Magellanic clouds andromeda milky way. Magellanic clouds. Star formation in the Large Magellanic Cloud


Magellanic Clouds

 - galaxies-satellites of our Galaxy; located relatively close to each other, form a gravitationally bound (double) system. To the naked eye, they look like isolated clouds of the Milky Way. For the first time, M. O. described Pigafetta, who participated in the circumnavigation of Magellan (1519-22). Both Clouds - Large (BMO) and Small (MMO) - yavl. wrong galaxies. The integral characteristics of M. O. are given in the table.

Integrated characteristics of the Magellanic Clouds

BMO IMO
Center coordinates05 h 24 m -70 o00 h 51 m -73 o
Galactic latitude-33o-45o
Angular diameter8o2.5o
Corresponding linear size, kpc9 3
Distance, kpc50 60
integral value, M V -17,9m -16,3m
Inclination to the line of sight27o60o
Average radial velocity, km/s+275 +163
Total weight,
Mass of interstellar hydrogen HI,

With the largest telescopes in MO, stars with a luminosity close to that of the sun can be resolved; at the same time due to mean. exceeding the distance to the M.O. over their diameter, the difference in the apparent stellar magnitudes of the objects included in the M.O. is equal to the difference in their abs. (for LMO the error does not exceed 0.1 m). Since M. O. are located on high galaxies. latitudes, the absorption of light by the interstellar medium of our Galaxy and the admixture of its stars distort the M.O. proximity. All this helps to study the relationship between stars of various types, clusters and diffuse matter (in particular, high-luminosity stars are visible there no further than 5-10 "from their birthplace). M. O. is called the "workshop of astronomical methods" (H. Shapley) In particular, the period-luminosity dependence for M. O. was discovered in M. O. Along with similarities, M. O. objects have a number of striking differences from similar members of the Galaxy, which indicates a connection between the structural features of galaxies and the characteristics of their population.

In M. O. there is a huge number of all possible ages and masses; The LMC cluster catalog includes 1600 objects, and their total number is approx. 5000. About a hundred of them look like galaxies and are very close to them in terms of masses and the degree of concentration of stars. However, the globular clusters of the Galaxy are all very old [(10-18) years], while in the Moscow Region, along with equally old clusters, there are a number of globular clusters (23 in the LMC) with ages of ~10 7 -10 8 years. The age of M. O. clusters unambiguously correlates with the chem. composition (young clusters contain relatively more heavy elements), while galactic clusters have. there is no such correlation.

There are also 120 large groups of young high-luminosity stars (OB associations) known in the LMC, which are associated, as a rule, with regions of ionized hydrogen (H II zones). In MMOs, there are an order of magnitude fewer such groupings; young stars are concentrated there in the main. body and in the "wing" of the MMO, extended to the LMO, while in the LMO they are scattered throughout the Cloud, and in the main. the body is dominated by stars with an age of 10 8 -10 10 years. Radio astronomical observations in the line = 21 cm of neutral hydrogen (HI) showed that there are 52 isolated HI complexes in the LMC with cf. with a mass and dimensions of 300–900 pc, while in the MMO the HI density increases almost uniformly towards the center. The share of HI in relation to the total mass in the LMC in several. times more than in the Galaxy, and in MMOs more by an order of magnitude. Even in the youngest objects of the LMC, the content of heavy elements is apparently somewhat less than in the Galaxy; in the MMO, it is undoubtedly lower by a factor of 2–4. All these features of M. O. can be explained by the fact that there was no initial violent outburst, which led to the exhaustion of the base in the Galaxy. gas reserves and the relatively rapid enrichment of its remnants with heavy elements during the first billion (or hundreds of millions) years of the existence of the Galaxy. The presence of old globular clusters and the RR Lyrae type proves, however, that star formation began in MO and in the Galaxy at about the same time. The presence of a large number of young globular clusters in MO (there are none in the Galaxy) may mean that their formation in the present. The disk of the Galaxy is hindered by a spiral density wave, which can also initiate star formation in gas clouds that have not reached a high degree of compression (see ).

About 10 3 Cepheids are known in each of the MOs, and the maximum in their distribution over periods is shifted to small periods in the MMO (compared to Cepheids in the Galaxy), which can also be explained by the lower content of heavy elements in the MMO stars. The distribution of Cepheids over periods is not the same in different parts of the MO, which, in accordance with the period-age dependence, is explained by the difference in the age of massive stars in these regions. The diameter of the regions in which Cepheids and clusters have similar ages is 300–900 pc. The objects in these star complexes are obviously genetically related to each other - they arose from the same gas complex.

In several RR Lyrae-type stars, which in the LMC have cf. magnitude 19.5 m with a very small dispersion, which implies a small dispersion of their luminosities and weak absorption of light in the LMC. Few dust nebulae have been found in the LMC (about 70), and only in some areas inside and near the giant HII Tarantula zone (30 Doradus) does the extinction reach 1–2 m. The ratio of the mass of dust to the mass of gas in the LMC is an order of magnitude smaller than in the Galaxy, and the low dust content should be reflected in the features of star formation in the M.O. and in the Galaxy, their diameters, like those of H II ring zones, reach 200 pc. There are 9 supergiant HII shells with a diameter of approx. 1 kpc. In M.O., the closest connection with the gas is shown not by 0-stars, but by . It has also been noted that the star-forming regions in the LMC are, as a rule, located in regions with the highest HI density gradient.

HII zones, supergiants, and planetary nebulae (137 of the latter discovered in the LMC and 47 in the MMO) make it possible to determine the center of rotation of the LMC. It is located 1 kpc from its optical. center. The discrepancy is explained, apparently, by the fact that the latter is determined by bright objects, the mass of which is not yavl. dominant. The fast rotation and small velocity dispersion (of the order of 10 km/s for young objects) indicate a high degree of oblateness of the LMC (some astronomers consider the LMC to be a spiral galaxy with a massive bar and weakly expressed spiral arms). Old globular clusters and, apparently, RR Lyrae stars are also concentrated in the disk, and not in the LMC corona. The peculiarity of the IMO kinematics and the very large surface density of the Cepheids in it can be explained by the fact that the IMO is oriented toward us with the end of its core. body, while the LMC is visible from a direction almost perpendicular to the plane of its disk.

A remarkable feature of the BMO yavl. a stellar super-association discovered in it, in the center of which there is a giant zone HII (30 Dorado, Fig. 2) with a diameter of approx. 250 pcs and weighing . In the center of the zone there is a compact cluster of very high luminosity stars with a total mass (Fig. 3). It is yavl. is the youngest known globular cluster and contains the most massive young stars. The central object of the cluster is brighter by 2 m the rest of the stars. Apparently, this is a compact group of hot stars that excite the H II region. According to a number of characteristics, the 30 Doradus cluster is similar to moderately active

Far in the southern sky, unattainable for the eyes of the inhabitants of the northern hemisphere of the Earth, elusive for the large telescopes that are built and installed in the northern hemisphere, there are two most remarkable objects of the sky, two treasures of astronomy - the Large and Small Magellanic Clouds.

The first description of observations of the Magellanic Clouds that has come down to us belongs to Pigafetta, a companion and historiographer of Magellan on a nerve-wracking trip around the world. When in 1519-1522. Magellan's ships sailed along the southern waters of the Atlantic, and then the Pacific and Indian oceans, Pigafetta drew attention to two shining nebulae standing high in the sky, steadily accompanying the Expedition, and described them. Nothing like this is seen in the northern sky.

The great importance of the Magellanic Clouds for science is determined by the fact that these are the galaxies closest to us. The next neighbor, the Sculptor system, is twice as far away. In addition, the Magellanic Clouds are galaxies with an extremely rich and diverse composition of objects. In this respect, they hold the palm in the Local system of galaxies. The system in Sculptor is a much less interesting galaxy, devoid of supergiant stars, star clusters, gaseous nebulae, and other objects that are important for studying the evolution of stars and stellar systems. The nearest galaxies comparable in composition to the Magellanic Clouds are the Andromeda Nebula (NGC 224) and the Triangulum Nebula (NGC 598). But they are located 10 times further. And this means that with a 60-cm telescope, the Magellanic Clouds can be studied with the same detail as NGC 224 and NGC 598 are studied using a giant 6-meter telescope. What interesting information could be obtained by pointing a 6-meter telescope at the Magellanic Clouds! However, as one observer noted, "God decided to play a joke by placing astronomers in the northern hemisphere of the Earth, and placing the Magellanic Clouds in the southern sky."

The countries of the northern hemisphere have long had a 5-meter telescope and a large number of telescopes with a lens diameter of two to three meters. And in 1976

In the Soviet Union, a six-meter telescope was put into operation.

Until recently, there were only two 180-cm telescopes in the southern hemisphere. With their help, the Magellanic Clouds were mainly observed. It was only very recently that the southern hemisphere was finally enriched with 4- and 3.7-meter telescopes. It will take years, ten years, before these telescopes will make a significant contribution to the study of the Magellanic Clouds.

Many objects are studied in the Magellanic Clouds even more successfully than in our Galaxy itself. This is due, firstly, to the fact that the most interesting objects of the Galaxy lie very close to its main plane, and since we are also located near this plane, observations are greatly hindered by the absorption of light by dark dusty matter, which is also concentrated near the main plane. Directions to the Large and Small Magellanic Clouds make angles of 33 and 45° with the plane of the Galaxy, so the absorption of light has a very weak effect. Another advantage of the Magellanic Clouds is the possibility, by comparing the apparent magnitudes of their stars, to compare the absolute magnitudes of the luminosity. Such a comparison is possible because the size of the Magellanic Clouds is small in comparison with the distance to them, and all the stars of each Cloud can be considered approximately equally distant from us. This condition is, of course, not fulfilled for the stars of our Galaxy, and how important its significance can be can be seen from the following historical example.

In 1910, G. Leavitt (USA), while observing Cepheids in the Small Magellanic Cloud, discovered that long-period Cepheids, which have a greater brightness, also have a longer period of change in brightness. Quite accurately, the rule was fulfilled, according to which a twice as long period corresponded to a Cepheid magnitude less by 0 m, 6. Since for stars in the Magellanic Clouds the difference in absolute stellar magnitudes is equal to the difference in apparent stellar magnitudes, Then a physical law was established - a twice as large period in the Cepheids of the Small Magellanic Cloud corresponds to an absolute stellar magnitude smaller by 0 m,6, i.e. 1.7 times the luminosity. Subsequently, it turned out that this law is universal. It is valid for long-period Cepheids of the Large Magellanic Cloud, the Galaxy, the Andromeda Nebula, and other galaxies; A similar relationship was also established for short-period Cepheids. The open dependence made it possible to develop a new method for determining distances, which played an important role in astronomy. If you need to determine the distance to a star cluster or galaxy, then it is enough to find a Cepheid in this system, observe the change in its brightness and determine the period, then determine the latter from the ratio between the period and the absolute magnitude M. It is also necessary to measure the apparent stellar magnitude m, and then the unknown distance r is calculated.

How important the method of determining distances from Cepheids is, can be judged by the fact that it has become the basis for determining distances to other galaxies.

If long-period Cepheids were not observed in the Magellanic Clouds, then the relationship connecting their periods and absolute stellar magnitudes could only be established much later, since the difference in distances to the long-period Cepheids of the Galaxy prevents this dependence from manifesting itself in a visible way.

The distance to each of the Magellanic Clouds, 46 kpc, is only one and a half times the diameter of the Galaxy, and the distance between the Large and Small Clouds is about 20 kpc. These distances are many times smaller than the average distance between neighboring galaxies in general and even than the average distances between neighboring galaxies in the Local System of Galaxies. Therefore, it is more correct to consider that the Galaxy and the Magellanic Clouds form a triple galaxy. The mutual influence in this triple system, where the Galaxy should be considered the main body, and the Magellanic Clouds as satellites, can be traced in the fact that, as radio observations show, both Magellanic Clouds are immersed in a common shell of neutral hydrogen and are additionally interconnected by a hydrogen bridge, and hydrogen, located near the main plane of the Galaxy, forms a protrusion directed towards the Magellanic Clouds. Something like a spiral branch stretches from the Big Cloud in the opposite direction from the Galaxy, and then there should be a similar branch, indistinguishable due to the perspective, towards the Galaxy. It is possible that the Big Cloud and the Galaxy are interconnected by a gas bridge.

The Large Magellanic Cloud is approximately 10 kpc across. It has a complex and varied structure. An elongated body is clearly looming, resembling jumpers at crossed spirals. There are many small details that are the result of groupings of supergiant stars. The Big Cloud is dominated by Type I stellar populations and is replete with prominent members of this population type. In this respect, the Large Magellanic Cloud surpasses even the region of the spiral arms of our Galaxy. It contains a lot of blue supergiants of extremely high luminosity. The French astronomer Vaucouler counted 4,700 supergiants in the Big Cloud, each of which radiates more powerfully than 10,000 suns, and it is here that the champions in luminosity among the stars known to us are located.

The table lists the known stars of the highest luminosity in various galaxies.

We see that the champion in luminosity among all the stars we distinguish (in distant galaxies we cannot distinguish individual stars) is the white star HD 33579, located in the Large Magellanic Cloud. This star is also called S Goldfish. Its absolute magnitude is -10m,1 and it shines like about a million suns. If HD 33579 were in place of the nearest star to us instead of a Centauri, then humanity on Earth would be provided with additional and brighter than at present night illumination. At this distance, HD 33579 would shine like five moons. The table shows; that in terms of the power of supergiant stars, the Large Magellanic Cloud ranks first; our Galaxy and the Triangulum Nebula (NGC 598) are in second place among nearby galaxies, and the Small Magellanic Cloud, the Andromeda Nebula (NGC 224) and NGC 6822 are in third place.

Due to the fact that all the stars of the Large Magellanic Cloud are almost at the same distance from us, it is more convenient in this system than in our Galaxy to determine the relative number of stars of different luminosity.

By counting the number of stars of different apparent magnitudes in one of the sections of the Big Cloud and knowing the distance, Thackeray obtained the results presented in the table

Unfortunately, Thackeray was only able to count supergiants and bright giants. If the 5-meter telescope were in the southern hemisphere, then the calculations could be extended to stars with M = +5 m, i.e., such as our Sun. This would provide very interesting information about the stellar population of the Magellanic Clouds. It follows from Thackeray's results that as the luminosity of supergiants and giants decreases, the number of stars of this luminosity increases. It would be interesting to know to what absolute, stellar magnitudes this regularity extends. Is the maximum number of stars reached at a certain value of luminosity, after which, with a further decrease in luminosities, the number of stars of a given luminosity already decreases? ,

The size of the Small Magellanic Cloud is approximately four times smaller than the Large one - 2.2 kpc. Despite the similarity in appearance, mutual proximity and, apparently, common origin, differences are found in the stellar population of the Clouds. In the Small Cloud, type I stellar population is not as richly represented and its representatives are not as outstanding specimens as in the Big Cloud.

We observe other galaxies through our galaxy. To determine the characteristics of individual stars in other galaxies, one must be able to distinguish, separate them from the stars of our Galaxy projecting onto these galaxies. Otherwise, if we take a weak and close star, located, for example, at a distance of 46 kpc, as a star that is part of the Large Magellanic Cloud, located a thousand times further, then the luminosity of the star will be exaggerated by 1000 2 - million times. So you can get a lot of fictitious "supergiants". A reliable way to protect the study from such errors is to determine the radial velocity of the star. If, for example, a star located in the direction of the Large Magellanic Cloud has a radial velocity that is not very different from the radial velocity of the cloud itself + 280 km / s, namely, if this radial velocity lies in the interval + 250- + 310 km / s , then, without a doubt, the star belongs to the Large Magellanic Cloud. If a star belongs to the Galaxy and is only projected onto the Large Magellanic Cloud, then its speed will not exceed +60 - +70 km/s. In this direction, other radial velocities, lying, for example, in the interval o r +70 to +260 km/s, do not occur.

You can also use your own movements. In the stars of other galaxies, they are always equal to zero due to very large distances. If a star has its own movement, it is definitely a star in our galaxy. The type I stellar population is characterized by the presence of large gaseous-hydrogen nebulae. And in this regard, the Large Magellanic Cloud, replete with hydrogen nebulae, stands out among nearby galaxies. In both Magellanic Clouds, there are 532 large gaseous nebulae, the predominant part of which is part of the Big Cloud. Here is also the most grandiose known gaseous nebula - 30 Goldfish, which has a diameter of about 200 ns and a mass equal to that of 500,000 Suns. For comparison, we point out that the largest known hydrogen nebula in our Galaxy has a diameter of 6 kpc and its mass is only 100 solar masses.

There are a lot of star clusters in the Magellanic Clouds. Back in 1847, John Herschel, who traveled specially to South Africa to observe the Magellanic Clouds, counted 919 in the Big Cloud, and 214 in the Small Cloud, star clusters and clouds of diffuse matter. Currently the total number; There are 1600 cataloged open clusters in the Large Cloud, and over 100 in the Small Cloud. All these clusters are comparable in size and luminosity to the richest open clusters in our Galaxy. One must think that in the Magellanic Clouds there are a large number of open clusters of smaller sizes and less rich in stars that have not yet been identified.

Globular clusters similar to the globular clusters of the Galaxy have been discovered in Big Cloud 35 and Small Cloud 5. But new objects have also been discovered that are not found in the Galaxy - globular clusters containing many bluish and white giants and therefore having a white color, while the so-called "Ordinary" globular clusters, including all globular clusters in the Galaxy, have only red giants and their color is yellow - orange. These globular clusters of a new type are of great interest. There is an assumption that their age is small, while "ordinary" globular clusters are old formations. It is necessary to find an answer to the question why there are blue globular clusters in the Large Magellanic Cloud, but they are not in the Galaxy.

The Magellanic Clouds abound with variable stars of various types. Only in these two galaxies, not counting ours, can long-period and short-period Cepheids be observed at the present time. This circumstance, as we shall see later, is extremely important for the development of correct methods for determining extragalactic distances.

The first outburst of a new star in the Small Cloud was observed in 1897, and in the Big Cloud in 1926. To date, more than a dozen such outbursts have been registered.

The Magellanic Clouds are also rich in diffuse matter. A study of the radio emission coming from them with a wavelength of 21 cm shows that hydrogen in them is not only concentrated in individual clouds, but is also distributed throughout the entire volume of galaxies. While in our Galaxy hydrogen makes up only 1-2% of the total mass, in the Magellanic Clouds its share is estimated at 6%.

Dust matter in the Magellanic Clouds cannot be directly observed. Direct observation of matter in galaxies is usually only possible when we see highly compressed galaxies edge-on or almost edge-on. Only in this case is the thickness of dusty matter along the line of sight so significant that it can be clearly seen. Therefore, to detect dusty matter in the Magellanic Clouds, an original method is used, which was first used by Shapley. The number of distant galaxies observed through the Magellanic Clouds is counted and compared with the number of galaxies in neighboring regions. For example, the number of distant galaxies observed through the central region of the Great 06^ Lacquer is approximately 10 times less than the number of galaxies of the same apparent magnitude observed in the same area in the neighboring region of the sky. This difference should be explained by the fact that the Large Magellanic Cloud contains dusty matter that attenuates the light of distant galaxies. Therefore, the more distant and weaker ones become invisible. From the fact that the number of galaxies, when observed through the Big Cloud, decreases by a factor of 10, it can be concluded that the dusty matter located there reduces the brightness of all objects by an average of 1m.7. For comparison, we point out that, according to observations and calculations, the brightness of galaxies that would be viewed through our Galaxy in the direction perpendicular to its main plane would be weakened on average by only 0m.7. Apparently, the Big Cloud is also richer in dust matter than our Galaxy. Light absorption is also found in the Small Magellanic Cloud.

The study of the Magellanic Clouds showed the unity, commonality of various star systems. All objects - stars of different spectral types, different luminosities, variable and stationary, various types of star clusters, gaseous and dusty matter, all the diversity that amazes the researcher of the Galaxy, finds its place in the Magellanic Clouds. This means that the laws governing the formation of stars and star clusters are the same in our Galaxy and in the Magellanic Clouds.

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Magellanic Clouds are satellite galaxies of the Milky Way. Both Clouds - the Large Magellanic Cloud and the Small Magellanic Cloud were previously considered irregular galaxies, but subsequently found features in the structure of barred spiral galaxies. They are located relatively close to each other and form a gravitationally bound (double) system. Visible to the naked eye in the Southern Hemisphere. One of the first descriptions was given by Antonio Pigafetta, a participant in the circumnavigation of Fernando Magellan (-). . Both Clouds float in a common hydrogen shell.

Magellanic clouds are located at high galactic latitudes, so the light from them is little absorbed by our Galaxy, in addition, the plane of the Large Magellanic Cloud is almost perpendicular to the line of sight, so for objects visible nearby it will often be true to say that they are spatially close. These features of the Magellanic clouds made it possible to study, using their example, the patterns of distribution of stars and star clusters.

Magellanic clouds have a number of features that distinguish them from the Galaxy. For example, star clusters with an age of 10 7 -10 8 years have been found there, while clusters of the Galaxy are usually older than 10 9 years. Also, apparently, the content of heavy elements is less in the Magellanic Clouds.

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Notes


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See what "Magellan clouds" are in other dictionaries:

    - (named after the traveler Magellan). Foggy spots in the sky, near the south pole, are visible to the naked eye. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. MAGELLANIC CLOUDS named after Magellan two ... ... Dictionary of foreign words of the Russian language

    - (Large and Small) two Galaxies close to us, satellites of the Galaxy. Magellanic clouds are visible in the sky in the Southern Hemisphere with the naked eye (respectively in the constellations Dorado and Toucan). In the B. Magellanic Cloud in February 1987 flared up ... ... Big Encyclopedic Dictionary

    MAGELLANIC CLOUDS, the two GALAXIES closest to us, visible to the naked eye as separate parts of the Milky Way in the sky in the form of the letter S. The Large Magellanic Cloud is located in the constellations Golden Fish and Table Mountain, the Small Magellanic Cloud ... ... Scientific and technical encyclopedic dictionary

    - ... Wikipedia

    - (Large and Small) two star systems (Galaxies) of irregular shape, closest to our star system (Galaxy (See Galaxy)), which includes the Sun. Visible in the southern sky with the naked eye in the form of foggy spots (on ... ... Great Soviet Encyclopedia

    - (Large and Small), two galaxies close to us, satellites of the Galaxy. Magellanic clouds are visible in the sky in the Southern Hemisphere with the naked eye (respectively in the constellations Dorado and Toucan). Their discovery is attributed to one of the participants ... ... encyclopedic Dictionary

    - (Large and Small) two galaxies close to us, satellites of the Galaxy. Magellanic clouds are visible in the sky in the Southern Hemisphere with the naked eye (respectively in the constellations Dorado and Toucan). In the Large Magellanic Cloud in February 1987 flashed ... Astronomical dictionary

    - (Nubecula major and N. minor) wonderful foggy spots lying in the southern hemisphere of the sky in the constellations Dorado and Toucan, at a distance of about 20 ° from one another. M. clouds are not solid spots like others; they represent amazing... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

    - (Large and Small), two galaxies close to us, satellites of the Galaxy. M.O. visible in the sky in South. hemispheres with the naked eye (respectively, in the constellations of the Dorado and Toucan). Their discovery is attributed to one of the participants in the circumnavigation F. ... ... Natural science. encyclopedic Dictionary

    Magellanic Clouds- Magellan Clouds a, Magellan Clouds (aster) ... Russian spelling dictionary


NASA and Pennsylvania State University researchers have completed the most detailed ultraviolet survey ever made of the Large and Small Magellanic Clouds using the Swift spacecraft. The resulting 160-megapixel mosaic of the Large Magellanic Cloud (LMC) and the 57-megapixel Small Magellanic Cloud (LMC) were presented on June 3, 2013 at the 222nd Congress of the American Astronomical Society.

The new images show approximately one million sources in the LMC and about 250,000 in the MMC, ranging from 1600 to 3300 angstroms (angstrom is an international unit of wavelength, equal to one ten-millionth of a millimeter), which corresponds to the ultraviolet wavelength range, most of which is completely blocked the earth's atmosphere.

To obtain a 160-megapixel LMO mosaic, it took 2,200 images of this object, and their addition took about five and a half days. The MMO image is somewhat simpler and consists of 656 parts; the processing time was about two days. Both obtained images have an angular resolution of 2.5 arcseconds, which is the maximum possible for this telescope.

Says Michael Siegel, lead researcher for Swift's Ultraviolet/Optical Telescope (UVOT) program:

“Until now, there have been very few ultraviolet observations of these galaxies, and there has not been a single study with such unprecedented resolution. Thus, this review closes many questions about the current state of the Large and Small Clouds. With the resulting mosaics, we can observe in one image how the stars go through all the stages of their lives, which is very difficult to understand when studying our Galaxy, since we are inside it. ”

LMC and MMO are located at a distance of 163 thousand and 200 thousand light years from us, respectively, and revolve around each other, as well as around the Milky Way. The LMC is about one-tenth the size of our galaxy and contains only one percent of its mass. MMO is half the size of LMO and contains two-thirds of its mass.

Studying galaxies in the ultraviolet allows astronomers to study in detail the stars that make up them. In the ultraviolet range, light from dim stars is suppressed, revealing the structure of hot clusters, gas clouds, and star-forming regions. To date, there are no analogs to the ultraviolet telescope installed on the Swift apparatus in terms of resolution and field of view.

    General view of the Large and Small Magellanic Clouds. Source: Axel Mellinger, Central Michigan Univ.

    Ultraviolet image of the Large Magellanic Cloud.

The rivals are two dwarf galaxies, the Large and Small Magellanic Clouds, which revolve around the Milky Way and around each other. Each of them draws matter from the other, and one still managed to pull out a huge cloud of gas from its companion.

The so-called "Forward Arm", consisting of interstellar gas, connects the Magellanic Clouds with our Galaxy. A huge concentration of gas is absorbed by the Milky Way and supports its star formation. But what kind of dwarf galaxy pulled out the gas that our stellar home now feasts on? After a long debate, scientists have received the answer to this riddle.

“The question arises: is this gas torn out of the Large Magellanic Cloud or the Small Magellanic Cloud? At first glance, it seems that it is returning to the Large Magellanic Cloud. But we approached this question in a different way, asking: what is the Front Sleeve made of? - explains Andrew Fox, author of the study from the Space Telescope Science Institute in Baltimore (USA).

Large Magellanic Cloud. Credit: AURA/NOAO/NSF

Fox's study is a continuation of his 2013 work, which focused on the feature behind the Large and Small Magellanic Clouds. Gas in a ribbon-like structure called the Magellanic Stream has been found in both dwarf galaxies. Now Fox was thinking about the Front Sleeve. Unlike the Magellanic Stream, this battered and elongated structure has already reached the Milky Way and made its journey into the interior of the galactic disk.

The anterior arm is an example of real-time gas accretion. It is very difficult to see it in galaxies far from the Milky Way. “Because these two galaxies are in our backyard, we got a front row seat to watch this action,” says Kat Barger of Texas Christian University (USA).

The Small Magellanic Cloud as seen by the VISTA telescope. Credit: ESO/VISTA VMC

In the new work, Fox and his team used Hubble's ultraviolet vision to chemically analyze the gas in the Front Arm. They observed the light of seven quasars, the bright nuclei of active galaxies, through this gaseous cloud. Using the space telescope's spectrograph, scientists measured how light is filtered.

In particular, they were looking for the absorption of ultraviolet light by oxygen and sulfur. These are good indications of how many heavy elements are in the gas. The team then compared the Hubble measurements with hydrogen measurements taken by the Robert Byrd National Science Foundation's Green Bank Observatory, as well as several other radio telescopes.

“With a combination of the Hubble and Green Bank observations, we can measure the composition and velocity of the gas to determine which dwarf galaxy is the culprit,” said Barger.

A cosmic tug-of-war has unfolded on the outskirts of our galaxy, and only the Hubble Space Telescope can see who is winning. Credit: D. Nidever et al., NRAO/AUI/NSF and A. Mellinger, Leiden-Argentine-Bonn (LAB) Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory, and A. Feild

The answer was found only thanks to the unique abilities of "Hubble". Due to the filtering effects of the Earth's atmosphere, ultraviolet cannot be studied with ground-based telescopes. After a lot of analysis, the team finally identified chemical "fingerprints" consistent with the origin of the Front Arm's gas. “We found that the gas is consistent with the Small Magellanic Cloud. This indicates that the Large Magellanic Cloud is winning the tug-of-war because it has ripped so much gas out of its smaller neighbor,” said Andrew Fox.

The gas from the Forward Arm now crosses the disk of our Galaxy. As it crosses, it interacts with the Milky Way's own gas and dissipates. This important study shows how gas enters galaxies and ignites stars. One day, planets and star systems in the Milky Way will be born from material that was once part of the Small Magellanic Cloud.

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