Omega Centauri star cluster
This video is a zoom in on the movement of the stars of Omega Centauri, a globular cluster that includes over ten million stars so close to each other that it is difficult to resolve individual stars. It is the largest globular cluster known to belong to the Milky Way (our galaxy).
It is the brightest star cluster observable from Earth and is found in the constellation Centaurus.
The video begins with an image on the ground of the giant star cluster Omega Centaurie and continues with an increasingly narrow zoom with shots taken by NASA's Hubble Space Telescope which is located in the outer layers of the Earth's atmosphere, about 600 kilometers above the ground. soil, in orbit around the Earth. In this simulation based on the detected data and images, the stars appear to move in random directions, like a swarm of bees.
The video was processed using material from NASA, the American space agency.
There is a strange cloud on Mars. It forms every day, for months, during the southern Martian spring. It is up to 1800 km long and 150 km wide. It starts from Arsia Mons, a former volcano almost 20 km high. In the past, some have even claimed that it was a plume indicating volcanic activity, but it is only clickbait: it is a cloud, made of water ice. Here we can see it in real colors as it appeared on September 21, 2018 from the Mars Express probe.
It's a strange cloud, I said. Firstly because Arsia Mons is the only place near the Martian equator where clouds are observed and secondly because it is the only place to have clouds this season. This cloud is so interesting that it even has a name: AMEC, which stands for "Arsia Mons Elongated Cloud". It's quite didactic, sure, but it indicates that this phenomenon deserves the attention of astronomers.
It has been seen over 100 times by 5 different missions since 1976, but only recently, with ESA's Mars Express probe, did we fully observe its cycle for the first time. AMEC is composed of a "head", round, and a long tail facing west. The head forms before dawn during the morning the tail, which grows for about 2 and a half hours at the remarkable speed of 600 km / h and at an altitude of 45 km. Reached the maximum length, the cloud "detaches" from the mountain and continues westwards and then evaporates shortly before local noon. Everything is repeated the next day, until the end of the season.
What happens? AVEC is a so-called “orographic cloud”: Arsia Mons forces the humid wind to rise along its slope until it reaches a high altitude, where low temperatures condense the water vapor thus forming the cloud on the other side of the mountain. It is the largest orographic cloud seen on Mars and larger than its terrestrial counterparts. The AMEC study will therefore improve the knowledge of Martian climate systems, but also of our own ones.
Credits: ESA / DLR / FU Berlin / J. CowartMars continues inexorably to lose those few traces of water left into space :(
Titan, Saturn and the rings. No, you are not looking at a painting or a simulation: it is a real photo. Titan is that moon of Saturn that makes Cassini's images seem even more alien and abstract.
The only satellite in the solar system with an atmosphere, Titan exceeds even the planet Mercury (by a little) in size, although its lower density makes it less massive than the planet. Only Ganymede, Jupiter's satellite, surpasses it in size. Its atmosphere, mainly nitrogen, is 50% denser than that of the Earth on the ground. Thanks to this and the satellite's low gravity, a human could fly using arm strength!
The wonders do not end there, because Titan is the only other body in the solar system to host liquids on its surface: colossal lakes of hydrocarbons, mainly liquid methane and ethane. This is because Titan is COLD: -180 ° C to be precise. Here the water is rock-hard ice.
There could therefore be no world more different from our Moon, arid and devoid of any atmosphere. Yet, Titan, the Moon and all the important satellites of our system share one characteristic: the tides. Tides that widen their orbit, stealing rotational energy from their planet.
In the case of the Earth and the Moon, the 'friction' necessary to transfer energy from the planet's rotation to the lunar orbit is made possible by the presence of terrestrial oceans: the Moon attracts the oceans and the oceans attract the Moon. It turns out that this process is also and above all active for the moons of gas giants, planets that are certainly not made of solid and non-deformable material.
Here, the researchers measured for the first time the rate of departure of Titan from Saturn: 11 centimeters per year, to be compared with the 3.8 of the Moon from Earth. Today, Titan orbits about 1.2 million kilometers from Saturn, but this recession rate is like 100 times higher than that calculated with the old models. A model from four years ago predicts exactly this value, a great confirmation that helps shed light on the mystery of the age of Saturn's moons and rings.
Image taken on May 10, 2006, from a distance of 2.9 million kilometers from Saturn. Recolored by Gordan Ugarkovic (Credits)
Press release - The analysis of ultraviolet observations of the hottest stars in the Omega Centauri star cluster allowed an international team of researchers, led by INAF astronomers, to shed light on the history of the formation of its second generation of stars, which occurred about 12 billion years ago. It is very likely that the progenitors of these stars, at the time of 'igniting' thanks to the nuclear fusion reactions within them, rotated much faster than normal stars. Scientists, in their study published in the journal Nature, attribute this strong rotation to the premature destruction of their protostellar disk of gas and dust, due to the gravitational interaction with other stars and favored by the particularly dense formation environment of stars
Rome, 22 June 2015 - The analysis of the ultraviolet observations of the hottest stars of the Omega Centauri star cluster has allowed an international team of researchers, led by INAF astronomers, to shed light on the history of the formation of its second generation of stars, which occurred about 12 billion years ago. It is very likely that the progenitors of these stars, at the time of 'igniting' thanks to the nuclear fusion reactions within them, rotated much faster than normal stars. Scientists, in their study published in the journal Nature, attribute this strong rotation to the premature destruction of their protostellar disk of gas and dust, due to the gravitational interaction with other stars and favored by the particularly dense formation environment of stars.
In globular clusters there are "multiple" generations of stars, chronologically very close, but of profoundly different chemical composition. In Omega Centauri, the richest and most splendid of celestial objects of this type that populate our Galaxy, it has been discovered already since ten years the presence of a generation, composed of a large number of stars in which the concentration of helium is much greater than that present in the primordial matter produced following the Big Bang. An international study led by INAF researchers and published today in preview on Nature magazine website adds new and important results to reconstruct the history of the formation of these "multiple" populations in star clusters. From the capillary analysis of the hot Omega Centauri stars observed in the ultraviolet with the Hubble Space Telescope of the NASA space agencies and ESA, the authors have shown how the existence of this group implies a very rapid ro tation
of their ancestors, contrary to what happens for other stars.
These stars, called "of the blue hook", belong to an advanced evolutionary stage of super ¬ rich helium stars, and some of their peculiarities indicate that they were formed in the chemically anomalous gas, lost in the stellar winds by the primeval stars, which has accumulated in the most central and dense areas of the cluster. Here the stars are very close to each other and gravitational perturbations, especially important in the early stages of evolution, can destroy the extensive accretion disk that usually accompanies star formation and which, like a gyroscope, stabilizes the slowly rotating newborn star.
"The frequency of encounters between stars and protostellar disks at the high stellar densities expected during the formation of the 'second generation' of stars in Omega Centauri, is high" explains Marco Tailo, PhD student at the '' La Sapienza '' University of Rome and associated INAF, first author of the letter. "If the loss of the disk occurs in the first million years of the star's life, when it is still extended and not very dense, its subsequent contraction causes it to accelerate to such high speeds of rotation as to significantly modify its subsequent evolution, the one that today makes her become one of the anomalous stars of the blue hook ».
Italian researchers, at the INAF facilities of Padua and Bologna, have the leadership of observational research in the study of multiple populations of globular clusters. Francesca D'Antona, corresponding author of the letter and associated with INAF, explains that "the group of the INAF-Osservatorio Astronomico di Roma played a predominant role in the study of stellar models for the formation of chemical anomalies in multiple populations and in predicting the presence of populations with a high concentration of helium. This last work was possible by synergistically combining the skills in the calculation of stellar models of Paolo Ventura and his team, at the INAF-Osservatorio Astronomico in Rome, with those in the calculation of dynamic models of the stars of the clusters of Enrico Vesperini at the Indiana University ".
The group of researchers who carried out the study, in addition to Marco Tailo and Francesca D'Antona, is composed of Marcella Di Criscienzo, Paolo Ventura and Thibaut Decressin (INAF-Astronomical Observatory of Rome), Annibale D'Ercole (INAF-Astronomical Observatory of Bologna), Vittoria Caloi (INAF-IAPS Rome), Enrico Vesperini (University of Indiana, USA), Antonino P. Milone and Aaron Dotter (Research School of Astronomy & Astrophysics, Australia), Andrea Bellini (Space Telescope Science Institute), Roberto Capuzzo-Dolcetta ("La Sapienza" University, Rome)
A stellar stream is created when stars from one galaxy get pulled from their home galaxy by another. Stellar flux is a long thin strand of stars produced by the elongation action of tidal forces. Only a dozen stellar streams have been named or studied in detail. Being a phenomenon that only occurs on a galactic scale, most stellar streams are too faint and distant to study very carefully.
The most familiar stellar stream and one of the first to confirm this is the Arcturus stream, just 37 light years away, which contains the star Arcturus. The Arcturus Stream is a remnant of a dwarf galaxy devoured by the Milky Way long ago. Over its lifetime, the Milky Way has likely consumed dozens or even hundreds of small dwarf galaxies, and continues to do so today. We also observe star clusters that appear to be the remnants of devoured galaxy cores, such as the Omega Centauri star cluster. We know that these are former galactic nuclei and unconventional open clusters because open clusters are made up of stars forming in the same period, while a galactic nucleus contains stars of very different ages.
One of the most studied stellar currents is the Magellanic flux, a bridge that connects together two stars of the galaxies closest to the Milky Way, the Small Magellanic Cloud and the Large Magellanic Cloud. Since Magellanic clouds are among the closest galaxies to ours, only 150,000 light-years away, we can observe individual stars in "clouds" and their parallaxes, making us a 3D map of galaxies and their stellar flux. .
Just like planets as the cause of Saturn's dust to form in rings around them, some galaxies tear apart and form into rings as well. A stellar flow in the shape of a ring is the Unicorn Ring, created as the Milky Way engulfs a dwarf galaxy, the Dog Major Dwarf Galaxy, about 100 times smaller than it.
Press release - Identified a group of stars that the Omega Centauri globular cluster, located in our Galaxy and about 18,000 light years away from us, is being lost, torn away by the tidal force of the Milky Way. Omega Centauri could be what remains of a dwarf galaxy partially disintegrated by the interaction with our Galaxy National Institute of Astrophysics - INAF
A team of researchers from the Astronomical Observatory of Strasbourg, the National Institute of Astrophysics and the University of Stockholm has identified the stars that the globular cluster Omega Centauri, located in our Galaxy and about 18,000 light years away from us, is losing, snatched away by the tidal force of the Milky Way. The so-called "tidal tails" identified by the team around the cluster and their distribution in space suggest that Omega Centauri is actually what remains of a dwarf galaxy partially disrupted by interaction with our Galaxy. The results of this study, published in an article in the latest issue of the journal Nature Astronomy, were obtained thanks to the analysis of the very accurate data on stellar position and proper motions provided by the European Space Agency's Gaia mission, which sees an important participation science of Italy with the National Institute of Astrophysics and the Italian Space Agency participating in the Data Processing and Analysis Consortium (DPAC).
In 1677, Edmond Halley gave the name "Omega Centauri" (ω Cen) to what he thought was a star in the constellation Centaurus. Later in 1830 John Herschel realized that it was actually a globular cluster that could be resolved into single stars. Today we know that Omega Centauri is the most massive globular cluster in the Milky Way, about 18,000 light years from us and made up of several million stars that are approximately 12 billion years old. The nature of Omega Centauri has long been debated, whether it was really a globular cluster or instead the heart of a dwarf galaxy that has lost the most peripheral stars, now scattered in the Milky Way. The latter hypothesis is based on fact
that ω Cen contains different populations of stars, with a wide range of metallicity (ie the content of heavy chemical elements) that betray star formation processes protracted over a long period of time, typical of the evolution of a galaxy. The researchers literally searched the regions surrounding the cluster, looking for "lost" stars along its orbit within the Milky Way. In fact, when a dwarf galaxy interacts with a massive galaxy like ours, at least some of its stars are torn from it by the tidal force. The stars torn from the cluster are no longer gravitationally linked to it but have similar orbits, and therefore arrange themselves in narrow and elongated structures on the path of the orbit (the tidal tails), which can remain consistent even for a long time.
Globular cluster Omega Centauri imaged by ESO's VST telescope.
Credits: ESO / INAF-VST / OmegaCAM
By analyzing the movements of the stars measured by the Gaia satellite with an algorithm called STREAMFINDER developed by the team, the researchers identified several streams of stars. One of them, called "Fimbulthul", named after one of the primeval rivers of Norse mythology, contains 309 stars that extend into the sky for an amplitude of over 18 degrees.
"By modeling the trajectories of the stars, we discovered that the Fimbulthul structure is a tidal current composed of stars torn from ω Cen, which extends into the sky to a great distance from the cluster" comments Michele Bellazzini, of the INAF of Bologna, who participated in the study. "Starting from this initial data, we were able to devise a selection criterion that made it possible to trace the tidal tails starting from the cluster up to join Fimbulthul. Spectroscopic observations of five stars of this flux made with the Canada-France Hawaii Telescope show that their speeds are very similar and that they have metallicities comparable to Omega Centauri stars. This property reinforces the idea that the tidal flow is connected to precisely that cluster ".
The data of the dynamic properties of the stars of Omega Centauri and of those in the surrounding regions obtained from the Gaia mission and the algorithm developed ad hoc allowed the researchers to demonstrate the presence of this stellar flow even in an area of the sky with a high density of stars in our galaxy. "The next step will be to improve the theoretical model that describes this structure, to reconstruct with greater precision the evolutionary history of the dwarf galaxy progenitor of ω Cen" concludes Bellazzini "We therefore expect to find even more stars lost by this celestial object in the halo of the Milky Way ".
The study was published in the journal Nature Astronomy in the article Identification of the long stellar stream of the prototypical massive globular cluster ω Centauri by Rodrigo A. Ibata, Michele Bellazzini, Khyati Malhan, Nicolas Martin and Paolo Bianchini.
Placed at an estimated distance of around 16,000 light-years, it appears to be one of the globular clusters closest to the Solar System. It is the largest globular cluster known belonging to the Milky Way, the second largest in the entire Local Group after Mayall II contains several million stars of Population II, for a total mass equal to that of five million Suns (the same mass as the smallest known dwarf galaxies). The magnitude of its brightest components is 11.5. 
Its age turns out to be about 12 billion years, which is similar to that of the Universe itself.  Omega Centauri is the only known globular cluster that presents a clear dispersion in its metal content which would give credence to the theory according to which Omega Centauri would be the nucleus of an ancient dwarf galaxy "engulfed" by ours. The nucleus of the galaxy, remained intact, would have assumed the characteristics of a globular cluster, with a population of very ancient stars other clusters with similar characteristics are known inside and outside the Milky Way.