On a clear night, when the conditions are right and there is not much light to darken the view, the starry sky is a breathtaking view. If you live in a rural area or just take a break from city life, you will be able to see the sky full of stars.
You may even be able to see a strip of light running through the sky that looks hazy (or "milky") in nature. Believe it or not, this is how our galaxy gets its name. Thousands of years ago, astronomers who looked up at the night sky noticed the same band and noticed the resemblance to the drink.
Over time, our understanding of the Milky Way has grown. Not only did we understand that the Milky Way is actually a massive collection of stars held together by gravity, we also learned that it was just one of billions (or even trillions) in the universe.
Ultimately, astronomers and cosmologists came to understand that the universe is breathtaking enormously, both in space and time. And while we still don't know where the universe extends (or if it is infinite), we have a pretty good idea of how long it has existed (approximately 1
For this reason, astronomers have taken a great deal of time and energy to look as far as possible through space and time to see the earliest galaxies. In doing so, they hope to learn how galaxies like our own have evolved and evolved over billions of years.
What are galaxies?
In simple terms, galaxies consist of massive groups of gravitationally connected stars, gas, and dust. However, all this is just the part of the galaxy that we can find because it either emits, absorbs, or emits light.
Beyond that, astronomers for decades have theorized that galaxies also include very dark matter, which is so-called. called because it is invisible as far as conventional detection is concerned.
The study of galaxies led astronomers to group them on the basis of their overall structure. While some galaxies correspond to a basic shape, with a central "bulge" and "weapon" extending from the center into vortices, astronomers note different variations.
From this, astronomers have come to classify galaxies based on three main categories. This classification scheme is known as the Hebble sequence, named after the famous American astronomer Edwin Hubble. The Hubble Scheme divides regular galaxies into three broad classes – elliptical lens-shaped and spiral galaxies – based on their visual appearance . The fourth class contains galaxies of the wrong type .
First, there are spiral galaxies such as the Milky Way, which are rich in gas and dust and still have stars forming in their arms. Then there are elliptical galaxies that have a relatively smooth, uncharacteristic distribution of light. They are relatively devoid of gas and dust, have a low star formation rate, and are so called because they have a circular structure.
There are also lens galaxies. They consist of a bright central bulge surrounded by an extended disc-like structure. Unlike spiral galaxies, the discs of lens galaxies do not have a visible spiral structure and do not actively form large stars. These include Messier 84 and the chariot galaxy.
Hubble's classification system also includes irregular galaxies. These are galaxies that do not fit into the Hubble sequence because they do not have the correct structure. Examples include Magellanic Clouds and M82.
Galaxies can also be classified based on their size, ranging from several hundred million stars (in the case of dwarf galaxies) to one hundred trillion stars (giant galaxies), each orbiting its center of the galaxy.
Strong and Quiet Galaxies
Outside of this scheme, astronomers also distinguish between galaxies that have what is called the Active Galactic Nucleus (AGN) and those that do not. AGN is a compact region in the center of a galaxy that has much higher than normal luminosity . Much of AGN's energy production is non-stellar, and many AGNs are strong X-rays, radio and ultraviolet radiation, as well as optical radiation.
One theory is that the non-stellar emission from AGN is the result of the accumulation of matter by a supermassive black hole (SMBH) at the center of its receiving galaxy, gas and even stars fall into a layered disk around the outer edge of the black hole (aka. Event Horizon). Over time, this matter slowly feeds into the face of the black hole.
The powerful gravity of the black hole causes the material to accelerate to the point where it begins to emit a tremendous amount of electromagnetic energy and radiation. This occurs in radio, microwave, infrared, optical, ultraviolet, X-ray and gamma-ray lengths. .
SMBHs are also known for rotating magnetic fields that interact with their accumulation disks to create powerful magnetic jets. The material in these jets can reach a fraction of the speed of light (also known as relativistic velocities), making them capable of reaching hundreds of thousands of light years away.
AGNs can be further divided into one of two categories based on their jets – "radio-quiet" and "radio-strong" nuclei. Radio AGNs are those that have radio emissions produced by their disks and jets, while radio silent AGNs show negligibly low emissions associated with jets.
The Milky Way
As noted, the Milky Way is a spiral galaxy with a relatively inactive galactic nucleus. According to recent estimates, the Milky Way is estimated to measure between 150,000 and 200,000 light-years in diameter and 1,000 light-years in thickness.
It is also estimated to be inhabited by between 100 and 400 billion stars and more than 100 billion planets. At its center, with a diameter of about 10,000 light years, is the central bulge.
This is the main area of our Milky Way and is also "barred" – meaning it has a central star-shaped structure, the size of this strip is up for debate, with estimates ranging from 3,000 to 16,000 light years.
The center of the Milky Way contains an intense radio source known as Sagittarius A * (pronounced Sagittarius A-star). It is thought to be the SMBH, which is more than 4 million times the mass of our Sun
Several spiral arms containing billions of stars and interstellar gas and dust extend from the center. The exact number and configuration of these weapons has been the subject of some debate and will change depending on new information. Recent observations have revealed that there can be four major helical arms – the Scootum-Centaur arm, the Karina-Sagittarius arm, Norma and the Outer arm, and Far-3 kiloparsec and Perseus. However, it is sometimes said that there are only two major weapons – Scott Centaur and Perseus, with the rest being secondary.
Our Sun is near a small, partial arm called the Arc of Orion or Orion Spur (or the Orion-Signus arm).
The existence of these weapons was determined by observation of parts of the Milky Way and other galaxies – not the result of direct observation.
This is an interesting fact for galaxy observation: astronomers can actually determine the size, structure, and shape of galaxies that are millions (or billions) of light-years away with greater confidence than they are our own.
If Space could be likened to a city and the solar system to be our own backyard, one would have the impression that our own neighborhood would be more familiar to us than those located on the other side of the city, there is a good reason for that reason and it all comes down to our point of view.
In simple terms, the solar system is nestled in the disk of the Milky Way, which makes it possible to gain an idea of its true dimensions quite difficult. It's also hard to see what's on the other side of the galaxy because of light distractions from the central bulge.
It has also recently been theorized that the Milky Way is actually curved in shape. If viewed from the side, the spiral arms would resemble an S.-shaped bend.
To date, no robotic mission has been able to see the Milky Way from an external point of view. Therefore, why any image you see in a galaxy as a whole is either not the Milky Way or is an artist's impression.
Where is the Solar System?
Our Sun is located in the Orion arm of the Milky Way, an area of space that is between two major arms of our galaxy. It is located about 27,000 light-years from the center of the galaxy and orbits it with other stars in the disk.
The sun takes about 240 million years to complete an orbit in what is known as a galaxy year (or space year). By that estimate, the Sun has completed just over 19 orbits since it formed about 4.6 billion years ago.
Based on its spectra, our Sun is classified as a yellow G-type dwarf, which makes it somewhat unusual for the stellar population of our galaxy. All told, about ten percent of the stars in the Milky Way galaxy are yellow dwarfs, which work up to about 20 to 40 billion Sun-like stars.
The Galaxy Study
The Galaxy Study goes back several millennia, although astronomers were not fully aware of what they were observing until the modern era. In general, the true nature of our galaxy is understood, and it wasn't until the 19th century that scientists realized that our galaxy was one of many.
The name "Milky Way", as applied to the central band of light in the night sky, is actually much revered in time. In ancient Rome, astronomers called it " Via Lactea" (Latin for "Milky Way" in Latin), which is the Greek word for "milk circle" ( " galaxías kýklos"  γαλαξίας κύκλος .
Over time, astronomers began to speculate that the Milky Way was actually stars concentrated in a tight band. For example, in the 13th century, Persian Din al Tussi provided the following description in his book, Tajikira :
“The Milky Way, ie the galaxy, is made up of a very large number of small, "flat stars, which appear to be cloudy spots due to their concentration and smallness. Therefore, he is likened to milk in color."
In 1610 Galileo Galilei launches his seminar paper Sidereus Nuncius ("The Star Messenger" "In Latin), which contains his descriptions of the Moon, Sun, and Jupiter. He also records his observations on the" foggy "stars contained in the Ptolemies' catalog.
Galileo's observations show that these objects are in fact innumerable stars that are so remote that they appear to be clustered and cannot be observed with the naked eye, or as described by Galileo, they are "congresses of innumerable stars, grouped together in clusters. "
Similar to Galileo's intercession for the heliocentric model of the universe (where the sun is surrounded by planets), this revelation further shows that the stars are actually much farther from Earth than previously thought.
By 1775, the German philosopher Immanuel Kant had made things even farther by proposing the Milky Way to be a large collection of stars united by mutual gravity. He also suggested that the galaxy was positioned as the solar system, with stars revolving around a common center and crashing into a disk.
In 1785, astronomer William Herschel tried to outline the structure of the Milky Way to reveal its true form. Unfortunately, his efforts were short on how large portions were obscured by gas and dust.
Another interesting development during this time was the publication of the Messier Catalog (1771 to 1781). This work was produced by Dutch astronomer Charles Messier, who began to record the "foggy" objects he initially took as comets.
At that time, telescopes were not yet sophisticated enough to permit these objects – most of which were star clusters or distant galaxies. By the 19th century, however, astronomers such as William Henry Smith (also an Admiral with the Royal Navy) were able to resolve individual stars in them.
By the 1920s, American astronomer Edwin Hubble had finally presented evidence that the spiral nebulae observed in the sky were in fact other galaxies. This finding also led astronomers to deduce what the true shape of the Milky Way is (ie, a blocked, spiral galaxy).
Hubble also showed that most galaxies are actually moving away from our own. This led to the realization that the universe is in a state of expansion. The rate at which it expands is known as the Hubble Constant, in honor of Hubble's discovery.
This find will drastically change our perception of the universe and give rise to theories such as the Big Bang and the Dark Energy. With the onset of the space age, our knowledge of the universe and galaxies has grown significantly.
Space telescopes, for example, are capable of observing distant objects without atmospheric disturbance. Terrestrial observatories have also improved significantly as a result of improvements in tools, methods and data exchange.
The first galaxies
According to the most widely accepted cosmological models, the first stars formed when the universe was only 100 million years old (about 13.7 billion years ago). About 1 billion years after the Big Bag, these stars and other baryonic matter begin to condense with halos of dark matter to form the first galaxies.
Over the next few billion years, the denser regions of the universe become gravitationally attracted to each other. This was known as the epoch of structure when the large-scale structure of the universe began to take shape.
It was during this period that things such as globular clusters, galactic bulges, SMBH, and other cosmic structures were thought to have formed. Stars, dust, and gas also fall into disk structures around central bulges and more material is added from intergalactic clouds and galaxy dwarfs.
Many believe that many have played a key role in regulation. galaxy growth by limiting the amount of matter added. They also affected the rate of star formation, as galaxies experienced a burst of star formation before they appeared.
As the earliest stars began to die, it is theorized that they release heavier elements in the interstellar environment. As a result, subsequent generations of stars are becoming richer in metals, which provides astronomers with a vital tool for age estimates.
Over time, this increase in the abundance of heavy elements in galaxies was thought to have allowed the formation of planets and moons, while residual matter became asteroids and comets that formed in belts around their stars.
How have they evolved since then?
Thanks to studies conducted by space telescopes such as Hubble and terrestrial observatories such as Atacama Large Millimeter / Submillimeter Array (ALMA), astronomers were able to see what galaxies looked like billions of years ago.
This, combined with more recent observations, gave astronomers a good idea of how galaxies have changed over time. For example, the earliest galaxies looked elliptical in shape and smaller. Over time, galactic mergers cause galaxies to grow and become more complex.
It is gradually believed that the influx of material caused their rotation to accelerate. В случая с Галактиката на Млечния път много астрономи смятат, че сливанията с галактики джудже са били доста често срещани – и това е процес, който все още продължава.
Всъщност най-близката до нас галактика е джуджето Canis Major галактика, която се намира на разстояние около 25 000 светлинни години от нашата Слънчева система и на 42 000 светлинни години от центъра на Млечния път. Доскоро астрономите не бяха наясно с неговото съществуване, защото беше затъмнен от космическия прах.
Въпреки това през 2003 г. международен екип от астрономи го засече като част от инфрачервеното изследване на Two Micron All Sky Survey (2MASS). Някои строномери от вярват, че галактиката джудже е в процес на раздробяване от гравитационното поле на по-масивната галактика Млечен път. Прекъсването на приливите и отливите причинява дълги нишки от звезди, които след него вървят около Млечния път, образувайки сложна структура, подобна на пръстен, понякога наричана Моноцерос пръстен която се увива около нашата галактика три пъти.
В продължение на почти 9 милиарда години след Големия взрив се смята, че силата на взаимното гравитационно привличане преобладава и като следствие Космосът се разширява много бавно. В резултат галактическите сливания може да са били много чести през първите няколко милиарда години след Големия взрив.
Въпреки това разширяването на Космоса в крайна сметка доведе до това, че галактиките стават по-отдалечени; в този момент се предполага, че влиянието на Тъмната енергия започва да се усеща.
Мнозина смятат, че това е довело до епохата за космическо ускорение (преди около 5 милиарда години), където космосът започна да се разширява в ускоряваща се скорост. В този момент галактическите сливания станаха много по-редки, но процесът все още се знае, че се случва … и ще се случи и при нас!
Бъдещето на нашата Галактика и Космоса
Както Хъбъл забеляза, огромното мнозинство от съседни галактиките се отдалечават от нашите собствени. Има обаче две, които се движат към нас: съседната Андромеда (известна още като Месиер 31) и триъгълна галактика (Месиер 33).
Въз основа на текущите оценки галактиките Млечен път и Андромеда се движат една към друга със скорост. от около 130 км / с. При тази скорост те ще се сблъскат помежду си след около 4,5 милиарда години.
Когато това се случи, те биха могли да образуват гигантска елипсовидна или лещовидна галактика (с прякор "Милкомеда" или "Milkdromeda"). Прекъсванията на приливите и отливите, причинени от сливането, могат да доведат до изхвърляне на някои звезди и сливане на SMBH.
Не е известно как това ще се отрази на Слънчевата система. Въпреки това се теоретизира, че нашето Слънце дотогава ще е изчерпало водородното си гориво и ще се превърне в червен гигант – което ще доведе до неговото разширяване и поглъщане на Земята, а може би и цялата Слънчева система.
Тези видове сливания са хипотезирани да стават все по-редки, докато Космосът продължава да се разширява и галактиките се изтласкват все по-далеч. В крайна сметка галактиките на Вселената ще станат по-тъмни и по-червени, тъй като по-краткотрайните звезди започват да умират.
Те включват всичко – от сини гиганти и супергиганти (тип O и тип B) до синьо-бели (тип A и F-тип), жълти и оранжеви джуджета (тип G и тип К). В крайна сметка ще останат само звездите от червено джудже от тип М – които имат най-дълъг естествен живот (до 10 трилиона години).
В крайна сметка галактиките ще станат толкова далеч, че всяка интелигентна форма на живот в Млечния път не би да бъде в състояние да видите всякакви други галактики. Същото важи и за жителите на всяка друга галактика, която ще вдигне поглед към нощното небе и ще види само слаби червени звезди.
След време самите галактики ще загинат, когато последните звезди се разпадат и цялата Вселена затъмнява. За щастие за нас това не се очаква да се случи от трилиони години. В този момент човечеството или ще е изчезнало, или ще е еволюирало далеч отвъд всичко, което би могло да се счита за човешко.