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

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 MarΓ­a 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.


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


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


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.


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.


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.


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

Jahed Abedi, Niayesh Afshordi


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