When did the Milky Way galaxy appear? Milky way galaxy. How many stars are in the Milky Way

02.11.2019

Milky Way- the galaxy in which the Earth is located, solar system and all individual stars visible to the naked eye. Refers to barred spiral galaxies.

The Milky Way, together with the Andromeda Galaxy (M31), the Triangulum Galaxy (M33) and more than 40 dwarf satellite galaxies - its own and Andromeda - form the Local Group of galaxies, which is part of the Local Supercluster (Virgo Supercluster).

Discovery history

Discovery of Galileo

The Milky Way revealed its secret only in 1610. It was then that the first telescope was invented, which was used by Galileo Galilei. The famous scientist saw through the device that the Milky Way is a real cluster of stars, which, when viewed with the naked eye, merged into a continuous faintly twinkling band. Galileo even succeeded in explaining the heterogeneity of the structure of this band. It was caused by the presence in the celestial phenomenon of not only star clusters. There are also dark clouds. The combination of these two elements creates amazing image nocturnal event.

Discovery of William Herschel

The study of the Milky Way continued into the 18th century. During this period, his most active researcher was William Herschel. Famous composer and the musician was engaged in the manufacture of telescopes and studied the science of the stars. The most important discovery of Herschel was the Great Plan of the Universe. This scientist observed the planets through a telescope and counted them in different parts of the sky. Studies have led to the conclusion that the Milky Way is a kind of stellar island, in which our Sun is also located. Herschel even drew a schematic plan of his discovery. In the figure, the star system was depicted as a millstone and had an elongated irregular shape. The sun at the same time was inside this ring that surrounded our world. This is how all scientists represented our Galaxy until the beginning of the last century.

It was not until the 1920s that the work of Jacobus Kaptein saw the light of day, in which the Milky Way was described in the most detailed way. At the same time, the author gave a scheme of the star island, which is as similar as possible to the one that is known to us at the present time. Today we know that the Milky Way is a Galaxy, which includes the solar system, the Earth and those individual stars that are visible to humans with the naked eye.

What shape is the Milky Way?

When studying galaxies, Edwin Hubble classified them into different kinds elliptical and spiral. Spiral galaxies are disk-shaped with spiral arms inside. Since the Milky Way is disk-shaped along with spiral galaxies, it is logical to assume that it is probably a spiral galaxy.

In the 1930s, R. J. Trumpler realized that the estimates of the size of the Milky Way galaxy made by Kapetin and others were erroneous, because the measurements were based on observations using radiation waves in the visible region of the spectrum. Trumpler came to the conclusion that a huge amount of dust in the plane of the Milky Way absorbs visible light. Therefore, distant stars and their clusters seem more ghostly than they really are. Because of this, in order to accurately image the stars and star clusters within the Milky Way, astronomers had to find a way to see through the dust.

In the 1950s, the first radio telescopes were invented. Astronomers have discovered that hydrogen atoms emit radiation in radio waves, and that such radio waves can penetrate dust in the Milky Way. Thus, it became possible to see the spiral arms of this galaxy. To do this, we used the marking of stars by analogy with marks when measuring distances. Astronomers realized that O and B stars could serve to achieve this goal.

Such stars have several features:

brightness– they are highly visible and often found in small groups or associations;
warm– they emit waves of different lengths (visible, infrared, radio waves);
short life time They live for about 100 million years. Given the speed at which stars rotate at the center of the galaxy, they do not move far from their birthplace.

Astronomers can use radio telescopes to accurately match the positions of O and B stars and, based on the Doppler shifts in the radio spectrum, determine their speed. After performing such operations on many stars, scientists were able to produce combined radio and optical maps of the Milky Way's spiral arms. Each arm is named after the constellation that exists in it.

Astronomers believe that the movement of matter around the center of the galaxy creates density waves (regions of high and low density), just like you see when you mix cake dough with an electric mixer. These density waves are thought to have caused the spiral character of the galaxy.

Thus, by examining the sky at different wavelengths (radio, infrared, visible, ultraviolet, X-ray) using various ground-based and space telescopes, one can obtain various images of the Milky Way.

Doppler effect. Just as the high pitched sound of a fire truck siren gets lower as the vehicle moves away, the movement of the stars affects the wavelengths of light that reach Earth from them. This phenomenon is called the Doppler effect. We can measure this effect by measuring the lines in the star's spectrum and comparing them to the spectrum of a standard lamp. The degree of Doppler shift indicates how fast the star is moving relative to us. In addition, the direction of the Doppler shift can show us the direction in which the star is moving. If the star's spectrum shifts to the blue end, then the star is moving towards us; if in the red direction, it moves away.

Structure of the Milky Way

If we carefully consider the structure of the Milky Way, we will see the following:

galactic disk. Most of the stars in the Milky Way are concentrated here.

The disk itself is divided into the following parts:

The nucleus is the center of the disk;
Arcs - areas around the nucleus, including directly the areas above and below the plane of the disk.
Spiral arms are areas that protrude outward from the center. Our solar system is located in one of the spiral arms of the Milky Way.

globular clusters. Several hundred of them are scattered above and below the plane of the disk.
Halo. This is a large, dim region that surrounds the entire galaxy. The halo consists of high temperature gas and possibly dark matter.

halo radius significantly more sizes disk and, according to some sources, reaches several hundred thousand light-years. The center of symmetry of the Milky Way halo coincides with the center of the galactic disk. The halo consists mainly of very old, dim stars. The age of the spherical component of the Galaxy exceeds 12 billion years. The central, densest part of the halo within a few thousand light-years of the center of the Galaxy is called bulge(translated from English "thickening"). The halo as a whole rotates very slowly.

Compared to halo disk spins much faster. It looks like two plates folded at the edges. The diameter of the disk of the Galaxy is about 30 kpc (100,000 light years). The thickness is about 1000 light years. The rotation speed is not the same different distances from the center. It rapidly increases from zero in the center to 200-240 km/s at a distance of 2 thousand light years from it. The mass of the disk is 150 billion times the mass of the Sun (1.99*1030 kg). Young stars and star clusters are concentrated in the disk. There are many bright and hot stars among them. The gas in the disk of the Galaxy is unevenly distributed, forming giant clouds. Main chemical element in our galaxy is hydrogen. About 1/4 of it consists of helium.

One of the most interesting regions of the Galaxy is its center, or nucleus located in the direction of the constellation Sagittarius. The visible radiation of the central regions of the Galaxy is completely hidden from us by powerful layers of absorbing matter. Therefore, it began to be studied only after the creation of receivers for infrared and radio radiation, which is absorbed to a lesser extent. The central regions of the Galaxy are characterized by a strong concentration of stars: there are many thousands of them in each cubic parsec. Closer to the center, regions of ionized hydrogen and numerous sources of infrared radiation are noted, indicating star formation taking place there. At the very center of the Galaxy, the existence of a massive compact object is assumed - a black hole with a mass of about a million solar masses.

One of the most notable formations is spiral branches (or sleeves). They gave the name to this type of objects - spiral galaxies. Along the arms, the youngest stars are mainly concentrated, many open star clusters, as well as chains of dense clouds of interstellar gas in which stars continue to form. In contrast to the halo, where any manifestations of stellar activity are extremely rare, a stormy life continues in the branches, associated with the continuous transition of matter from interstellar space to stars and back. The spiral arms of the Milky Way are largely hidden from us by absorbing matter. Their detailed study began after the advent of radio telescopes. They made it possible to study the structure of the Galaxy by observing the radio emission of interstellar hydrogen atoms, which are concentrated along long spirals. According to modern concepts, spiral arms are associated with compression waves propagating across the disk of the galaxy. Passing through the compression regions, the matter of the disk becomes denser, and the formation of stars from the gas becomes more intense. The reasons for the appearance of such a peculiar wave structure in the disks of spiral galaxies are not entirely clear. Many astrophysicists are working on this problem.

The place of the sun in the galaxy

In the vicinity of the Sun, it is possible to trace sections of two spiral branches that are about 3 thousand light years away from us. According to the constellations where these areas are found, they are called the Sagittarius arm and the Perseus arm. The sun is almost in the middle between these spiral arms. True, relatively close (by galactic standards) from us, in the constellation of Orion, there is another, not so pronounced branch, which is considered an offshoot of one of the main spiral arms of the Galaxy.

The distance from the Sun to the center of the Galaxy is 23-28 thousand light years, or 7-9 thousand parsecs. This suggests that the Sun is located closer to the edge of the disk than to its center.

Together with all nearby stars, the Sun revolves around the center of the Galaxy at a speed of 220–240 km/s, making one revolution in about 200 million years. This means that for the entire time of its existence, the Earth flew around the center of the Galaxy no more than 30 times.

The speed of rotation of the Sun around the center of the Galaxy practically coincides with the speed with which the compression wave, which forms the spiral arm, moves in the given region. Such a situation is generally unusual for the Galaxy: the spiral arms rotate at a constant angular velocity, like the spokes of a wheel, while the movement of stars, as we have seen, obeys a completely different pattern. Therefore, almost the entire stellar population of the disk either gets inside the spiral branch or leaves it. The only place where the speeds of stars and spiral arms coincide is the so-called corotation circle, and it is on it that the Sun is located!

For the Earth, this circumstance is extremely favorable. After all, violent processes occur in the spiral branches, generating powerful radiation, destructive for all living things. And no atmosphere could protect him from it. But our planet exists in a relatively quiet place in the Galaxy and has not experienced the influence of these cosmic cataclysms for hundreds of millions and billions of years. Perhaps that is why life could originate and survive on Earth.

For a long time, the position of the Sun among the stars was considered the most ordinary. Today we know that this is not so: in a certain sense it is privileged. And this must be taken into account when discussing the possibility of the existence of life in other parts of our Galaxy.

The location of the stars

On a cloudless night sky, the Milky Way is visible from anywhere on our planet. However, only a part of the Galaxy, which is a system of stars located inside the Orion arm, is accessible to the human eye. What is the Milky Way? The definition in space of all its parts becomes most understandable if we consider the star map. In this case, it becomes clear that the Sun, illuminating the Earth, is located almost on the disk. This is almost the edge of the Galaxy, where the distance from the nucleus is 26-28 thousand light years. Moving at a speed of 240 kilometers per hour, the Luminary spends 200 million years on one revolution around the core, so that for the entire time of its existence it traveled across the disk, rounding the core, only thirty times. Our planet is in the so-called corotation circle. This is a place in which the speed of rotation of the arms and stars are identical. This circle is characterized elevated level radiation. That is why life, as scientists believe, could only arise on that planet, near which there is a small number of stars. Our Earth is such a planet. It is located on the periphery of the Galaxy, in its most peaceful place. That is why on our planet for several billion years there were no global cataclysms that often occur in the Universe.

What will the death of the Milky Way look like?

The cosmic story of the death of our galaxy begins here and now. We can blindly look around, thinking that the Milky Way, Andromeda (our elder sister) and a bunch of unknowns - our space neighbors - this is our home, but in reality there is much more. It's time to explore what else is around us. Go.

Triangulum Galaxy. With a mass of about 5% of that of the Milky Way, it is the third largest galaxy in the Local Group. It has a spiral structure, its own satellites and may be a satellite of the Andromeda galaxy.
Large Magellanic Cloud. This galaxy is only 1% of the mass of the Milky Way, but is the fourth largest in our local group. It is very close to our Milky Way—less than 200,000 light-years away—and is undergoing active star formation as tidal interactions with our galaxy cause gas to collapse and create new, hot, and big stars in the Universe.
Small Magellanic Cloud, NGC 3190 and NGC 6822. All of them have masses from 0.1% to 0.6% of the Milky Way (and it is not clear which one is larger) and all three are independent galaxies. Each contains over a billion solar masses of material.
Elliptical galaxies M32 and M110. They may be "only" satellites of Andromeda, but each of them has more than a billion stars, and they can even exceed the masses of numbers 5, 6 and 7.

In addition, there are at least 45 other known galaxies - smaller ones - that make up our local group. Each of them has a halo of dark matter surrounding it; each of them is gravitationally attached to the other, located at a distance of 3 million light years. Despite their size, mass and size, none of them will remain in a few billion years.

So the main thing

As time passes, galaxies interact gravitationally. They not only pull together due to gravitational attraction, but also interact tidally. We usually talk about tides in the context of the Moon pulling terrestrial oceans and ebbs and flows, and this is partly true. But from the point of view of the galaxy, the tides are a less noticeable process. The part of the small galaxy that is close to the big one will be attracted with more gravitational force, and the part that is further away will experience less attraction. As a result, the small galaxy will stretch out and eventually break apart under the influence of gravity.

Small galaxies that are part of our local group, including both Magellanic Clouds and dwarf elliptical galaxies, will be torn apart in this way, and their material will be incorporated into the large galaxies with which they merge. “So what,” you say. After all, this is not quite death, because large galaxies will remain alive. But even they will not exist forever in this state. In 4 billion years, the mutual gravitational pull of the Milky Way and Andromeda will drag the galaxies into a gravitational dance that will lead to a big merger. Although this process will take billions of years, the spiral structure of both galaxies will be destroyed, resulting in the creation of a single, giant elliptical galaxy at the core of our local group: the Milkweeds.

A small percentage of the stars will be ejected during such a merger, but the majority will remain unharmed, and there will be a large burst of star formation. Eventually, the rest of the galaxies in our local group will also be sucked in, leaving one big giant galaxy to gobble up the rest. This process will take place in all related groups and clusters of galaxies throughout the universe, while dark energy will push individual groups and clusters apart from each other. But even this cannot be called death, because the galaxy will remain. And for a while it will be. But the galaxy is made up of stars, dust and gas, and everything will eventually come to an end.

Across the Universe, galactic mergers will take place over tens of billions of years. During the same time, dark energy will pull them all over the Universe to a state of complete solitude and inaccessibility. And although the last galaxies outside our local group will not disappear until hundreds of billions of years have passed, the stars in them will live. The longest-lived stars in existence today will continue to burn their fuel for tens of trillions of years, and new stars will emerge from the gas, dust, and stellar corpses that populate each galaxy—albeit with fewer and fewer.

When the last stars burn out, only their corpses will remain - white dwarfs and neutron stars. They will shine for hundreds of trillions or even quadrillions of years before they go out. When that inevitability happens, we're left with brown dwarfs (failed stars) that accidentally fuse, re-ignite nuclear fusion, and create starlight for tens of trillions of years.

When the last star goes out tens of quadrillion years in the future, there will still be some mass left in the galaxy. So this can not be called "true death."

All masses gravitationally interact with each other, and gravitational objects different masses exhibit strange properties when interacting:

Repeated "approaches" and close passes cause exchanges of speed and momentum between them.
Objects with low mass are ejected from the galaxy, and objects with higher mass sink into the center, losing speed.
Over a sufficiently long period of time, most of the mass will be ejected, and only a small part of the remaining mass will be firmly attached.

At the very center of these galactic remnants will be a supermassive black hole, in every galaxy, and the rest of the galactic objects will orbit a larger version of our own solar system. Of course, this structure will be the last, and since the black hole will be as large as possible, it will eat everything it can reach. At the center of Mlecomeda there will be an object hundreds of millions of times more massive than our Sun.

But will it end too?

Thanks to the phenomenon of Hawking radiation, even these objects will one day decay. It will take about 10 80 to 10 100 years, depending on how massive our supermassive black hole becomes as it grows, but the end is coming. After that, the remains, rotating around the galactic center, will untie and leave only a halo of dark matter, which can also randomly dissociate, depending on the properties of this very matter. Without any matter, there will be nothing that we once called a local band, milky way and other dear names.

Mythology

Armenian, Arabic, Wallachian, Jewish, Persian, Turkish, Kyrgyz

According to one of the Armenian myths about the Milky Way, the god Vahagn, the ancestor of the Armenians, harsh winter stole straw from the ancestor of the Assyrians, Barsham, and disappeared into the sky. When he walked with his prey across the sky, he dropped straws on his way; from them a light trail was formed in the sky (in Armenian “Straw thief’s road”). The myth about scattered straw is also spoken of by Arabic, Jewish, Persian, Turkish and Kyrgyz names (Kirg. samanchynyn jolu- the path of the strawman) of this phenomenon. The inhabitants of Wallachia believed that Venus stole this straw from St. Peter.

Buryat

According to Buryat mythology, good forces create the world, modify the universe. Thus, the Milky Way arose from the milk that Manzan Gurme drew from her breast and splashed out after Abai Geser, who had deceived her. According to another version, the Milky Way is a "seam of the sky" sewn up after the stars fell out of it; on it, like on a bridge, tengri walk.

Hungarian

According to Hungarian legend, Attila will descend the Milky Way if the Székelys are in danger; the stars represent sparks from the hooves. Milky Way. accordingly, it is called the "road of warriors."

ancient greek

Etymology of the word Galaxias (Γαλαξίας) and its association with milk (γάλα) reveal two similar ancient Greek myths. One of the legends tells about the mother's milk spilled across the sky of the goddess Hera, who was breastfeeding Hercules. When Hera learned that the baby she was breastfeeding was not her own child, but the illegitimate son of Zeus and an earthly woman, she pushed him away, and the spilled milk became the Milky Way. Another legend says that the spilled milk is the milk of Rhea, the wife of Kronos, and Zeus himself was the baby. Kronos devoured his children, as it was predicted to him that he would be overthrown by his own son. Rhea has a plan to save her sixth child, the newborn Zeus. She wrapped a stone in baby clothes and slipped it to Kronos. Kronos asked her to feed her son one more time before he swallowed him. The milk spilled from Rhea's chest on a bare rock was subsequently called the Milky Way.

Indian

The ancient Indians considered the Milky Way to be the milk of an evening red cow passing through the sky. In the Rig Veda, the Milky Way is called Aryaman's Throne Road. The Bhagavata Purana contains a version according to which the Milky Way is the belly of a celestial dolphin.

Inca

The main objects of observation in Inca astronomy (which was reflected in their mythology) in the sky were the dark sections of the Milky Way - a kind of "constellation" in the terminology of Andean cultures: Lama, Lama Cub, Shepherd, Condor, Partridge, Toad, Snake, Fox; as well as the stars: the Southern Cross, the Pleiades, Lyra and many others.

Ketskaya

In the Ket myths, similarly to the Selkup ones, the Milky Way is described as the road of one of the three mythological characters: the Son of Heaven (Esya), who went to hunt on the western side of the sky and froze there, the hero Albe, who pursued the evil goddess, or the first shaman Dokh, who climbed this road to the sun.

Chinese, Vietnamese, Korean, Japanese

In the mythologies of the Sinosphere, the Milky Way is called and compared to a river (in Vietnamese, Chinese, Korean and Japanese the name "silver river" is retained. The Chinese also sometimes called the Milky Way the "Yellow Road", after the color of the straw.

Indigenous peoples of North America

The Hidatsa and the Eskimos call the Milky Way "Ash". Their myths speak of a girl who scattered ashes across the sky so that people could find their way home at night. The Cheyenne believed that the Milky Way was dirt and silt raised by the belly of a turtle floating in the sky. Eskimos from the Bering Strait - that these are the traces of the Creator Raven walking across the sky. The Cherokee believed that the Milky Way was formed when one hunter stole another's wife out of jealousy, and her dog began to eat unattended cornmeal and scattered it across the sky (the same myth is found among the Khoisan population of the Kalahari). Another myth of the same people says that the Milky Way is the trail of a dog dragging something across the sky. The Ctunah called the Milky Way "the dog's tail", the Blackfoot called it the "wolf road". Wyandot myth says that the Milky Way is a place where the souls of dead people and dogs come together and dance.

Maori

In Maori mythology, the Milky Way is considered to be the Tama-rereti boat. The nose of the boat is the constellation Orion and Scorpio, the anchor is the Southern Cross, Alpha Centauri and Hadar are the rope. According to legend, one day Tama-rereti was sailing in his canoe and saw that it was already late, and he was far from home. There were no stars in the sky, and, fearing that Tanif might attack, Tama-rereti began to throw sparkling pebbles into the sky. The heavenly deity Ranginui liked what he was doing, and he placed the Tama-rereti boat in the sky, and turned the pebbles into stars.

Finnish, Lithuanian, Estonian, Erzya, Kazakh

The Finnish name is Fin. Linnunrata- means "The Way of the Birds"; the Lithuanian name has a similar etymology. Estonian myth also connects the Milky ("bird's") Way with bird flight.

The Erzya name is "Kargon Ki" ("Crane Road").

The Kazakh name is “Kus Zholy” (“Way of the Birds”).

Interesting facts about the Milky Way galaxy

The Milky Way began forming as a cluster of dense regions after the Big Bang. The first stars to appear were in globular clusters that continue to exist. These are the oldest stars in the galaxy;
The galaxy has increased its parameters by absorbing and merging with others. Now she is picking stars from the Sagittarius Dwarf Galaxy and the Magellanic Clouds;
The Milky Way moves in space with an acceleration of 550 km / s with respect to the background radiation;
Lurking at the galactic center is the supermassive black hole Sagittarius A*. By mass, it is 4.3 million times greater than the solar one;
Gas, dust and stars revolve around the center at a speed of 220 km/s. This is a stable indicator, implying the presence of a shell of dark matter;
In 5 billion years, a collision with the Andromeda galaxy is expected.

We are used to the fact that the Milky Way is a cluster of stars in the sky, according to which our ancestors navigated. But in fact, this is more than ordinary night luminaries - this is a huge and unexplored world.

This article is intended for persons over 18 years of age.

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The structure of the Milky Way galaxy

Sometimes it seems incredible how dynamic space science is developing. It is hard to imagine, but 4 centuries ago, even the statement that the Earth revolves around the Sun caused condemnation and rejection in society. Judgments about these and other cosmic phenomena could lead not only to imprisonment, but also to death. Fortunately, times have changed, and the study of the Universe has long been a priority in science. Particularly important in this regard is the study of the Milky Way - a galaxy of thousands of stars, one of which is our Sun.

The study of the structure of the galaxy and its development helps to answer the main questions that have interested humanity since the beginning of time. These are such sacramental mysteries about how the solar system arose, what factors contributed to the emergence of life on Earth, and whether life exists on other planets.

The fact that the Milky Way galaxy is a huge arm of an infinite star system became known relatively recently - a little more than half a century ago. The structure of our galaxy is similar to a colossal spiral in which our solar system is located somewhere on the periphery. From the side, it looks like a giant magnifying glass with a double-sided convex center with a crown.

What is the Milky Way galaxy? These are billions of stars and planets, which are interconnected by a certain algorithm for the structure of the Universe. In addition to stars, the Milky Way contains interstellar gas, galactic dust, and stellar globular clusters.

The disk of our galaxy constantly revolves around the central part, which is located in the constellation Sagittarius. It takes 220 million years for the Milky Way to make one complete revolution around its axis (and this despite the fact that the rotation occurs at a speed of 250 kilometers per second). Thus, all the stars of our galaxy move in unison over the course of many years, and our solar system along with them. What makes them revolve around the nucleus at a truly frantic speed? Scientists suggest that both the colossal weight of the center and the almost incomprehensible amount of energy (it can exceed the size of 150 million suns).

Why don't we see either spirals or a giant core, why don't we feel this universal rotation? The fact is that we are in the sleeve of this spiral Universe, and the frantic rhythm of its life is perceived by us everyday.

Of course, there will be skeptics who will deny such a structure of our galaxy, arguing that there is no (and cannot be) an exact picture of the galactic disk. The fact is that the Universe is by no means limited to the Milky Way galaxy and there are a lot of such formations in space. They are very similar to our galaxy in structure - these are the same disks with a center around which the stars revolve. That is, outside of our Milky Way, there are billions of systems similar to the Sun.

The nearest galaxy to us is the Large and Small Magellanic Clouds. They can be seen with the naked eye in southern hemisphere. These two small luminous dots, similar to clouds, were first described by the great traveler, from whose name the names originated. space objects. The diameter of the Magellanic Clouds is relatively small - it is less than half the Milky Way. And there are much fewer star systems in the Clouds.

Whether business Nebula Andromeda. This is another spiral-shaped galaxy that is very similar in appearance and composition to the Milky Way. Its dimensions are amazing - according to the most conservative estimates, it is three times larger than our Way. And the number of such gigantic galaxies in the Universe has long exceeded a billion - this is only what we can see at this stage in the development of astronomy. It is possible that in a few years we will become aware of another, previously unnoticed galaxy.

Characteristics of the Milky Way

As mentioned earlier, the Milky Way is a cluster of millions of stars with their own systems, similar to the Sun. How many planets there are in our galaxy is a real mystery, over the solution of which more than one generation of astronomers has been struggling. Although, to be honest, they are more concerned about another question - what is the probability that within our galaxy there is a star system whose characteristics are similar to ours? Scientists are especially interested in stars that have a rotation rate similar to that of the Sun and specifications, as well as occupying our place on the scale of the galaxy. This is because on planets that have the approximate age and conditions of our Earth, there is a high probability of the presence of intelligent life.

Unfortunately, attempts by scientists to find at least something similar to the solar system in the arms of the galaxy were unsuccessful. And this is perhaps for the best. It is still unknown who or what may be waiting for us in an unfamiliar constellation.

Black Hole - the killer of planets or the creator of galaxies?

At the end of its life, a star sheds its gas envelope, and its core begins to shrink very quickly. Provided that the mass of the star is large enough (1.4 times more than the Sun), a Black Hole is formed in its place. This is an object with a critical speed that no object can overcome. As a result, what falls into the Black Hole disappears in it forever. That is, in fact, this cosmic element is a one-way ticket. Any object that gets close enough to the Hole will disappear forever.

Sad, isn't it? But there is also a positive point in the Black Hole - thanks to it, various space objects are gradually pulled up and new galaxies are formed. It turns out that the core of each of the known star systems is a Black Hole.

Why is our galaxy called the Milky Way?

Each nation has its own legends about how the visible part of the Milky Way was formed. For example, the ancient Greeks believed that it was formed from the spilled milk of the goddess Hera. But in Mesopotamia there was a legend about a river from the same drink. Thus, many peoples associated a large cluster of stars with milk, thanks to which our galaxy got its name.

How many stars are in the Milky Way?

It is rather difficult to accurately calculate the number of stars in our galaxy, because they say that there are more than 200 billion of them. As you understand, it is very problematic to study them all with the modern development of science, so scientists turn their attention only to the most interesting representatives these space objects. Take at least an alpha star from the constellation Carina (Kiel). This is a supergiant star, which for a long time held the title of the largest and brightest.

The sun is also one of the stars in the Milky Way, which, however, does not have any outstanding characteristics. This is a small yellow dwarf, which became famous only for the fact that for millions of years it has been the source of life on our planet.

Astronomers from all over the world have long compiled lists of stars that have an outstanding mass or brightness. But this does not mean at all that each of them received given name. Usually the names of stars consist of letters, numbers and the names of the constellations to which they refer. So, the brightest star in the Milky Way is indicated on astronomical maps as R136a1, and R136 is nothing more than the name of the nebula from which it comes from. This star has an indescribable power that cannot be compared with anything. R136a1 shines 8.7 million times brighter than our Sun, and therefore it is very difficult to imagine at least some life near it.

But colossal power does not mean at all that the R136a1 has impressive dimensions. The list of the largest stars is headed by UY Shield, which is 1.7 thousand times the size of our star. That is, if instead of the Sun there was this star, then it would take up the entire place from the center of our system to Saturn.

No matter how big and powerful these stars would be, the total number of their mass does not compare with the mass of the Black Hole, which is located in the center of the galaxy. It is her colossal energy that holds the Milky Way, forcing it to move in a certain order.

Our galaxy is not just a scattering of stars in the night sky. This is a huge system that consists of hundreds of billions of stars, among which is our Sun.

The solar system is immersed in a huge star system - the Galaxy, numbering hundreds of billions of stars of the most different luminosity and color (Stars in the section: "The Life of Stars"). Properties different types The stars of the Galaxy are well known to astronomers. Our neighbors are not just typical stars and other celestial objects, but rather representatives of the most numerous "tribes" of the Galaxy. At present, all or almost all stars have been studied in the vicinity of the Sun, with the exception of very dwarf ones, which emit very little light. Most of them are very faint red dwarfs - their masses are 3-10 times less than that of the Sun. Stars similar to the Sun are very rare, only 6% of them. Many of our neighbors (72%) are grouped into multiple systems, where the components are connected to each other by gravitational forces. Which of the hundreds of nearby stars can claim the title of the nearest neighbor of the Sun? Now it is considered a component of the well-known triple system Alpha Centauri - the faint red dwarf Proxima. The distance to the proxima is 1.31 pc, the light from it takes 4.2 years to reach us. The statistics of the circumsolar population gives an idea of the evolution of the galactic disk and the galaxy as a whole. For example, the luminosity distribution of solar-type stars shows that the age of the disk is 10-13 billion years.

In the 17th century, after the invention of the telescope, scientists first realized how large the number of stars in outer space is. In 1755, the German philosopher and naturalist Immanuel Kant suggested that the stars form groups in space, just as the planets make up the solar system. These groups he called "star islands". According to Kant, one of these innumerable islands is the Milky Way - a grandiose cluster of stars visible in the sky as a bright foggy band. In ancient Greek, the word "galactikos" means "milky", which is why the Milky Way and similar star systems are called galaxies.

Dimensions and structure of our Galaxy

Based on the results of his calculations, Herschel attempted to determine the dimensions and forms a kind of thick disk: in the plane of the Milky Way, it extends to a distance of no more than 850 units, and in the perpendicular direction - 200 units, if we take the distance to Sirius as a unit. According to the modern scale of distances, this corresponds to 7300X1700 light years. This estimate generally correctly reflects the structure of the Milky Way, although it is highly inaccurate. The fact is that in addition to stars, the disk of the Galaxy also includes numerous gas and dust clouds, which weaken the light of distant stars. The first explorers of the Galaxy did not know about this absorbing substance and believed that they could see all its stars.

The true dimensions of the Galaxy were established only in the 20th century. It turned out that it is a much flatter formation than previously thought. The diameter of the galactic disk exceeds 100 thousand light years, and the thickness is about 1000 light years. Due to the fact that the Solar System is located practically in the plane of the Galaxy, filled with absorbing matter, many details of the structure of the Milky Way are hidden from the gaze of an earthly observer. However, they can be studied on the example of other galaxies similar to Shashi. So, in the 40s. XX century, observing the galaxy M 31, better known as the Andromeda Nebula, the German astronomer Walter Baade noticed that the flat lenticular disk of this huge galaxy is immersed in a more rarefied spherical star cloud - a halo. Since the nebula is very similar to our Galaxy, he suggested that the Milky Way also has a similar structure. The stars of the galactic disk have been called population type I, while the stars in the halo have been called population type II.

As modern studies show, the two types of stellar population differ not only in their spatial position, but also in the nature of their movement, as well as in their chemical composition. These features are associated primarily with the different origin of the disk and the spherical component.

Structure of the Galaxy: Halo

The boundaries of our Galaxy are determined by the size of the halo. The radius of the halo is much larger than the size of the disk and, according to some data, reaches several hundred thousand light-years. The center of symmetry of the Milky Way halo coincides with the center of the galactic disk. The halo consists mainly of very old, dim, low-mass stars. They occur both singly and in the form of globular clusters, which can include more than a million stars. The age of the population of the spherical component of the Galaxy exceeds 12 billion years. It is usually taken as the age of the Galaxy itself. A characteristic feature of halo stars is their extremely small proportion of heavy chemical elements. The stars that form globular clusters contain hundreds of times less metals than the Sun.

The stars of the spherical component are concentrated towards the center of the Galaxy. The central, densest part of the halo within a few thousand light-years from the center of the Galaxy is called the "bulge" ("thickening"). Stars and stellar halo clusters move around the center of the Galaxy in very elongated orbits. Due to the fact that the rotation of individual stars occurs almost randomly, the halo as a whole rotates very slowly.

Structure of the Galaxy: Disk

Compared to the halo, the disk rotates noticeably faster. The speed of its rotation is not the same at different distances from the center. It rapidly increases from zero in the center to 200-240 km/s at a distance of 2 thousand light years from it, then decreases somewhat, increases again to approximately the same value, and then remains almost constant. The study of the features of disk rotation made it possible to estimate its mass. It turned out that it is 150 billion times more than the mass of the Sun. The disk population is very different from the halo population. Near the plane of the disk, young stars and star clusters are concentrated, the age of which does not exceed several billion years. They form the so-called flat component. There are a lot of bright and hot stars among them.

The gas in the disk of the Galaxy is also concentrated mainly near its plane. It is located unevenly, forming numerous gas clouds - giant superclouds of inhomogeneous structure, several thousand light-years long, to small clouds no larger than a parsec in size. Hydrogen is the main chemical element in our galaxy. Approximately 1/4 of it consists of helium. Compared to these two elements, the rest are present in very small amounts. On average, the chemical composition of stars and gas in the disk is almost the same as that of the Sun.

Structure of the Galaxy: Core

One of the most interesting regions of the Galaxy is considered to be its center, or core, located in the direction of the constellation Sagittarius. The visible radiation of the central regions of the Galaxy is completely hidden from us by powerful layers of absorbing matter. Therefore, they began to study it only after the creation of receivers for infrared and radio radiation, which is absorbed to a lesser extent. The central regions of the Galaxy are characterized by a strong concentration of stars: each cubic parsec near the center contains many thousands of them. Distances between stars are tens and hundreds of times less than in the vicinity of the Sun. If we lived on a planet near a star located near the core of the Galaxy, then dozens of stars would be visible in the sky, comparable in brightness to the Moon, and many thousands brighter than the most bright stars our sky.

In addition to a large number of stars in the central region of the Galaxy, there is a circumnuclear gaseous disk, consisting mainly of molecular hydrogen. Its radius exceeds 1000 light years. Closer to the center, there are regions of ionized hydrogen and numerous sources of infrared radiation, indicating that star formation is taking place there. In the very center of the Galaxy, the existence of a massive compact object is assumed - a black hole with a mass of about a million solar masses. In the center there is also a bright radio source Sagittarius A, the origin of which is associated with the activity of the nucleus.

The Milky Way Galaxy contains the solar system, the Earth and all the stars that are visible to the naked eye. Together with the Triangulum Galaxy, Andromeda and dwarf galaxies and satellites, it forms the Local Group of galaxies, which is part of the Virgo Supercluster.

By ancient legend When Zeus decided to make his son Hercules immortal, he placed him on the breast of his wife Hera to drink milk. But the wife woke up and, seeing that she was feeding a step-child, pushed him away. A stream of milk splashed and turned into the Milky Way. In the Soviet astronomical school, it was simply called "the Milky Way system" or "our Galaxy." Outside of Western culture, there are many names for this galaxy. The word "milky" is replaced by other epithets. The galaxy consists of about 200 billion stars. Most of them are located in the form of a disk. Most of the mass of the Milky Way is contained in a halo of dark matter.

In the 1980s, scientists put forward the view that the Milky Way is a barred spiral galaxy. The hypothesis was confirmed in 2005 using the Spitzer telescope. It turned out that the central bar of the galaxy is larger than previously thought. The diameter of the galactic disk is approximately 100 thousand light years. Compared to the halo, it spins much faster. At different distances from the center, its speed is not the same. Studies of the disk's rotation helped to estimate its mass, which is 150 billion more than the mass of the Sun. Near the plane of the disk, young star clusters and stars are collected, which form a flat component. Scientists suggest that many galaxies have black holes in their core.

A large number of stars are collected in the central regions of the Milky Way Galaxy. The distance between them is much smaller than in the vicinity of the Sun. The length of the galactic bridge, according to scientists, is 27 thousand light years. It passes through the center of the Milky Way at an angle of 44 degrees ± 10 degrees to the line between the center of the galaxy and the Sun. Its component is predominantly red stars. The jumper is surrounded by a ring, which is called the "Ring of 5 kiloparsecs". It contains a large amount of molecular hydrogen. It is also an active star-forming region in the galaxy. Viewed from the Andromeda galaxy, the bar of the Milky Way would be its brightest part.

Since the Milky Way Galaxy is considered a spiral galaxy, it has spiral arms that lie in the plane of the disk. Around the disk is a spherical corona. The solar system is located 8.5 thousand parsecs from the center of the galaxy. According to recent observations, we can say that our Galaxy has 2 arms and a couple more arms in the inner part. They transform into a four-arm structure, which is observed in the neutral hydrogen line.

The halo of the galaxy has a spherical shape, which extends beyond the Milky Way by 5–10 thousand light years. Its temperature is approximately 5 * 10 5 K. The halo consists of old, low-mass, dim stars. They can be found in the form of globular clusters, and one by one. The main mass of the galaxy is dark matter, which forms a halo of dark matter. Its mass is approximately 600–3000 billion solar masses. Star clusters and halo stars move around the galactic center in elongated orbits. The halo rotates very slowly.

History of the discovery of the Milky Way Galaxy

Many celestial bodies are combined into a variety of rotating systems. Thus, the Moon revolves around the Earth, and the satellites of the major planets form their systems. The earth and other planets revolve around the sun. Scientists had a completely logical question: is the Sun included in an even larger system?

For the first time, William Herschel tried to answer this question. He calculated the number of stars in different parts of the sky and found out that there is a large circle in the sky - the galactic equator, dividing the sky into two parts. Here the number of stars was the greatest. The closer this or that part of the sky is located to this circle, the more stars there are on it. Ultimately, it was discovered that the Milky Way is located at the equator of the galaxy. Herschel came to the conclusion that all the stars form one star system.

Initially it was believed that everything in the universe is part of our galaxy. But even Kant argued that some nebulae can be separate galaxies, like the Milky Way. Only when Edwin Hubble measured the distance to some spiral nebulae and showed that they could not be part of the Galaxy, Kant's hypothesis was proven.

Future of the Galaxy

In the future, collisions of our Galaxy with others, including Andromeda, are possible. But there are no concrete predictions yet. It is believed that in 4 billion years the Milky Way will be swallowed up by the Small and Large Magellanic Clouds, and in 5 billion years it will be swallowed up by the Andromeda Nebula.

Planets of the Milky Way

Despite the fact that stars are constantly born and die, their number is clearly counted. Scientists believe that at least one planet revolves around every star. This means that there are from 100 to 200 billion planets in the Universe. The scientists who worked on this statement studied "red dwarf" stars. They are smaller than the Sun and make up 75% of all stars in the Milky Way Galaxy. Special attention was given to the star Kepler-32, which "sheltered" 5 planets.

Planets are much harder to spot than stars because they don't emit light. We can confidently say about the existence of a planet only when it obscures the light of a star.

There are also planets that are similar to our Earth, but there are not so many of them. There are many types of planets, such as pulsar planets, gas giants, brown dwarfs... If a planet is composed of rocks, it will not look much like Earth.

Recent studies claim that there are between 11 and 40 billion Earth-like planets in the galaxy. Scientists examined 42 sun-like stars and found 603 exoplanets, 10 of which matched the search criteria. It has been proven that all Earth-like planets can support desired temperature, for the existence of liquid water, which, in turn, will help the emergence of life.

At the outer edge of the Milky Way, stars have been discovered that move in a special way. They drift off the edge. Scientists suggest that this is all that is left of the galaxies that were swallowed up by the Milky Way. Their encounter happened many years ago.

satellite galaxies

As we have said, the Milky Way Galaxy is a spiral galaxy. It is an irregularly shaped spiral. For years scientists could not find an explanation for the bulge of the galaxy. Now everyone has come to the conclusion that this is due to satellite galaxies and dark matter. They are very small and cannot affect the Milky Way. But as dark matter moves through the Magellanic Clouds, waves are created. They also influence gravitational attraction. Under this action, hydrogen escapes from the galactic center. Clouds revolve around the Milky Way.

Although the Milky Way is called unique in many ways, it is not a rarity. If we take into account the fact that there are approximately 170 billion galaxies in the field of view, we can assert the existence of galaxies similar to ours. In 2012, astronomers found exact copy Milky way. It even has two satellites that correspond to the Magellanic Clouds. By the way, they assume that in a couple of billion years they will dissolve. Finding such a galaxy was an incredible stroke of luck. Named NGC 1073, it looks so much like the Milky Way that astronomers study it to learn more about our galaxy.

Galactic year

An Earth year is the time it takes a planet to complete one revolution around the sun. In the same way, the solar system revolves around the black hole, which is located in the center of the galaxy. Its full rotation is 250 million years. When describing the solar system, they rarely mention that it moves in outer space like everything else in the world. The speed of its movement is 792,000 km per hour relative to the center of the Milky Way Galaxy. If we compare, then we, moving at a similar speed, could go around the whole world in 3 minutes. A galactic year is the time it takes for the sun to complete one revolution around the Milky Way. At last count, the sun lived for 18 galactic years.

The science

Each person has their own idea of what a home is. For some it's a roof over their heads, for others home is planet Earth, a rocky ball that plows outer space along its closed path around the Sun.

No matter how big our planet seems to us, it is just a grain of sand in giant star system whose size is hard to imagine. This star system is the Milky Way galaxy, which can also rightly be called our home.

Arms of the galaxy

Milky Way- a spiral galaxy with a bar that runs along the center of the spiral. Approximately two-thirds of all known galaxies are spiral, and two-thirds of them are barred. That is, the Milky Way is included in the list most common galaxies.

Spiral galaxies have arms that extend out from the center like wheel spokes that spiral. Our solar system is located in the central part of one of the arms, which is called Orion arm.

The Orion Arm was once thought to be a small "offshoot" of larger arms such as Perseus arm or Shield-Centaurus arm. Not so long ago there was an assumption that the Orion arm is indeed offshoot of the Perseus arm and does not leave the center of the galaxy.

The problem is that we cannot see our galaxy from the outside. We can observe only those things that are around us, and judge what shape the galaxy has, being, as it were, inside it. However, scientists were able to calculate that this sleeve has a length of approximately 11 thousand light years and thickness 3500 light years.

Supermassive black hole

The smallest supermassive black holes that scientists have discovered are approximately in 200 thousand times heavier than the sun. For comparison: ordinary black holes have the mass of everything 10 times greater than the mass of the sun. At the center of the Milky Way is an incredibly massive black hole, the mass of which is hard to imagine.

For the past 10 years, astronomers have been monitoring the activity of stars in orbit around the star. Sagittarius A, the dense region at the center of our galaxy's spiral. Based on the movement of these stars, it was determined that at the center Sagittarius A*, which is hidden behind a dense cloud of dust and gas, there is a supermassive black hole whose mass is 4.1 million times more than the mass of the sun!

The animation below demonstrates real movement stars around a black hole from 1997 to 2011 around one cubic parsec at the center of our galaxy. As stars approach a black hole, they loop around it at incredible speeds. For example, one of these stars, S 0-2 moving at a speed 18 million kilometers per hour: black hole first attracts it, and then sharply repels it.

More recently, scientists observed how a cloud of gas approached a black hole and was torn to pieces its massive gravitational field. Parts of this cloud were swallowed up by the hole, and the remaining parts began to resemble long thin pasta more than 160 billion kilometers.

Magneticparticles

In addition to having a supermassive all-consuming black hole, the center of our galaxy boasts incredible activity: old stars die, and new ones are born with enviable constancy.

Not so long ago, scientists noticed something else at the galactic center - a stream of high-energy particles that extend into the distance 15 thousand parsecs across the galaxy. This distance is about half the diameter of the Milky Way.

The particles are invisible to the naked eye, however, using magnetic imaging, you can see that the particle geysers take up about two thirds of the visible sky:

What is behind this phenomenon? For one million years, stars have come and gone, feeding never stopping flow, directed towards the outer arms of the galaxy. The total energy of a geyser is a million times greater than that of a supernova.

The particles move at an incredible speed. Based on the structure of the particle stream, astronomers built model magnetic field that dominates our galaxy.

Newstars

How often do new stars form in our galaxy? Researchers have been asking this question for years. It was possible to map the areas of our galaxy where there is aluminum-26, an isotope of aluminum that appears where stars are born or die. Thus, it was possible to find out that every year in the Milky Way galaxy, 7 new stars and about twice in a hundred years a large star explodes, forming a supernova.

The Milky Way Galaxy is not the manufacturer of the a large number stars. When a star dies, it releases into space such raw materials, like hydrogen and helium. After hundreds of thousands of years, these particles coalesce into molecular clouds, which eventually become so dense that their center collapses under their own gravity, thus forming a new star.

It looks like a kind of eco-system: death nourishes new life . Particles of a particular star in the future will be part of a billion new stars. This is how things are in our galaxy, so it evolves. This leads to the formation of new conditions under which the probability of the emergence of planets similar to the Earth increases.

Planets of the Milky Way Galaxy

Despite the constant death and birth of new stars in our galaxy, their number has been calculated: The Milky Way is home to about 100 billion stars. Based on new research, scientists suggest that every star has at least one or more planets orbiting it. That is, everything in our corner of the universe has 100 to 200 billion planets.

The scientists who came to this conclusion studied stars like red dwarfs of spectral class M. These stars are smaller than our Sun. They make up 75 percent from all the stars in the Milky Way. In particular, the researchers drew attention to the star Kepler-32, who sheltered five planets.

How do astronomers discover new planets?

Planets, unlike stars, are difficult to detect because they do not emit their own light. We can say with certainty that there is a planet around a star only when it stands in front of his star and obscures its light.

The planets of the star Kepler -32 behave exactly like exoplanets orbiting other M dwarf stars. They are located approximately at the same distance and have similar sizes. That is, the Kepler-32 system is typical system for our galaxy.

If there are over 100 billion planets in our galaxy, how many planets are Earth-like? It turns out, not so much. There are dozens various types planets: gas giants, pulsar planets, brown dwarfs, and planets that rain molten metal from the sky. Those planets that are composed of rocks can be located too far or too close to the star, so they are hardly similar to the Earth.

The results of recent studies have shown that in our galaxy, it turns out, more planets earth type than previously thought, namely: 11 to 40 billion. The scientists took as an example 42 thousand stars, similar to our Sun, and began to look for exoplanets that can revolve around them in a zone where it is not too hot and not too cold. Was found 603 exoplanets, among which 10 matched the search criteria.

By analyzing stellar data, scientists have proven the existence of billions of Earth-like planets that they have yet to officially discover. Theoretically, these planets are able to maintain temperatures for existence of liquid water which, in turn, will allow life to emerge.

Collision of galaxies

Even if new stars are constantly formed in the Milky Way galaxy, it will not be able to increase in size, if not receive new material from somewhere else. And the Milky Way is really expanding.

Previously, we were not sure exactly how the galaxy manages to grow, but recent discoveries have suggested that the Milky Way is cannibal galaxy, meaning it has devoured other galaxies in the past and will likely do so again, at least until some larger galaxy engulfs it.

Using a space telescope Hubble and information gained from photographs taken over the course of seven years, scientists have discovered stars near the outer edge of the Milky Way, which moving in a special way. Instead of moving towards or away from the center of the galaxy like other stars, they sort of drift off the edge. It is assumed that this star cluster is all that is left of another galaxy that was swallowed up by the Milky Way galaxy.

This collision appears to have taken place several billion years ago and it probably won't be the last. Given the speed at which we are moving, our galaxy through 4.5 billion years will collide with the Andromeda galaxy.

Influence of satellite galaxies

Although the Milky Way is a spiral galaxy, it is not exactly a perfect spiral. At its center there is peculiar bulge, which appeared as a result of the fact that the molecules of gaseous hydrogen escape from the flat disk of the spiral.

For years, astronomers have puzzled over why the galaxy has such a bulge. It is logical to assume that the gas is drawn into the disk itself, and does not break out. The longer they studied this issue, the more confused they became: the bulge molecules are not only pushed outward, but also vibrate at their own frequency.

What can cause such an effect? Today, scientists believe that dark matter and satellite galaxies are to blame - Magellanic Clouds. These two galaxies are very small: together they make up only 2 percent from total mass Milky way. It's not enough to have an impact on him.

However, when dark matter moves through the Clouds, it creates waves that apparently affect the gravitational attraction, strengthening it, and hydrogen under the influence of this attraction escaping from the center of the galaxy.

The Magellanic Clouds revolve around the Milky Way. The spiral arms of the Milky Way, under the influence of these galaxies, seem to sway in the place where they float.

twin galaxies

Although the Milky Way galaxy can be called unique in many ways, it is not a rarity. The universe is dominated by spiral galaxies. Considering that only in our field of vision are about 170 billion galaxies, we can assume that somewhere there are galaxies very similar to ours.

But what if somewhere there is a galaxy - an exact copy of the Milky Way? In 2012, astronomers discovered such a galaxy. It even has two small satellites that orbit it and match exactly with our Magellanic Clouds. By the way, only 3 percent spiral galaxies have similar companions whose lifetimes are relatively short. The Magellanic Clouds are likely to dissolve in a couple of billion years.

Finding such a similar galaxy with satellites, a supermassive black hole in the center and the same size is an incredible stroke of luck. This galaxy is called NGC 1073 and it looks so much like the Milky Way that astronomers study it to find out more. about our own galaxy. For example, we can see it from the side and thus better imagine what the Milky Way looks like.

Galactic year

On Earth, a year is the time it takes the Earth to make complete revolution around the sun. Every 365 days we return to the same point. Our solar system revolves around the black hole at the center of the galaxy in the same way. However, it makes a full turn for 250 million years. That is, since the dinosaurs disappeared, we have made only a quarter of a complete revolution.

In descriptions of the solar system, it is rarely mentioned that it moves in outer space, like everything else in our world. Relative to the center of the Milky Way, the solar system moves at a speed 792 thousand kilometers per hour. For comparison: if you were moving at the same speed, you could travel around the world in 3 minutes.

The period of time it takes for the Sun to make a complete revolution around the center of the Milky Way is called galactic year. It is estimated that the Sun has lived only 18 galactic years.