Classification of galaxies. History and essence of scientific discovery

MOST IMPORTANT SCIENTIFIC DISCOVERIES
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Classification of galaxies. History and essence of scientific discovery

The most important scientific discoveries

Directory / The most important scientific discoveries

The history of the "discovery" of the world of galaxies is very instructive. Over two hundred years ago Herschel built the first model of the Galaxy, underestimating its size fifteen times. Studying numerous nebulae, the variety of forms of which he first discovered, Herschel came to the conclusion that some of them are distant star systems "of the type of our star system." He wrote: "I do not consider it necessary to repeat that the heavens consist of areas in which the suns are collected in systems." And one more thing: "... these nebulae can also be called the Milky Ways - with a small letter, in contrast to our system."

However, in the end, Herschel himself took a different position regarding the nature of nebulae. And it was no accident. After all, he managed to prove that most of the nebulae discovered and observed by him do not consist of stars, but of gas. He came to a very pessimistic conclusion: "Everything outside our own system is shrouded in the darkness of the unknown."

The English astronomer Agnes Clarke wrote in The System of the Stars in 1890: “It is safe to say that no competent scientist, with all the available evidence, would be of the opinion that even one nebula is a star system comparable in size to Milky Way. It has been practically established that all objects observed in the sky (both stars and nebulae) belong to one huge aggregate "...

The reason for this point of view was that for a long time astronomers were not able to determine the distances to these star systems. So, from the measurements carried out in 1907, it allegedly followed that the distance to the Andromeda Nebula does not exceed 19 light years. Four years later, astronomers came to the conclusion that this distance is about 1600 light years. In both cases, the impression was created that the mentioned nebula is indeed located in our Galaxy.

In the twenties of the last century between the astronomers Shapley and Curtis broke out a fierce dispute about the nature of the Galaxy and other objects visible with telescopes. Among these objects is the famous Andromeda Nebula (M31), which is only visible to the naked eye as a star of the fourth magnitude, but unfolds into a majestic spiral when viewed through a large telescope. By this time, outbursts of new stars had been registered in some of these nebulae. Curtis suggested that, at maximum brightness, these stars radiate the same amount of energy as new stars in our Galaxy. So, he found that the distance to the Andromeda Nebula is 500 light years. This gave Curtis reason to argue that spiral nebulae are distant stellar universes like the Milky Way. Shapley did not agree with this conclusion, and his reasoning was also quite logical.

According to Shapley, the entire Universe consists of one of our Galaxy, and spiral nebulae like M31 are smaller objects scattered inside this Galaxy, like raisins in a cake.

Suppose, he said, that the Andromeda Nebula has the same dimensions as our Galaxy (300 light-years, according to him). Then, knowing its angular dimensions, we find that the distance to this nebula is 000 million light years! But then it is not clear why the new stars observed in the Andromeda Nebula have a greater brightness than in our Galaxy. If the brightness of the novae in this "nebula" and in our Galaxy is the same, then it follows that the Andromeda Nebula is 10 times smaller than our Galaxy.

Curtis, on the contrary, believed that M31 is an independent island galaxy, not inferior in dignity to our Galaxy and distant from it by several hundred thousand light-years. The creation of large telescopes and the progress of astrophysics led to the recognition of the correctness of Curtis. Shapley's measurements turned out to be wrong. He greatly underestimated the distance to the M31. Curtis, however, was also wrong: it is now known that the distance to M31 is more than two million light years.

The nature of spiral nebulae has finally been established Edwin Hubble, who at the end of 1923 discovered the first Cepheid in the Andromeda Nebula, and soon several more Cepheids. Estimating their apparent magnitudes and periods, Hubble found that the distance to this "nebula" is 900 light years. Thus, the belonging of spiral "nebulae" to the world of stellar systems such as our Galaxy was finally established.

If we talk about the distances to these objects, then they still had to be clarified and revised. So, in fact, the distance to the galaxy M 31 in Andromeda is 2,3 million light years.

The world of galaxies turned out to be surprisingly huge. But even more surprising is the diversity of its forms.

The first and rather successful classification of galaxies according to their appearance was already undertaken by Hubble in 1925. He proposed to attribute galaxies to one of the following three types: 1) elliptical (denoted by the letter E), 2) spiral (S) and 3) irregular (1 g).

Elliptical galaxies included those galaxies that look like regular circles or ellipses and whose brightness gradually decreases from the center to the periphery. This group is subdivided into eight subtypes from EO to E7 as the apparent contraction of the galaxy increases. SO lenticular galaxies are similar to highly oblate elliptical systems, but have a well-defined central stellar core.

Spiral galaxies, depending on the degree of development of spirals, are divided into subclasses Sa, Sb and Sc. In Sa-type galaxies, the main component is the core, while the spirals are still weakly expressed. The transition to the next subclass is a statement of the fact of the increasing development of spirals and a decrease in the apparent size of the nucleus.

Parallel to normal spiral galaxies, there are also so-called criss-crossed spiral systems (SB). In galaxies of this type, a very bright central core is crossed in diameter by a transverse band. From the ends of this bridge, the spiral branches begin, and, depending on the degree of development of the spirals, these galaxies are divided into subtypes SBa, SBb, and SBc.

Irregular galaxies (Ir) are objects that do not have a clearly defined nucleus and do not have rotational symmetry. Their typical representatives are the Magellanic Clouds.

"I used it for 30 years," the famous astronomer Walter Baade later wrote, "and although I stubbornly searched for objects that could not really fit into the Hubble system, their number turned out to be so insignificant that I can count them on the fingers." The Hubble classification continues to serve science, and all subsequent modifications of the creature did not affect it.

For some time it was believed that this classification has an evolutionary meaning, i.e., that galaxies "move" along Hubble's "tuning fork diagram", successively changing their shape. This view is now considered erroneous.

Among the several thousand brightest galaxies, there are 17 percent elliptical, 80 percent spiral, and about 3 percent irregular.

In 1957, the Soviet astronomer B.A. Vorontsov-Velyaminov discovered the existence of "interacting galaxies" - galaxies connected by "bars", "tails", as well as "gamma-forms", i.e. galaxies in which one spiral "twists", while the other "unwinds". Later, compact galaxies were discovered, the size of which is only about 3000 light-years, and star systems isolated in space with a diameter of only 200 light-years. In their appearance, they practically do not differ from the stars of our Galaxy.

The new general catalog (NOC) contains a list of about ten thousand galaxies, along with their most important characteristics (luminosity, shape, distance, etc.) - and this is only a small fraction of the ten billion galaxies that are in principle distinguishable from Earth. A fabulous giant, capable of covering a hundred or two million light-years, looking at the Universe, would see that it is filled with cosmic fog, of which galaxies are droplets. At times there are clusters of thousands of galaxies clustered together. One such giant cluster is in the constellation Virgo.

Author: Samin D.K.

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The sun makes men hungry 24.07.2022

To maintain a figure, men should be less in the sun. This was found out by the staff of Tel Aviv University. Analyzing the statistics of a large medical project that collected various data on three thousand people aged 25 to 65, the researchers found that during the warm season, men consume 17% more calories than women.

The most obvious explanation here is that the sun somehow stimulates appetite, and only in men. Experiments with volunteers confirmed this: if men and women are specially brought out into the sun, and then asked how much they want to eat, it turns out that men feel more hungry after the sun. But women will not feel the difference - the sun does not excite additional hunger in them.

Appetite and the feeling of hunger depend on many physiological signals, including the hormone ghrelin, which is called the hunger hormone. (In general, there are several hunger hormones, but ghrelin is one of the most famous.) Ghrelin is synthesized in the stomach, from the stomach it enters the pituitary gland and hypothalamus, stimulating eating behavior, that is, it excites appetite, makes you focus on finding food, etc. Ghrelin levels rise before meals and, as it has now turned out, in the sun: in men who took a sunbath, the level of ghrelin in the blood increased (in women, its level in the sun remained the same).

The same thing happened to mice that were irradiated with medium-wave ultraviolet, or ultraviolet B. Medium-wave ultraviolet is part of the solar radiation reaching the earth's surface, and mice were irradiated with it in such a way that the exposure was equal to a half-hour dose of the sun on a clear noon somewhere on latitude of Mexico, Cuba or Florida. The mice were irradiated every day for ten days, and those males who received regular portions of UV light tried to eat more often than females or males who were not irradiated.

Ghrelin is synthesized not only in the gastrointestinal tract, it is also secreted by fat cells in the skin, and they secrete it under the action of the p53 protein. It is called the guardian of the genome because p53 monitors DNA damage: it either stimulates DNA repair or causes the cell to commit suicide so that it does not harm others with its mutations. Under the influence of ultraviolet activity of the p53 gene increases, because ultraviolet damages DNA. As a result, fat skin cells release more ghrelin. This is what happens in males; in females, the sex hormone estrogen suppresses the activity of the p53 gene, and the level of ghrelin in response to UV radiation does not increase in them.

It can be assumed that the same mechanism with dermal ghrelin and p53 works in humans. But so far, it is impossible to say this with certainty. Other experts point out that little attention is paid to people in general in this study. Here we need to conduct an experiment with a large number of participants, and we also need to carefully monitor additional factors that can tie together the sun and appetite in men. However, in any case, we should be more careful with the sun: although we get vitamin D thanks to it, no one has canceled sunburn and ultraviolet mutations in skin cells.

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