study are available in Physical Review Letters.

Gravity: it would react differently to very high energies

" When we study the primitive universe, we perform an experiment with particles at very high temperatures,  " said Tom Giblin, an associate professor of physics at Kenyon College in Ohio and co-author of the study. " The transition from the cold inflationary period to the warm period should contain essential evidence about the particles that actually exist at these extremely high energies."

A fundamental question that still afflicts physicists is how gravity behaves to the extreme energies present during inflation. Albert Einstein's theory of general relativity defines that all matter is affected by gravity in the same way, where the force of gravity is constant, regardless of the energy of the particle. However, because of the strange properties of quantum mechanics, scientists now think that at very high energies matter reacts differently to gravity.

The team incorporated this hypothesis into their model by modifying the interaction force of particles with gravity. They then discovered that the more they increased the force of gravity, the more the inflaton effectively transferred energy to produce the Hot Bang's field of hot material particles.

Additional clues needed to support the model

" The universe contains so many secrets, encoded in a very complex way  ," said Giblin. " It's our job to study the nature of reality by offering a 'decoding device' - a way to extract information from the universe. For this, we use simulations to predict what the universe should look like, so that we can actually begin to decode it. This warm-up period should have left an imprint somewhere. We just have to find it  . "

But identifying this footprint could prove to be a very complex task. Our first glimpse of the Universe is a "bubble of radiation" left a few hundred thousand years after the Big Bang: the cosmic microwave background (CMB). However, the CMB only evokes the state of the universe during the first critical seconds of its birth. Physicists hope that future observations of gravitational waves will provide the additional clues needed to support their model.


Source

Thursday, 7 November 2019

A new study suggests that the Universe is actually spherical and closed (not flat)


The study of the curvature of the Universe is an active field of research in cosmology. In recent years, the many data collected by observation missions such as WMAP and Planck have shown a locally null curvature of the Universe, indicating that the latter is certainly flat. The data match so well with each other that the model of the flat Universe is today integrated into the standard cosmological model. However, an anomaly derived from data collected by the Planck Space Observatory in 2018, concerning the cosmic microwave background, could be interpreted as a sign of a closed spherical universe.

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On the basis of data collected last year by the Planck satellite of the European Space Agency, cosmologists have argued that the Universe is actually curved and closed, like an expanding sphere. This means that a beam of photons drawn in a straight line would eventually return to its starting point, crossing other beams in its path; whereas these beams would remain parallel in the scenario of the flat Universe.

According to an international team of astronomers led by Eleonora Di Valentino of the University of Manchester in the United Kingdom, their findings present a "cosmological crisis" that calls for "radical rethinking of the current model of cosmological concordance". The key in determining the curvature of the Universe lies in the way gravity curves the path of light, an effect predicted by Einstein and called the gravitational lens .

Unlike a flat Universe (zero curvature) where light beams would continue indefinitely their stroke in a straight line, in a closed Universe (positive curvature), they would eventually return to their starting point. Credits: Lucy Reading-Ikkanda

Anomaly A lens : it could be explained by a closed sphere Universe

It is not about any light but the cosmic microwave background (CMB), that is to say the electromagnetic radiation bathing the Universe, whose first emission dates back to 380,000 years after the Big Bang during a phase called Recombination (capture of electrons by atomic nuclei).

The Planck satellite data, particularly from 2018, show that CMB has a more pronounced gravitational lens effect than expected. The Planck Collaboration has called this anomaly A lens , and this has not yet been resolved, but the team believes that an explanation could be the curvature of the Universe. The study was published in the journal Nature Astronomy.

The researchers showed that the anomaly in the spectrum of the cosmic microwave background could be interpreted as the sign of a closed universe (blue). Credits: Eleonora Di Valentino et al. 2019

"A closed universe can provide a physical explanation for this, with the Planck CMB spectrum now pointing to a positive curvature of greater than 99% confidence. Here we study further evidence of a closed universe collected by Planck, showing that positive curvature naturally explains the abnormal amplitude of the lens effect, "the researchers write.

An interpretation incompatible with all current data

A curved universe may explain this anomaly, but there are several important issues, including the fact that all other analyzes of Planck datasets, including the same data from 2018, concluded that the standard cosmological model is correct, including concerning a flat universe.

There are also other problems, and the team took care to note them in its article. One is Hubble's constant, which gives the rate of expansion of the Universe; it is a real problem in cosmology today. The different measures of this constant give different values, and to consider a curved universe makes this measurement even more complex.

The interpretation of the authors of the article (red and blue) is incompatible with the current data from different missions of cosmological observation (gray). Credits: Eleonora Di Valentino et al. 2019


Data from baryonic acoustic oscillation studies on dark energy are also inconsistent with the Closed Universe model, as are data on gravitational distortion obtained from observations of weak gravitational lenses . One other article also suggests that the anomaly A lens is simply a statistical bias in the data collected.

Future studies are needed to clarify the nature of the anomaly

Astrophysicists George Efstathiou and Steven Gratton of the University of Cambridge also analyzed Planck's 2018 data and found signs of curvature. But when compared to other Planck data sets and baryonic acoustic oscillations data, they found "solid evidence to support a spatially flat universe".

Much of the data seems to be in favor of a flat universe rather than a closed universe, except for the anomaly A lens . " Future steps will be needed to clarify whether the observed discrepancies are due to undetected systematics, new physics, or simply statistical fluctuation, " the researchers conclude.

Source

Wednesday, 6 November 2019

Mercury Transit: A rare astronomical event to observe on November 11, 2019


The year 2019 has been rich in observable astronomical phenomena, and it will end on November 11 with a relatively infrequent event: the transit of Mercury. The first planet in the Solar System will travel on a path through the solar disk. The event will be visible from most of the Earth's surface, with the appropriate equipment.

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Such a sight is relatively rare seen from Earth. From our point of view, only the transits of Mercury and Venus are visible. This event will be the fourth of the 14 Mercury transits that will take place in the 21st century. In contrast, Venus transits occur in pairs, with each pair spaced more than a century apart.

Mercury will take about 5.5 hours to travel in front of the Sun. Transit will be widely visible from most of the Earth, including from the Americas, the Atlantic and Pacific Oceans, New Zealand, Europe, Africa and West Asia. However, it will not be visible in Central and East Asia, Japan, Indonesia and Australia.

On May 9, 2016, Mercury made a spectacular transit, many astronomers having observed its passage in front of the Sun. The transit of 11 November should be identical. Credits: NASA's Goddard Space Flight Center / SDO / Genna Duberstein

A transit in several stages visible from the Earth

Transit begins before sunrise for observers in western North America. The transit ends after sunset for Europe, Africa, West Asia and the Middle East. The entire transit will be visible from end to end over eastern North America, Central and South America, southern Greenland and a small part of West Africa.

In France , it will be possible to observe the beginning of the passage and the maximum (minimum distance between the center of Mercury and the center of the Sun). However, the rest of the passage, and its end, will not be observable because the Sun will be lying down.

Times of observation of the transit of Mercury according to the different time zones. In Paris (UTC + 1), the hours of passage are those you see under UTC, adding 1h (for example 14h35 for Contact 1). Credits: Space.com

The first contact takes place when the disk of Mercury touches for the first time the eastern edge of the Sun. It takes about two minutes for the Mercury disk to move completely to the Sun's disk (second touch). The most important transit occurs when Mercury appears closest to the center of the Sun. The third contact is when the leading edge of Mercury reaches the western edge of the Sun. Two minutes later, Mercury completely leaves the solar disk (fourth touch).

Observation of the transit of Mercury: precautions are necessary

Mercury will appear as a black dot, representing only about 0.5% of the Sun's diameter. It will take a magnifying telescope at least 50 times to see it.

Special precautions should be taken when viewing the solar disk. Be careful never to look directly at the sun with a telescope. The visual requirements are the same as those for observing sunspots and partial solar eclipses - you need to use special sunscreens to protect your eyes.

It is much safer to project the image of the Sun using a telescope on a white card or a screen. If you use a telescope with a large aperture, for example 20 centimeters or more, place a circular mask in front of the lens or mirror to fix the image, reducing the amount of light and heat striking the lens or mirror.

A different transit depending on the time of the year

Since the orbit of Mercury is inclined 7 degrees from the plane of Earth's orbit, most of the time, when Mercury arrives at a lower conjunction (when it is between the Earth and the Sun), it moves above or below the Sun and does not pass through the solar disk from our terrestrial point of view. But in two points of the orbit of Mercury, it crosses the orbital plane of the Earth (called "node").

Astronomical characteristics of the transit of Mercury of November 11, 2019. Credits: F. Espenak

The Earth crosses the knot line every year on May 8th or 9th, then six months later, on November 10th and 11th. Transit may occur when a lower conjunction of Mercury occurs several days after these dates. When a transit occurs in May, Mercury is near the point of aphelion in its orbit - the furthest point from the Sun and closest to the Earth. If Mercury passes in the center of the Sun in May, the transit time can last nearly 8 hours.

When a transit takes place in November, as it will be this month, Mercury is near the point of perihelion of its orbit - the closest point to the Sun and farthest from the Earth, and where its apparent velocity is faster. As such, a central transit in November lasts only 5.5 hours, which is about what we will see on November 11th. And the number of transits in November is twice as large as the number of transits in May.

Predictability of mercurial transits

Mercury transits do not happen at random. At intervals of 13 and 33 years, Mercury and the Earth return almost simultaneously to the same points in their respective orbits, often resulting in repeated transit after this time interval. So, in connection with the coming transit of November 11, we can go back and find transits that happened 13 years ago, November 8, 2006, and 33 years ago, November 13, 1986.

Interestingly, the transits of May 9, 1970 and November 10, 1973, both fell on a Saturday, while the transits of May 9, 2016 and November 11, 2019 are both on a Monday. The next transit of Mercury will not take place before November 13, 2032.

Source

Astrophysicists confirm that the Voyager 2 probe has entered interstellar space


Begun in 1972, the Voyager program aims to study planets outside the Solar System. In 1977, the Voyager 1 and Voyager 2 space probes were launched and, for several years, will fly over the giants and their satellites, collecting valuable data on these planets. In September 2013, NASA confirmed that Voyager 1 left the heliosphere and entered interstellar space. And, according to new studies jointly published on the data collected by Voyager 2, the latter also officially entered the interstellar space in November 2018.

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After a careful analysis of the data, the astrophysicists confirmed it: like Voyager 1, the space probe is now out of the heliopause and sinks into the interstellar space. Through five articles in the journal Nature Astronomy , astrophysicists confirm that Voyager 2 penetrated interstellar space on November 5, 2018, at a distance of 119 astronomical units (17.8 billion kilometers) from the Sun.

And, since Voyager 1's plasma study instrument was broken during the heliopause crossing six years ago, this is the first time researchers have been able to study a complete set of in situ profile data. plasma of this important boundary.


The two Voyager probes were launched in 1977 to study the External Solar System. Voyager 2 was sent first, with a two-week lead, but Voyager 1 had a shorter trajectory in the Solar System.

Mission Voyager Interstellar : en route to the interstellar medium

In addition, Voyager 2 was slowed down by its flight over Neptune in 1989, Voyager 1 was ahead of schedule. After this 1989 survey, the two probes had achieved their main objective, but they were far from having finished their work. " At that time, the mission became the Voyager Interstellar mission, " said astronomer Ed Stone of Caltech.

Nobody knew how long it would take probes to reach interstellar space. Via a supersonic wind of ionized plasma, the Sun creates a bubble around the Solar System. This bubble is called the heliosphere and its limit - where the external pressure exerted by the solar wind is no longer strong enough to oppose the wind of interstellar space - is called the heliopause.

At present, both Voyager 1 and 2 probes have entered interstellar space. This phase is the last leg of the Voyager Interstellar mission. Credits: NASA / JPL

" This contact surface is the limit, and we try to both understand the nature of the latter, where these two cosmic winds meet and mix, and how that happens,  " says Stone. Voyager 1 officially passed the heliopause on August 25, 2012, at a distance of 121.6 astronomical units (18.1 billion kilometers).

Valuable data on heliosphere dynamics and heliopause

When the probe made its historic crossing, the researchers could confirm this fact only eight months later, through oscillations of electronic plasma to infer an interstellar plasma density. Astronomers did not really know when Voyager 2 would do the same - the heliosphere is a little flickering and changes shape slightly frequently - but in October of last year, it began recording an increase in cosmic radiation similar to that of Travel 1 in 2012.

This time, the detection of plasma density was done directly. And, interestingly, what the five Voyager 2 instruments captured shows a smoother, finer heliopause, with a stronger magnetic field. According to plasma observations, the probe passed through the heliopause in less than a day. The Voyager 2 cosmic ray instrument also detected something that had not been detected with Voyager 1: the existence of a layer between heliopause and interstellar space, where both winds interact.

The valuable data collected by the two probes allows astrophysicists to better understand the complex dynamics of the heliosphere and its interaction with the interstellar medium. Credits: NASA

Voyager 1 detected galactic cosmic rays and the interstellar magnetic field invading the heliogaine. Voyager 2 discovered that the interstellar magnetic field wrapped around the heliopause and that the cosmic rays inside the Solar System were moving along it. This indicates that the heliopause is not a simple smooth contact boundary, but is much more complex and dynamic.

Different travel conditions for Voyager 1 and Voyager 2

The reasons for the differences between the results of the two probes are not entirely clear, but there are a number of possible explanations. Time was running out - Voyager 1 crossed this boundary as the Sun entered its maximum of solar activity, the active peak of its 11-year cycle, when the solar wind is much stronger. Voyager 2 made this crossing while the Sun is just coming out of its minimum activity.

The heliopause is only a limit of the influence of the Sun. The gravitational influence of our star is much, much larger, extending through the cloud of Oort up to 100'000 astronomical units (15 trillion kilometers). Unfortunately, it is extremely unlikely that Voyager probes will remain operational at this distance. Nevertheless, the data collected by the two probes are extremely valuable to better understand the dynamics of the Sun and the astrophère of other stars.

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Monday, 4 November 2019

One of the mechanisms behind thermonuclear supernovae recreated in the laboratory


All stars do not end their lives in the same way. The most massive stars, once their thermonuclear reactions exhausted, explode into a phenomenon called supernova. Supernovas can be classified into two types: thermonuclear supernovae (type Ia) and collapsing supernovas (type II, Ib, Ic). One of the possible mechanisms behind type Ia supernovas is the deflagration-detonation transition (DDT). Recently, physicists have developed a model of experimentally validated DDT, allowing a better understanding of this mechanism, which could also allow to develop new means of propulsion.

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The nature of type Ia supernovae (SNIa), the thermonuclear supernovae, is still very little constrained. There is a general consensus that SNIa explosions are caused by rapid thermonuclear combustion of stars with a mass near or below the Chandrasekhar mass limit (1.4 solar masses). Beyond these models, however, the exact mechanisms of the SNIa remain unclear, with a number of possible scenarios.

In some forms of supernovae and chemical explosions, a flame moving at subsonic velocities (deflagration) spontaneously evolves into supersonic shock (detonation) -speed, greatly increasing power. The mechanism of this deflagration-detonation transition (DDT) is still poorly understood.

Recreate the detonation mechanism of supernovae in the laboratory

A team of physicists has developed a unified theory of the turbulence-induced DDT mechanism, which describes the mechanism and conditions of initiation of detonation during unconfined chemical and thermonuclear explosions. The model was validated using experiments with chemical flames and numerical simulations of thermonuclear flames. The study was published in the journal Science.

Physicists have recreated the detonation-detonation mechanism in which a flame encounters a shock wave, resulting in a sudden detonation. Credits: Alexei Y. Poludnenko et al. 2019

" When we started deepening the question, we discovered that we can actually achieve this mechanism between a passive flame and a flame that becomes very active, " says Ahmed. " It reaches a point producing a detonation, which is essentially a supernova ."

The death of stars 10 to 100 times larger than the Sun generates an explosion called supernova. In a galaxy like the Milky Way, a supernova occurs every 50 years or so. But the mechanism underlying the initiation of the supernova is still little understood by astrophysicists.

The mechanism of the explosion-detonation transition experimentally validated

" How do the flames accelerate spontaneously and turn into detonations? We know that the detonations exist, but the question was: what is the missing link explaining how the star goes from a combustion mode to a detonation mode so brutally? Ahmed explains.

The mechanism explored by Ahmed's team takes a passive flame, like that of a candle, and turns it into an energetic flame. " When we started to notice that the flames could accelerate, we had to develop this unique facility to explore the phenomenon,  " says Ahmed.

The researchers first modeled the DDT mechanism using plasma and then experimentally confirmed. Credits: Alexei Y. Poludnenko et al. 2019

The installation was in the form of a 5 x 5 cm shock tube, which induces turbulence and allows the passive flame to interact with it until it propels itself until a detonation.

This study will not only provide a better understanding of the explosion-detonation mechanism of Type Ia supernovae, but also the development of hypersonic propulsion means on Earth.

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Saturday, 2 November 2019

For the first time, astrophysicists could have detected a "mini black hole"


The black holes are certainly part of the most mysterious objects in the cosmic catalog. Planned from the beginning of the 20th century as part of general relativity, current models describe several types: stellar black holes, intermediate black holes and supermassive black holes. Each of these types has been detected in recent years. But the models also provide other hypothetical black holes, such as primordial black holes, black micro holes or even mini black holes. The latter would be black holes whose mass would be between that of a neutron star and that of a stellar black hole . And for the first time, cosmologists could have detected one.

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Astronomers generally look for black holes in our galaxy by observing the X-rays that are emitted when black holes absorb material from nearby stars. The thermal friction within the accretion disk generates, in fact, the emission of a powerful electromagnetic radiation. In more distant galaxies , this search may involve the detection of gravitational waves produced by the fusion of two black holes.

But a group of researchers wondered if there might be relatively low mass black holes that do not emit the tell-tale X-ray signals. Such hypothetical black holes would probably exist in a binary system with another star, although they orbit sufficiently far from this star not to absorb too large quantities.

Mini black holes: they would betray themselves by the variations of brightness of their companion star

The researchers speculated that these small black holes would not emit detectable X-rays and would therefore remain invisible to astronomers, according to Todd Thompson, a professor of astronomy at Ohio State University. " We are pretty sure there must be many, many of these black holes in the binary systems with stars in the galaxies, but we have not detected them because they are hard to find ."

Thompson and his colleagues looked for evidence of these black holes in the stellar companions of the proposed objects. They screened the data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), containing information on the light spectrum of more than 100,000 stars in our galaxy.

The information in this study revealed changing spectra for each of these stars. Such a change could mean that a particular star is gravitating around an invisible companion. After conducting this analysis, the researchers examined changes in brightness of a subset of stars that could gravitate around black holes, using data from another mission called ASA-SN (All-Sky Automated Survey). for Supernovae).

An object too massive to be a neutron star ... but not massive enough to be a stellar black hole

This is how the researchers discovered a massive black object, caught in a gravitational embrace with a giant star in rapid rotation, located about 10'000 light-years from Earth, on the edge of our galaxy (near the constellation of the Coachman).

They estimated that the mass of this object was about 3.3 times that of our Sun, too massive to be a neutron star and not massive enough compared to that of known black holes. The results were published in the journal Science.

Graphic presenting the observational constraint posed on the mass of the object. The most accurate result indicates about 3.3 solar masses. Credits: Todd A. Thompson et al. 2019

The most massive neutron stars that astrophysicists know are 2.1 solar masses, while the least massive black hole known is about five to six times the mass of our Sun, according to Thompson. However, the lower mass limit of the new object found corresponds to 2.6 times the mass of the Sun, which, according to astronomers, constitutes the theoretical upper limit of star mass. More massive than that, the neutron star would collapse into a black hole.

The realistic hypothesis of the detection of a black mini-hole

So, this dark and mysterious object " could be the most massive neutron star ever seen. Just at the border after which she can no longer exist. In fact, I would be even more excited if that were true. But it is more than likely a relatively low mass black hole, theorized but never discovered before, "says Thompson.

Mini black holes, black holes whose mass is located between that of neutron stars and stellar black holes, have been theorized for many years. Credits: LIGO-Virgo, Frank Elavsky, Northwestern (Modified by Todd Thompson)

Dejan Stojkovic, a cosmologist and professor of physics at the University of Arts and Sciences, Buffalo, confirms these results. " It's probably a black hole, because it's too massive to be a neutron star, unless it's a kind of unusual star. The discovery seems very reasonable, but not unexpected, because astronomers know that there are black holes of lower mass .

Thompson said he was eagerly awaiting future discoveries, such as information on the inclination of the star's orbit around the dark object that the European Space Agency's Gaia spacecraft could muster during the day. a next mission. This could help researchers to more accurately measure the mass of the dark object.

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Tuesday, 29 October 2019

The expansion of the universe is much faster than expected, causing a "crisis of cosmology"


Experimentally confirmed at the beginning of the 20th century, the expansion of the Universe is a dynamic phenomenon resulting in a recessionary movement of the galaxies . In 1998, cosmologists Adam Riess and Saul Perlmutter demonstrate that this expansion is accelerating. From there, many measurements of the rate of expansion will be made via the Hubble constant. However, to the surprise of cosmologists, a problem has emerged: the different measured values ​​do not agree with each other. The values ​​determined by the study of the cosmic microwave background (Planck) do not correspond to the values ​​determined via the study of quasars (H0liCOW, etc.). In other words, the acceleration of expansion is faster than the standard cosmological model predicts.

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A team of researchers confirmed this dilemma via data collected using a new telescope technology based on shape-changing mirrors. According to their study, published in the journal MNRAS , accurate measurements of the rate of expansion of the Universe do not correspond to the standard model used by cosmologists for decades. Other studies published earlier this year have reached similar conclusions.

" This is where the crisis of cosmology lies, " says Chris Fassnacht, astrophysicist. " This inadequacy is growing and has reached such a point that it is really no longer possible to consider it a coincidence. This disparity could not plausibly happen by chance, "said Adam Riess, a Nobel Prize winner for physics, for highlighting the acceleration of expansion.


Expansion 9% faster than predicted by standard cosmological model

To determine the rate of expansion of the Universe, in a way the speed at which expansion occurs, cosmologists study the cosmic microwave background (CMB). Based on these observations, they found that after the Big Bang, the Universe had first developed very rapidly. Then, expansion slowed down under the gravitational effect of dark matter. However, current measurements of the Hubble constant show that the expansion accelerates much faster than predicted by the standard model of cosmology.

Illustration showing the three basic steps that astronomers use to calculate the speed at which the universe expands over time, a value called Hubble's constant. All steps involve the construction of a "cosmic distance scale", starting by measuring precise distances to nearby galaxies and then moving to more distant galaxies. This "scale" consists of a series of measurements of different types of astronomical objects having a certain luminosity, which researchers can then use to calculate distances. Credits: NASA / ESA / A. Feild (STScI)

Riess's April study found that the Universe was growing 9% faster than predicted by CMB-based calculations. " It's not just two experiences that disagree. We measure something fundamentally different. One is a measure of the speed at which the Universe is developing today, as we see it. The other is a prediction based on the physics of the young Universe and on measures of the speed with which it should develop. If these values ​​do not match, it is very likely that we miss something ".


A difference in values ​​confirmed by the study of quasars

For the new study, researchers used a state-of-the-art mirror system at the Keck Observatory telescope in Hawaii. The camera uses flexible mirrors capable of correcting distortions caused by the Earth's atmosphere and rendering extremely clear images of objects in the sky. The researchers directed the telescope to three bright, highly active galaxy systems, called quasars.

They studied quasars using a process called the gravitational lens , which measures how light bends when moving around massive objects on its path to Earth. A massive object (like a giant galaxy, for example) bends the light in different directions, allowing scientists to see different distorted versions of the same quasar, at times slightly different from its past.

Images of the three quasars used in the study. Credits: G Chen / C Fassnacht / UC Davs

They can then compare these different images to calculate the time needed to light a quasar to reach us, and gather information about the development of the Universe during this period.

As in previous studies, the new results showed that the Universe was growing faster than expected by the standard model. The researchers compared their results to the Hubble Space Telescope data. The results obtained were consistent.

" A difference in the Hubble constant between early and late Universe means something is missing in our current standard model, " says astrophysicist Sherry Suyu. " For example, it could be a dark exotic energy, a new relativistic particle, or a new physics to discover ."

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Friday, 25 October 2019

Astronomers accidentally discover an invisible "galactic monster" from the primitive universe

This is what the newly discovered galactic monster might look like. | James Josephides / Christina Williams / Ivo Labbe
While researchers were making observations through the Atacama Large Millimeter / Submillimeter Antenna System (a set of 66 antennas) in Chile, they noticed a very interesting light source ... And it turns out that the latter comes from a real "galactic monster" invisible, coming from the primitive universe.

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The light radiation discovered by scientists would be a glow emanating from the particles of gas and dust heated by the stars that form in the hidden galaxy . However, this dust blocks other wavelengths, including that of stars.

In a sense, the newly discovered galaxy is therefore, for most of its elements, invisible. " It's debatable whether it's just the tip of the iceberg, with a whole new kind of galaxy population just waiting to be discovered,  " said Kate Whitaker, co-author of the research.

The observations suggest that this galaxy is about 12.5 billion light years away , which means that the observed light was emitted 12.5 billion years ago. At that time, the Universe was in its infancy: it was barely a billion years old. This galaxy could therefore give clues to the rapid formation of gigantic mature galaxies at the beginning of the Universe.

Christina Williams, a postdoctoral researcher at the University of Arizona and lead author of the article, was the first to discover the galaxy. " It was very mysterious. The light did not seem to be related to a known galaxy. When I saw that this galaxy was invisible at any other wavelength, I was very excited because it meant it was probably far away and hidden by clouds of dust,  "Williams said.

The video below shows what the new galaxy might look like (artist's view) in the primitive universe, with newly formed bursts of stars illuminating the clouds of gas and dust surrounding it:


This discovery could help solve a true mystery about galaxies : indeed, the new galaxy seems to contain about the same number of stars as our own galaxy, but it is much more active: it produces new stars at a speed 100 times faster than the Milky Way.

Right now, we know that large, mature galaxies appeared early in the Universe's history, whereas it was about a billion years old (or, as astrophysicists say, about 10% of its current age). But these galaxies seemed to come out of nowhere, growing and converting the gas into stars much faster than predicted the best theoretical models, before settling down again.

However, scientists have never observed this process directly. Indeed, NASA's Hubble Space Telescope has now spotted smaller galaxies at the beginning of the Universe, but none are growing fast enough to become as big ... However, a large active galaxy producing stars as well quickly could help astronomers determine what is missing from their models: " This hidden galaxy has precisely the right ingredients to be that missing link  ," Williams said.

The researchers hope that future telescopes will be able to reveal more details about this galaxy or other objects of the same kind. At present, it is difficult to observe the galaxy or to find others with current telescopes, because it is invisible and the brightness of the surrounding dust clouds is very (too) weak. " We are excited that the James Webb Space Telescope (JWST) is examining these objects,  " Williams said.

The James Webb Space Telescope, consisting of 18 hexagonal mirrors, is standing in the gigantic clean room at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Credits: NASA / Chris Gunn
The James Webb Space Telescope (JWST) is expected to be launched on March 30, 2021. It has already been fully assembled by NASA, and is located at the Northrop Grumman facility (California, USA). It must now be tested before its official launch.

Once in space, the JWST telescope will study each phase of the universe's history to understand how the first stars and galaxies were formed, how the planets were born and where there might be life. In the universe. Rather cheerful as a program.


A folding beryllium mirror, 6.4 meters wide, will help the telescope to observe distant galaxies in detail and capture extremely weak signals. " The JWST will be able to look through the dust veil so that we can understand how big these galaxies are and how fast they grow, in order to better understand why our current models fail to explain them,  " he said. said Williams.

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Thursday, 24 October 2019

Finally, we have a clearer idea of ​​the formation process of the heavy elements of the Universe


Shortly after the Big Bang, the first light atomic nuclei formed during primordial nucleosynthesis. Later, in the heart of the stars, will be forged heavier atoms until iron. But to form even heavier atoms, a process of fast neutron capture , called the r process, is necessary. Such a process takes place only under extreme physical conditions. Recently, astrophysicists have identified the formation of strontium during the fusion of neutron stars , revealing that the formation of such heavy elements takes place during this type of cosmic event.

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Astrophysicists have detected the formation of a heavy element in space, forged as a result of a collision between two neutron stars. The results also confirmed that " neutron stars contain many neutrons, " said Darach Watson, an astrophysicist at the Niels Bohr Institute at the University of Copenhagen. " It sounds really stupid, but it's something we do not know for sure. Now all we have found is pointing to elements that have only formed in the presence of many neutrons . "


The three lightest elements of the Universe - hydrogen, helium and lithium - were created in the very first moments of the cosmos, just after the Big Bang, during an event called primordial nucleosynthesis. Most elements heavier than lithium, up to the iron, were forged billions of years later, in the heart of the stars.

R process and fusion of neutron stars
But the way in which elements heavier than iron, such as gold and uranium, have been created, has long been uncertain. Previous research suggested a key clue: for atoms to reach large sizes, they needed to absorb neutrons quickly. Such fast neutron capture, known as the r-process, occurs only in nature, in extreme environments where atoms are bombarded by a large number of neutrons.

Diagram explaining the phenomenon of rapid capture of free neutrons by an atomic nucleus; still called process r. Credits: Rachel Freed
Previous work has suggested that a probable source of r-shaped elements could be the cosmic cataclysm caused by the fusion of neutron stars. In such stars, the internal pressure is so high that the electrons penetrate the protons to form neutrons.

In 2017, astronomers witnessed the fusion of two neutron stars. Astrophysicists made this discovery by detecting gravitational waves emitted from a collision about 130 million light years from Earth. Following the discovery of this fusion, dubbed GW170817, the researchers continued to make observations from Earth. " This explosion was moving at 30% of the speed of light, so it went from about 100 kilometers to the size of the Solar System in a day, " says Watson.

Kilonovas: cosmic sources of heavy elements

Watson and his colleagues suspected that if heavier elements were formed during GW170817, signatures of these elements could be detected in the explosive suites of fusion, known as kilonovas. They focused on the wavelengths of light (spectrum) that astrophysicists have linked by spectroscopy to specific elements.

Previous studies suggested the presence of heavy elements in kilonovas, but so far astronomers have not been able to locate individual elements. This is because " heavier elements can produce mixtures of tens of millions of spectral lines. We could never distinguish one element from another, "says Watson.

However, by re-analyzing the data from the 2017 merger, Watson and his colleagues identified the signature of the heavy strontium element. The results of the study were published in the journal Nature . On Earth, strontium occurs naturally in the soil and is concentrated in certain minerals. Strontium compounds even help give the fireworks a bright red color.

Detection facilitated by strontium structure

The key to this discovery lies in the atomic structure of strontium, relatively simple for such a heavy element. Due to its structure, the electrically charged version of strontium produces two powerful spectral lines in blue and infrared light. This discovery was surprising because, if strontium is a heavy element, it is also one of the lightest elements from process r.

The simple atomic structure of strontium facilitated its detection. Credits: SciencePhotoLibrary

In previous research, astrophysicists expected to find " heavier heavy elements, or heavier elements from the r process, looking at a kilonova, " says Watson. The discovery may be related to neutrinos, which normally cross the material but may occasionally collide with protons or neutrons.

" In order to create a relatively light heavy element like strontium, you must first destroy some neutrons. You have to bombard them with neutrinos, enough to disintegrate faster into protons and electrons . This tells us a little more about what happens in neutron stars and during such mergers.

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