There was a time when people believed that the Earth is the center of the Universe, around which all celestial bodies revolve. Now we know that this is not at all the case: our solar system is just a tiny part of a huge galaxy called the Milky Way – colossal by earthly standards and at the same time infinitely small against the backdrop of a vast universe.
To understand how grand galactic scales are, it is enough to give a small example. The diameter of the Sun is more than a hundred times greater than the diameter of the Earth. But compared to the size of the galaxy, this is a completely insignificant figure. Their ratio is approximately the same as if we were comparing the point at the end of this sentence with the whole continent. But galaxies in the universe are innumerable, and they are not located close to each other. And they are all so different …
For every taste and color
Elliptical galaxies, contrary to the name, are not necessarily elliptical. Their shape varies from elongated to almost round (in the photo – NGC1404), and the brightness gradually decreases from the center to the edges. In elliptical galaxies, there is practically no main building material of the universe – gas and dust, so new stars do not form there. Such galaxies consist predominantly of red and yellow giants and dwarfs, with rare intersperses of dim white stars.
NGC 1365, a spiral galaxy with a jumper (Photo: ESO / IDA / Danish 1.5 m / R. Gendler, J-E. Ovaldsen, C. Thöne, and C. Feron) – NGC 1365, a spiral galaxy with a jumper
Spiral galaxies, unlike elliptical ones, are a “space incubator” for stars. The star formation process is especially active in the so-called sleeves. But there are old stars in these galaxies too. Some of them are located in the center – in a luminous elliptical seal called a bulge. Others are distributed over the entire area of the spherical halo surrounding the bulge and sleeves. Most of the observed spiral galaxies have jumpers emanating from the center of bright stars called bars. A typical example is our Milky Way. According to astronomers, the bars stimulate the star formation process by passing gas from spiral branches through themselves. Over time, they disappear, and the galaxy turns into an ordinary spiral.
From a distance, a spiral galaxy, viewed from the side, resembles a flat disk, so in a sense, ancient people were still right in saying that you and I live on a disk. Only the scale was a little mistaken (NASA, ESA and the Hubble Heritage Team (STScI / AURA)
NGC 5866 (NASA, ESA, and The Hubble Heritage Team (STScI / AURA)
Lenticular galaxies come from spiral ones when they spend or lose most of their interstellar matter. Such galaxies combine the features of the two previous ones. Like spiral ones, they have the shape of a disk, so it can be difficult to distinguish between these two types of galaxies. However, like elliptical, lenticular galaxies consist mainly of old stars. New ones are rarely formed in them, since interstellar matter is not enough for this.
The Barnard Galaxy is wrong, but with a jumper!
About a quarter of all observed galaxies are irregular (irregular) – they cannot be unambiguously classified. In some, one can distinguish a certain semblance of the former structure, in others the stars are located completely randomly. Most often, irregular galaxies result from the collision of two galaxies. Sometimes galaxies do not have a clear structure, not at all due to external influences, but because they have not yet been fully formed – in such galaxies, most stars are much younger than our Sun.
The Centaurus A Galaxy is the only elliptical galaxy with spiral elements. According to astronomers, spiral fragments are nothing but “undigested” remnants of an absorbed spiral galaxy (photo: ESO / WFI (Optical); MPIfR / ESO / APEX / A. Weiss et al. (Submillimetre); NASA / CXC / CfA / R. Kraft et al. (X-ray))
Ring world
(Photo: NASA)
Accustomed to strict accounting and classification, astronomers were perplexed for a long time when they discovered the formation of the Hog Object in the constellation Snakes. The fact is that in the center of this galaxy there is a core of old yellow stars, around which there is an absolutely regular-shaped ring of young blue stars. Researchers first suggested that these two parts are not interconnected, but then they came up with a separate class of ring galaxies for the Hog object. In which he, by the way, is not the only representative – if you look closely, then in the photo you can see in the distance another exactly the same galaxy.
From small to large
The sizes of galaxies are striking in variety. The largest of the currently discovered ones is the lenticular IC 1101 from the Abell 2029 cluster with a diameter of about 6 million light years (that is, light from the center to the outskirts will go 3 million years). The second largest Hercules-A galaxy is four times smaller, while its mass is still a thousand times larger than the mass of our galaxy. The third largest galaxy NGC 262 is slightly smaller than Hercules-A – its diameter is 1.3 million light-years.
Six million light-years in one shot (photo: David A. Aguilar (CfA))
Scientists have discovered the smallest galaxy known to mankind – Segue 2, near the Milky Way. This galaxy is very old: its stars, of which there are only a thousand, are already billions of years old. Most likely, there are even fewer galaxies, but they are still quite difficult to detect. Large galaxies usually have a large number of dwarf satellites orbiting them.
Segue 2 – “space gnome”, or rather, dwarf (Garrison-Kimmel, Bullock / UCI)
Galaxies of all sizes and shapes can also be radio galaxies. All galaxies “shine” in the radio range, but only those that emit in it especially intensely are referred to radio galaxies. The most powerful ones are Swan A (3C 405), Centaurus A (NGC 5128), Virgo A (NGC 4486) and Furnace A (NGC 1316). Observation of the irregular galaxy M82 led scientists to the conclusion that a strong explosion in the nucleus could cause intense radio emission.
Swan A, a powerful source of radio waves (J. McKean and M. Wise / ASTRON)
Space predators
There are two main hypotheses on how galaxies form. According to hierarchical theory, galaxies began to form when the stars that appeared after the Big Bang began to gather in clusters under the influence of gravity. According to proponents of inflationary theory, galaxies and stars appeared simultaneously. They gradually formed from the heterogeneities that appeared after the Big Bang. Subsequently, such inhomogeneities were transformed into gas nebulae, from which galaxies arose. The transitional stage of their formation is protogalaxies, giant clouds of interstellar gas, 75% of which are hydrogen and 25% are helium. The force of gravity acts on the protogalaxy for several billion years before a full-fledged galaxy is formed from it.
When would you know what litter galaxies are made of!
There is no consensus on the evolution of galaxies. But the fact that they repeatedly change throughout their lives no longer causes astronomers doubts. According to one version, the life cycle begins with shapeless irregular galaxies with large reserves of necessary building materials – gas and dust. Then they are converted into spiral. When the star formation process becomes less and less intense, the spiral galaxy gradually turns into an elliptical until it reaches the ideal spherical shape.
The second version is similar to the first, only the process is going in a different direction. Elliptical galaxies eventually flatten to lenticular, and they, in turn, transform into spiral ones, then begin to lose shape with the cessation of star formation and eventually become irregular.
There is also a version that galaxies, in principle, do not evolve, but are initially formed as they are. In this case, they change shape due to interaction with each other.
Galaxies swallow each other (NASA, ESA, the Hubble Heritage Team (STScI / AURA) -ESA / Hubble Collaboration and A. Evans (University of Virginia, Charlottesville / NRAO / Stony Brook University), K. Noll (STScI), and J . Westphal (Caltech))
The galaxies interact with each other very often, since they all move continuously and fairly quickly in different directions and, in addition, have a tendency to cosmic cannibalism. As a rule, the larger the galaxy, the more neighbors it swallowed. The Andromeda Nebula and our native Milky Way, which simply attract their victims due to powerful gravity, are enviable appetites.
If a giant collides with a dwarf, then most likely, only the leftovers will remain from the last – star flows, and a memory jumper in the center of the devourer, if it is spiral. If complete absorption fails, traces of interaction will still remain: for example, the irregular shape of the Big and Small Magellanic Clouds (satellites of the Milky Way) is the merit of our galaxy.
However, the spiral giants mentioned above also attract each other: according to scientists, in three billion years the Milky Way and the Andromeda Nebula will collide and merge into a huge elliptical galaxy. In this case, the appetite of the new space formation will only double – as the observations of the Centaurus A galaxy have shown, the “old people” are also not opposed to refresh themselves with young spiral galaxies.
Invisible power
Invisible and gluttonous: supermassive black hole through the eyes of the artist
Perhaps the reason for the constant hunger lies in the device of the galaxies themselves, which have great attraction. After all, each of them itself is formed around a powerful source of gravity. In the center of most galaxies is a supermassive black hole – a celestial body with an attraction of such force that neither matter nor radiation can leave it. For example, in the center of the Milky Way is a black hole, the mass of which is from two to five million solar masses. And this is far from a record.
Scientists have yet to thoroughly investigate how supermassive black holes form. Now they can only relatively accurately determine their presence by observing the center of galaxies in the radio and infrared ranges. However, there is a sign that clearly indicates that there is a black hole in the galaxy. This is a quasar.
It’s better not to come across this ray
It is believed that quasars result from the merger of galaxies. Supermassive black holes in the centers of galaxies attract stars with such greed that a quasar is formed around them, which emits millions of times more energy than the brightest stars. These emissions are so strong that the flares accompanying them are easily visible even in the visible spectrum. Quasars emit radio waves, infrared, ultraviolet, x-rays and gamma rays of incredible strength.
The influence of black holes can be traced in the life of another variety of galaxies – Seyfert, named after the researcher Karl Seyfert. Their characteristic feature is the active core, the emission spectrum of which contains many bright wide bands. These bands are caused by powerful emissions of gas from the core, which moves at speeds up to several thousand kilometers per second. Seyfert galaxies are usually irregular or spiral.
Thanks to the “exhaust” of the nucleus at NGC 1097, new star formation regions appeared
However, black holes, quasars and blazars are not the only constituents of galaxies that cause many questions among scientists. Dark matter remains no less mysterious. Scientists guessed its very existence only because of the anomalously high speed with which the peripheral regions of galaxies rotate. Dark matter is practically invisible, because it does not emit electromagnetic radiation and does not interact with it, but it has a very strong gravitational effect, many times larger than visible matter. For example, the elliptical galaxy NGC 1132 is surrounded by a huge halo of dark matter, the mass of which is thousands of times larger than the galaxy itself.
The effect of dark matter is especially noticeable in galactic clusters. This became known during experiments with gravitational lensing. The basis of these experiments is the fact that any mass deforms the space, distorting the rays of light like a lens. The distortion arising in a cluster of galaxies is so great that it is easy to notice.
Giant space magnifying glass
In addition, without dark matter, galaxies could not have formed. One attraction of fragments of matter that arose after the Big Bang would not be enough for this. By and large, dark matter of various types makes up 95% of the mass of the universe. It holds together the existing galactic communities and fills the space between them.
Old-timers of the Universe
(Photo: NASA / CXC / NRC / C. Cheung et al; NASA / STScI; NSF / NRAO / VLA)
According to the standard cosmological model, the age of the universe is 13.7 billion years. And the light of the quasar GB 1428, which arose due to the oldest supermassive black hole, took 13.2 billion years, only to reach the Earth. This means that a black hole already existed at most 500 million years after the Big Bang. This seems unlikely, since the quasar simply did not have enough time to form. The earliest quasars discovered before were 12.4 billion years old.
In order to somehow explain this phenomenon, some scientists even suggested that the Universe is perhaps a couple of billion years larger, since space objects that appeared simultaneously with the conventional beginning of time are rare, but they are found.
Space families
Like stars inside galaxies, the galaxies themselves also unite into large formations – galactic clusters. Galaxies are held together by gravity, forming a single system. Accumulations are of two types. Regular ones consist of elliptical and spiral galaxies, with giant elliptical galaxies located in the center of the cluster. Such clusters have a spherical shape. Irregulars, however, do not have a strict form, they have fewer galaxies, and most of them are spiral.
The local group, which includes our Milky Way, consists of more than five dozen galaxies, and this figure is constantly increasing as scientists discover new ones. In turn, the Local Group is part of the Local Virgo Supercluster. Other superclusters closest to us are called Hydra-Centauri, Hair of Veronica, Pisces-Perseus, Peacock-Indian, Phoenix, Ophiuchus, Hercules, Leo, Sculptor and Shaply.
The Great Five – Stephen’s Quintet (NASA, ESA, and the Hubble SM4 ERO Team)
For a long time it was believed that superclusters are the largest structural formations in the Universe. However, recent studies have shown that they are only part of a complex of galactic superclusters – threads, or filaments. In addition to filaments, scientists also discovered voids – space of incredible sizes, free from galaxies and stars. Most likely, the voids are composed of dark matter and protogalactic clouds.
The threads form the “great walls” – relatively flat structures surrounded by voids. The largest of which are the Great Wall of Hercules – the Northern Crown, the Great Wall of Sloan and the Great Wall of CfA2. The first is the largest known so far: its length is 10 billion light-years, and before its discovery in 2013, the Great Wall of Sloan was considered to be such, the size of which is much smaller – about a billion light-years.
Find your supercluster! (Photo: Andrew Z. Colvin)
Another large-scale structure of the Universe is the Huge group of quasars (astronomers do not seem to be very bothered by coming up with names), it is also Huge-LQG or U1.27, located in the constellation Leo. This is the second largest space superstructure of 4 billion light-years.
By the way, if you look at the illustrations of galactic filaments, you can see that they are extremely reminiscent of a network of neurons. However, this probably has some kind of not too esoteric explanation. Perhaps this is simply the most convenient form of association and interaction for the simplest elements.
All that does not shine is dark matter
It remains only to observe
Mankind obviously will not be able to leave the solar system in the near future and look at distant stellar bodies live. However, even in such conditions, scientists are not discouraged, but explore the remote corners of the Universe, as they say, on the spot. Telescopes help them in this. Given that space objects produce the most diverse types of radiation, the most complete picture is formed if several types of data are “superimposed” on each other – for example, a photograph in the visible spectrum, infrared, x-ray, ultraviolet and gamma radiation.
Galaxies prefer infrared filter
Investigations of the Universe are best done outside the Earth, as its atmosphere does not allow many types of cosmic radiation to pass through. The largest and most famous observatory in orbit is the Hubble telescope, a joint project of NASA and the European Space Agency. “Hubble” allows you to take photos of stunning clarity, since its images are not subject to distortion of the atmosphere, which makes its resolution 7-10 times higher than its counterparts. Most recently, the telescope managed to photograph the galaxies that formed in the first billion years after the Big Bang.
Hubble’s probably the coolest Instagram photos (Photo: NASA, ESA)
To capture not only visible radiation, but also what is hidden behind clouds of gas and dust, infrared telescopes are needed. Today, the largest of them is the 4.1-meter VISTA of the European Southern Observatory, which is located in Chile and uses a 3-ton camera for wide-angle shooting of the sky.
VISTA, the highest ground-based telescope (Photo: ESO)
By the way, the Hubble at the near-Earth post will also be replaced by the infrared telescope – James Webb, whose distinguishing feature is that the mirrors are three times larger than their predecessor (6.5 meters in diameter). It is planned that this will happen in 2018, and another ten years later the European Space Agency plans to launch into space the largest X-ray satellite telescope Athena in history. Thanks to such devices, binary stars, pulsars, and the active nuclei of galaxies were discovered, but planets, for example, could not be seen with their help – in X-rays, space looks different than in the optical range.
Infrared Andromeda Nebula Core (photo: S. Murray, M. Garcia, et al., Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep .: Jay Norris)
By the way, there are telescopes of a completely natural origin, and astronomers use them with great pleasure. We are talking about the gravitational lenses mentioned above, which, by the way, are much more powerful than any of the telescopes created by man, and at the same time are completely free. Such a lens enhances brightness and increases distant dim objects. By combining the efforts of a natural telescope, for example, with the Hubble, you can get incredible results.
The gravitational lens deflects the light coming from a distant object behind it, so that we can see this object
Star catalogs
The main passion of the French astronomer Charles Messier, who lived in the 18th century, was comets. He was confused only by the fact that in the starry sky there were quite a few motionless objects that were easily confused with comets. To clarify, Messier decided to create a catalog, which included all the star clusters and nebulae observed by him. True, the optical instruments of that time did not differ in high resolution, so a lot of all cosmic good was included in the Messier catalog: distant galaxies, planetary nebulae, and all kinds of clusters. The first edition contained a list of 45 objects, but later the English astronomer William Herschel expanded it to 102. In this form, the Messier catalog was first published in 1784. It should be noted that this catalog mainly includes nebulae and clusters,
In addition to the Messier catalog, the New General Catalog of Nebulae and Star Clusters (NGC) is widely known. This catalog was compiled by John Dreyer from information compiled by the aforementioned Herschel. In the original version, it already included 7840 objects, moreover, observed not only in the Northern, but also in the Southern Hemisphere. A little later, it was expanded with two Index catalogs of nebulae and stars, after which the list of objects increased to 13,226. At the moment, NGC is one of the largest non-specialized catalogs.
Both catalogs – Messier and NGC – for many amateur astronomers to this day serve as a kind of “star alphabet”, which helps them in their first space research.
Pandora’s mysterious cluster, seen through a gravitational lens (Photo: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)
Admiring the beautiful pictures of distant galaxies, all the time we have to remind ourselves how far they are from us in space and time. What we see is actually a journey into the distant past, since light takes a huge amount of time to get from its source to the Earth. At the moment, all these galaxies may look very different, and we can only notice changes when millions of years have passed. But maybe there is a way to do this before. After all, science will not stand still all this time.
