How the Birth of New Supernova Stars Occurs

During the final stages of its life cycle, a red supergiant star experiences significant instability, leading to the expulsion of a substantial amount of gas. This expulsion is then followed by a powerful explosion, resulting in the creation of a supernova star.

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In a groundbreaking development, scientists have recently witnessed the demise of a red supergiant star, marking a truly exceptional event within the field of astronomy. This unprecedented observation offers the scientific community an unparalleled opportunity to gain insights into the intricate processes that contribute to the occurrence of supernovae.

The star in question, located in the NGC 5731 galaxy approximately 120 million light-years away from Earth, possessed a mass ten times greater than that of our Sun at the moment of its explosive transformation. If this star had been situated within our own solar system, it would have extended its reach to the orbit of Jupiter.

A breathtaking snapshot of the celestial phenomenon SN 2020tlf within the NGC 5731 galaxy, situated approximately 120 million light-years away from our planet. This supernova appears as a luminous speck positioned towards the lower left side of the galaxy’s central region. The credit for this mesmerizing image goes to the University of Berkeley.

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It’s as if we’re witnessing the detonation of a ticking time bomb

In an article published in The Astrophysical Journal, scientists from California State University at Berkeley recounted their observations of the process by which the star transformed into a Type II supernova.

“This discovery represents a true breakthrough in our understanding of what occurs in the final moments of massive star’s life,” remarked lead researcher Wynne Jacobson-Galan, a National Science Foundation investigator at UC Berkeley. “Never before has the activity of a red supergiant preceding the birth of a Type II supernova been documented. This marks the first instance of us witnessing the explosion of a red supergiant.”

A g-band image of the PS1YSE flare in the NGC 5731 galaxy, which is the parent galaxy of the Type II 2020tf SN. This image was captured by the University of Berkeley.

Red supergiants, while not the brightest or most massive stars, are the largest in terms of volume in the entire Universe. It was previously believed that red supergiants tend to behave peacefully before a supernova occurs, which is considered to be the end of their lifespan. However, recent findings have presented evidence that contradicts this belief.

"It’s comparable to witnessing an imminent detonation," commented Raffaella Margutti, an associate professor specializing in astronomy and astrophysics at the University of California, Berkeley, and the senior author of the research. "Prior to this, there was no substantiated evidence of such extreme activity emanating from a dying red supergiant. We have observed it emit such potent radiation before collapsing and incinerating."

Red supergiant. The birth of a supernova star. Towards the end of their lifespan, red supergiants become highly unstable, expelling substantial quantities of gas, followed by an explosion and the emergence of a supernova. University of Berkeley

Astronomers Desire Additional Data on Supernova Stars

Astronomers initially observed indications of uncommon activity 130 days prior to the occurrence of a supernova event in the star known as NGC 5731. The Pan-STARRS astronomical observatory, located at the University of Hawaii’s Institute of Astronomy on Maui’s Haleakala volcano, detected the powerful emission during the summer of 2020.

Just a few months later, they witnessed the emergence of a supernova star named SN 2020tlf. Moving forward, astrophysicists aspire to identify more phenomena resembling the genesis of SN 2020tlf as part of their ongoing efforts to enhance comprehension of stellar evolution and eventual demise.

During the year 2019, an extraordinary event occurred in the vast expanse of the Milky Way. Betelgeuse, a majestic red supergiant, experienced a significant decrease in brightness, reaching its lowest observed level. This unprecedented phenomenon has sparked speculation among astronomers, who are now contemplating the possibility of a supernova eruption on the horizon. However, unlike its stellar counterpart NGC 5731, Betelgeuse has managed to remain unscathed, at least for the time being.

With a staggering age of approximately ten million years, Betelgeuse has reached a crucial stage in its existence. Deep within its core, intense thermonuclear reactions involving heavy nuclei are taking place. As a result, the star’s envelope has undergone some changes, lending it its distinct and captivating red hue. It is crucial to note that once the density of this colossal celestial body reaches a critical point, a cataclysmic explosion known as a supernova will ensue. However, accurately predicting the exact moment of this extraordinary event remains a formidable challenge, with estimates suggesting that it may still be several thousand years away.

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Supernova or supernova outbreak is a phenomenon in which the brightness of a star suddenly changes by 4-8 orders of magnitude (equivalent to a dozen stellar magnitudes), followed by a relatively slow decline of the outburst [1] [2]. It occurs as a result of a cataclysmic process that takes place at the end of the evolution of certain stars, accompanied by the release of immense energy.

Typically, supernova events are observed retrospectively, meaning that they are observed after the event has already occurred and its radiation has reached Earth. This is why the nature of supernovae has long been a mystery. However, there are now several proposed scenarios that can lead to these types of outbursts, although the fundamental principles are already quite clear.

The detonation is accompanied by the expulsion of a significant quantity of material from the outer layer of the star into the space between stars, and from the remaining core material of the exploded star, typically resulting in the formation of a compact object known as a neutron star, if the star’s mass before detonation exceeded 8 solar masses (M☉), or

An extensive examination of previously acquired spectra and light curves, combined with investigations of remnants and potential progenitor stars, enables us to construct more intricate models and analyze the prevailing conditions at the time of the explosion.

One of the things that is noteworthy is that the material expelled during an outburst contains a significant portion of the fusion products that have formed over the course of the star’s existence. It is through supernovae that the entire universe, as well as individual galaxies, undergo chemical evolution.

The term “supernova” is derived from the historical practice of observing stars that experience significant changes in brightness over time, commonly known as new stars.

The label of the name is composed of SN followed by the year of discovery, with a one- or two-letter ending. The first 26 supernovae of the current year are assigned designations with one or two letters, ending the name with capital letters from A to Z. The remaining supernovae are given two-letter designations using lowercase letters: aa, ab, and so on. Unconfirmed supernovae are identified by the letters PSN (English: possible supernova) with celestial coordinates in the format: Jhhmmssss+ddmmsss..

• 1 Overview
• 1.1 Light curves
• 1.2 Spectra
• 1.3 Observations beyond the optical range
• 1.4 Frequency of flares
• 1.4.1 Observations of supernova remnants
• 1.5.1 Analysis of observations
• 1.5.2 The occurrence of a thermonuclear explosion
• 1.5.3 The collapse of the core due to gravitational forces
• 1.5.4 A model representing a young supernova remnant
• 1.5.4.1 The theory explaining the evolution of a supernova remnant
• 1.5.4.2 The theory explaining the origin of synchrotron radiation
• 2.1 The search for remnants of supernovae
• 2.2 The search for stars that could be progenitors of supernovae
• 2.3 The theory explaining supernova Ia
• 3.1 The chemical evolution of the Universe and the origin of elements with atomic numbers higher than iron
• 3.1.1 The r-process
• 3.1.2 The ν-process

Overall view [ ]

Light curves for type I exhibit a high level of similarity: there is a rapid increase in brightness over a span of 2-3 days, followed by a substantial decrease (by 3 stellar magnitudes) over a period of 25-40 days, and then a gradual decline, which can be described as almost linear when viewed on the scale of stellar magnitudes. On average, the absolute stellar magnitude at the peak of Ia flares is M B = – 19.5 m =-19.5^> , while for Ib\c flares it is M B = – 18 m =-18^> .

Type II light curves, on the other hand, exhibit a wide range of characteristics. Some of them resemble type I light curves, but with a slower and more gradual decrease in brightness at the beginning of the linear stage. On the other hand, there are also cases where the light curve reaches its peak and remains at that level for up to 100 days, before sharply declining and entering the linear “tail” phase. The absolute magnitude of the peak varies significantly, ranging from -20m to -13m. On average, the absolute magnitude for Type IIp is -18m, while for Type II-L it is -17m.

Spectra [ ]

The classification mentioned above already encompasses several key characteristics of different types of supernova spectra. However, there are some important aspects that are not included. One such aspect is the broadness of the main lines, which has posed a significant challenge in deciphering these spectra.

Type II and Ib\c supernova spectra exhibit the following features:

• Presence of narrow absorption components near the peak intensity and narrow, unbiased emission components.
• Observation of [NIII], [NIV], [CIII], [CIV] lines in the ultraviolet range.

Observations beyond the visible spectrum [ ]

Flashing rate [ ]

The rate of bursts depends on the number of stars in the galaxy or, in the case of normal galaxies, the brightness. A commonly accepted measure that describes the frequency of eruptions in various types of galaxies is SNu [6] :

1 S N u = 1 S N 10 10 L ⊙ ( B ) ∗ 100 y e a r L_<\odot >(B)*100year>>> ,

where L ⊙ ( B ) (B)> represents the luminosity of the Sun in the B filter. For different types of bursts, its magnitude is [6] :

Ib/c and II supernovae are attracted to the spiral arms.

Observation of remnants of exploding stars

Another way to observe the remnants of exploding stars is through the collapse of the star’s core. The mass of the core should be equal to the mass of the resulting neutron star. By substituting typical values, we can calculate the following [11]:

where M = 0, R = 10 km, and G is the gravitational constant. The characteristic time at this point is:

where ρ12 represents the density of the star normalized to 10^12 g/cm^3.

The resulting value is 100 times greater than the shell’s kinetic energy. A carrier is required to both carry away the released energy and not interact with matter. Neutrinos are well-suited for this role.

Several processes contribute to their production. The first and most important for destabilizing the star and initiating contraction is the neutronization process [11]:

4 He + e – → 3 H + n + ν e ^He+e^\to <>^H+n+

u _> 56 Fe + e – → 56 Mn + ν e ^Fe+e^\to <>^Mn+

u _> Neutrinos from these reactions carry away 10% of the energy. However, the URCA processes (neutrino cooling) play the main role in cooling: Atomic nuclei can also serve as carriers, forming an unstable isotope that undergoes beta decay:

The compression leads to an increase in the intensity of these processes, thereby expediting it. The dispersion of neutrinos on degenerate electrons, which results in their thermalization and entrapment within the material, prevents this process. A sufficient concentration of degenerate electrons is attained at densities of ρ n u c = 2.8 × 10^14 g/cm^3.

It should be noted that neutronization processes occur only at densities of 10^11 /cm^3, which can only be achieved in the star’s core. This implies that the hydrodynamic equilibrium is only disrupted in the core. The outer layers remain in local hydrodynamic equilibrium, and the collapse only begins once the central core contracts and forms a solid surface. The rebound from this surface initiates the shell reset.

Model of a young supernova remnant [ ]

The theory of the evolution of the supernova remnant [ ]

There are three stages in the evolution of a supernova remnant:

1. Free-spreading. This stage ends when the mass of the swept-up material equals the mass of the ejected material: R s = (3 M 0 / (4 π ν m H n 0 )) ≃ 2 pc, t = R s V s ≃ 200 years.
2. Adiabatic expansion (Sedov stage). The supernova explosion at this stage is considered as a strong point explosion in a medium with constant heat capacity. The self-similar solution is given by R S = 13.5 (E 51 n 0 )^0.2 (t 10^4 year)^0.4 = 13.5(n 0 )^(year) pk T S = 1.5 (E 51 n 0 ) R S , (pc)^-3 10^10 = 1.5 R_^10^ K
3. The stage of intense highlighting starts when the temperature behind the front reaches the maximum on the radiation loss curve. According to numerical calculations, this occurs at the moment: tcool = 2.7E510.24n0-0.52*104 = 2.7E^n^*10> years. The corresponding radius of the external shock wave and its velocity are: Rcool = 20E510.29n0-0.41 = 20E^.29n^> pc, Vcool = 280E510.055n0000.11 = 280E^n^n^> km/s

The expansion of the shell stops when the gas pressure of the remnant equals the gas pressure in the interstellar medium. The remnant then starts to dissipate by colliding with chaotically moving clouds. The dissipation time reaches:

Now we will delve into the specifics of supernova stars, exploring their distinctions from new stars, their explosive capabilities, and the various types they come in. We will focus on type II supernovae as our main example, and towards the end, we will touch upon type I supernovae that originate from binary systems.

Table of Contents

Cassiopeia A supernova remnant in artificial colors.

Some facts about supernovae

• The most well-known supernova is SN 1054, also known as the Crab Nebula, which occurred 6500 light years away.
• The last supernova observed in our galaxy was SN 1604, located 14,000 light-years away.
• The concept of “supernova” was first introduced in 1933 by Walter Baade and Fritz Zwicky.
• The last bright supernova was SN 1987 in the Large Magellanic Cloud, which was located 160,000 light-years away.
• The blast wave velocity from a supernova can reach up to 30,000 kilometers per second.
• The annual number of supernovae found is in the hundreds.
• Supernova explosions occur in the galaxy approximately every 50 years.
• There are several types of supernovae, including IA, IB, IC, IIP, and IIL.

The matter surrounding supernova 1987A is heated by shock waves.

Phenomena occurring within supernovae

When you gaze into our galaxy, the Milky Way, you can observe stars of various sizes and classifications. If we were to scale down the Sun to the size of a bowling ball, you would see an abundance of bowling balls of all imaginable sizes scattered throughout the galaxy, including massive inflatable balls. As anticipated from such a diverse assortment, each star possesses a unique life cycle, although they all begin their journey by burning hydrogen, just like our Sun. Stars similar to the Sun (which can be compared to golf balls, tennis balls, or basketballs in our solar system) undergo the red giant stage and eventually transform into a white dwarf, similar to the one described earlier. On the other hand, larger stars conclude their existence in a more dramatic fashion and play a crucial role in the development of life on Earth.

To put it briefly, the existence of every celestial body initiates from a contracting cluster of cosmic debris. The contraction becomes stable once the temperature within the core of the protostar attains a level at which the nuclear reactions for converting hydrogen into helium commence. As soon as the hydrogen is exhausted, the contraction persists, causing the interior of the star to heat up, and leading to the ignition of helium and remnants of unburned hydrogen. For stars with a mass not exceeding six times that of the Sun, this is where their life comes to an end, as they are too light to initiate additional nuclear cycles due to the influence of high temperatures. Consequently, such a star evolves into a white dwarf.

The life cycle of stars with masses ranging from nine to ten times that of the Sun is unique. These massive stars have enough mass to undergo both continued compression and the burning of nuclear fuel. Like the Sun, the process begins with the burning of hydrogen in the core, which then transitions to the burning of the resulting helium (where three helium nuclei combine to form the nucleus of a carbon atom). This burning process also leads to the burning of the remaining hydrogen in the outer layer surrounding the star’s core. At this stage, the star has a carbon core surrounded by a shell of helium, which is further surrounded by a shell of unburned hydrogen. As compression resumes, the temperature increases in all of these regions. In the core, carbon (with six protons and six neutrons) combines with another carbon nucleus to form oxygen (with eight protons and eight neutrons), along with other heavier elements. The helium in the outer shell burns to form carbon, while the hydrogen burns to form helium in the next shell.

Novae and supernovae

The term “new” in the name of a star is associated with a recurring celestial event: the sudden appearance of a star in the sky where it was previously unseen. Presently, our understanding acknowledges a multitude of distinct mechanisms that can result in the emergence of new stars, and we assign varying names to these phenomena based on their underlying causes.

Nova phenomenon occurs when a white dwarf star, which is in a binary system with another star, starts pulling matter from its companion. This matter, mainly consisting of hydrogen, accumulates on the surface of the white dwarf. Once a sufficient amount of hydrogen has accumulated, thermonuclear reactions begin, converting hydrogen into helium. These reactions result in the formation of a shock wave within the hydrogen shell of the white dwarf, causing it to be ejected into space. This ejection is accompanied by a bright flash, known as a nova flash. Afterward, the process of matter accumulation and eruption may occur again, leading to subsequent nova events.

There is often confusion between novae and supernovae Novae are only the stars that experience periodic increases in brightness. On the other hand, a supernova is a phenomenon that occurs when a star explodes, leading to a series of dramatic events.

The point of no return

Iron is the end product of nuclear fusion. It is not possible to obtain energy from iron through any means. It accumulates in the core of a star, similar to embers in a wood stove, setting the stage for one of the most awe-inspiring phenomena in the entire Universe. The iron core accumulates and is unable to resist compression from its own gravitational force. The electrons in the iron core briefly generate pressure that counteracts gravity. Consequently, the core of a massive star becomes akin to a white dwarf, but composed solely of iron.

When the mass of a star surpasses that of the Sun by 40%, a critical point is reached where iron “embers” begin to accumulate at its core. At this point, electrons start combining with protons in the iron nuclei, forming neutrons. As each electron disappears, the remaining particles lose their ability to resist gravitational compression. Eventually, the core becomes a mass of neutrons, resulting in a catastrophic collapse.

The duration of this compression depends on the star’s mass and continues until the neutrons can no longer be compressed any further. Alternatively, it may continue further and lead to the formation of a black hole, which will be discussed later. For now, let’s consider the remnants of this star, which consist of a giant, bulb-shaped shell of heavy elements formed during thermonuclear reactions.

The constellation serpentine is home to the recurring nova RS serpentine.

The Explosion of Supernovae

The shell of RS serpentine experienced a sudden loss of support, causing it to collapse inward and collide with the neutron core. This collision created shock waves and triggered a massive explosion within the star. As a result of the thermonuclear reactions, heavy elements including uranium were formed. This cataclysmic event gives rise to a new celestial object in the sky: a supernova is born.

A series of events occur during a supernova explosion.

The expelled outer shell expands into the vastness of interstellar space, carrying with it the dense elements created within the star. Over the coming millennia, these clusters of matter will cool down and blend with the surrounding interstellar medium, becoming integral components of the gas and dust clouds that will eventually give rise to emerging stars and fresh planetary systems. The birth of our Solar System occurred after the Milky Way Galaxy had already undergone multiple stages of evolution. Consequently, the Sun, planets, and even living organisms all possess heavy elements that originated from the first generation of long-extinct stars.

The phenomenon we described above is known as a “type II supernovae” in historical terms. The formation of type I supernovae follows a different scenario, but still results in a powerful explosion. Type I supernovae occur in binary star systems where one star has already reached the end of its life and become a white dwarf. In some cases, the white dwarf may pull material from its companion star, increasing its mass until it exceeds 40% of the Sun’s mass. At this point, an explosion will occur.

Let’s contemplate upon the origins of supernovae in the grand scheme of our Galaxy’s history. It all traces back billions of years ago to a primordial cloud composed of hydrogen and helium remnants from the Big Bang. Through the life and demise of massive, short-lived stars that undergo explosive supernova events, the production of heavy elements commences and continues to escalate. Thus, one can envision the Milky Way as an immense apparatus, extracting hydrogen from its primary matter reserves and replenishing them with increasingly substantial elements.

In the event that you’re curious, astronomers anticipate the eventual supernova eruption of star 1K located in the Pegasus constellation, which lies approximately 150 light-years away from us. This cosmic event is projected to unfold as a Type I supernova within the next few million years or so.

In the early months of 2002, the Hubble Space Telescope captured a series of captivating images depicting the extraordinary star V838 Mon in the constellation Unicorn experiencing a sudden and remarkable expansion. This expansion caused the star to heat up and illuminate the dust clouds encompassing it.

A supernova, also known as a supernova explosion, is the awe-inspiring event that occurs when a massive star reaches the end of its life cycle. This event involves an immense explosion that releases an enormous amount of energy, resulting in a dramatic increase in luminosity by billions of times. The outer layers of the star are expelled into space, forming what is known as a nebula, while the core undergoes compression to the point where it either becomes a neutron star or collapses into a black hole.

Supernovae play a crucial role in shaping the chemical composition of the universe. These powerful explosions release heavy elements that were synthesized through thermonuclear reactions during the star’s lifetime, propelling them into space. Subsequently, these remnants give rise to protostars accompanied by planetary nebulae, which eventually evolve into stars and planets.

Just like how the Earth came into existence, all the substance that encompasses us and makes up our beings originated within the depths of stars, even prior to the formation of the Sun.

A supernova is easily noticeable – the burst from the explosion is so powerful that it surpasses the brightness of all the other stars in the galaxy.

The process of the explosion

As you may be aware, a star emits tremendous amounts of energy due to the thermonuclear reaction occurring in its core. The thermonuclear reaction is the conversion of hydrogen into helium and heavier elements, accompanied by the release of energy. However, when the hydrogen in the star’s interior is depleted, the outer layers of the star start collapsing towards the center. Once the critical point is reached, the matter undergoes a literal explosion, further compressing the core and propelling the upper layers of the star with a shockwave.

Within a relatively compact space, a significant amount of energy is generated, necessitating the emission of neutrinos, which possess negligible mass.

Type Ia Supernovae

These supernovae originate not from stars, but from white dwarfs. Notably, all of these celestial objects possess identical luminosity. By determining the luminosity and type of object, one can calculate its velocity through redshift. The search for Type Ia supernovae holds great significance as it was through their study that the accelerating expansion of the universe was discovered and subsequently proven.

Maybe they will erupt tomorrow

There is a complete list containing potential supernova star candidates. Determining the exact timing of the explosion is, of course, quite challenging. Here are some of the closest ones that are currently known:

• IKPegasus. This binary star system is situated in the Pegasus constellation and is located within a distance of 150 light-years from us. Its companion is a massive white dwarf that has already ceased fusion energy production. As the host star expands into a red giant and increases in radius, the white dwarf will start gaining mass at its expense. Once its mass reaches 1.44 solar masses, a supernova explosion may take place.
• Antares. Antares is a red supergiant situated in the Scorpius constellation, approximately 600 light years away from Earth. It is accompanied by a hot blue star.
• Betelgeuse. Betelgeuse is a similar object to Antares and can be found in the Orion constellation. It is located at a distance of 495 to 640 light years from the Sun. Despite being a relatively young celestial body (around 10 million years old), it is believed to have entered the carbon burnout phase. In the next one or two millennia, we may have the opportunity to witness the spectacular explosion of a supernova.

Impact on Earth

The explosion of a nearby supernova star is bound to have an impact on our planet. Take Betelgeuse, for instance, when it explodes, it will increase in brightness by approximately 10,000 times. The star will appear as a dazzling point of light, shining as brightly as a full moon, for several months. However, if any of Betelgeuse’s poles are facing towards Earth, our planet will be bombarded with a stream of gamma rays emitted by the star. This could lead to an increase in the northern lights and a decrease in the ozone layer, potentially having a highly detrimental effect on life on Earth. These are all theoretical calculations, though, and it is impossible to predict the actual consequences of the explosion of this supergiant star with certainty.

To the people living on Earth, the stars appear to be everlasting and unchanging. At first sight, they all appear similar and devoid of any distinctions. However, the reality is quite different. Contemporary astronomers have provided evidence that the life cycle of a celestial body consists of various stages. The evolution of stars is an exceptionally lengthy and intricate process that cannot be observed solely through visual means. Thanks to their extraordinary knowledge and advancements in technology, scientists have acquired the ability to identify the different types of stars, construct models illustrating their development, and elucidate the phenomena taking place in the far reaches of the cosmos.

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Phases of stellar evolution

The concept of stellar evolution studies the modifications in the physical and chemical properties of stars that are associated with the age of the celestial object. The primary phases include:

• creation of a protostar from a gas cloud;
• formation of stars with varying masses, which, through thermonuclear processes, will develop into either a giant or a supergiant;
• the life cycle of low-mass stars concludes with their transformation into white dwarfs;
• a massive star transforms into a neutron star or a black hole through gravitational collapse.

Gravitational collapse refers to the extremely rapid compression of cosmic bodies due to the influence of gravitational forces.

Source

Protostar

Every star’s life starts with its birth. In the initial phases, a large cloud forms, where molecules are created. Due to the force of gravity, the cloud of interstellar gas compresses and gradually takes on a spherical form. During this compression, gravitational energy transforms into heat, causing the temperature to rise in the star’s central region. However, the temperature is still not high enough to trigger thermonuclear reactions.

During the initial phase of its evolutionary progression, the entity is commonly known as a protostar. The procedure of creating a fresh entity occurs over an extensive duration and can span millions of years. Protostars that possess a developed core and envelope are categorized as a distinct type, known as pre-main sequence stars. These stars possess a low temperature but exhibit a high level of luminosity. Eventually, the star commences its transition towards the main sequence and derives its energy from gravitational forces.

Source

The process of contraction in protostars is a very slow one. For instance, it took 30 million years for the Sun to transition into the main sequence.

Red giant and supergiant stars.

Just as there are no two identical individuals, there are also no identical stars in the vast universe. Among them, there is a group of massive stars that emit thousands of times more light than our Sun. These objects possess significant size (ranging from 10 to 1,000 times the radius of our Sun) and low density (approximately 10 -2 – 10 -4 kg/m 3 ). Additionally, some of these giants have a strong outflow of gaseous matter from their surfaces.

Red giants are some of the most fascinating and distinctive examples of large stars. These particular stars possess relatively low temperatures, with an average range of 3,000 to 5,000 degrees Celsius, and their size is hundreds of times larger than that of our Sun. Notably, the luminosity of red giants is approximately 100 times greater than that of our own star. The majority of the radiation emitted by these celestial objects is concentrated in the red and infrared regions of the electromagnetic spectrum. According to the theory of stellar evolution, red giants are formed when the central region of a main-sequence star has nearly exhausted its supply of hydrogen fuel.

Once an ordinary star transforms into a red giant, its composition undergoes significant changes. A compact core enriched with helium forms at its center, surrounded by a thin layer responsible for energy production and an expansive outer shell. Red giants have a mass ranging from 1.5 to 15 times that of our Sun, with a density of less than 0.001 g/cm 3 , significantly lower than that of our star. In the field of astronomy, red giants encompass various stellar entities:

Within this group of stars, there exist a specific subset of massive celestial bodies that have been categorized as red supergiants. So far, the scientific community has only been able to identify a limited number of these stars. What sets them apart is their significant size, with a luminosity that can reach up to 105 times that of the Sun. Interestingly, these objects are 50 times more massive than our Sun, yet their radii can extend to thousands of times the radius of our Sun. Red supergiants have a temperature range of 3,000 to 5,000 degrees Celsius. Their spectra display molecular absorption bands, with the highest emission occurring in the red and infrared regions. The spectral classification of red supergiants falls under the categories of K and M. One of the most well-known examples of a red supergiant is Betelgeuse.

White dwarfs

The formation of white dwarfs is considered as one of the stages in the evolution of stars. These stars take the place of red giants once they have lost their mass and shed their shells, revealing their core. The discovery and exploration of these celestial bodies began in 1914 when American astronomer W. Adams identified Sirius, which is now the most well-known star in the night sky. Sirius is located in the constellation Canis Major, also known as the Big Dog. It is an example of a classic white dwarf, a relatively rare type of star in the universe. These stars have low luminosity, which is why they were initially discovered in close proximity to the Sun. However, with the advancement of powerful space telescopes, astronomers have also found white dwarfs in globular clusters located at significant distances from Earth.

According to calculations by scientists, young white dwarfs in their initial stages of development are undergoing a process of contraction. Their radius is gradually decreasing. In fact, within the first million years of their existence, their size is reduced to just a few hundred kilometers. This phenomenon can be attributed to the gradual cooling of the white dwarf. These celestial objects have a mass ranging from 0.6 to 1.44 times that of the Sun. The surface temperature of white dwarfs can reach up to 200,000 degrees Celsius. Moreover, the density of their substance is remarkably high, measuring between 10^5 and 10^9 grams per cubic centimeter.

The duration of these entities is determined solely by the period of their full cooling. The spectral features of white dwarfs are markedly distinct from those of main-sequence stars and red giants. They are categorized as a distinct spectral class D.

Pulsars and neutron stars

When a star’s life comes to an end, it undergoes a fascinating transformation, resulting in the creation of a neutron star. Neutron stars are compact celestial bodies with a radius of less than 10 kilometers and a mass approximately 1.4 times that of our sun. Composed primarily of neutrons, these stars are incredibly intriguing astronomical entities that captivate the attention of scientists and astrophysicists worldwide.

The composition of these objects includes superconductivity, superfluidity, the emission of neutrinos, the presence of extremely strong magnetic fields, and other unique characteristics. The density of a neutron star is incredibly high, resulting in its remarkable mass despite its small size. The structure of a neutron star is truly one-of-a-kind. Inside, there is boiling hot matter surrounded by a thin solid shell, with a raging hot plasma above it. Additionally, this celestial body possesses a magnetic field that surpasses the magnetic field of the Sun by trillions of times.

Source

Academician L.D. Landau provided evidence for the existence of macroobjects primarily composed of neutrons in the Universe. The concept that neutron stars are formed during supernova explosions was proposed in 1934 by American scientists F. Zwicky and V. Baade. However, due to their limited brightness, neutron stars remained undetectable for a significant period. These celestial bodies are also known as pulsars. Their magnetic fields continually attract electrons from the plasma layer, causing the emission of radio signals.

In 1967, British scientists from Cambridge made a groundbreaking discovery when they detected radio pulses emanating from specific regions of the sky. While studying cosmic radio sources, D. Bell, under the guidance of E. Hushin (the renowned discoverer of pulsars and recipient of the 1974 Nobel Prize in Physics), identified a highly regular signal. Some researchers initially speculated that these signals could be attributed to extraterrestrial civilizations, leading to the classification of their work. However, it was later confirmed that this phenomenon is simply a natural occurrence.

Hushin’s group’s findings were shared with other scientists, who quickly concluded that radio pulsars and neutron stars are essentially the same thing. Interestingly, scientists had actually observed neutron stars five years before the discovery of radio pulsars, but they had used X-rays rather than radio waves to make these observations.

In 1962, researchers equipped a rocket with a specialized detector, which enabled them to detect a strong source of X-rays in the Scorpius constellation. This was a significant breakthrough, as conducting such studies from Earth was not possible due to our atmosphere’s absorption of X-rays.

In 1970, several similar objects had already been identified by experts. All of these objects were part of binary systems and extracted matter from the nearby neutron star. This matter reached speeds close to the speed of light and, upon colliding with the surface of the neutron star, converted into heat, emitting X-rays at temperatures reaching several million degrees.

Currently, modern science has discovered fascinating binary systems composed of two neutron stars. These systems rapidly approach each other due to the influence of gravitational waves.

Consequently, within a timeframe shorter than the lifespan of the Universe, these two entities will collide, unleashing a colossal quantity of energy that surpasses the magnitude of a supernova explosion. In fact, one such system was discovered and documented in 1970 by R. Hulse and Jd. Taylor, whose groundbreaking research earned them the prestigious Nobel Prize in Physics.

The merger of two neutron stars as a source

What are black holes

Neutron stars are formed through the evolution of stars with masses ranging from 8 to 40 solar masses. On the other hand, black holes are formed from larger celestial bodies. These celestial entities are the most extraordinary objects in the cosmos. In this realm, the laws governing our world lose their power as time and space interchange, leaving no escape route. This is due to the immense gravitational force exerted by such a cosmic entity, which cannot be resisted by anything in the known universe.

Black holes are celestial bodies that exhibit the opposite behavior of ordinary stars. While stars emit light, black holes have the ability to absorb it, as well as anything else that happens to be in their vicinity, such as planets, stars, comets, and other objects. The gravitational pull inside black holes is so immense that it is difficult for scientists to fully comprehend.

Black holes represent the final stage in the life cycle of supermassive stars, containing a staggering 0.1% of the mass of our entire Galaxy.

The term “black hole” was coined in 1968 by American physicist John Wheeler. Astronomers first stumbled upon the existence of a black hole while studying double star systems. They noticed that one of the stars in such a system emitted an unusually intense shine. Through calculations, it was determined that a black hole was present nearby, invisibly absorbing matter from its neighboring star.

The process of absorbing a star by a black hole

Mysterious entities actively consume the material of their neighboring stars, simultaneously heating it to temperatures reaching millions of degrees. These extreme conditions cause the black hole to emit X-ray radiation. In the vicinity of these celestial objects, the fabric of space is heavily distorted, resulting in even the trajectory of light being altered over vast distances. This phenomenon has led to the discovery of fascinating phenomena known as gravitational lenses, providing evidence that black holes are concealed within their cores.

Currently, scientists have knowledge of the whereabouts of 20 immense and 200 supermassive black holes. Additionally, there have been identified another 220 potential locations for these enigmatic entities. The reason for the particular interest of scientists in these phenomena is rather straightforward. Quite recently, the American telescope “Hubble” has documented a fascinating yet somewhat unsettling discovery. It appears that the black hole GROJ 11655 – 40, situated in the Scorpius constellation, is directly approaching our Sun, devouring everything in its path towards the stars. This invisible entity is positioned quite a distance away from us – 600 light-years to be precise. However, its velocity stands at an astounding 40,000 kilometers per hour, sparking fear among contemporary researchers.

The most renowned black hole is situated in the Swan constellation. This purportedly unidentified object is a staggering 15 times more massive than our Sun.

Binary, multiple, and variable stars

Advancements in astronomical technology have revealed that some of the stars we observe are actually systems consisting of two celestial objects with varying masses and spectral classes. Detecting the close proximity of these celestial bodies can be challenging and often requires specialized modern equipment and meticulous calculations.

Scientists refer to these paired stars as double stars, as they revolve around a shared center of mass in elliptical orbits due to the force of gravity. These stars are located in close proximity to each other, resulting in a mutual gravitational attraction. The size ratios of these bodies can vary, with relatively equal twin stars moving around their common center of mass. In cases where one star is significantly smaller than its counterpart, it becomes a satellite of its neighboring star.

The identification of dual space objects can be achieved through various methods. Some objects, such as visual-double stars, can be easily recognized through ordinary observation using a telescope. On the other hand, spectrally dual objects require a more detailed analysis of their spectral lines to determine their nature.

Eclipsing double stars pose a particular challenge for scientists. The periodicity of their brightness fluctuations, caused by one star temporarily obscuring the other as they rotate around a common center, often leads to extensive research to confirm their dual nature. Through careful investigation, it becomes evident that these objects are indeed double stars.

Aside from binary stars, there exist numerous celestial systems in the vast expanse of the Universe wherein three or more stars orbit a shared center of mass, driven by the omnipotent force of gravity. Such systems are referred to as multiple stars.

The chances of finding a multiple star system decrease as more luminaries are included. This is due to the system’s instability, as any of the stars could undergo a transformation such as becoming a dwarf, exploding into a supernova, or turning into a black hole. These processes would cause significant gravitational perturbations, disrupting the system of multiple objects.

As a result, most multiple star systems are composed of only 3 or 4 bodies. Currently, there are two known systems, AR Cassiopeia and Nu Scorpius, which consist of 7 objects.

Within triple systems, a pair of stars engage in a mutual orbit, while a third star maintains a more distant orbit around them. One notable example of this intricate arrangement is found in the Alpha Centauri system. Within this system, Alpha Centauri A and Alpha Centauri B, both classified as yellow dwarfs akin to our Sun, revolve around a shared center, or barycenter, over a span of 79 years. Meanwhile, Proxima Centauri, the third star, follows its own distinct orbit, requiring approximately 500,000 years to complete a full revolution around its stellar companions.

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Among the most fascinating phenomena in the celestial sphere, which can be observed even with the unaided eye, are variable stars – celestial bodies that have the ability to alter their luminosity over time. Some stars are capable of transforming their brilliance within minutes, whereas others may require several months.

The reasons behind these fluctuations in stellar brightness can range from chromospheric activity and supernova eruptions to eclipses occurring within binary star systems, and more.

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The presence of certain conditions gives rise to various categories of variable stars:

1. Eclipse-variable stars – their luminosity changes in a predictable manner. These celestial bodies are not single stars, but rather binary systems that are closely intertwined. The stars in these systems move in such a way that one periodically eclipses the other, similar to a solar eclipse. The brightness of these stars varies. When a brighter star eclipses a fainter one, observers on Earth witness an increase in brightness, and vice versa. Examples of such stars include Algol, β Lyrae, and W of the Big Dipper.

Pulsating variable stars are stars whose brightness changes as a result of fluctuations in the star’s volume. These stars expand and contract, with the phenomenon being caused by the instability of internal pressure and gravitational forces. The pulsations lead to an increase in the photosphere of the star, causing the radiated surface area to grow. This, in turn, affects the temperature parameters and color of the star. The discovery of the first pulsating star, Mira Kita, dates back to 1596. Cepheids, which are giants with flickering periods of 1.5-50 days, also fall into the category of pulsating variable stars. One of the most well-known variable stars is Polaris, which has a period of 4 days. Another intriguing subset of pulsating stars are the RV stars of Taurus, which have periods lasting between 30-150 days.

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1. Pulsating stars encompass a diverse group of irregular variable stars. These stars are characterized by unpredictable changes in luminosity, lacking any discernible periodicity. They are the least extensively researched in this field. Betelgeuse is a prime example, with its fluctuating brilliance attributed to the presence of both dark and light spots on its surface.

Emergence of New Stars and Supernovae

Occasionally, scientists witness a sudden and intense flash in the sky that is unrelated to the flickering of variable stars. This phenomenon marks the birth of new stars and supernovae. The term “new stars” originated from the misconception that these objects originated from empty space. However, in the 20th century, when the sky was regularly photographed, it was discovered that a faintly visible star existed at the location of the “new” luminaries. At a certain point, this star experienced a significant increase in brightness.

Every few years, there are new stars that burst forth. Despite the fact that they emit light thousands of times brighter, they are so far away that they cannot be observed with the naked eye.

A supernova explosion is a considerably larger phenomenon. The amount of energy generated during the explosion is equivalent to the amount of energy that the sun emits over billions of years. Supernovae are even more infrequent. This event occurs both within our own galaxy and beyond. In 1054, the explosion of a supernova star was recorded in the Chinese and Japanese chronicles, and it was even visible during daylight hours. In 1987, thanks to modern equipment, scientists were able to observe a complete supernova eruption from start to finish. This event took place in the Large Magellanic Cloud galaxy.

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Supernovae present a unique phenomenon in the universe. In the constellation of Taurus, a bright cloud of gas known as the Crab Nebula has been observed by scientists. Currently, the nebula is expanding, allowing experts to measure its rate of expansion. By studying the consistency of this rate over time, scientists have been able to determine that approximately 1000 years ago, the material from the nebula was concentrated in one location – the epicenter of a supernova star event. This discovery confirms that the Crab Nebula is indeed the remnants of a supernova explosion. Subsequently, more similar nebulae have been identified. The most intriguing aspect is the presence of a pulsar star at the center of the Crab Nebula. This star is significantly denser than white dwarfs and plays a crucial role in the formation of supernova explosions when massive stars reach the end of their lifecycle and become unstable.