There are 10-20 times more galaxies in the observable Universe than previously thought
- Popular Science,
- Astronomy
Image taken by the Hubble telescope (Source: NASA/ESA)
The Hubble telescope helped astronomers make an interesting discovery that could have an impact on the entire future of astronomical science. As it turns out, there are 10-20 times more galaxies in the observable Universe than scientists previously thought. This conclusion was made after analyzing a large number of photographs of deep space sent to Earth by the Hubble telescope. In the course of their work, scientists studied other images taken by astronomers at observatories on Earth.
The conclusion that there are more galaxies in the Universe than people previously thought was made by scientists from the University of Nottingham, led by Christopher Conselice. Most of these galaxies (about 90%) are relatively small and faint, so they are not easy to spot. According to scientists, such galaxies are similar to satellites of the Milky Way. "We missed the vast majority of galaxies because they are too dim and very far away," says Professor Conselis.
“The actual number of galaxies in the Universe is one of the fundamental questions in astronomy, and the fact that more than 90% of galaxies have not yet been studied is frightening. Who knows what interesting properties of these objects we will discover when we begin to study galaxies using new generation telescopes?” the scientist asks.
The video posted above is a speech by Carl Sagan at a school, where he explains to schoolchildren the immensity of the Universe. “In total, there are about 100 billion other galaxies here (in the observable Universe), each of which has about 100 billion stars. Imagine how many stars, planets and life forms there could be in this vast and amazing Universe,” says Sagan.
The Hubble Orbital Telescope helps experts study the visible part of the Universe. It has been operating for about 20 years, and during all this time, Earth scientists have received a huge amount of vital information, including data on the number of galaxies in the Universe. Previously, it was believed that there were 100-200 billion galaxies in the observable Universe. But it seems that this number can be safely multiplied by 10 or even 20.
Count galaxies in the Universe - not an easy task. Firstly, as mentioned above, we do not see most of such objects due to their dimness and small size. The problem, in fact, is not the galaxies, but that the equipment used by humans to observe them is imperfect. Secondly, so far we are able to study only a small fraction of the space that is available for observation. Images of the Hubble Deep Field are only a millionth of what a human could observe. Here's an animation that shows how tiny the region of space that Hubble is observing is.
Scientists from the University of Nottingham made their conclusions after working on analyzing Hubble images for 15 years. The work was started by graduate student Aaron Wilkinson, who received a large grant for a galaxy counting project. The data he obtained formed the basis for a much larger study carried out by Professor Conselis together with colleagues from the University of Edinburgh and Leiden. They used data from Wilkinson, images taken by Hubble, and images from other observatories around the world. Mathematical analysis has shown that the “population” density of the Universe is higher than previously thought.
In addition, scientists have tried to count the number of galaxies in the ancient Universe, billions of years ago. In their opinion, in the past there were even more galaxies than now - at least ten times.
“We know that since their appearance, galaxies have evolved, merged with other objects, and increased in size. The fact that there were more galaxies in the past indicates a very active evolutionary process that led to the merger of many systems,” the scientists said in a statement. This evolutionary process is the merging of smaller galaxies into larger objects. The new data will help scientists form a more accurate model of the evolution of the Universe than ever before.
Scientists, talking about the large number of galaxies in the Universe, remembered Olbers' paradox. This is one of the paradoxes of pre-relativistic cosmology, which consists in the fact that in a stationary Universe, uniformly filled with stars (as was then believed), the brightness of the sky (including the night sky) should be approximately equal to the brightness of the solar disk. In theory, in the cosmological model of the Big Bang, this paradox is completely resolved by taking into account the finiteness of the speed of light and the finiteness of the age of the Universe.
Why is our sky dark at night and not glowing? We could observe approximately this picture if the Universe were static (
The outer space around us is not just lonely stars, planets, asteroids and comets sparkling in the night sky. Space is a huge system where everything is in close interaction with each other. Planets are grouped around stars, which in turn gather into a cluster or nebula. These formations can be represented by single luminaries, or they can number hundreds, thousands of stars, forming larger-scale universal formations - galaxies. Our star country, the Milky Way galaxy, is only a small part of the vast Universe, in which other galaxies also exist.
The universe is constantly in motion. Any object in space is part of a particular galaxy. Following the stars, galaxies also move, each of which has its own size, a specific place in the dense universal order and its own trajectory of movement.
What is the real structure of the Universe?
For a long time, humanity's scientific ideas about space were built around the planets of the solar system, stars and black holes that inhabit our stellar home - the Milky Way galaxy. Any other galactic object detected in space using telescopes was automatically included in the structure of our galactic space. Accordingly, there was no idea that the Milky Way is not the only universal formation.
Limited technical capabilities did not allow us to look further, beyond the Milky Way, where, according to conventional wisdom, the void begins. Only in 1920, the American astrophysicist Edwin Hubble was able to find evidence that the Universe is much larger and, along with our galaxy, there are other, large and small galaxies in this huge and endless world. There is no real boundary of the Universe. Some objects are located quite close to us, only a few million light years from Earth. Others, on the contrary, are located in the far corner of the Universe, being out of sight.
Almost a hundred years have passed and the number of galaxies today is already estimated at hundreds of thousands. Against this background, our Milky Way looks not at all so huge, if not quite tiny. Today, galaxies have already been discovered whose sizes are difficult even for mathematical analysis. For example, the largest galaxy in the Universe, IC 1101, has a diameter of 6 million light years and consists of more than 100 trillion stars. This galactic monster is located more than a billion light years from our planet.
The structure of such a huge formation, which is the Universe on a global scale, is represented by emptiness and interstellar formations - filaments. The latter, in turn, are divided into superclusters, intergalactic clusters and galactic groups. The smallest link of this huge mechanism is the galaxy, represented by numerous star clusters - arms and gas nebulae. It is assumed that the Universe is constantly expanding, thereby causing galaxies to move at tremendous speed in the direction from the center of the Universe to the periphery.
If we imagine that we are observing space from our Milky Way galaxy, which is supposedly located at the center of the universe, then a large-scale model of the structure of the Universe will look like this.
Dark matter - aka emptiness, superclusters, clusters of galaxies and nebulae - are all consequences of the Big Bang, which marked the beginning of the formation of the Universe. Over the course of a billion years, its structure undergoes a transformation, the shape of galaxies changes, as some stars disappear, swallowed up by black holes, while others, on the contrary, transform into supernovae, becoming new galactic objects. Billions of years ago, the arrangement of galaxies was completely different from what we see now. One way or another, against the background of constant astrophysical processes occurring in space, we can draw certain conclusions that our Universe does not have a constant structure. All space objects are in constant motion, changing their position, size and age.
To date, thanks to the Hubble telescope, it has been possible to detect the location of the galaxies closest to us, determine their sizes and determine the location relative to our world. Through the efforts of astronomers, mathematicians and astrophysicists, a map of the Universe has been compiled. Single galaxies have been identified, but for the most part, such large universal objects are grouped in groups of several dozen in a group. The average size of galaxies in such a group is 1-3 million light years. The group to which our Milky Way belongs contains 40 galaxies. In addition to groups, there are a huge number of dwarf galaxies in intergalactic space. As a rule, such formations are satellites of larger galaxies, such as our Milky Way, Triangulum or Andromeda.
Until recently, the dwarf galaxy “Segue 2”, located 35 kiloparsecs from our star, was considered the smallest galaxy in the Universe. However, in 2018, Japanese astrophysicists discovered an even smaller galaxy - Virgo I, which is a satellite of the Milky Way and is located at a distance of 280 thousand light years from Earth. However, scientists believe that this is not the limit. There is a high probability that galaxies of much more modest sizes exist.
After groups of galaxies come clusters, regions of outer space in which there are up to hundreds of galaxies various types, shapes and sizes. The clusters are colossal in size. As a rule, the diameter of such a universal formation is several megaparsecs.
A distinctive feature of the structure of the Universe is its weak variability. Despite the enormous speeds at which galaxies move in the Universe, they all remain part of one cluster. Here the principle of preserving the position of particles in space, which are affected by dark matter formed as a result of the big bang, operates. It is assumed that, under the influence of these voids filled with dark matter, clusters and groups of galaxies continue to move in the same direction for billions of years, neighboring each other.
The largest formations in the Universe are galactic superclusters, which unite groups of galaxies. The most famous supercluster is the Great Clown Wall, an object of universal scale, stretching over 500 million light years. The thickness of this supercluster is 15 million light years.
Under current conditions, spacecraft and technology do not allow us to examine the Universe to its full depth. We can only detect superclusters, clusters and groups. In addition, our space has giant voids, bubbles of dark matter.
Steps towards exploring the Universe
A modern map of the Universe allows us not only to determine our location in space. Today, thanks to the availability of powerful radio telescopes and the technical capabilities of the Hubble telescope, man has been able not only to approximately calculate the number of galaxies in the Universe, but also to determine their types and varieties. Back in 1845, British astronomer William Parsons, using a telescope to study clouds of gas, was able to reveal the spiral nature of the structure of galactic objects, focusing on the fact that in different areas the brightness of star clusters can be greater or lesser.
A hundred years ago, the Milky Way was considered the only known galaxy, although the presence of other intergalactic objects was mathematically proven. Our space yard got its name back in ancient times. Ancient astronomers, looking at the myriads of stars in the night sky, noticed characteristic feature their locations. The main cluster of stars was concentrated along an imaginary line, reminiscent of a path of splashed milk. Milky Way Galaxy, celestial bodies Another well-known galaxy, Andromeda, are the very first universal objects from which the study of outer space began.
Our Milky Way has the complete set of all galactic objects that a normal galaxy should have. There are clusters and groups of stars here, the total number of which is approximately 250-400 billion. There are clouds of gas in our galaxy that form arms, there are black holes and solar systems similar to ours.
At the same time, the Milky Way, like Andromeda and Triangulum, are only a small part of the Universe, part of the local group of the Virgo supercluster. Our galaxy has the shape of a spiral, where the bulk of star clusters, gas clouds and other space objects move around the center. The diameter of the outer spiral is 100 thousand light years. The Milky Way is not a large galaxy by cosmic standards, its mass is 4.8 x 1011 Mʘ. Our Sun is also located in one of the arms of Orion Cygnus. The distance from our star to the center of the Milky Way is 26,000 ± 1,400 light years. years.
For a long time, it was believed that the Andromeda nebula, one of the most popular among astronomers, is part of our galaxy. Subsequent studies of this part of space provided irrefutable evidence that Andromeda is an independent galaxy, and much larger than the Milky Way. Images obtained using telescopes showed that Andromeda has its own core. There are also clusters of stars here and there are nebulae of their own, moving in a spiral. Each time, astronomers tried to look deeper and deeper into the Universe, exploring vast areas of outer space. The number of stars in this universal giant is estimated at 1 trillion.
Through the efforts of Edwin Hubble, it was possible to establish the approximate distance to Andromeda, which could not possibly be part of our galaxy. This was the first galaxy to be studied so closely. Subsequent years brought new discoveries in the field of exploration of intergalactic space. The part of the Milky Way galaxy in which our solar system is located has been studied more thoroughly. Since the middle of the 20th century, it has become clear that in addition to our Milky Way and the well-known Andromeda, there are a huge number of other formations on a universal scale in space. However, order required the ordering of outer space. While stars, planets and other cosmic objects could be classified, the situation with galaxies was more complicated. This was due to the enormous size of the areas of outer space under study, which were not only difficult to study visually, but also to evaluate at the level of human nature.
Types of galaxies in accordance with the accepted classification
Hubble was the first to take such a step, making an attempt in 1962 to logically classify the galaxies known at that time. Classification was carried out based on the shape of the objects under study. As a result, Hubble managed to arrange all the galaxies into four groups:
- the most common type are spiral galaxies;
- followed by elliptical spiral galaxies;
- with galaxy bar (bar);
- irregular galaxies.
It should be noted that our Milky Way is a typical spiral galaxy, but there is one “but”. Recently, the presence of a bridge - a bar, which is present in the central part of the formation - has been revealed. In other words, our galaxy does not originate from the galactic core, but flows out of the bridge.
Traditionally, a spiral galaxy looks like a flat, spiral-shaped disk, which necessarily contains a bright center—the galactic core. There are most of these galaxies in the Universe and they are designated Latin letter S. In addition, there is a division of spiral galaxies into four subgroups - So, Sa, Sb and Sc. Small letters indicate the presence of a bright core, the absence of arms, or, conversely, the presence of dense arms covering the central part of the galaxy. In such arms there are clusters of stars, groups of stars that include our Solar System, and other space objects.
The main feature of this type is the slow rotation around the center. The Milky Way completes a revolution around its center every 250 million years. The spirals located closer to the center consist mainly of clusters of old stars. The center of our galaxy is a black hole, around which all the main movement occurs. The length of the path, according to modern estimates, is 1.5-25 thousand light years towards the center. During their existence, spiral galaxies can merge with other smaller universal formations. Evidence of such collisions in earlier periods is the presence of halos of stars and halos of clusters. A similar theory underlies the theory of the formation of spiral galaxies, which were the result of the collision of two galaxies located in the neighborhood. The collision could not pass without a trace, giving a general rotational impulse to the new formation. Next to the spiral galaxy there is a dwarf galaxy, one, two or several at once, which are satellites of a larger formation.
Close in structure and composition to spiral galaxies are elliptical spiral galaxies. These are huge, the largest universal objects, including a large number of superclusters, clusters and groups of stars. In the largest galaxies, the number of stars exceeds tens of trillions. The main difference between such formations is their highly extended shape in space. The spirals are arranged in the shape of an ellipse. Elliptical spiral galaxy M87 is one of the largest in the Universe.
Barred galaxies are much less common. They account for approximately half of all spiral galaxies. Unlike spiral formations, in such galaxies the origin comes from a bridge, called a bar, flowing from the two brightest stars located in the center. A striking example Such formations are our Milky Way and the Large Magellanic Cloud galaxy. Previously, this formation was classified as irregular galaxies. The appearance of the jumper is currently one of the main areas of research in modern astrophysics. According to one version, a nearby black hole sucks and absorbs gas from neighboring stars.
The most beautiful galaxies in the Universe are the types of spiral and irregular galaxies. One of the most beautiful is the Whirlpool Galaxy, located in the celestial constellation Canes Venatici. IN in this case the center of the galaxy and the spirals rotating in the same direction are clearly visible. Irregular galaxies are chaotically located superclusters of stars that do not have a clear structure. A striking example of such a formation is the galaxy number NGC 4038, located in the constellation Raven. Here, along with huge gas clouds and nebulae, you can see a complete lack of order in the arrangement of space objects.
conclusions
You can study the Universe endlessly. Every time, with the advent of new technical means, a man lifts the curtain of space. Galaxies are the most incomprehensible objects in outer space for the human mind, both from a psychological point of view and from a scientific perspective.
If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them
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 summer job, which was also partially funded by a research grant awarded to senior 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 in different eras– time slices on a galactic scale - for the entire 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 there were more early stage development of the Universe, the number of galaxies was much greater 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 systems with light weight, 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 we will find when we study these galaxies with the next generation of telescopes?”
Translation of the article “Density distribution of galaxies at Z< 8 и ее последствия».
Октябрь 2016.
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, consequently, 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 the total number of galaxies in the Universe up to $z = 8$ is: $2.0 (+0.7\choose -0.6) \times (10^(12)) $ or just $2.0 \times (10^(12))$ (two trillion!), i.e. almost ten times more than has been seen in all sky-based surveys. We discuss the implications of these results for understanding the process evolution of galaxies, 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 region 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 .
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 . Here an approximate answer to one of these questions has been given - 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. 2007; Lin et al. 2008; Jogee et al. 2009; Conselice et al. 2011; Bluck et al. 2012; Conselice 2014; Ownsworth et al. 2014). The number of galaxies in the observable Universe also reveals information about the density of matter (matter and energy) of the Universe, background light at different wavelengths, and an understanding of 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 ( Williams et al. 1996). Subsequently, research was continued within the framework of (Williams et al., 2000), (Giavalisco et al. 2004), a survey in the infrared spectrum (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) (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 is an interesting question because we know that the star formation rate increases and then decreases with z< 8 (например, Bouwens et al. 2009;
; 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 limits 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 finite nature speed of light and, apparently, will 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 . 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 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 results. previous works. 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 distortion.
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 . These mass and luminosity functions are now just beginning to be measured at high redshifts, 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 Fontana et al. ( , ), Tomczak et al. (2014), and for galaxies at z< 3. Для самых высоких значений красного смещения мы используем функции масс,
опубликованные
,
и
. Мы упорядочили все эти функции масс из каждого вышеуказанного исследования на основе
для звезд от $0.1M_\odot$ до $100M_\odot$. Мы использовали
плотности галактик из этих функций масс, соответствующие их объемам, в отличие от физических объемов. Это говорит о том, как количество галактик
изменяется в одном и том же эффективном объеме, при этом эффекты расширения Хаббла исключаются. Эти функции масс показаны на
{{ show1_MathJax ? "Закрыть":"Рисунке 1" }} до предела масс, взятых из ранее упомянутых исследований, которые также перечислены в Таблице 1.
Picture 1. The mass functions we use in this paper are plotted using All these values are taken from various studies mentioned in §2. The mass functions are presented depending on the values of , 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 и для z >3 taken from work.
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 giving stellar mass functions up to z ~ 8 (e.g. ; , we can now make this calculation for the first time. Another issue is whether it can be extrapolated below the limit of the data for which it was originally suitable. This is a question which we will 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 a parameterized form, given by the function Schechter (1976) 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 , 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 integrate 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 cosmological redshifts as when we use the power law () to calculate the mass function at high cosmological redshifts .
1. page 170-183 Lectures on stellar astronomy. Loktin A.V., Marsakov V.A., 2009.
2.
3.
4., a section of the NASA 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.
8. This work introduced the double Schechter luminosity function. Section 4.2 on page 10.
9. 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 Fontana et al. ( , ), And . These stellar mass functions are determined by measuring the stellar masses of objects using the SED 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 dispersion (). 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 () - 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). List of values, which 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 (), 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 in the number of galaxies, since this value has a significant impact on the number of faint galaxies with low mass in a given volume (§3.2). Therefore, we exclude mass function results from studies using α GOODS (Great Observatories Origins Deep Survey project) as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, as well as from .
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 surveys, including the 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 density of the number 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 a simple merger model is able to reproduce the decline 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.
(Astronomy@Science_Newworld).
More recently, in 1920, the famous astronomer Edwin Hubble was able to prove that our Milky Way is not the only galaxy in existence. Today we are already accustomed to the fact that space is filled with thousands and millions of other galaxies, against the background of which ours looks very tiny. But exactly how many galaxies in the universe are close to us? Today we will find the answer to this question.
From one to infinity.
It sounds incredible, but even our great-grandfathers, even the most scientists, considered our Milky Way a metagalaxy - an object covering the entire observable universe. Their error was quite logically explained by the imperfection of telescopes of that time - even the best of them saw galaxies as blurry spots, which is why they were universally called nebulae. It was believed that stars and planets would eventually form from them, just as our solar system once formed. This guess was confirmed by the discovery of the first planetary nebula in 1796, in the center of which there was a star. Therefore, scientists believed that all other nebulous objects in the sky were the same clouds of dust and gas, in which stars had not yet formed.
First steps.
Naturally, progress did not stand still. Already in 1845, William Parsons built the Leviathan telescope, gigantic for those times, the size of which was close to two meters. Wanting to prove that the "Nebulae" are actually made of stars, he seriously brought astronomy closer to the modern concept of a galaxy. He was able for the first time to notice the spiral shape of individual galaxies, and also to detect differences in luminosity in them, corresponding to especially large and bright star clusters.
However, the debate lasted well into the 20th century. Although it was already generally accepted in the progressive scientific community that there were many other galaxies besides the Milky Way, official academic astronomy needed irrefutable evidence of this. Therefore, telescopes from all over the world are looking at the large galaxy closest to us, which was also previously mistaken for a nebula - the Andromeda Galaxy.
The first photograph of Andromeda was taken by Isaac Roberts in 1888, and additional photographs were taken throughout 1900-1910. They show both the bright galactic core and even individual clusters of stars. But the low resolution of the images allowed for errors. What was taken for star clusters could be nebulae, or simply several stars that “stuck together” into one during the exposure of the image. But a final solution to the issue was not far off.
Modern painting.
In 1924, using a telescope - a record holder at the beginning of the century, Edwin Hubble managed to more or less accurately estimate the distance to the Andromeda galaxy. It turned out to be so huge that it completely ruled out that the object belonged to the Milky Way (despite the fact that Hubble’s estimate was three times less than the modern one. The astronomer also discovered many stars in the “Nebula,” which clearly confirmed the galactic nature of Andromeda. In 1925, despite the criticism of colleagues , Hubble presented the results of its work at the American Astronomical Society conference.
This speech gave rise to a new period in the history of astronomy - scientists “Rediscovered” nebulae, assigning them the title of galaxies, and discovered new ones. In this they were helped by the developments of Hubble itself - for example, the discovery of the red shift. The number of known galaxies grew with the construction of new telescopes and the launch of new ones - for example, the widespread use of radio telescopes after the Second World War.
However, until the 90s of the 20th century, humanity remained in the dark about the real number of galaxies surrounding us. The earth's atmosphere prevents even the largest telescopes from getting an accurate picture - gaseous shells distort the image and absorb starlight, blocking the horizons of the universe from us. But scientists managed to get around these limitations by launching the Hubble Space Telescope, named after an astronomer you already know.
Thanks to this telescope, people for the first time saw the bright disks of those galaxies that previously seemed like small nebulae. And where the sky previously seemed empty, billions of new ones were discovered - and this is not an exaggeration. However, further research has shown that even the thousands of billions of stars visible to Hubble are at least a tenth of their actual number.
Final count.
And yet, exactly how many galaxies are there in the universe? Let me warn you right away that we will have to count together - such questions are usually of little interest to astronomers, since they are devoid of scientific value. Yes, they catalog and track galaxies - but only for larger purposes like studying the large-scale structure of the universe.
However, no one undertakes to find the exact number. Firstly, our world is infinite, which is why knowledge full list galaxies is problematic and devoid of practical meaning. Secondly, to count even those galaxies that are within the visible universe, an astronomer’s entire lifetime will not be enough. Even if he lives 80 years, starts counting galaxies from birth, and spends no more than a second on discovering and registering each galaxy, the astronomer will find only 2 trillion objects - much less than the number of galaxies that actually exist.
To determine the approximate number, let's take one of the high-precision space studies - for example, the "Ultra Deep Field" of the Hubble telescope from 2004. In an area equal to 1/130 of the entire area of the sky, the telescope was able to detect 10 thousand galaxies. Given that other in-depth studies at the time showed a similar picture, we can average the result. Therefore, within Hubble's sensitivity we see 130 billion galaxies from across the universe.
However, that's not all. After Ultra Deep Field, many other shots were taken that added new details. And not only in the visible spectrum of light, which Hubble operates, but also in infrared and x-rays. As of 2014, within a radius of 14 billion light years, 7 trillion 375 billion galaxies are available to us.
But this, again, is a minimum estimate. Astronomers believe that dust accumulations in intergalactic space take away 90% of the objects we observe - 7 trillion easily turns into 73 trillion. But this figure will rush even further to infinity when the James Webb telescope enters the orbit of the sun. This device will reach in minutes where Hubble took days to reach, and will penetrate even further into the depths of the universe.
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.
Helpful 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 Greek name of 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. Each component of the galaxy responds differently to these influences under different conditions. 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
