Gravity can not only attract, but also repel - how do you like this statement? And not in some new mathematical theory, but in fact - the Big Repulser, as a group of scientists called it, is responsible for half the speed at which our Galaxy moves through space. Sounds fantastic, doesn't it? Let's figure it out.
First, let's take a look around and get to know our neighbors in the Universe. Over the past few decades, we have learned a lot, and the word “cosmography” today is not a term from the science fiction novels of the Strugatskys, but one of the branches of modern astrophysics that deals with compiling maps of the part of the Universe accessible to us. Our Milky Way's closest neighbor is the Andromeda galaxy, which can be seen in the night sky with the naked eye. But it won’t be possible to see a few dozen more companions - the dwarf galaxies that revolve around us and Andromeda are very dim, and astrophysicists are still not sure that they have found all of them. However, all of these galaxies (including those not discovered), as well as the Triangulum galaxy and the NGC 300 galaxy, are included in the Local Group of Galaxies. There are currently 54 known galaxies in the Local Group, most of which are the already mentioned faint dwarf galaxies, and its size exceeds 10 million light years. The Local Group, along with about 100 other galaxy clusters, is part of the Virgo Supercluster, more than 110 million light years in size.
In 2014, a group of astrophysicists led by Brent Tully from the University of Hawaii found that this supercluster itself, consisting of 30 thousand galaxies, is part of another O greater structure - Laniakea supercluster, which already contains more than 100 thousand galaxies. It remains to take the last step - Laniakea, together with the Perseus-Pisces supercluster, is part of the Pisces-Cetus supercluster complex, which is also a galactic thread, that is, an integral part of the large-scale structure of the Universe.
Observations and computer simulations confirm that galaxies and clusters are not scattered chaotically throughout the Universe, but form a complex sponge-like structure with filaments, nodes and voids, also known as voids. The Universe, as Edwin Hubble showed almost a hundred years ago, is expanding, and superclusters are the largest formations that are kept from moving away by gravity. That is, to simplify, the filaments scatter from each other due to the influence of dark energy, and the movement of objects inside them is largely due to the forces of gravitational attraction.
And now, knowing that there are so many galaxies and clusters around us that attract each other so strongly that they even overcome the expansion of the Universe, it’s time to ask the key question: where is all this going? This is exactly what a group of scientists is trying to answer, together with Yehudi Hoffman from the Hebrew University of Jerusalem and the already mentioned Brent Tully. Their joint work, released in Nature, is based on data from the Cosmicflows-2 project, which measured the distances and velocities of more than 8,000 nearby galaxies. This project was launched in 2013 by the same Brent Tully along with colleagues, including Igor Karachentsev, one of the most highly cited Russian observational astrophysicists.
A three-dimensional map of the local Universe (with Russian translation), compiled by scientists, can be viewed at this video.
Three-dimensional projection of a section of the local Universe. On the left, blue lines indicate the velocity field of all known galaxies of nearby superclusters - they are obviously moving towards the Shapley Attractor. On the right, the anti-velocity field (reverse values of the velocity field) is shown in red. They converge at a point where they are “pushed out” by the lack of gravity in this region of the Universe.
Yehuda Hoffman et al 2016
So where is all this going? To answer, we need an accurate velocity map for all massive bodies in the nearby Universe. Unfortunately, Cosmicflows-2 data is not enough to construct it - despite the fact that this is the best that humanity has, it is incomplete, heterogeneous in quality and has large errors. Professor Hoffman applied Wiener estimation to the known data - a statistical technique for separating the useful signal from the noise, which came from radio electronics. This assessment allows us to introduce a basic model of system behavior (in our case, the Standard Cosmological Model), which will determine the general behavior of all elements in the absence of additional signals. That is, the movement of a particular galaxy will be determined by the general provisions of the Standard Model, if there is insufficient data for it, and by measurement data, if any.
The results confirmed what we already knew - the entire Local Group of galaxies is flying through space towards the Great Attractor, a gravitational anomaly in the center of Laniakea. And the Great Attractor itself, despite its name, is not so great - it is attracted by the much more massive Shapley Supercluster, towards which we are heading at a speed of 660 kilometers per second. The problems began when astrophysicists decided to compare the measured speed of the Local Group with the calculated one, which is derived from the mass of the Shapley Supercluster. It turned out that despite its colossal mass (10 thousand masses of our Galaxy), it could not accelerate us to such a speed. Moreover, by constructing a map of anti-velocities (a map of vectors that are directed in the direction opposite to the velocity vectors), scientists found an area that seems to push us away from itself. Moreover, it is located exactly on the opposite side from the Shapley Supercluster and repels at exactly the same speed as to give the required 660 kilometers per second in total.
The entire attractive-repulsive structure resembles the shape of an electric dipole, in which lines of force go from one charge to another.
Classic electric dipole from a physics textbook.
Wikimedia commons
But this contradicts all the physics we know - antigravity cannot exist! What kind of miracle is this? To answer, let's imagine that you are surrounded and pulled in different directions by five friends - if they do this with the same force, then you will remain in place, as if no one is pulling you. However, if one of them, standing on the right, lets you go, then you will move to the left - in the opposite direction from him. In the same way, you will move to the left if the five pulling friends are joined by a sixth, who stands on the right and begins to push you rather than pull you.
Relative to what we are moving in space.
Separately, you need to understand how speed in space is determined. There are several different methods, but one of the most accurate and often used is the use of the Doppler effect, that is, measuring the shift of spectral lines. One of the most famous lines of hydrogen, Balmer alpha, is visible in the laboratory as a bright red emission at a wavelength of 656.28 nanometers. And in the Andromeda galaxy, its length is already 655.23 nanometers - a shorter wavelength means that the galaxy is moving towards us. The Andromeda Galaxy is an exception. Most other galaxies fly away from us - and the hydrogen lines in them will be caught at longer waves: 658, 670, 785 nanometers - the further from us, the faster the galaxies fly and the greater the shift of spectral lines to the region of longer waves (this is called redshift). However, this method has a serious limitation - it can measure our speed relative to another galaxy (or the speed of a galaxy relative to us), but how to measure where we are flying with that same galaxy (and whether we are flying anywhere)? It's like driving a car with a broken speedometer and no map - we overtake some cars, some cars overtake us, but where are they all going and what is our speed relative to the road? In space there is no such road, that is, an absolute coordinate system. There is generally nothing stationary in space to which measurements could be tied.
Nothing but light.
That's right - light, more precisely thermal radiation, which appeared immediately after the Big Bang and spread evenly (this is important) throughout the Universe. We call it cosmic microwave background radiation. Due to the expansion of the Universe, the temperature of the cosmic microwave background radiation is constantly decreasing and now we live in such a time that it is equal to 2.73 kelvin. The homogeneity - or, as physicists say, isotropy - of the cosmic microwave background radiation means that no matter which way you point the telescope in the sky, the temperature of space should be 2.73 kelvin. But this is if we do not move relative to the cosmic microwave background radiation. However, measurements, including those carried out by the Planck and COBE telescopes, showed that the temperature of half the sky is slightly less than this value, and the other half is slightly more. These are not measurement errors, due to the same Doppler effect - we are shifting relative to the CMB, and therefore part of the CMB, towards which we are flying at a speed of 660 kilometers per second, seems to us a little warmer.
Map of the cosmic microwave background radiation obtained by the COBE space observatory. The dipole temperature distribution proves our movement in space - we are moving away from a colder area (blue colors) towards a warmer area (yellow and red colors in this projection).
DMR, COBE, NASA, Four-Year Sky Map
In the Universe, the role of attracting friends is played by galaxies and clusters of galaxies. If they were evenly distributed throughout the Universe, then we would not move anywhere - they would pull us with the same force in different directions. Now imagine that there are no galaxies on one side of us. Since all the other galaxies remained in place, we will move away from this void, as if it were repelling us. This is exactly what happens with the region that scientists have dubbed the Great Repulsor, or the Great Repeller - several cubic megaparsecs of space are unusually poorly populated with galaxies and cannot compensate for the gravitational attraction that all these clusters and superclusters exert on us from other sides. How exactly this space is poor in galaxies remains to be seen. The fact is that the Great Repeller is very poorly located - it is located in the avoidance zone (yes, there are a lot of beautiful, incomprehensible names in astrophysics), that is, a region of space closed from us by our own galaxy, the Milky Way.
Velocity map of the local Universe, approximately 2 billion light years in size. The yellow arrow in the center emerges from the Local Group of galaxies and indicates its speed of movement approximately in the direction of the Shapley attractor and exactly in the opposite direction from the repeller (indicated by the yellow and gray outline in the right and upper area).
Yehuda Hoffman et al 2016
A huge number of stars and nebulae, and especially gas and dust, prevent light from distant galaxies located on the other side of the galactic disk from reaching us. Only recent observations with X-ray and radio telescopes, which can detect radiation freely passing through gas and dust, have made it possible to compile a more or less complete list of galaxies in the avoidance zone. There are indeed very few galaxies in the Great Repulsor region, so it appears to be a candidate for a void - a giant empty region of the cosmic structure of the Universe.
In conclusion, it must be said that no matter how high the speed of our flight through space is, we will not be able to reach either the Shapley Attractor or the Great Attractor - according to scientists’ calculations, it will take time thousands of times greater than the age of the Universe, so no matter how accurate No matter how the science of cosmography has developed, its maps will not be useful to travel enthusiasts for a long time.
Marat Musin
Any person, even lying on the couch or sitting near the computer, is in constant motion. This continuous movement in outer space has a variety of directions and enormous speeds. First of all, the Earth moves around its axis. In addition, the planet rotates around the Sun. But that's not all. We cover much more impressive distances together with the Solar System.
The Sun is one of the stars located in the plane of the Milky Way, or simply the Galaxy. It is distant from the center by 8 kpc, and the distance from the plane of the Galaxy is 25 pc. The stellar density in our region of the Galaxy is approximately 0.12 stars per 1 pc3. The position of the Solar System is not constant: it is in constant motion relative to nearby stars, interstellar gas, and finally, around the center of the Milky Way. The movement of the Solar System in the Galaxy was first noticed by William Herschel.
Moving relative to nearby stars
The speed of movement of the Sun to the border of the constellations Hercules and Lyra is 4 a.s. per year, or 20 km/s. The velocity vector is directed towards the so-called apex - the point towards which the movement of other nearby stars is also directed. Directions of star velocities, incl. The suns intersect at a point opposite the apex, called the antiapex.
Moving relative to visible stars
The movement of the Sun in relation to bright stars that can be seen without a telescope is measured separately. This is an indicator of the standard movement of the Sun. The speed of such movement is 3 AU. per year or 15 km/s.
Moving relative to interstellar space
In relation to interstellar space, the Solar system is already moving faster, the speed is 22-25 km/s. At the same time, under the influence of the “interstellar wind”, which “blows” from the southern region of the Galaxy, the apex shifts to the constellation Ophiuchus. The shift is estimated to be approximately 50.
Navigating around the center of the Milky Way
The solar system is in motion relative to the center of our Galaxy. It moves towards the constellation Cygnus. The speed is about 40 AU. per year, or 200 km/s. It takes 220 million years to complete a revolution. It is impossible to determine the exact speed, because the apex (the center of the Galaxy) is hidden from us behind dense clouds of interstellar dust. The apex shifts by 1.5° every million years, and completes a full circle in 250 million years, or 1 galactic year.
Journey to the edge of the Milky Way
Movement of the Galaxy in outer space
Our Galaxy also does not stand still, but is approaching the Andromeda Galaxy at a speed of 100-150 km/s. A group of galaxies, which includes the Milky Way, is moving towards the large Virgo cluster at a speed of 400 km/s. It is difficult to imagine, and even more difficult to calculate, how far we travel every second. These distances are enormous, and the errors in such calculations are still quite large.
The Universe amazes with its size and speed. All objects (stars, planets, asteroids, star dust) in it are in constant motion. Many of them have similar trajectories of movement, since the same laws apply to them. The movement of the Solar System in the Galaxy has its own characteristics, which may seem unusual at first glance, although it is subject to the same laws as other space objects.
A Brief History of Astronomy
Previously, people thought that the Earth was flat and covered with a crystal cap, and the stars, the Sun and the Moon were attached to it. In Ancient Greece, thanks to the works of Ptolemy and Aristotle, it was believed that the Earth was spherical in shape, and all other objects moved around it. But already in the 17th century, doubt was first expressed that the Earth was the center of the world. Copernicus and Galileo, observing the movement of the planets, came to the conclusion that the Earth rotates along with other planets around the Sun.
Modern scientists have gone even further and determined that the Sun is not a center and, in turn, revolves around the center of the Milky Way galaxy. But this turned out to be not entirely accurate. Near-Earth orbital telescopes have shown that our Galaxy is not the only one. There are billions of galaxies and star clusters, clouds of cosmic dust in space, and the Milky Way galaxy also moves relative to them.
Light
The Sun is the main driving force behind the movement of the Solar System in the Galaxy. It moves in an elliptical, almost perfectly circular circle, and pulls with it the planets and asteroids that are part of the system. The Sun rotates not only around the center of the Milky Way galaxy, but also around its own axis. Its axis is shifted to the side by 67.5 degrees. Since it (with such an inclination) practically lies on its side, from the outside it seems that the planets that make up the Solar System rotate in a vertical, and not in an inclined plane. The Sun rotates counterclockwise around the center of the Galaxy.
It also moves in the vertical direction, periodically (every 30 million years) either lowering or rising relative to the central point. Perhaps this trajectory of motion of the Solar system in the Galaxy is due to the fact that the core of the Milky Way galaxy rotates around its own axis like a top - periodically tilting in one direction or the other. The Sun only repeats these movements, since according to the laws of physics it must move strictly along the equator line of the central body of the Galaxy, in which, according to scientists, there is a giant black hole. But it is quite possible that such a trajectory is a consequence of the influence of other large objects.
The speed of movement of the Solar System in the Galaxy is equal to the speed of the Sun - about 250 km/s. It makes a complete revolution around the center in 13.5 million years. Over the entire history of the Milky Way galaxy, the Sun has made three full revolutions.
Laws of motion
When determining the speed of movement of the Solar system around the center of the Galaxy and the planets that make up this system, one should take into account the fact that Newton’s laws, in particular the law of attraction or gravitation, operate inside the Solar system. But when determining the trajectory and speed of movement of planets around the center of the Galaxy, Einstein’s law of relativity also applies. Therefore, the speed of the Solar system is equal to the speed of revolution of the Sun, since about 98% of the total mass of the system is located in it.
Its movement in the Galaxy obeys the second. In the same way, the planets of the Solar system obey this law. According to him, they all move in the same plane around the center of the Sun.
Toward or away from the center?
In addition to the fact that all the stars and planets move around the center of the Galaxy, they also move in other directions. Scientists have long determined that the Milky Way galaxy is expanding, but it is happening more slowly than it should be. This discrepancy was identified through computer modeling. The discrepancy puzzled astronomers for a long time until the existence of black matter was proven, which prevents the Milky Way galaxy from disintegrating. But the movement away from the center continues. That is, the Solar system moves not only in a circular orbit, but also shifts in the opposite direction from the center.
Movement in infinite space
Our Galaxy also moves in space. Scientists have found that it is moving towards the Andromeda nebula and will collide with it in a few billion years. At the same time, the movement of the Solar System in the Galaxy occurs in the same direction, since it is part of the Milky Way, at a speed of 552 km/s. Moreover, its speed of movement towards the Andromeda nebula is much higher than the speed of revolution around the center of the Galaxy.
Why doesn't the solar system fall apart?
Outer space is not empty. All space around stars and planets is filled with cosmic dust or dark matter, which surrounds all galaxies. Large accumulations of cosmic dust are called clouds and nebulae. Clouds of cosmic dust often surround large objects - stars and planets.
The solar system is surrounded by such clouds. They create the effect of an elastic body, which gives it more strength. Another factor that prevents the solar system from disintegrating is the strong gravitational interaction between the Sun and the planets, as well as the large distance to the stars closest to it. Thus, the star closest to the Sun, Sirius, is located at a distance of about 10 million light years. To understand how far this is, it is enough to compare the distance from the star to the planets that make up the solar system. For example, the distance from it to Earth is 8.6 light minutes. Therefore, the interaction between the Sun and other objects within the Solar System is much stronger than that of other stars.
How do planets move in the Universe?
The planets move in the Solar System in two directions: around the Sun and with it around the center of the Galaxy. All objects that are part of this system move in two planes: along the equator and around the center of the Milky Way, repeating all the movements of the star, including those that occur in the vertical plane. At the same time, they move at an angle of 60 degrees relative to the center of the Galaxy. If you look at how the planets and asteroids of the Solar System move, their movement is spiral. The planets move behind and around the Sun. Every 30 million years, a spiral of planets and asteroids rises upward along with the star and descends just as smoothly.
The movement of planets within the solar system
In order for the picture of the motion of the system in the Galaxy to acquire a complete form, we should also consider at what speed and in what orbit the planets move around the Sun. All planets move counterclockwise, and they also rotate around their own axis counterclockwise, with the exception of Venus. Many have multiple satellites and rings. The farther a planet is from the Sun, the more elongated its orbit. For example, the dwarf planet Pluto has such an elongated orbit that when passing perihelion it passes closer to it than Uranus. The planets have the following speeds of revolution around the Sun:
- Mercury - 47.36 km/s;
- Venus - 35.02 km/s;
- Earth - 29.02 km/s;
- Mars - 24.13 km/s;
- Jupiter - 13.07 km/s;
- Saturn - 9.69 km/s;
- Uranus - 6.81 km/s;
- Neptune - 5.43 km/s.
The pattern is obvious: the further the planet is from the star, the lower the speed of its movement and the longer the path. Based on this, the spiral of motion of the solar system has the highest speed near the center and the lowest on the outskirts. Until 2006, Pluto was considered the outermost planet (move speed 4.67 km/s), but with a change in classification it was classified as a large asteroid - dwarf planet.
The planets move unevenly, in elongated orbits. The speed of their movement depends on the point at which a particular planet is located. Thus, at the perihelion point the linear speed of movement is higher than at aphelion. Perihelion is the farthest point on the elliptical trajectory of the planet from the Sun, aphelion is the closest to it. Therefore, the speed may vary slightly.
Conclusion
The earth is one of billions of grains of sand wandering in infinite space. But its movement is not chaotic, it is subject to certain laws of motion of the Solar system. The main forces that influence its movement are gravity. It is affected by the forces of two objects - the Sun as the star closest to it and the center of the Galaxy, since the solar system, which the planet is part of, rotates around it. If we compare the speed of its movement in the Universe, then it, together with the other stars and planets, moves in the direction of the Andromeda nebula at a speed of 552 km/s.
