понедельник, 2 декабря 2019 г.

‘The Cockpit’ Prehistoric Stone Circle, Moor Divock, Askham, Cumbria, 30.11.19.

‘The Cockpit’ Prehistoric Stone Circle, Moor Divock, Askham, Cumbria, 30.11.19.



* This article was originally published here

Cambridge to return looted Benin statue


A Cambridge University college has said it will return a bronze cockerel statue looted from Nigeria, which formed the focus of protests over symbols of Britain's colonial past.

Cambridge to return looted Benin statue
The statue known as "Okukor" was taken in 1897 from the former kingdom of Benin
[Credit: Chris Loades, AFP]
The statue known as "Okukor" was taken in 1897 from the former kingdom of Benin, which is now part of southern Nigeria, and given to Jesus college in 1905 by the father of a student.

In a statement issued on Wednesday (27th Nov.), the college said the recommendation to return it was made by a working group investigating the legacy of slavery.


"This royal ancestral heirloom belongs with the current Oba (king) at the Court of Benin," it said, adding that the details of how and when it would be returned had yet to be resolved.

The statue was removed from display in 2016 following protests by students, who said it was looted by British troops during a "punitive expedition" as revenge for the killing of officers.

Around the same time, Oxford University faced an angry but unsuccessful campaign to remove a statue of 19th-century British imperialist Cecil Rhodes.

Nigerian royals in Benin City have repeatedly called for the return of hundreds of ancient artefacts, known as the Benin Bronzes, which were looted by the British in the 19th century.


The highly decorative pieces, depicting the oba and his courtiers from centuries earlier, are still housed at leading museums around the world, including the British Museum in London.

There has been resistance to any return from western institutions, primarily because of concern about how the treasures would be maintained.

But the young brother of the current oba, Prince Edun Akenzua, told AFP in 2016: "If a man stole my car and admitted that he stole it and returned it to me, what is his business whether I have a garage or not to keep the car?

"These artefacts belong to our ancestors. They must be returned to us. It's nobody's business how we preserve them."

Source: AFP [November 28, 2019]



* This article was originally published here

Black Hole or Newborn Stars? SOFIA Finds Galactic Puzzle

Artist’s concept of a jet from an active black hole that is perpendicular to the host galaxy (left) compared to a jet that is launching directly into the galaxy (right) illustrated over an image of a spiral galaxy from the Hubble Space Telescope. SOFIA found a strange black hole with jets that are irradiating the host galaxy, called HE 1353-1917. The galaxy has 10 times more ionized carbon than its stars could produce. The gas, illustrated in blue in the right image, is concentrated near the galaxy’s center, which indicates that the intense radiation from the black hole’s jet is the source of the excess gas. This contradicts the long-held assumption that ionized carbon primarily indicates the presence of newborn stars, and forces scientists to reevaluate the effect black holes have on galaxies. Credits: ESA/Hubble&NASA and NASA/SOFIA/L. Proudfit

Even celestial objects can seem like they're playing tricks. In a new study, scientists are puzzled by a black hole that seems to be changing its galactic surroundings in a way that is usually associated with newborn stars.

Black holes are inherently strange, with gravitational forces so strong that nothing, not even light, can escape. As active black holes consume gas and dust, some of that material is instead launched outward as jets of high-energy particles and radiation. Usually these jets are perpendicular to the host galaxy, but NASA's Stratospheric Observatory for Infrared Astronomy, or SOFIA, found one that is shooting directly into its galaxy.

That jet is heating up gas around the galaxy's center in a way that's characteristic of stars being born. This is prompting scientists to reevaluate their ideas about a key gas associated with baby stars, and about how black holes affect their host galaxies generally.

“The black hole’s jet orientation is so peculiar,” said Irina Smirnova-Pinchukova, scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany. “It transforms the surroundings in the same way newborn stars would, but stars alone could not cause what we observed.”

Stars are born deep inside celestial clouds of dust and gas, a process hidden from our view in visible light. But infrared light, which our eyes cannot see, can penetrate these clouds. SOFIA, for example, uses infrared light to study how stars are born. But even with powerful telescopes, astronomers cannot see details like newborn stars in extremely distant galaxies. Instead, they hunt for signatures of gas that is heated by newborn stars, called ionized carbon. Because ionized carbon is so often found in connection with newborn stars, scientists often assume star formation is occurring when they find the gas in distant galaxies.

But when scientists on SOFIA studied five nearby galaxies with active black holes, they discovered that the one with the lowest rate of star birth contained the most ionized carbon. In fact, there was 10 times more than in other galaxies of similar size and composition. But the star birth rate is so low that it can only produce 25% of the gas they detected. In other words, newborn stars alone could not explain the abundance of ionized carbon. There must be some other explanation for this important chemical signature.

The team used SOFIA’s instrument called the Field Imaging Far-Infrared Line Spectrometer, or FIFI-LS, to closely examine the galaxy, HE 1353-1917. They found that the black hole’s jet is shooting radiation directly into the galaxy, rather than into the space surrounding it. Most of the ionized carbon is concentrated near the galaxy’s active black hole, indicating that the mysterious source of the gas is the intense radiation the black hole’s jet generates.

This contradicts the long-held assumption that ionized carbon is primarily a signature of newborn stars. The results are published in the journal Astronomy and Astrophysics.

“Without numerous observations of nearby galaxies, we might not find such exceptional cases where a black hole is a source of ionized carbon,” said Smirnova-Pinchukova. “This gas is one of the most important tools we have for studying extremely distant galaxies that cannot be seen in great detail.”

Information from nearby galaxies, such as how black holes can create ionized carbon and affect a galaxy’s subsequent evolution, are crucial for understanding the data from other observatories including the Atacama Large Millimeter/submillimeter Array, or ALMA observatory, in Chile. Radio telescopes like ALMA study some of the most distant and faint galaxies, which are often so far away that even powerful telescopes can only detect them as a point of light. That light is full of information, but details about nearby galaxies gathered by SOFIA are required to interpret data from the most distant regions of the universe. Now scientists know that high levels of ionized carbon in a distant galaxy may indicate not only that a lot of stars are being born, but also that a black hole's jet may be responsible for the same kinds of chemical signatures.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.

Media Contact

Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Editor: Kassandra Bell





* This article was originally published here

Galaxy formation in separate universes

Summary sketch of the Separate Universe Formalism: structure formation in special regions of our Universe is equivalent to structure formation in appropriately modified/separate Universes. The blue line is a mass perturbation: regions above the dashed line have more mass than the average. © MPA, Background image: Tess Cholson, Hi-res image

Rather than trying to study special regions in large-volume simulations, scientists at MPA have used the IllustrisTNG model to create whole separate universes with a modified cosmology. Their study of these separate universes shows that when the baryon density (the density of ordinary matter) changes, the number of galaxies can increase or decrease depending on how this number is measured. Also, the large-scale distribution of matter is affected by the effects of baryons, with various measures reacting differently.

Imagine we are travelling across the Universe and want to measure some property such as the number of galaxies around us. This number is not going to be the same everywhere during our journey because various regions of the Universe are not equal. For example, in some regions, there was a slight excess of mass and energy at the beginning of the Universe, the Big Bang, which means there was more material to form galaxies, and so we would count more galaxies there. Astrophysicists need to take this variability into account when analysing observational data. In particular, it could be the case that the observed part of the Universe is special and not representative of the whole Universe. Such an analysis can be performed with the aid of so-called Response Functions, which tell us how a given statistical measurement of the Universe changes when the properties of the underlying region change.

Researchers at MPA have been interested in studying response functions and their applications for some time now. This can be done with the “Separate Universe Formalism”, which establishes that structures forming in our Universe in a special (e.g. over- or under-dense) region are the same as the structures that would form in a normal region of a different/separate Universe (see Fig. 1). Studying responses is easier in this formalism, because numerical simulations can easily be used to study structure formation in other Universes -- this is much easier than to simulate structure formation in special regions of our Universe. In the past, numerical studies of response functions were done with simulations that took into account only the effect of gravity. A team of researchers at MPA has recently gone beyond this limitation by running separate universe simulations with the IllustrisTNG galaxy formation model, which, for the first time, allowed them to study response functions including also important baryonic effects such as hydro- dynamical forces, gas cooling, star and black hole formation.

Galaxy formation with an excess of baryons

Sketch of a compensated isocurvature perturbation (CIP): the total matter stays the same, but in some regions, more baryons are compensated by less dark matter. © MPA

Matter in the Universe can broadly be divided into two types: (i) dark matter, which does not interact with light and comprises the majority of the mass (80 %), and (ii) all the rest. This rest is made up of the particles detected in particle physics experiments, which are called baryons. While dark matter is the dominant source of gravitational energy that drives structure formation, stars and galaxies are made up of baryons. Therefore the number of galaxies should depend on the amount of baryons available inside some observed region. In other words, the number of galaxies responds to the baryonic density.

A few theoretical models of the very early Universe (also known as the period of Inflation) predict that there should be regions in the Universe with an excess of baryons that is exactly compensated by a suppression in the number of dark matter particles; these are called compensated isocurvature perturbations (CIP), see Fig. 2. Researchers at MPA have studied how the number of galaxies responds to these perturbations using the separate universe formalism by simulating galaxy formation in Universes with different total amounts of baryons and dark matter.

The results of this study showed that, indeed, the number of galaxies depends strongly on the amount of baryonic matter. More interestingly, however, the sign of this dependency depends also on the quantity used to classify the galaxies. If the number of galaxies is measured as a function of total mass (dark matter + baryons), the response to CIP perturbations is negative, i.e., there are fewer galaxies with a given total mass. However, if the number of galaxies is measured as a function of the mass in stars (not the total mass), the response now displays the opposite trend, i.e. there are more galaxies with a given stellar mass. The MPA researchers traced back the origin of this change of sign to the modifications that the CIP perturbations induce on the relation between total mass and stellar mass in the galaxies.

This study provided the first ever prediction of the impact of CIP perturbations on the observed number of galaxies, which can now be incorporated in theoretical models of the distribution of galaxies in the Universe. This in turn will allow astronomers to use the statistics of galaxies to look for important signatures from the early Universe.

Using responses to predict weak gravitational lensing

The top image shows a simulated weak-lensing map of the sky, as well as 2-, 3- and 4-point functions drawn on top. The lower panel shows the percentage impact of the baryonic effects on the N-point functions. The quantity on the x-axis is inversely proportional to distance: large scales on the left, smaller scales on the right. The vertical dashed lines correspond to those scales, where the effect of baryons exceed 1%. All N-point functions are affected by baryonic effects on small scales, but they all respond differently. © MPA

The separate universe formalism can also be applied to large-scale maps of the total matter distribution. The light emitted by distant galaxies travels towards Earth along trajectories that are perturbed by the gravitational effect of the intervening matter. This effect, known as weak gravitational lensing, distorts the observed images of the distant galaxies and can be used to construct sky maps of the total mass between Earth and the galaxies, see Fig. 3. These maps contain information about the physics of our Universe and a popular way to organize this information is in N-point correlation functions: how does the matter density correlate between N points.

For quite some time, cosmologists have considered only the effect of gravity to obtain theoretical predictions for these statistics, but recently the community became aware of the critical importance of baryonic effects. For example, the heating and ejection of gas by black holes at the centre of massive galaxies can significantly alter the total distribution of the mass that weak lensing observations are sensitive to. The impact of baryonic effects on higher-order functions has remained largely unexplored, but researchers at MPA have recently made progress on this front. Specifically, separate universe simulations of galaxy formation were used to measure the impact of baryonic effects on the response of the 2-point function, which was in turn used in theoretical models to predict the impact of baryons on 3- and 4-point functions.

The fractional impact of the baryonic effects on 2-, 3- and 4-point correlation functions is shown in Fig. 3.All statistics display a suppression of their amplitude of approximately 5%-20% on the smallest scales (right part). This is as expected from the impact of black hole activity, which makes the density field smoother and the correlation of perturbations weaker. A key aspect revealed by this study was the fact that, quantitatively, the various N-point functions are affected differently by the same black hole activity. This work by the MPA researchers opens up a new window to study important effects on galaxy formation (like black hole activity) using combined analysis of different weak-lensing N-point functions.

Source: Max Planck Institute for Astrophysics



Author

Postdoc
Tel.: 2241

for the team: Alexandre Barreira, Giovanni Cabass, Dylan Nelson, Rüdiger Pakmor, Fabian Schmidt and Volker Springel



Original publications

1. A. Barreira, G. Cabass, D. Nelson, F. Schmidt
Baryon-CDM isocurvature galaxy bias with IllustrisTNG
Submitted to JCAP

2. A. Barreira, D. Nelson, A. Pillepich, V. Springel, F. Schmidt, R. Pakmor, L. Hernquist, M. Vogelsberger Separate Universe Simulations with IllustrisTNG: baryonic effects on power spectrum responses and higher-order statistics MNRAS, Volume 488, Issue 2, September 2019, Pages 2079–2092,  




* This article was originally published here

2019 December 2 Mercury Crosses a Quiet Sun Video Credit: NASA,...



2019 December 2

Mercury Crosses a Quiet Sun
Video Credit: NASA, SDO, NASA’s Science Visualization Studio; Music: Gustav Sting (Kevin MacLeod) via YouTube

Explanation: What’s that black dot crossing the Sun? The planet Mercury. Mercury usually passes over or under the Sun, as seen from Earth, but last month the Solar System’s innermost planet appeared to go just about straight across the middle. Although witnessed by planet admirers across the globe, a particularly clear view was captured by the Solar Dynamics Observatory (SDO) in Earth orbit. The featured video was captured by the SDO’s HMI instrument in a broad range of visible light, and compresses the 5 ½ hour transit into about 13 seconds. The background Sun was unusually quiet – even for being near Solar Minimum – and showed no sunspots. The next solar transit by Mercury will occur in 2032.

∞ Source: apod.nasa.gov/apod/ap191202.html



* This article was originally published here

Aesica or Great Chesters Roman Fort, Hadrian’s Wall, Haltwhistle, Northumberland,...

Aesica or Great Chesters Roman Fort, Hadrian’s Wall, Haltwhistle, Northumberland, 30.11.19.

This fort is the ‘secret’ site of Hadrian’s Wall; far fewer tourists make it this way and as a result the Roman fort is far more evocative. Many walls remain and few farms can boast a Roman strongroom with arched roof and a temple with a standing altar.



* This article was originally published here

Oddendale Prehistoric Stone Circle, Oddendale, Shap, Cumbria, 30.11.19.

Oddendale Prehistoric Stone Circle, Oddendale, Shap, Cumbria, 30.11.19.



* This article was originally published here

Bronze Age Burial Cairn with Cist, Moor Divock Prehistoric Complex, Askham, Cumbria, 30.11.19.

Bronze Age Burial Cairn with Cist, Moor Divock Prehistoric Complex, Askham, Cumbria, 30.11.19.



* This article was originally published here

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