Discuss Cumulus clouds, takes us as a reference to what the groupings of some things are. An example at the astronomical level is that of star clusters. These are attracted to each other by their mutual gravity and is what comes to form the cluster as such. Regarding star clusters, these have traditionally been classified in two ways: globular clusters and open clusters, which are also called galactic clusters.
These groups are of great interest to NASA and even has teams specially trained to search for them. A notorious record of this event was made last 2016 in the month of January, where a search was carried out that was specifically called the XXL Hunt for galaxy clusters. This name was chosen because the XXL sounding was carried out through X-rays of the southern area.
In this sense, another term that needs to be explained is that of galaxy clusters. This classification of space clusters are massive congregations of galaxies that also house immense reserves of hot gas that have temperatures so high that they produce X-rays. This allows them to become useful structures for astronomers in their studies of the universe and its components.
The great interest arises since it is believed that the construction of these is influenced by the strangest components of the universe, which are: dark matter and dark energy. Studies have indicated that properties at different stages in the history of the Universe record that galaxy clusters could shed light on the little-known dark side of the Universe.
XXL hunt for galaxy clusters
The group of specialists in charge of this hunt was made up of more than 100 astronomers from all over the world. The search for these cosmic monsters specifically began in 2011. Now, on the one hand, the high energy radiation from x-rays it reveals that their location is sucked into Earth's atmosphere. However, in addition to this, it can be detected by X-ray observatories in space.
To carry out this research, what they did was combine the ESA XMM-Newton sounding, this was what involved the largest allotment of observing time ever given to this telescope in orbit. It was also produced together with observations from ESO and other observatories. As a result, they obtained a huge and growing collection of data from across the electromagnetic spectrum, which has been collectively called the XXL survey.
The main purpose of this survey, which was numbered XXL, was to provide a specific and defined sample of approximately 500 galaxy clusters found at a distance where the Universe was half its current age, according to Marguerite Pierre of CEA, Saclay, France. What managed to capture as such the images of two areas of the sky, was the XMM-Newton telescope.
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The areas that were found in the sky were each one hundred times the size of the full moon. In fact, this size could have been determined in an attempt to discover a large number of previously unknown galaxy clusters. This team that makes up the XXL survey has published its conclusions in a series of scientific articles that refer to the 100 brightest clusters that were discovered during the scan time.
Observations with EFOSC2 instrument
Similarly, a group of observations that were made with the EFOSC2 instrument was also used for this survey. This instrument was installed on the New Technology Telescope (NTT), accompanied by the FORS instrument, which was also attached to ESO's Very Large Telescope (VLT). What was envisioned when this team was assembled was to carefully analyze the light coming from galaxies within these galaxy clusters.
But the bottom line of this is that it allowed the team to make exact distance measurements to galaxy clusters. This was what then provided a three-dimensional view of the cosmos, which was required to make the most precise measurements on the mysterious dark matter and the dark energy. From this the XXL survey is expected to generate a number of interesting and unexpected results. However, even with a fifth of the final data, important and surprising findings have already emerged.
Among the scientific articles published, regarding the search for star clusters, specifically this mentioned survey, the discovery of five new super clusters is reported above all. This means that it is about clusters of clusters of galaxies that are added to those already known, such as our own supercluster which is called Heaven.
In addition to this important piece of information for the astronomy, there is also another report revealing follow-up observations to a particular galaxy cluster (informally known as XLSSC-116). This cluster of galaxies is located at a distance of six billion light-years, and using the VLT's MUSE instrument, an unusually bright and diffuse light source was observed in the cluster.
galaxy clusters
For the first time, it has been possible to analyze in detail the diffused light observed in a distant galaxy cluster, which has demonstrated the power of MUSE for these valuable investigations, according to analyzes carried out by the Laboratory of Astrophysics in Marseille, France. Within this team, the data confirming the concept that postulates that the clusters of galaxies were versions of the current ones were also used.
This research also shows that these are reduced scales of those we have currently observed, since they are clusters of galaxies that existed in the past. These types of discoveries are important to be able to understand theoretically, what has reference to the evolution of clusters along the history of the universe. Since the way to know what happened in space in past times, can only be done through scientific and astronomical inquiries.
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Only the act of counting the galaxy clusters in the XXL data managed to further confirm a rather peculiar previous result. It turns out that there are fewer distant clusters than would be expected, based on predictions with cosmological parameters which were calculated by ESA's Planck telescope. However, the reason for this discrepancy is still unknown, for this reason the team hopes to understand this cosmological curiosity with the complete sampling of clusters in the near future.
The aforementioned results are quite relevant to science and, apart from this, they are only an advance way of showing what is expected to be achieved with this enormous survey of some of the most massive objects in the Universe. Most of the Scientific articles that describe this survey can be found in the renowned journal Astronomy & Astrophysics.
Classification of star clusters
Among the different types of clusters that exist in space, it is important to describe what one of them is about, in this case we will explain what they are globular clusters and the open clusters. Seeing that initially it was explained what the groups of galaxies are, the importance of their explorations and surveys carried out for the elaboration of their studies.
First of all, it is necessary to define what are the globular clusters. These are fairly dense clusters with hundreds of thousands or millions of old stars. When we talk about old stars, we mean that they are more than a billion years old. And it is these stars that make up this type of grouping and characterize it mainly.
On the other hand, there are also open clusters that generally have hundreds or thousands of young stars. In this case it is about those stars that are less than a hundred million years old or even those of intermediate age, that is, between a hundred million and a billion years. Something that characterizes open clusters is that they are broken up over time.
This implies that in open clusters the stars disperse and this occurs due to their gravitational interaction with the stars. molecular clouds in its movement through the galaxy. On the other hand, in denser globular clusters, there is greater stability against their disintegration. However in the long run, they also end up being destroyed.
Differences between globular and open clusters
What is mainly mentioned among the differences of these clusters, is the number of stars that there are between them, this is what their mass size or the mass of star clusters. Another difference is the age between the two traditional types of cumulus, as mentioned earlier. On the other hand, it is also possible to distinguish them by their metallicity.
The metallicity of open clusters is usually much higher, since these clusters are rich in metals, while on the other hand globular clusters are poor with respect to metals. Another big difference between clusters lies in its orbit, since open clusters concern the population of the disk of the galaxy; on the other hand, globular clusters belong to the halo. Contradictorily, there are no large differences between the sizes of the cores of both types of clusters, which in both cases is a few parsecs.
Past Classification
For the decade of the 80's and 90's, an important discovery occurred in which the traditional classification was made, which in reality did not cover all the existing star clusters in all of universal space. An example of them is the Magellanic Cloud. Within it, there are clusters that are as massive as the globular ones but young (R136, the core of 30 Doradus, is the most notorious case).
On the other hand, they were discovered in other galaxies (for example, M82) in those years super star clusters as massive or more massive than globular clusters, but young. Furthermore, in some of these super star clusters (NGC 3603, Westerlund 1), they have also been identified in the plane of our own galaxy, hidden behind large clouds of dust. that hinder vision.
In the same way, it was found that the difference between stellar clusters (which are bound objects, that is, bound by their gravitational attraction) and stellar associations (groupings that are not gravitationally bound and slowly disperse) is not well marked. Some stellar groupings are born as clusters, others as stellar associations, others as clusters surrounded by associations and others in a borderline state between clusters and associations.
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However, sooner or later they all end up disintegrating. Although as we have already mentioned, the globular clusters (which when they are young are called super stellar clusters) are the ones that last the longest. It can be seen that there are globular clusters that formed early in the life of our galaxy. But on the other hand, it is also possible to see how some globular clusters have tidal tails.
tidal tails
These tidal tails that some globular clusters have, are traces of stars that have been detached from the cluster throughout its history and that presage its final dispersion. However, there is also a modern classification of stellar groups (clusters or associations) that must include at least three variables: age, mass and gravitational state; and perhaps two more, which are the metallicity and the type of orbit to which it belongs.
astronomy and clusters
There is a marked astronomical interest in clusters, among which it is essential to mention the globular cluster G1 in M31. These stellar clusters are the ones that have collaborated in the understanding of what stellar evolution is, as they are stars formed at the same time from the material of a molecular cloud. In addition to this, they represent a fundamental step in determining the scale of the Universe.
On some occasions, the nearest open clusters can be used to measure their absolute distances by means of the parallax technique. One of the great meters, in fact, is the Hertzsprung-Russell diagram of these clusters, which can be represented with absolute luminosity values. On the other hand, the diagrams that are similar and that also evaluate the clusters whose distance is not known, can be compared with those of calibrated distance estimating the distance that separates them from us.
Globular cluster specificity
It is important to mention in more detail what a globular cluster is or also known as a globular cluster, in English. It is a type of star cluster consisting of a grouping of 100.000 to 1.000.000 old stars. This means that it is from Population II. The stars of this type of cluster are gravitationally bound, with an approximately spherical distribution and orbit around a galaxy in a similar to a satellite.
These old stars they are what give globular clusters their typical distinctive golden color, which are only visible through color photography. They are generally composed of hundreds of thousands of old stars, of the same type as those that make up the bulge of a spiral galaxy, but confined to a volume of only a few cubic parsecs.
Actually some globular clusters, such as the omega centauri in the Milky Way and G1 in M31 in the Andromeda Galaxy, are extraordinarily massive, on the order of several million solar masses. On the other hand, there are also others like M15. This last one is another cluster that is located in our Milky Way, they have extremely massive nuclei, which makes us suspect the presence of black holes in their centers.
Adding to this mystery, every globular cluster appears to have a definite age, with a few notable exceptions, of course. This means that all the stars in a globular cluster are at approximately the same stage of their evolution, suggesting that they all formed at the same time. It was the recognition of this fact, studying the Hertzsprung–Russell diagrams of globular clusters, which gave rise to a first theory of the evolution of stars.
stellar density
Each globular cluster has a stellar density very high. In this way, there are strong interactions between its component stars and, in addition, collisions usually occur with relative frequency. Some types that are exotic among stars, such as blue stragglers, millisecond pulsars, and low-mass X-ray-emitting binaries, are much more prevalent in globular clusters.
Number of globular clusters
In space there are a fairly large number of globular clusters. There are at least 150 known clusters in the Milky Way. It is even probable that there are 10 or 20 more that have not yet been discovered. In fact, larger galaxies like M31 tend to have even more (M31 would have at least 500). Some giant elliptical galaxies, like M87, they could have 10.000 globular clusters or even more. The clusters orbit around the galaxy at a great distance, typically about 100 kiloparsecs or more.
metallicity
The metal content of globular clusters is quite peculiar, since they are generally formed by stars belonging to Population II. These stars have low metal content, compared to Population I stars, which are roughly like the Sun. Astronomically, all elements that are heavier than helium, such as helium, are called metals. carbon, oxygen, among others.
Also in astronomy, a "metal" is that element other than hydrogen, helium or lithium. The reason is that these last mentioned elements are the only elements that are found naturally without the need for nuclear fusion that occurs in the stars. Another aspect to consider at this point is that in many galaxies, especially massive elliptical galaxies, there may be two populations of globular clusters with different metallicities.
This is called cumulus subpopulations and are commonly known as "metal-poor" and "metal-rich". On the other hand, the composition of the one that contains more metals does not reach the metallicity of the Sun. According to different authors, many theories have been suggested to explain these subpopulations, such as violent galactic mergers, the accretion of dwarf galaxies and the multiple phases of star formation in a single galaxy.
With respect to our Milky Way galaxy, clusters that have low metallicity are associated with the galactic halo, and the "rich" are those who can be associated with the galactic bulge.
Observation of galaxy clusters
Astronomically it has observed the formation of a cluster of galaxies, especially from the year 2014 was when the most innovative findings about this phenomenon or spatial event in the early universe began. These cosmic objects are the clusters of galaxies and are the largest objects that exist in the universe.
It is important to note that they are held together by gravity, but how they form is still not well understood. Now, a complete census of star formation has been carried out on such an object in the primitive universe. On the other hand, MRC 1138-262, known as the Cobweb Galaxy, has been studied for many years because it is believed to be one of the best examples of a protocluster in the process of merging.
However, a team of investigators was suspicious that this story was missing pieces. For this reason, they decided that they should study the dark side of star formation and thus find out how many of the stars that were forming in the star cluster spider web galaxy They were hidden from our view. That is, behind the dust.
For the investigation, the team used the LABOCA camera, installed in the APEX telescope, in Chile. In this way, this Cobweb cluster could be observed at millimeter wavelengths, allowing one to look through most of the thick dust clouds.
Revealed Observations
Astronomers conducted firm studies and research, regarding clusters. In this sense, the observations revealed that, compared to the surrounding sky, four times more sources had been determined in the Spider Web area that were not known before.
On the other hand, carefully comparing the new data with the complementary considerations made in different wavelengths, were able to confirm that many of these sources were at the same distance as the galaxy cluster itself, which implies that they must be parts of the cluster in formation.
However, while observing the place where they had discovered this focus of star birth, they got another surprise. What they really expected was to find this region of star formation in the great filaments that connect the galaxies. But what happened was that they found it concentrated for the most part in one region, and that region is not even centered on the Spiderweb Galaxy, which is in the protocluster center.
Milky Way belongs to a larger super cluster
Our planet is specifically located in the Milky Way galaxy, in which according to studies it has been suggested that our galaxy actually belongs to a super cluster that is much larger. The reason is that we belong to a super cluster 100 times larger than previously thought. This analysis was done by a team of astronomers who named the supercluster .
Laniakea is a super cluster of galaxies that includes the Milky Way. Its size is 100 times larger in volume and mass than previously anticipated. The astronomers who made this discovery have mapped the enormous region and named it Laniakea, due to its Hawaiian meaning, which is that of “huge sky”.
What happens in space is that galaxies tend to get closer, until they form groups called clusters. In addition to this, the regions where these clusters are densely populated are known as "super clusters”. But the definition of these massive cosmic structures is imprecise. This novel study is the one that describes a new way to define where one super cluster ends and the other begins.
cosmic speed
The team that discovered this super cluster used a database that gathers the speeds of 8 galaxies, which are calculated after subtracting the average speed of cosmic expansion. These deviations are due to gravitational pull that the galaxies around them feel, the one that comes from the mass. The researchers used an algorithm to translate these velocities into a three-dimensional field of galaxy flux and density.
Astronomers affirm that it has not yet been possible to affirm having a good understanding of cosmology if they cannot explain this movement. This is a method that is better than just mapping the location of matter. And the reason is that it allows scientists to build a map of unstudied regions of the Universe, as indicated by astrophysicists at the Valongo Observatory, part of the Federal University of Rio de Janeiro. The method relies on detecting the influence of galaxies rather than seeing them directly.
Moreover, the galaxy movements they manage to reflect the distribution of all the matter and this is not only with what is visible with the telescopes of the research team, including dark matter. Subtracting cosmic expansion, his map shows streamlines that galaxies follow under the effect of gravity in their local region.
