How many known galaxies? How many galaxies in the Universe are known to modern man?

Everyone has ever thought about how large and unknown the world around us is. Being part of an immeasurably vast Universe, we often ask ourselves with curiosity: “How big is the Universe?”, “What does it consist of?”, “Is there intelligent life besides us?”, “How many galaxies are there in the Universe?” and many others.

This article seeks to answer some of them and expand on general knowledge and ideas about the Universe and its constituent parts and systems.

Universe

The universe includes everything that exists. From cosmic dust to giant stars; from the smallest hydrogen atoms to subjective ideas and abstract concepts. Everything that is located and functions in space is part of the Universe.

It is studied by various sciences. Physics, astronomy and cosmology are pioneers in the study of the Universe in objective reality. They are the ones who are trying to answer the question of what the cosmos is made of or how many galaxies there are in the Universe. From its very first days, philosophy has been studying the Universe in subjective reality. The mother of all sciences is not concerned about how many galaxies there are in the Universe, but about how it and its perception affect our life and development.

Given the incredible size of the Universe and the mass of bodies and substances found in it, it is not surprising that we have accumulated a huge amount of knowledge; It is also not surprising that many more questions remain unanswered. Only a small part of the Universe can be physically studied at a certain point in time; we can only guess about the rest. The past and future of the Universe are only assumptions and predictions, and its present is revealed to us only to a tiny extent.

What do we know for sure about her?

We are absolutely sure that the Universe is huge, and with a high degree of probability we can say that it is immeasurable. To measure distances between cosmic objects, a completely “universal” unit is used - the light year. This is the distance that a beam of light can travel in a year.

The matter that makes up the Universe surrounds our planet at a distance of at least 93 billion light years. For comparison, our galaxy occupies a place that can be covered in 100 thousand light years.

Scientists divide cosmic matter into a cluster of atoms - understandable and studied physical matter, which is also called baryonic matter. However, most of the Universe is occupied by unexplored dark energy, the properties of which are unknown to scientists. Also, a considerable part of the visible space of the Universe is occupied by dark or hidden mass, which scientists call invisible matter.

The accumulation of baryonic matter forms stars, planets and other cosmic bodies, which, in turn, form galaxies. The latter are in motion and moving away from each other. It is impossible to answer the question of how many galaxies there are in the Universe with precision.

What can we only guess?

The past of the Universe and the process of its formation are precisely unknown. Scientists suggest that the Universe is almost 14 billion years old and formed after the expansion of concentrated hot matter, which in cosmology is called the Big Bang Theory.

Scientists obtain everything on which the main theoretical models of the evolution of the Universe are based by observing the part of it visible to us. It is impossible to prove how true any of the currently existing models is. Most scientists agree with the theory of the expansion of the Universe - after the “big bang”, cosmic matter continues its movement from its center.

It is worth remembering that all these models are theoretical, and it is impossible to test them in practice for many reasons. Therefore, it is worth concentrating on accessible and proven knowledge that answers the questions about how many stars are in the galaxy, and how many galaxies are in the Universe. The photo, taken with the help of modern technology, called Hubble (from Hubble Ultra Deep Field), allows you to see the location of many galaxies in a small visible part of the sky.

What is a galaxy?

A galaxy is a collection of stars, gas, dust and hidden mass. The gravitational interaction of baryonic matter and dark cosmic mass unites the galaxy into a tightly connected group of cosmic bodies. Galaxies move at a certain speed, which confirms the theory of the expansion of the Universe, but the gravitational center of the galaxy does not allow the movement of the Universe to influence its formation. All bodies in the galaxy revolve around a gravitational center.

Galaxies may be various types, sizes and consist of many systems. There is no single answer to the question of how many galaxies there are in the Universe, since the existence of two identical galaxies is unlikely. By type they are divided into:

• elliptical;
• spiral;
• lenticular;
• with jumper;
• incorrect.

Based on their size, galaxies are classified as dwarf, medium, large and giant. There is no clear answer to the question of how many systems there are in a galaxy, since the number of systems and star clusters depends on the set various factors, such as the gravitational field of stars, the size of the galaxy, and many others.

Scale of galaxies

Each galaxy consists of star systems, clusters and interstellar clouds. Several neighboring galaxies can be attracted to each other and form a local group. It can contain from three to 30 galaxies of various types and sizes.

Clusters of local groups, in turn, form huge clouds of stars called superclusters of galaxies. The gravitational interdependence of galaxies in relation to their neighbors from the local group, as well as from the supercluster, is based on the interaction of atoms of baryonic matter with hidden matter.

Milky Way

Our home galaxy - Milky Way- is a disk-shaped spiral with a jumper. The core of the galaxy is made up of old stars - red giants. The Milky Way shares its local group with two neighboring galaxies: the Andromeda nebula and the Triangulum galaxy. The supercluster to which they belong is called the Virgo Supercluster.

In the local group of the Milky Way, in addition to three large galaxies, there are about 40 dwarf satellite galaxies, which are attracted by stronger gravitational fields their big neighbors. There may be as many black holes and dark matter spaces in the Virgo Supercluster as there are galaxies. The exact number of stars in the Milky Way is unknown, but according to rough estimates there are 200 billion. The diameter of the Milky Way is one hundred thousand light years, and the average thickness of the disk is one thousand light years.

The youngest stars and their clusters are located closer to the surface of the disk, while the center of the galactic core, according to scientists, is a huge black hole, around which there is a very high concentration of stars. Main star Our system - the Sun - is located closer to the surface of the disk.

solar system

The solar system is 4.5 billion years old and is located in the shape of a disk. The heaviest element of the system is its center - the Sun; it accounts for almost all the mass, which determines the strong gravitational attraction. The eight planets orbiting it make up just 0.14% of the system's total mass. Earth belongs to the four small terrestrial planets, along with Mars, Venus and Mercury. The remaining planets are called gas giants because they consist mostly of gases.

An international team of astronomers led by Christopher J. Conselice, professor of astrophysics at the University of Nottingham, found that The Universe contains at least 2 trillion galaxies, ten times more than previously thought. The team's work, which began with a grant from the Royal Astronomical Society, was published in the Astrophysical Journal on October 14, 2016.

Astronomers have long sought to determine how many galaxies exist in the observable universe, the part of space where light from distant objects has managed to reach us. Over the past 20 years, scientists have used images from the Hubble Space Telescope to estimate that the universe we see contains about 100 to 200 billion galaxies. Current astronomical technology allows us to study only 10% of these galaxies, and the remaining 90% will only be visible once bigger and better telescopes are developed.

Professor Conselice's research is the culmination of 15 years of work, which was also part-funded by a Royal Astronomical Society research grant awarded to undergraduate student Aaron Wilkinson. Aaron, currently a PhD candidate at the University of Nottingham, began by reviewing all previous galaxy counting studies, which provided the fundamental basis for establishing a larger study.

Professor Conselice's team has converted narrow images of deep space from telescopes around the world, and especially from the Hubble Telescope, into 3D maps. This allowed them to calculate the density of galaxies, as well as the volume of one small region of space after another. This painstaking research allowed the team to determine how many galaxies had been missed in earlier studies. We can say that they conducted an intergalactic archaeological excavation.

The results of this study are based on measurements of the number of observed galaxies at different epochs - time slices on a galactic scale - throughout the history of the Universe. When Professor Conselice and his team from Nottingham, in collaboration with scientists from the Leiden Observatory at Leiden University in the Netherlands and the Institute of Astronomy at the University of Edinburgh, examined how many galaxies there were in each era, they found that at an earlier stage in the development of the Universe the number of galaxies was significantly higher than now.

It appears that when the universe was only a few billion years old, the number of galaxies in a given volume of space was ten times greater than in a similar volume today. Most of these galaxies were low-mass systems, i.e. with masses similar to those of the galaxies currently surrounding the Milky Way.

Professor Conselis said: “This is very surprising because we know that over the 13.7 billion years of cosmic evolution since the Big Bang, the size of galaxies has increased through star formation and mergers with other galaxies. Establishing the fact of existence more galaxies in the past implies that significant evolution must have occurred to reduce their number through extensive mergers of systems. We miss the vast majority of galaxies because they are very faint and distant. The number of galaxies in the Universe is a fundamental question in astronomy, and it is amazing since 90% of galaxies in space are still unexplored. Who knows what interesting properties will we find when studying these galaxies with the next generation of telescopes?”

Translation of the article “Density distribution of galaxies at Z< 8 и ее последствия». Октябрь 2016. Ссылка на arXiv. Права на перевод принадлежат
Authors:
Christopher J. Conselice, School of Physics and Astronomy, University of Nottingham, Nottingham, England.
Aaron Wilkinson, Leiden Observatory Leiden University, The Netherlands
Kenneth Duncan, Royal Observatory, Institute of Astronomy, University of Edinburgh, Scotland

Annotation

The distribution of the density of galaxies in the Universe and, therefore, the total number of galaxies is a fundamental question in astrophysics that influences the resolution of many problems in the field of cosmology. However, before the publication of this article, there had never been a similar detailed study of this important indicator, as well as the definition of a clear algorithm for finding this number. To solve this problem, we used observed galactic stellar mass functions up to $z \sim 8$ to determine how the galaxy number density varies as a function of time and the mass limit. We have shown that the increase in the total density of galaxies ($\phi_T$) more massive than $M_* = 10^6M_\odot$ decreases as $\phi_T \sim t^(-1)$, where t is the age of the Universe . We further showed that this trend reverses and rather increases with time at higher mass limits $M_* > 10^7M_\odot$. Using $M_* = 10^6M_\odot$ as a lower limit, we justified that total quantity galaxies in the Universe up to $z = 8$ is equal to: $2.0 (+0.7\choose -0.6) \times (10^(12))$ or just $2.0 \times (10^(12))$ (two trillion!), t .e. nearly ten times larger than was seen in all Hubble Ultra-Deep Field-based sky surveys. We will discuss the implications of these results for understanding the process of galaxy evolution, and also compare our results with the latest models of galaxy formation. These results also indicate that cosmic background light in the optical and near-infrared regions likely originates from these unobserved faint galaxies. We will also show how these results address the question of why the night sky is dark, otherwise known as Olbers' paradox.

1. Introduction

When we discover the Universe and its properties, we always want to know absolute values. For example, astronomical interest is to calculate how many stars are in our Galaxy, how many planets surround these stars (Fressin et al. 2013), the overall density of the Universe (e.g. Fukugita & Peebles 2004), among other absolutes in the properties of the Universe . An approximate answer to one of these questions has been given here - this is the total density of the number of galaxies and, therefore, the total number of galaxies in the Universe.

This question is not just an idle curiosity, but is related to many other questions in cosmology and astronomy. The density distribution of galaxies is related to questions such as galaxy formation/evolution by number of systems formed, changing ratios of giant galaxies to dwarf galaxies, distant supernova and gamma-ray burst rates, the rate of star formation in the Universe, and how new galaxies are created/destroyed through mergers ( for example, Bridge et al. 2008; Conselice et al. 2014; The number of galaxies in the observable Universe also reveals information about the density of matter (substance and energy) of the Universe, background light on different lengths waves, as well as about understanding Olbers' paradox. However, there is still no good measurement of this fundamental quantity. Our ability to study the density distribution of galaxies using telescopes only arose with the advent of CCD cameras. Ultra-long-range exploration of distant galaxies began in the 1990s (e.g. Koo & Kron 1992; Steidel & Hamilton 1992; Djorgovski et al. 1995), and reached its current depth with Hubble Space Telescope projects, especially Hubble Deep Field (Williams et al. 1996). Subsequently, research was continued within the framework of the Hubble Deep Field South (Williams et al., 2000), the Great Observatories Origins Survey (Giavalisco et al. 2004), and the CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) survey in the infrared spectrum ( Grogin et al. 2011; Koekemoer et al. 2011), and culminated in the Hubble Ultra Deep Field (Beckwith et al. 2006), which remains the deepest optical and near-infrared survey of our Universe to date.
However, despite all these studies, it is still unclear how the overall number density of galaxies evolves over time. This interesting question, since we know that the star formation rate increases and then decreases with z< 8 (например, Bouwens et al. 2009; Duncan et al. 2014 ; Madau & Dickinson 2014), в то же время галактики становятся более крупными и менее своеобразными (например, Conselice et al. 2004; Papovich et al. 2005; Buitrago et al. 2013; Mortlock et al. 2013; Lee et al. 2013; Conselice 2014; Boada et al. 2015). Однако мы не знаем, как изменяется общее количество галактик во времени и как это связано с общим образованием популяции галактик в целом.
There are several reasons why it is not easy to determine the total number of galaxies based on the results of ultra-long-range surveys. One of them is that all ultra-long-range observations are incomplete. This is due to limitations in exposure time and depth, causing some galaxies to be detected more easily than others. The result of this is an incomplete picture even in the most long-range surveys, which can be corrected but which still leaves some uncertainty. However, the more important problem is that these observations do not reach the faintest galaxies, even though we know from theory that there should be many more faint galaxies beyond the boundaries of what we can currently observe.
It is also important to pay attention to what we mean by the total density of galaxies in the Universe. It is not a simple quantity that can be defined as the total density that currently exists, the total density that is observable in principle, and the total density that can be observed using modern technology, are different questions with different answers. There is also the problem that we are limited to the cosmological horizon above what we can observe, and therefore there are galaxies that we cannot see beyond it. Even the number of galaxies that exist in the Universe today, that is, if we could consider the entire Universe as it is at the present moment, rather than being limited by the transit time of light, is a complex question. Galaxies in the distant universe have evolved beyond what we can currently observe due to the finite nature of the speed of light and are likely to be similar to those in the visible universe. We address all of these issues in this paper, namely how the galaxy number density varies within the current observable universe up to z ~ 8.
For comparison purposes, in the Appendix to this work, we also analyze the number of galaxies that are visible to modern telescopes at all wavelengths and that we can currently observe. We then compare this data with measurements of the total number of galaxies that could potentially be observed in the Universe based on the measured mass functions. We will also discuss how these results reveal information about the evolution of the galaxy and the background radiation of the Universe. We also provide information about future studies and what fraction of galaxies they will observe.
This article is divided into several sections. §2 describes the data we use in this analysis, §3 describes the results of this work, including methods for analyzing galaxy stellar mass functions to obtain the total number of galaxies present in the Universe, §4 describes the implications of these results, and §5 presented summary articles. In this work we use standard cosmology: H 0 = 70 km s −1 Mpc −1 , and Ω m = 1 − Ω λ = 0.3.

2. Data

The data we use for this article comes from numerous sources and previous work. In the Appendix we describe how many galaxies we can currently observe in the Universe, based on the deepest observations available to date. Here in the main article, we explore the question of how many galaxies could potentially be detected in the Universe if deep imaging at all wavelengths was performed in all parts of the sky without any galactic interference or other distortions.
For much of this analysis and the results of this work, we use mass functions of galaxies from the observable Universe down to z ~ 8 to determine how the galaxy number density evolves with time and cosmological redshift. These mass and luminosity functions are now just beginning to be measured for large values redshift, and our primary data comes from mass functions calculated using high-precision infrared and optical surveys from Hubble and ground stations.
As presented in the next section, the mass functions we use are taken from Perez-Gonzalez et al. (2008), Kajisawa et al. (2009) , Fontana et al. ( , ), Caputi et al. (2011), Pozzetti et al. (2007), Mortlock et al. (2011), Tomczak et al. (2014), Muzzin et al. (2013) , and Mortlock et al. (2015) for galaxies at z< 3. Для самых high values redshift we use the mass functions published by Duncan et al. 2014, Grazian et al. (2015) , Caputi et al. (2011) and Song et al. (2015) We have ordered all these mass functions from each study above based on the Salpeter initial mass function for stars from $0.1M_\odot$ to $100M_\odot$. We used galaxy densities from these mass functions corresponding to their volumes, as opposed to physical volumes. This tells us how the number of galaxies varies within the same effective volume, while eliminating the effects of the Hubble expansion. These mass functions are shown in $(!! show1_MathJax ? "Close":"Figure 1" !$ до предела масс, взятых из ранее упомянутых исследований, которые также перечислены в Таблице 1.!}

Figure 1. The mass functions we use in this paper are plotted using the Schechter luminosity function. All these values ​​are taken from various studies mentioned in §2. Mass functions are presented depending on the values ​​of cosmological redshift, the left graph shows systems at z< 1, средний график показывает 1 < z < 3 и z >3 (far right). These mass functions are shown so that the solid colored lines are mass functions up to the limit of the corresponding data in which they are complete, and the dotted lines show our extrapolation to $M_* = 10^6 M_\odot$. The “flattest” graph of the mass function for 1< z < 3 взят из работы Muzzin et al. (2013) и для z >3 taken from Grazian et al. (2015)

3. Galaxy density distribution

3.1 Introduction and Cautions

The main method we use to determine the density of galaxies in the Universe is to integrate the number of galaxies through established mass functions for a given cosmological redshift. This requires extrapolating established stellar mass functions to reach a minimum limit on the mass of the galaxy population. There are many ways this can be done, which we will discuss below. One of the most important questions is the lower limit from which we should start counting the number of galaxies as a function of mass functions. Thanks to recent publications that provide stellar mass functions up to z ~ 8 (e.g. Duncan et al. 2014, Grazian et al. (2015), Song et al. (2015), we can now make this calculation for the first time. Another challenge is whether the Schechter luminosity function can be extrapolated below the limit of the data for which it was originally suitable is a question we explore in detail.
This complements the directly observed approach presented in the Appendix and is a more accurate way to measure the number of galaxies in the currently observable Universe if the mass functions are correctly measured and accurately parameterized. However, this method has potential pitfalls that need to be carefully considered and analyzed. This is not least due to the fact that measurements depend on much more factors than just photometry and object identification problems that are always present when simply measuring the number of galaxies. The situation here is related to other uncertainties associated with measuring stellar masses and redshifts. However, if we can account for these uncertainties, integration of the established mass functions can tell us about the densities of galaxies at a given redshift interval with some measured uncertainty.
We use this method to calculate the total density of galaxies within the currently observable Universe as a function of redshift. To do this, we do not directly integrate the observed mass functions, but use the parameterized form given by Schechter's (1976) function to determine the total galaxy number density as a function of redshift. The form of this function is given:

$\phi(M) = b\times\phi^\ast\ln(10)^(1+\alpha)$ $\times\exp[-10^(b(M-M^\ast))] . . . . .(1)$

where b = 1 for the mass function, b = 0.4 for the luminosity function, which will be written in terms of absolute values. For a mass function, $M^*$ is the typical mass in logarithmic units and determines where the mass function changes slope, and $M = \log(\frac(M_*)(M_\bigodot))$ is the mass in logarithmic units. Similarly for the luminosity function, $M^*$ corresponds to a typical value. For both functions, $\phi^*$ has a normalization, and $\alpha$ determines the slope for fainter and less massive galaxies. Our method uses published values ​​of $\phi^*$, $\alpha$ and $M^*$ to calculate the integrated number of galaxies at different redshifts.
We use the Schechter luminosity function as a tool for calculating the overall density since it generally describes well the distribution of galaxy masses at all redshifts in the ranges we study. However, we do not know at what lower mass limit it remains valid, which is one uncertainty in our analysis. Next we discuss the use of $M_*>10^6 M_\bigodot$ as a limit and the rationale for using it as our lower limit. We also discuss how our results would have changed if we had used a different value for the lower mass limit.
Since we are integrating mass functions across the entire history of the universe, we must use many surveys to account for the number of galaxies at different redshifts. Different redshift ranges require studies performed at different wavelengths, and different studies sometimes find different meanings Schechter parameters. In this work, we attempt to comprehensively study mass functions that, especially at low redshift, can produce widely divergent density values ​​and evolutionary shapes. We get almost the same results when we use Schechter's double luminosity function to calculate the mass function at low values ​​of cosmological redshift, as when we use the power-law to calculate the mass function at high values cosmological redshift.

1. page 170-183 Lectures on stellar astronomy. Loktin A.V., Marsakov V.A., 2009.
2. The same lectures on stellar astronomy in HTML format on astronet.ru
3. I.V. Chilingaryan, Classification of objects by energy distribution in the spectrum
4. Knowledge Base for Extragalactic Astronomy and Cosmology, section of the NASA extragalactic database (NASA/IPAC Extragalactic Database, NED) - the largest repository of images, photometry and spectra of galaxies obtained from sky surveys in the microwave, infrared, optical and ultraviolet (UV) ranges.
5.
6.
7. Cosmological function of galactic masses
8. Properties and luminosity functions of extremely dim galaxies. Michael R. Blanton. In this work, the double Schechter luminosity function was presented. Section 4.2 on page 10.
9. Left and right truncated Schechter brightness function for quasars. Lorenzo Zaninetti. May 29, 2017. A Left and Right Truncated Schechter Luminosity Function for Quasars

In the cosmological redshift range z ~ 0 - 3 we use the established values ​​of the mass functions and their errors from the work carried out by Perez-Gonzalez et al. (2008), Kajisawa et al. (2009) , Fontana et al. ( , ), Caputi et al. (2011), Pozzetti et al. (2007), Mortlock et al. (2011) , and Mortlock et al. (2015) These stellar mass functions are determined by measuring the stellar masses of objects using the SED fitting (spectral energy distributions fitting) procedure. Despite the large scatter in the various measurements of the parameters of the Schechter function, we use all this information to take into account various methods measurements and models used, as well as cosmic variance. These mass functions, parameterized by the Schechter function, are shown in Figure 1. We also convert those studies that use the initial Chabrier mass functions (Chabrier IMF) - Pozzetti et al. (2007), Duncan et al. (2014), Mortlock et al. (2015) and Muzzin et al. (2013) which uses the initial Kroupa mass functions (Kroupa IMF) into the initial Salpeter mass functions (Salpeter IMF). The list of values ​​we use in our analysis is shown in $(!! show2_MathJax ? "Close": "Table 1" !$!} Note- This table lists the parameters of the given Schechter functions that we use to perform our calculations. They are all normalized to produce comparable values ​​of the initial Salpeter mass functions (Salpeter IMF), although Pozzetti et al. (2007), Duncan et al. (2014) and Mortlock et al. (2015) used initial Chabrier mass functions (Chabrier IMF) in their works, and Muzzin et al. (2013) used Kroupa initial mass functions (Kroupa IMF).

$(!! show2_MathJax ? "Close": "Table 1" !$ .!}

Note that we consider only those mass functions where the parameter α changes are permitted in applicable Schechter models. If the result of the mass function is obtained from a fixed value α , then this leads to a distortion of the number of galaxies, since this value has significant influence by the number of faint galaxies with low mass in a given volume (§3.2). Therefore, we exclude mass function results from studies using α CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey), as well as from HUDF (Hubble Ultra Deep Field).
For high values ​​of cosmological redshift, mass functions are a relatively new parameter, so in order to obtain consistent and consistent data, we also analyzed the obtained luminosity functions in the ultraviolet range, mainly at 1500˚A. To do this, we used data published in Bouwens et al. (2011), McLure et al. (2009), McLure et al. (2013), Bouwens et al. (2015) and Finkelstein et al. (2015). McLure et al. (2013) and Bouwens et al. (2015) analyze data from the most distant Hubble Space Telescope surveys, including the 2012 Hubble Ultra Deep Field HUDF12 survey, which examined galaxies at the highest cosmological redshifts at $z = 8$ and $z = 9$.
To convert the stellar mass limit to the UV magnitude limit, we use the ratios between these two quantities calculated in Duncan et al. (2014). Duncan et al. (2014) modeled the linear relationship between mass and light in the UV and how it develops under different meanings cosmological redshift. We use these to determine the UV magnitude limit corresponding to our standard mass limit $M_* = 10^6M_\odot$. Thus we can relate our stellar mass limit to the absolute magnitude limit in the UV. We do not use these values ​​in our calculations, but use these luminosity functions to check the consistency of our results obtained from the stellar mass functions. We find high consistency with stellar mass functions, including using different variations of the stellar mass-to-UV luminosity conversion (e.g., Duncan et al. 2014; Song et al. 2015). Moreover, all of our mass functions for high values ​​of cosmological redshift are more or less consistent, with the exception of Grazian et al. (2015), the results of which lead to a slightly lower value of $\phi_T$.

5. Brief summary of the study

We investigated the fundamental question of the density distribution of galaxies in the Universe. We analyze this problem in several ways and discuss implications for galactic evolution and cosmology. We use recently derived mass functions for galaxies up to z ∼ 8 to determine the density distribution of galaxies in the Universe. Our main conclusion is that the number density of galaxies decreases over time as $\phi_T(z) \sim t^(-1)$, where t is the age of the Universe.
We next discuss the implications of this increase in galaxy density with hindsight for a variety of key astrophysical questions. By integrating the density of the number of galaxies, we calculated number of galaxies in the Universe, the value of which was $2.0 (+0.7\choose -0.6) \times (10^(12))$ for $z = 8$, which in principle can be observed. This is approximately ten times more than with direct calculation. This means that we have yet to discover a large population of faint, distant galaxies.

In terms of the astrophysical evolution of galaxies, we show that the increase in the integrable mass functions of all galaxies with redshift is explained by the merger model. We show that simple model merger is capable of reproducing a decrease in the number of galaxies with a merger time scale of $\tau=1.29 ± 0.35 Gyr$. The resulting merger rate at z = 1.5 is R ∼ 0.05 mergers $Gyr^(−1) Mpc^(−3)$, close to the value obtained from structural and pairwise analysis. Most of these convergent galaxies are lower-mass systems, increasing in galaxy number density over time from the lower limit to higher masses when calculating the total density.

Finally, we discuss the implications of our findings for future research.

In the future, as mass functions become better known through better SED modeling and deeper and broader data from JWST and Euclid/LSST, we will be able to more accurately measure the overall galaxy number density and thus obtain a better measure of this fundamental quantity.

Those who have a little idea about the Universe are well aware that the cosmos is constantly in motion. The universe is expanding every second, becoming larger and larger. Another thing is that on the scale of human perception of the world, it is quite difficult to understand the size of what is happening and imagine the structure of the Universe. In addition to our galaxy, in which the Sun is located and we are located, there are dozens, hundreds of other galaxies. Nobody knows the exact number of distant worlds. How many galaxies are in the Universe can only be known approximately by creating a mathematical model of the cosmos.

Therefore, given the size of the Universe, we can easily assume that tens or a hundred billion light years from Earth, there are worlds similar to ours.

Space and worlds that surround us

Our galaxy, which received the beautiful name “Milky Way,” was, according to many scientists, the center of the universe just a few centuries ago. In fact, it turned out that this was only part of the universe, and there are other galaxies various types and sizes, large and small, some further, others closer.

In space, all objects are closely interconnected, moving in in a certain order and occupy the allotted space. Planets known to us, well-known stars, black holes and our own solar system located in the Milky Way galaxy. The name is not accidental. Even ancient astronomers, observing the night sky, compared the space around us to a milk track, where thousands of stars look like drops of milk. The Milky Way Galaxy, the celestial galactic objects in our field of vision, make up the nearby cosmos. What may be beyond the visibility of telescopes became known only in the 20th century.

Subsequent discoveries, which expanded our cosmos to the size of the Metagalaxy, led scientists to the theory of the Big Bang. A grandiose cataclysm occurred almost 15 billion years ago and served as an impetus for the beginning of the processes of formation of the Universe. One stage of the substance was replaced by another. From dense clouds of hydrogen and helium, the first beginnings of the Universe began to form - protogalaxies consisting of stars. All this happened in the distant past. The light of many celestial bodies, which we can observe in the strongest telescopes, is only a farewell greeting. Millions of stars, if not billions, dotted our sky, located a billion light years from Earth, and have long ceased to exist.

Map of the Universe: nearest and farthest neighbors

Our Solar System and other cosmic bodies observed from Earth are relatively young structural formations and our closest neighbors in the vast Universe. For a long time, scientists believed that the dwarf galaxy closest to the Milky Way was the Large Magellanic Cloud, located only 50 kiloparsecs. Only very recently have the real neighbors of our galaxy become known. In the constellation Sagittarius and in the constellation Canis Major small dwarf galaxies are located, the mass of which is 200-300 times less than the mass of the Milky Way, and the distance to them is just over 30-40 thousand light years.

These are one of the smallest universal objects. In such galaxies the number of stars is relatively small (on the order of several billion). As a rule, dwarf galaxies gradually merge or are absorbed over large formations. The speed of the expanding Universe, which is 20-25 km/s, will unwittingly lead neighboring galaxies to a collision. When this will happen and how it will turn out, we can only guess. The collision of galaxies is happening all this time, and due to the transience of our existence, it is not possible to observe what is happening.

Andromeda, two to three times the size of our galaxy, is one of the closest galaxies to us. It continues to be one of the most popular among astronomers and astrophysicists and is located just 2.52 million light years from Earth. Like our galaxy, Andromeda is a member of the Local Group of galaxies. The size of this giant cosmic stadium is three million light years across, and the number of galaxies present in it is about 500. However, even such a giant as Andromeda looks short in comparison with the galaxy IC 1101.

This largest spiral galaxy in the Universe is located more than a hundred million light years away and has a diameter of more than 6 million light years. Despite containing 100 trillion stars, the galaxy is primarily composed of dark matter.

Astrophysical parameters and types of galaxies

The first space explorations carried out at the beginning of the 20th century provided plenty of food for thought. The cosmic nebulae discovered through the telescope lens, of which over time were counted more than a thousand, were the most interesting objects in the Universe. Long time these bright spots in the night sky were considered to be gas accumulations that were part of the structure of our galaxy. Edwin Hubble in 1924 was able to measure the distance to a cluster of stars and nebulae and made a sensational discovery: these nebulae are nothing more than distant spiral galaxies, independently wandering across the scale of the Universe.

An American astronomer was the first to suggest that our Universe is made up of many galaxies. Space exploration in the last quarter of the 20th century, observations made using spacecraft and technology, including the famous Hubble telescope, confirmed these assumptions. Space is limitless and our Milky Way is far from the largest galaxy in the Universe and, moreover, is not its center.

Only with the advent of powerful technical means of observation did the Universe begin to take on clear outlines. Scientists are faced with the fact that even such huge formations as galaxies can differ in their structure and structure, shape and size.

Through the efforts of Edwin Hubble, the world received a systematic classification of galaxies, dividing them into three types:

• spiral;
• elliptical;
• incorrect.

Elliptical and spiral galaxies are the most common types. These include our Milky Way galaxy, as well as our neighboring Andromeda galaxy and many other galaxies in the Universe.

Elliptical galaxies have the shape of an ellipse and are elongated in one direction. These objects lack sleeves and often change their shape. These objects also differ from each other in size. Unlike spiral galaxies, these cosmic monsters do not have a clearly defined center. There is no core in such structures.

According to the classification, such galaxies are designated by the Latin letter E. All currently known elliptical galaxies are divided into subgroups E0-E7. The distribution into subgroups is carried out depending on the configuration: from almost circular galaxies (E0, E1 and E2) to highly elongated objects with indices E6 and E7. Among the elliptical galaxies there are dwarfs and true giants with diameters of millions of light years.

There are two subtypes of spiral galaxies:

• galaxies presented in the form of a crossed spiral;
• normal spirals.

The first subtype stands out the following features. In shape, such galaxies resemble a regular spiral, but in the center of such a spiral galaxy there is a bridge (bar), giving rise to arms. Such bridges in a galaxy are usually a consequence of physical centrifugal processes that divide the galactic core into two parts. There are galaxies with two nuclei, the tandem of which makes up the central disk. When the nuclei meet, the bridge disappears and the galaxy becomes normal, with one center. There is also a bridge in our Milky Way galaxy, in one of the arms of which our Solar system is located. From the Sun to the center of the galaxy, the path, according to modern estimates, is 27 thousand light years. The thickness of the Orion Cygnus arm, in which our Sun and our planet reside, is 700 thousand light years.

In accordance with the classification, spiral galaxies are designated by the Latin letters Sb. Depending on the subgroup, there are other designations for spiral galaxies: Dba, Sba and Sbc. The difference between the subgroups is determined by the length of the bar, its shape and the configuration of the sleeves.

Spiral galaxies can range in size from 20,000 light-years to 100,000 light-years in diameter. Our Milky Way galaxy is in the “golden mean”, its size gravitating toward medium-sized galaxies.

The rarest type is irregular galaxies. These universal objects are large clusters of stars and nebulae that do not have a clear shape or structure. In accordance with the classification, they received the indices Im and IO. As a rule, structures of the first type do not have a disk or it is weakly expressed. Often such galaxies can be seen to have similar arms. Galaxies with IO indices are a chaotic collection of stars, clouds of gas and dark matter. Prominent representatives of this group of galaxies are the Large and Small Magellanic Clouds.

All galaxies: regular and irregular, elliptical and spiral, consist of trillions of stars. The space between stars and their planetary systems is filled with dark matter or clouds of cosmic gas and dust particles. In the spaces between these voids there are black holes, large and small, which disturb the idyll of cosmic tranquility.

Based on the existing classification and research results, we can answer with some confidence the question of how many galaxies there are in the Universe and what type they are. There are more spiral galaxies in the Universe. They constitute more than 55% of the total number of all universal objects. There are half as many elliptical galaxies - only 22% of the total number. There are only 5% of irregular galaxies similar to the Large and Small Magellanic Clouds in the Universe. Some galaxies are neighboring us and are in the field of view of the most powerful telescopes. Others are in the farthest space, where dark matter predominates and the blackness of endless space is more visible in the lens.

Galaxies up close

All galaxies belong to certain groups that are modern science are usually called clusters. The Milky Way is part of one of these clusters, which contains up to 40 more or less known galaxies. The cluster itself is part of a supercluster, a larger group of galaxies. Earth, together with the Sun and Milky Way part of the Virgo supercluster. This is our actual cosmic address. Together with our galaxy, there are more than two thousand other galaxies in the Virgo cluster, elliptical, spiral and irregular.

The map of the Universe, which astronomers rely on today, gives an idea of ​​what the Universe looks like, what its shape and structure are. All clusters gather around voids or bubbles of dark matter. It is possible that dark matter and bubbles are also filled with some objects. Perhaps this is antimatter, which, contrary to the laws of physics, forms similar structures in a different coordinate system.

Current and future state of galaxies

Scientists believe that it is impossible to create a general portrait of the Universe. We have visual and mathematical data about the cosmos that is within our understanding. The real scale of the Universe is impossible to imagine. What we see through a telescope is starlight that has been coming to us for billions of years. Perhaps the real picture today is completely different. As a result of cosmic cataclysms, the most beautiful galaxies in the Universe could already turn into empty and ugly clouds of cosmic dust and dark matter.

It cannot be ruled out that in the distant future, our galaxy will collide with a larger neighbor in the Universe or swallow a dwarf galaxy existing next door. What the consequences of such universal changes will be remains to be seen. Despite the fact that the convergence of galaxies occurs at the speed of light, earthlings are unlikely to witness a universal catastrophe. Mathematicians have calculated that just over three billion Earth years are left before the fatal collision. Whether life will exist on our planet at that time is a question.

Other forces can also interfere with the existence of stars, clusters and galaxies. Black holes, which are still known to man, are capable of swallowing a star. Where is the guarantee that such monsters of enormous size, hiding in dark matter and in the voids of space, will not be able to swallow the galaxy entirely?

Our Galaxy is just one of many, and no one knows how many there are in total. More than a billion have already been opened. Each of them contains many millions of stars. The most distant ones already known are located hundreds of millions of light years from earthlings, therefore, by studying them, we are peering into the most distant past. All galaxies are moving away from us and from each other, it seems that the Universe is still expanding and that scientists have not in vain come to the conclusion about big bang like its original.

In science, the word “Universe” has a special meaning. It refers to the largest volume of space, together with all the matter and radiation contained in it, that can affect us in any way. Earth scientists can observe only one Universe, but no one denies the existence of others, just because our (far from perfect) instruments cannot detect them.

The Sun is one of billions of stars. There are stars much larger than the Sun (giants), and there are also smaller ones (dwarfs); the Sun is closer in its properties to dwarf stars than to giants. There are hot stars (they have a white-bluish color and a temperature of over 10,000 degrees on the surface, and some up to one hundred thousand degrees), there are cold stars (they are red, the surface temperature is about 3 thousand degrees). The stars are very far from us; it takes 4 years to fly to the nearest star at the speed of light (300,000 km/s), while you can fly to the Sun at that speed in 8 minutes.

Some stars form pairs, triplets (double, triple stars) and groups (open star clusters). There are also globular star clusters; they contain tens and hundreds of stars and are spherical in shape, with a concentration of stars towards the center. Open clusters contain young stars, while globular clusters are very ancient and contain old stars. There are planets near some stars. Whether there is life on them, much less civilization, has not yet been established. But they may well exist.

Stars form giant systems - Galaxies. The galaxy has a center (core), flat spiral arms in which most stars are concentrated, and a periphery, a voluminous cloud of rare stars. Stars move in space, they are born, live and die. Stars like the Sun live for about 10-15 billion years, and the Sun is a middle-aged star. So he still has a long way to go. Massive and hot stars “burn out” faster, and can explode as “supernovae” stars, leaving behind very small and super-dense formations - white dwarfs, neutron stars or “black holes”, in which the density of matter is so high that no particles can overcome the forces of gravity and escape from there. In addition to stars, the Galaxy contains clouds of cosmic dust and gas that form nebulae. The plane of the Galaxy, where the maximum number of stars, gas and dust is visible in the sky as the Milky Way.

There are many more millions of Galaxies, consisting of a huge number of stars. For example, the Magellanic Clouds, the Andromeda Nebula are other Galaxies. They are located at unimaginably large distances from us.

In our sky, the stars seem motionless, since they are very far from us, and their movement becomes noticeable only after tens and hundreds of thousands of years have passed.

Useful information

Galaxy– a gravitationally bound system of stars, interstellar gas, dust and dark matter. All objects within galaxies participate in motion relative to a common center of mass. The word "galaxy" comes from the Greek name for our Galaxy. Core- an extremely small region in the center of the galaxy. When it comes to galactic nuclei, we most often talk about active galactic nuclei, where the processes cannot be explained by the properties of the stars concentrated in them. The photographs of galaxies show that there are few truly lonely galaxies. About 95% of galaxies form galaxy groups. If the average distance between galaxies is no more than an order of magnitude larger than their diameter, then the tidal influences of the galaxies become significant. These influences each component of the galaxy in different conditions responds differently. Milky Way, also called simply Galaxy, is a large barred spiral galaxy with a diameter of about 30 kiloparsecs and a thickness of 1000 light

> How many galaxies are there in the Universe

How many galaxies exist in the observable universe: research, calculation on the size, mass and volume of the Universe, Hubble review, future role of James Webb.

Science is interesting because it does not get hung up on facts, but constantly revises them, creates new theories and looks for better ways to solve problems. Sometimes in this process she manages to find aspects that were unknown before. That's why it's so interesting to know how many galaxies are in the universe?

Distant galaxies captured by the Hubble telescope

How many galaxies are there in the Universe?

So, the numbers are constantly changing, as are various facts, such as the total number of galaxies in space. How many galaxies are there in total? The observable Universe spans 13.8 billion light years in all directions. That is, the most distant light left its point 13.8 billion years ago. But let's not forget about the expansion, which increases this distance to 46 billion light years. That is, what was visible or ultraviolet radiation in the past has shifted to infrared and microwave radiation at the very edge of the accessible Universe.

We know the universal volume and mass (3.3 x 10 54 kg, including ordinary matter and dark matter). In addition, the relationship between regular matter and dark matter is open to us, so we can calculate the total amount of regular mass.

Once upon a time, astronomers divided total weight to the number of observed galaxies in Hubble and counted 200 billion.

Now scientists have used a new technique for recalculation. They used photos from the Hubble Telescope and looked into an empty part of the sky to count the number of galaxies. It's about about the Hubble Deep Fiel, thanks to which it was possible to obtain an incredibly amazing picture. You can explore this Hubble image below.

From this photograph they created a three-dimensional map showing the size and location of the galaxy. To do this, we used knowledge about the nearest galaxies (for example, 50 neighbors). Having learned which of the large galaxies were larger, they brought in smaller and fainter ones that were not shown in the image.

That is, if the distant Universe resembles the known one, then the galactic structures are also repeated. This does not mean that the Universe is much larger than expected or that there are more stars in it. It just accommodates more galaxies with fewer stars. There are large main galaxies, followed by smaller ones and so on to dwarf ones.

But visible galaxies are just the tip of the iceberg. For each imprinted one, there are 9 more weaker and unnoticeable ones. Of course, it won't be long before we can capture them too. In 2018, everyone is expecting the appearance of the powerful James Webb telescope, whose area is 25 m2 (Hubble's is 4.5 m2). Those faint spots that now seem like stars to us will become clear and understandable objects for James Webb.

If galaxies are everywhere, then why can't we see them with the naked eye? It's all about Olbers' paradox, described in 1700. The point is, no matter where you look, you will always hit a star. This means that the space should be bright, but it is dark. How so? The same paradox applies to galaxies that for some reason you can't see.

So, galaxies are everywhere. But they are red-shifted from the visible spectrum to the infrared, so the retina simply does not perceive them. If you look at everything in microwaves, then the space will glow.

According to calculations, there are 10 times more galaxies in the Universe than previously assumed - 2 trillion. But there is no need to multiply the number of stars or mass, since these numbers remain the same.

Now you know how many galaxies there are. But what will happen with the appearance of James Webb? Will there be more galaxies? Or some new one will open interesting information? The universe hides many secrets, so you can expect anything.