Covid : en ville ou à la campagne, évaluez le risque de croiser une personne infectée

Difficile de ne pas se poser la question en entrant dans un restaurant, dans un magasin ou dans un bureau : combien de personnes sont potentiellement contaminées autour de soi ? Chacun peut désormais estimer ce risque en fonction du lieu où il se trouve et du nombre de personnes qui l'entourent. Le site CovidTracker, créé et animé par un jeune ingénieur en informatique, vient en effet de mettre en ligne un outil aussi simple que pertinent pour prendre la mesure de la circulation du virus autour de soi. Cette simulation, mise au point avec Élias Orphelin, peut s'avérer utile alors que le nombre de nouveaux cas bat des records, avec plus de 52 000 contaminations en 24 heures annoncées dimanche 25 octobre.

Par un simple calcul de probabilité, ce simulateur permet de faire le lien entre un taux d'incidence (soit le nombre de personnes infectées pour 100 000 habitants) et un nombre de personnes croisées à un instant T. « Prenons un exemple théorique, propose le jeune fondateur du site, Guillaume Rozier, dans un mariage de 200 personnes qui aurait lieu à Saint-Étienne, où le taux d'incidence est actuellement de 1 020, le risque de croiser une personne positive parmi les convives serait de 87 %. Si vous êtes invité à une soirée étudiante à Paris, on peut également utiliser des taux d'incidence disponibles par tranche d'âge. Ainsi, dans ce dernier exemple, dans une soirée privée qui rassemblerait 30 étudiants de la capitale, il y aurait une chance sur cinq de tomber sur un invité Covid+. » Avec cet outil, on comprend bien pourquoi les rassemblements sont limités et pourquoi, à certains endroits, mieux vaut les éviter au maximum.

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Le Point - France

Astronomy picture of the day - NGC 6357: The Lobster Nebula

 2020 October 28

NGC 6357: The Lobster Nebula
Image Credit & Copyright: Steven Mohr

Explanation: Why is the Lobster Nebula forming some of the most massive stars known? No one is yet sure. Cataloged as NGC 6357, the Lobster Nebula houses the open star cluster Pismis 24 near its center -- a home to unusually bright and massive stars. The overall blue glow near the inner star forming region results from the emission of ionized hydrogen gas. The surrounding nebula, featured here, holds a complex tapestry of gas, dark dust, stars still forming, and newly born stars. The intricate patterns are caused by complex interactions between interstellar winds, radiation pressures, magnetic fields, and gravity. NGC 6357 spans about 400 light years and lies about 8,000 light years away toward the constellation of the Scorpion.

Astronomy picture of the day : Reflections of the Ghost Nebula

2020 October 26

Reflections of the Ghost Nebula
Image Credit & Copyright: Bogdan Jarzyna

Explanation: Do any shapes seem to jump out at you from this interstellar field of stars and dust? The jeweled expanse, filled with faint, starlight-reflecting clouds, drifts through the night in the royal constellation of Cepheus. Far from your own neighborhood on planet Earth, these ghostly apparitions lurk along the plane of the Milky Way at the edge of the Cepheus Flare molecular cloud complex some 1,200 light-years away. Over two light-years across and brighter than the other spooky chimeras, VdB 141 or Sh2-136 is also known as the Ghost Nebula, seen at toward the bottom of the featured image. Within the reflection nebula are the telltale signs of dense cores collapsing in the early stages of star formation. 

Astronomy picture of the day : Dark Matter in a Simulated Universe

 2020 October 25

Dark Matter in a Simulated Universe
Illustration Credit & Copyright: Tom Abel & Ralf Kaehler (KIPAC, SLAC), AMNH

Explanation: Is our universe haunted? It might look that way on this dark matter map. The gravity of unseen dark matter is the leading explanation for why galaxies rotate so fast, why galaxies orbit clusters so fast, why gravitational lenses so strongly deflect light, and why visible matter is distributed as it is both in the local universe and on the cosmic microwave background. The featured image from the American Museum of Natural History's Hayden Planetarium previous Space Show Dark Universe highlights one example of how pervasive dark matter might haunt our universe. In this frame from a detailed computer simulation, complex filaments of dark matter, shown in black, are strewn about the universe like spider webs, while the relatively rare clumps of familiar baryonic matter are colored orange. These simulations are good statistical matches to astronomical observations. In what is perhaps a scarier turn of events, dark matter -- although quite strange and in an unknown form -- is no longer thought to be the strangest source of gravity in the universe. That honor now falls to dark energy, a more uniform source of repulsive gravity that seems to now dominate the expansion of the entire universe.

UGC 1810: Wildly Interacting Galaxy from Hubble - Science & Technology

 2020 October 18

UGC 1810: Wildly Interacting Galaxy from Hubble
Image Credit: NASA, ESA, Hubble, HLA; Processing & Copyright: Domingo Pestana

Explanation: What's happening to this spiral galaxy? Although details remain uncertain, it surely has to do with an ongoing battle with its smaller galactic neighbor. The featured galaxy is labelled UGC 1810 by itself, but together with its collisional partner is known as Arp 273. The overall shape of UGC 1810 -- in particular its blue outer ring -- is likely a result of wild and violent gravitational interactions. This ring's blue color is caused by massive stars that are blue hot and have formed only in the past few million years. The inner galaxy appears older, redder, and threaded with cool filamentary dust. A few bright stars appear well in the foreground, unrelated to UGC 1810, while several galaxies are visible well in the background. Arp 273 lies about 300 million light years away toward the constellation of Andromeda. Quite likely, UGC 1810 will devour its galactic sidekick over the next billion years and settle into a classic spiral form.

Science & Technology - Astronomy picture of the day : Planetary Nebula Abell 78

 2020 October 16

Planetary Nebula Abell 78
Image Credit & Copyright: Bernhard Hubl

Explanation: Planetary nebula Abell 78 stands out in this colorful telescopic skyscape. In fact the colors of the spiky Milky Way stars depend on their surface temperatures, both cooler (yellowish) and hotter (bluish) than the Sun. But Abell 78 shines by the characteristic emission of ionized atoms in the tenuous shroud of material shrugged off from an intensely hot central star. The atoms are ionized, their electrons stripped away, by the central star's energetic but otherwise invisible ultraviolet light. The visible blue-green glow of loops and filaments in the nebula's central region corresponds to emission from doubly ionized oxygen atoms, surrounded by strong red emission from ionized hydrogen. Some 5,000 light-years distant toward the constellation Cygnus, Abell 78 is about three light-years across. A planetary nebula like Abell 78 represents a very brief final phase in stellar evolution that our own Sun will experience ... in about 5 billion years.

Science & Technology - Tour of Asteroid Benn

 

Science & Technology - Astronomy picture of the day : Galaxies in Pegasus

 2020 October 15

Galaxies in Pegasus
Image Credit & Copyright: Robert Eder

Explanation: This sharp telescopic view reveals galaxies scattered beyond the stars of the Milky Way, at the northern boundary of the high-flying constellation Pegasus. Prominent at the upper right is NGC 7331. A mere 50 million light-years away, the large spiral is one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. The disturbed looking group of galaxies at the lower left is well-known as Stephan's Quintet. About 300 million light-years distant, the quintet dramatically illustrates a multiple galaxy collision, its powerful, ongoing interactions posed for a brief cosmic snapshot. On the sky, the quintet and NGC 7331 are separated by about half a degree.

Science & Technology - Astronomy picture of the day : The Colorful Clouds of Rho Ophiuchi

 2020 October 14

The Colorful Clouds of Rho Ophiuchi
Image Credit & Copyright: Amir H. Abolfath

Explanation: The many spectacular colors of the Rho Ophiuchi (oh'-fee-yu-kee) clouds highlight the many processes that occur there. The blue regions shine primarily by reflected light. Blue light from the Rho Ophiuchi star system and nearby stars reflects more efficiently off this portion of the nebula than red light. The Earth's daytime sky appears blue for the same reason. The red and yellow regions shine primarily because of emission from the nebula's atomic and molecular gas. Light from nearby blue stars - more energetic than the bright star Antares - knocks electrons away from the gas, which then shines when the electrons recombine with the gas. The dark brown regions are caused by dust grains - born in young stellar atmospheres - which effectively block light emitted behind them. The Rho Ophiuchi star clouds, well in front of the globular cluster M4 visible here on the upper right, are even more colorful than humans can see - the clouds emits light in every wavelength band from the radio to the gamma-ray.

Ciência e Tecnologia - Morte por 'esparguetificação'. Como um buraco negro engoliu uma estrela - Video

 ‘Esparguetificação’ quer dizer exatamente aquilo que parece. Imagine um fio de esparguete nos lábios e sugue-o até ele desaparecer dentro da boca. Basicamente foi isto que o buraco negro fez à estrela e os telescópicos do Observatório Astronómico do Sul (ESO), o Very Large Telescope (VLT) e o New Technology Telescope (NTT), estavam de lentes postas na situação.

Quando uma estrela infeliz se aproxima demasiado de um buraco negro supermassivo situado no centro de uma galáxia, a extrema atração gravitacional exercida pelo buraco negro desfaz a estrela em finas correntes de matéria,” explica Thomas Wevers, autor do estudo e bolseiro do ESO em Santiago do Chile, em comunicado de imprensa.

A estrela AT2019qiz, estava localizada num galáxia em espiral na constelação de Erídano, a cerca de 215 milhões de anos-luz da Terra. A estrela tinha uma massa equivalente à do nosso Sol, mas ficou reduzida a metade depois do encontro com o buraco negro que tinha mais de um milhão de vez a massa da estrela.

Observador - Portugal