A star is considered variable if it has the ability to alter its brightness. This means that, from the perspective of an Earth observer, the star’s apparent magnitude undergoes periodic changes. These changes can occur over the course of years or even just seconds, and they can range from a difference of 1/1000th magnitude to 20th magnitude.
There are over 100,000 known variable stars, and thousands more are suspected to exhibit variability. Even our own Sun is a variable star, with its luminosity fluctuating by 1/1000th magnitude over an 11-year period.
The Past
An artistic representation of a binary system that undergoes eclipses, which includes a Cepheid variable star
The exploration of variable stars started with the observation of Omicron Keith (Mira) by David Fabricius in 1596. Johannes Hogwalds later noticed its pulsations for 11 months in 1638. This discovery was significant as it challenged the notion of stars being eternal (as proposed by Aristotle). The study of supernovae and variable stars has revolutionized the field of astronomy.
Mira, the variable star, exhibits a tail that can only be detected in the ultraviolet spectrum.
In a span of just one century, four similar variables to Mira were discovered. Surprisingly, it was found that these stars were already known in ancient China and Korea, predating their appearance in Western records.
Algol, the variable eclipsing star, was first identified in 1669, although its variability was not explained until John Goodrick’s discovery in 1784. Another star, Hy Swan, was observed in 1686 and 1704. Subsequently, seven more variable stars were discovered over the next 80 years.
Since 1850, the search for variables has been on the rise, thanks to the rapid development of photography. To put this into perspective, there have been over 46,000 variables discovered in the Milky Way alone since 2008.
Characterization and Composition
Variability in stars can be attributed to various factors, such as changes in luminosity or mass, as well as obstacles that obstruct light from reaching Earth. This leads to the categorization of different types of variable stars. Pulsating variable stars expand and contract in size. Double eclipsing stars experience a decrease in brightness when one star overlaps with another. Some variable stars consist of two nearby stars exchanging mass.
There are two main classifications of variable stars. Internal variables undergo changes in brightness due to pulsation, size variation, or eruptions. External variables, on the other hand, experience changes in brightness due to eclipses caused by their mutual rotation.
An image depicting the central region of the Milky Way showcases three variable Cepheids, which serve as crucial indicators of distance and age for celestial objects.
Variable stars in the inner region
Cepheids, known for their extraordinary brightness that surpasses the luminosity of the Sun by 500-300,000 times, exhibit a periodicity ranging from 1 to 100 days. These stars belong to the pulsating type, capable of undergoing significant expansions and contractions within a short timeframe. Their significance lies in their ability to accurately determine the distances to various celestial bodies and formations.
The star RS Puppis is an example of a Cepheid-class variable star.
There are also other types of pulsating variables in the universe. One such example is RR Lyra, which has a shorter period and is considered to be older. Another type is RV calves, which are supergiants that exhibit a noticeable wobble. If we look at long period stars, we find objects known as Mira-type stars, which are cool red supergiants. Semi-regular variables are red giants or supergiants with periods that span 30-1000 days. One of the most well-known examples of a semi-regular variable star is Betelgeuse.
It is also important to mention the variable star Cepheid V1, which played a significant role in the study of the universe. It was through the observation of Cepheid V1 that Edwin Hubble realized that the nebula it was located in was actually a separate galaxy. This discovery expanded our understanding of space beyond the confines of the Milky Way.
Cataclysmic variables, also known as “explosive” variables, emit light due to sudden and extremely powerful bursts caused by thermonuclear reactions. This category includes novae, supernovae, and dwarf novae.
Supernovae are characterized by their intense activity. The energy released during these events can sometimes surpass the total energy output of an entire galaxy. They can reach a magnitude of 20, making them 100 million times brighter. Most often, supernovae occur when a massive star reaches the end of its life, although a neutron star or a planetary nebula may also form.
For instance, in 2007, V1280 Scorpius reached its peak brightness. The brightest nova in the past 70 years was Nova Swan. Another remarkable event was the explosion of V603 in the Eagle constellation in 1901. At its brightest point in 1918, it was as luminous as Sirius.
Dwarf novae are binary white stars that undergo mass transfer, leading to regular outbursts. Among them are symbiotic variables, which consist of a red giant and a hot blue star.
Eruptions are prominent in eruptive variables, which can interact with surrounding material. There are numerous subtypes, including flaring stars, supergiants, protostars, and Orion variables. Certain types of eruptive variables also function as binary systems.
Stars with Outer Variables
Stars with outer variables are stars that exhibit periodic light-blocking when observed. These stars may also have their own planetary systems, where the eclipse phenomenon similar to that of the Earth-Moon system occurs. Algol is one example of such a star. During its mission, NASA’s Kepler spacecraft discovered over 2,600 eclipsing double stars.
This is a representation of an eclipse occurring in a binary star system.
Rotating stars are interesting celestial objects that display minor changes in brightness due to the presence of surface spots. Many of these stars are actually binary systems, shaped like ellipses, which leads to fluctuations in brightness as they move.
At the heart of the Milky Way, there are two pulsating stars known as Cepheids. These remarkable celestial bodies serve as invaluable tools for astronomers as they provide crucial information about the radii, mass, temperature, and visibility of other stars. Additionally, they aid in unraveling the composition and studying the evolutionary path of stars. However, the study of these stars is a meticulous and time-consuming endeavor that requires the use of specialized instruments as well as amateur telescopes.
Exploring Further
In the future, it is imperative to continue researching these pulsating stars. By delving deeper into their properties and behavior, astronomers can gain a more comprehensive understanding of the cosmos and its vast wonders.
Certain variables hold significant importance, like the Cepheids, which play a crucial role in estimating the age of the entire Universe and unveiling the mysteries of far-off galaxies. Equally noteworthy are the world variables, which shed light on the enigmas surrounding our Sun. Supernovae provide a wealth of information on the expansion process, while cataclysmic variables offer insights into active galaxies and supermassive black holes. Consequently, variable stars serve to elucidate the reasons behind the lack of stability in certain aspects of the universe.
- Flaring stars, also known as UV Kita-type stars, are a type of variable star that undergoes dramatic and non-periodic increases in brightness across a broad range of wavelengths, from radio waves to X-rays.
Flaring stars are characterized by their small masses and dimness, with many of them being red dwarfs. Flares have also been observed on brown dwarfs. Although they are the most abundant class of variable stars, their dimness makes them difficult to detect, and only a few are currently known, all located within 60 light-years of Earth. Notably, several of the closest stars to the Sun, such as Proxima Centauri, DX Cancer, and Wolf 359, belong to this class.
Flares can range in duration from minutes to several hours, with the average time between flares varying from an hour to tens of days. The start of a flare is significantly quicker than the fading, as a star can double its brightness in just a few seconds. During a flare, the star’s spectrum undergoes a drastic change, with a continuous stream of radiation being emitted in the blue and ultraviolet regions.
It is believed that solar flares have a similar nature, albeit much weaker. Additionally, solar flares are not only weaker in terms of relative magnitude (as the Sun is much brighter than red dwarfs that exhibit UV Keith-type flares), but also in the amount of energy released during the flare.
Related concepts
BY Dragon type variables are stars that belong to the main-sequence category and have late spectral classes, typically K or M. The prime example of this group of stars is BY Dragon. Variations in their brightness occur due to their rotation, as they possess sunspots on their surface, similar to those found on the Sun but covering a much larger area. Additionally, these stars exhibit chromospheric activity. The range of brightness fluctuations is typically less than 0.5 stellar magnitude, and the duration of the cycles corresponds to the star’s rotation period (from.
A blue giant refers to a star with a spectral class of O or B. Blue giants are young, hot, and massive stars that fall within the main sequence region on the Hertzsprung-Russell diagram. Blue giants can have masses ranging from 10-20 times that of the Sun, and their luminosity is thousands to tens of thousands of times greater than that of the Sun.
A hypergiant is a star of massive magnitude and magnitude that is classified as class 0 on the Hertzsprung-Russell diagram. Hypergiants are known as the most dominant, weighty, brilliant, and concurrently the scarcest and briefest-lived supergiants. Typically, supergiants that are brighter than -8m are regarded as hypergiants. KY Swan serves as an instance of a star that borders on the classification; an entity with a lesser magnitude would cease to be identified as a hypergiant.
References in the literature
Up to this point, we have primarily discussed nebulae that are formed during supernova explosions of the 1572 supernova remnant. The solid lines depicted here represent optical fibers. The two concentric circles outline the region that emits X-ray photons from the stars. What can we infer about the stars themselves that are undergoing these eruptions? As previously stated, these observations pertain to supernovae occurring in other star systems. In our own Milky Way galaxy, the most recent outburst of this kind was witnessed in 1604. Specifically, astronomer Kepler observed this particular star. However, it is worth noting that during this time period, the telescope had not yet been invented, and the powerful astronomical research technique of spectral analysis would not come into use for another two and a half centuries….
Continuation of Related Concepts
Subdwarfs, previously designated as sd (e.g., sdM5e), refer to stars with a luminosity class of VI in the Yerkes classification system. These stars have a luminosity that is 1.5-2 magnitudes fainter than main-sequence stars of the same spectral class. On the Hertzsprung-Russell diagram, subdwarfs are located below the main sequence.
Here is a compilation of the nearest stars to Earth, arranged in order of increasing distance. This list includes stars that are within a 5 parsec (16.308 light-years) radius from Earth. Currently, there are 57 stellar systems, including the Sun, that are believed to be within this proximity. These systems consist of a total of 64 stars and 13 brown dwarfs.
A yellow supergiant is a supergiant star that falls under the spectral classes F or G. These stars typically have a mass of 15-20 times that of the Sun.
Cepheids are a type of pulsating variable stars that have a relatively accurate relationship between their period and luminosity. They were named after the star δ Cepheus. One of the most well-known Cepheids is Polaris. Astronomers consider Cepheids to be like guiding lights because their period-luminosity relationship is used as a standard for measuring distances to faraway objects.
An astronomical source can be said to have an infrared excess when its measured infrared flux is greater than what would be expected if the star emitted radiation as a perfect black body. On the left, you can see the spectral energy distribution of the white dwarf G29-38. At wavelengths longer than 2 microns, the detected emission is stronger than what would be predicted from the extrapolated visible spectrum, indicating an excess of infrared radiation.
A red supergiant is a tremendously large and massive star that belongs to the spectral class K or M and luminosity class I. Prominent examples of red supergiants include Antares and Betelgeuse.
Polars, also known as AM Hercules-type variables or AM Her, are a specific type of cataclysmic variable found in binary star systems with an incredibly powerful magnetic field. These systems consist of a dwarf star with a spectral class of dK-dM and a hot, compact object with a strong magnetic field (M). Typically, the amplitude of the brightness variation is around 1 magnitude, but the average brightness can increase by up to 3 magnitudes when the primary component is exposed to X-rays. The total amplitude of luminosity variation can be quite significant.
There are three categories of stars that closely resemble the Sun: solar-type stars, solar analog stars, and solar doubles. The study of these stars is crucial for gaining a better understanding of the Sun’s properties and determining whether it is unique or typical compared to other stars. Additionally, it helps us explore the possibility of habitable planets existing in other solar-type stars.
A substellar object, also known as a substar, refers to an astronomical object with a mass lower than the minimum required for hydrogen combustion nuclear reactions (approximately 0.08 solar mass). This includes brown dwarfs and EF Eridanus B-type stars, and potentially planetary-mass objects, regardless of their formation mechanism or relationship to the host star. Assuming that the substellar object has a composition similar to the Sun and a mass equal to or greater than that of Jupiter.
Wolf-Rayet stars are a type of stars that have a very high temperature and luminosity. They are different from other hot stars because their spectrum shows broad bands of hydrogen, helium, as well as oxygen, carbon, and nitrogen in varying degrees of ionization (N – N, C – C, O – O). These stars are named after the French astronomers Charles Wolf and Georges Rayet, who first noticed these features in their spectra in 1867.
The chromosphere, which comes from the Greek words χρομα (color) and σφαίρα (ball, sphere), is the outer layer of the Sun and other stars. It is about 10,000 km thick and surrounds the photosphere.
Phoenix (Latin: Phoenix, Phe) is a constellation located in the southern hemisphere of the sky. It covers an area of 469.3 square degrees and contains 68 stars that can be seen without the aid of a telescope.
Cataclysmic variables, also known as CVs, are a class of astronomical objects that belong to the category of variable stars and display cataclysmic activities such as flares. These objects are close binary systems consisting of a main star, which is typically a white dwarf, and a companion star, usually a low-mass red dwarf. However, in some cases, the companion can be another object.
A debris disk is a disk of dust and debris that orbits around a star. These disks may be a transitional phase in the formation of planetary systems, following the protoplanetary disk phase. Another theory suggests that debris disks are formed and sustained by the remnants of collisions between planetesimals.
A globular star cluster, also known as a globular cluster, is a cluster of stars that are closely bound by gravity and orbit around the galactic center as a satellite. Unlike dispersed star clusters, which are found in the galactic disk, globular clusters are located in the halo of the galaxy. They are much older and contain a larger number of stars. These clusters have a symmetrical spherical shape and are characterized by an increasing concentration of stars towards their center. They exhibit spatial concentrations.
Luminous blue variables (LBV), also referred to as S Doradus variables (SDOR), are highly luminous blue pulsating hypergiants that derive their name from the star S Dor in the Large Magellanic Cloud. These stars exhibit irregular (and sometimes cyclic) fluctuations in brightness, with amplitudes ranging from 1m to 7m. They typically stand out as the most brilliant blue stars within their respective galaxies. In general, LBVs are found in association with diffuse nebulae, which often surround them.
The galactic halo, also known as the stellar halo, represents an imperceptible constituent of a galaxy, constituting the primary component of its spherical subsystem. This halo possesses a spherical configuration and extends beyond the visible boundaries of the galaxy. It primarily consists of rarefied hot gas, stars, and dark matter, which collectively constitute the majority of the galaxy’s mass.
The following is a list of the most prominent stars that can be seen from Earth in the optical range, based on their apparent stellar magnitude. In cases where there are multiple stars, the combined stellar magnitude is provided.
Naugol (also known as Norma in Latin) is a constellation located in the southern hemisphere of the sky. It is situated southwest of Scorpius and north of the Southern Triangle, with a point of contact with the Circulus. While both branches of the Milky Way pass through this constellation, it is not abundant in bright stars. There are no stars in this constellation that are brighter than a visual sidereal magnitude of 4.0. However, there are a total of 42 stars that can be seen with the naked eye, and the constellation covers an area of 165.3 square degrees in the sky. The best time for observing this constellation is during May and June, and it is partially visible in southern Russia (south of 48 N).
Eclipsed stars (also known as eclipsed interlaced stars, eclipsed doubles, or photometric doubles) are stellar systems that exhibit periodic changes in brightness due to one star eclipsing another.
Absolute stellar magnitude is a scientific measurement that describes the intrinsic luminosity of an astronomical object. Various definitions of absolute magnitude are used for different types of celestial bodies.
Beta Painter is a moving group of stars situated in close proximity to the Solar System. This young group of stars shares a common motion and origin.
Interstellar dust is composed of tiny solid particles that fill the space between stars, along with interstellar gas. Scientists currently believe that these dust particles have a core made of refractory material, which is then surrounded by either organic matter or an icy shell. The composition of the core depends on the atmosphere of the stars in which the particles formed. For instance, if the particles formed in the atmosphere of carbon stars, they would consist of graphite and silicon carbide.
Slow irregular variables are a type of variable star that exhibit changes in brightness without any clear pattern or periodicity. Sometimes, these changes may occur only sporadically. It is often difficult to classify these stars as slow irregular variables due to limited research on them. Further study may reveal that some of these stars are actually semi-regular variables or belong to other types of variable stars.
Puppis (Latin: Puppis) is a constellation located in the southern hemisphere of the celestial sphere and can be found in the Milky Way. It covers an area of 673.4 square degrees and contains a total of 241 stars that can be seen without the aid of a telescope. The visibility of Puppis varies depending on the observer’s location, with more of the constellation being visible the further south one is. The brightest star in Puppis, ζ Puppis, can be seen starting at a latitude of 50 degrees. In Adler, this star rises at approximately 6 degrees 30 minutes, while in the southern part of Dagestan it rises at around 8 degrees 30 minutes. The southernmost cities also have the opportunity to observe this constellation.
Redshift is the displacement of the spectral lines of chemical elements towards the red end of the spectrum, usually associated with a longer wavelength. This occurrence can be attributed to various factors such as weak diffuse scattering, the Doppler effect, gravitational redshift, or a combination of these phenomena. Conversely, when the spectral lines shift towards the violet end of the spectrum, it is referred to as blue shift. The French physicist Hippolyte Fizeau was the first to describe the shift of spectral lines in celestial bodies’ spectra in 1848, proposing the Doppler effect as the cause behind this shift.
An intermediate polar (also known as a transitional polar or Hercules DQ-type variable) refers to a specific category of cataclysmic variables found in binary star systems. In the majority of cataclysmic variables, material from a main sequence companion star is expelled onto a white dwarf in the form of an accretion disk. Occasionally, another object like a subgiant or a red giant can act as the companion star. However, in the case of intermediate polars, the magnetic field of the white dwarf disrupts the accretion disk, leading to its destruction. Ultimately, this process leads to the termination of the system.
A close binary system is a type of binary system in which, during certain stages of its development, its individual components can transfer mass between each other. The distance between the stars in a close binary system is comparable to the size of the stars themselves. As a result, more complex effects occur in these systems in addition to simple gravitational attraction, such as tidal distortion of shape and heating from a brighter companion. The exchange of matter significantly influences the evolution of the stars in close binaries.
Foxglove, also known by its Latin name Vulpecula, is a faint constellation located in the northern hemisphere. It is situated within the Summer Triangle.
Supergiants are among the most massive stars. They are located at the top of the Hertzsprung-Russell diagram. In the Yerkes classification, supergiants are classified as either class Ia (bright supergiants) or class Ib (less bright supergiants). The total absolute stellar magnitude of a supergiant usually falls between -5m and -12m. Supergiants that are exceptionally bright, with a magnitude brighter than -8m, are often classified as hypergiants.
Surface gravity refers to the acceleration of free fall experienced on the surface of an astronomical or other object. It can be thought of as the acceleration due to attraction experienced by a hypothetical test particle located near the surface of an object, with a negligibly small mass so as not to disturb it.
Earth mass (denoted as M⊕ in astronomy, where ⊕ represents the Earth symbol) refers to the mass of the planet Earth and serves as a unit of mass in astronomy. 1 M⊕ is equivalent to (5.9722 ± 0.0006) × 1024 kg.
The diagram of Hertzsprung-Russell (also known as Hertzsprung-Ressell diagram, Russell diagram, G-P diagram, or color-stellar magnitude, spectrum-luminosity diagram) illustrates the correlation between absolute stellar magnitude, luminosity, spectral class, and surface temperature of a star. Stars on this diagram can be observed in distinct regions.
A giant star is a celestial body that has a significantly larger radius and higher luminosity compared to main-sequence stars with the same surface temperature. Generally, giant stars have radii ranging from 10 to 100 times that of the sun and luminosities ranging from 10 to 1000 times that of the sun. Stars with even greater luminosities than giant stars are known as supergiants and hypergiants. White giants, on the other hand, refer to hot and bright main-sequence stars. Additionally, their large radius and high luminosity make them easily distinguishable.
A circumstellar disk refers to a cluster of matter in the shape of a torus or ring, composed of gas, dust, planetesimals, or asteroids, that orbits around a star.
Stellar rotation refers to the spinning motion of a star around its axis. The speed of rotation can be determined by observing the displacement of lines in its spectrum or by tracking the movement of active elements, known as “starspots,” on its surface. As a star rotates, it develops a bulge around its equator due to centrifugal forces. Additionally, because stars are not solid objects, they may exhibit differential rotation, meaning that the equator of a star may rotate at a different rate than areas near the poles.
A planetary nebula is a celestial entity comprising of a shell of ionized gas surrounding a central star known as a white dwarf. These nebulae are created during the final stages of evolution of red giants and supergiants, when their outer layers (shells) are shed. The formation of a planetary nebula is a relatively rapid process in astronomical terms, lasting only a few tens of thousands of years, while the lifetime of the progenitor star is several billion years. Currently, there are numerous planetary nebulae in existence.
Blue stragglers are stars in globular star clusters that have higher temperatures than normal stars, and their spectra are significantly shifted towards the blue region compared to other stars in the cluster with the same brightness. This characteristic sets them apart from other stars in the Hertzsprung-Russell diagram for the cluster. In terms of their appearance, the blue stragglers defy the conventional theories of stellar evolution, which apply to all stars that form.
The evolution of a star in the field of astronomy refers to the series of transformations that a star experiences throughout its lifespan, which can span millions or billions of years, as long as it continues to emit light and heat. These changes are quite substantial over such immense time periods.
“New stars” are commonly referred to as “Novae” in astronomical literature. Novae are stars that experience a sudden increase in luminosity by a factor of approximately 10^3-10^6 (on average, the luminosity increases by a factor of around 10^4, resulting in a luminosity increase of approximately 12 stellar magnitudes).
All newly formed stars, including those that resemble new stars and cataclysmic variables, are binary systems consisting of a white dwarf and a companion star. The companion star can either be on the main sequence or have reached the red giant stage during its evolution and filled its Roche cavity. In these systems, the outer layers of the companion star transfer matter to the white dwarf through the Lagrangian point L1. This matter forms an accretion disk around the white dwarf, and the rate at which it accretes onto the white dwarf remains constant. This rate is determined by the parameters of the companion star and the mass ratio of the two stars in the binary system. The gas that falls onto the white dwarf has a composition that is typical for the outer layers of red giants and main-sequence stars, with hydrogen making up more than 90% of the gas.
The pressure of a degenerate gas is temperature-dependent: the emergence of a new (CNO-cycle reaction) flare occurs on a flat section.
White dwarfs are the remnants of red giants that have shed their outer layers during their evolution; their composition is determined by the mass of the original star: less massive stars evolve into helium white dwarfs, while higher-mass stars undergo triple helium reactions in their cores and become carbon white dwarfs. However, two factors are crucial for the occurrence of a new flare: a very low hydrogen content and the degenerate state of the white dwarf matter.
Following the ignition of the flare, a fresh cycle of accretion takes place on the white dwarf and the hydrogen layer gradually builds up. After a certain period of time, determined by the rate of accretion and the characteristics of the white dwarf, the flare occurs once again. The time interval between flares can vary greatly, ranging from several decades for recurrent novae to several millennia for classical novae.
During his observation of supernova SN 1572 in the constellation Cassiopeia, astronomer Tycho Brahe perceived it as a new star (de stella nova), thus coining the term “nova.” In his writings, he reasoned that since the movement of nearby objects should be detectable in relation to fixed stars, the nova must be situated at a considerable distance.
Over a span of 2200 years (532 B.C. to 1690 A.D.), approximately 90 instances of Novae flashes were documented in Chinese and Japanese historical records. Following the invention of the telescope in 1609 and prior to the Eta Kiel outburst in 1843, European scientists only recorded 5 occurrences of Novae flares. Starting from the latter half of the 19th century, Novae flares were regularly observed on an annual basis. In 1866, William Huggins conducted the first spectroscopic observations of a Nova star, specifically Nova Northern Corona 1866, and detected the presence of a luminous gas shell surrounding it, emitting hydrogen lines. Throughout the 20th century, there were only 5 years in which no Nova flares were observed: 1908, 1911, 1923, 1965, and 1966. In the 21st century, it is customary to observe up to 10 Nova flares per year. The majority of Novae have a luminosity surpassing that of 12 stars, although it rarely exceeds 6 stars.
The new novae may have a promising opportunity to serve as standard candles. Let’s assume, for instance, that the distribution of their absolute stellar magnitude is characterized by two distinct peaks, one major peak at -7.5 and a minor peak at -8.8. Additionally, the absolute stellar magnitude of the nova remains relatively constant at -5.5 for approximately 15 days following the explosion. Utilizing novae to determine the distances of galaxies and galaxy clusters yields comparable accuracy to that of using Cepheids.
Before 1925, stars that were discovered were given names based on Friedrich Argelander’s 1862 system for variable stars. The name consisted of a letter index representing the order of discovery in the constellation, followed by the name of the constellation. For example, a star discovered in 1901 in the constellation Perseus would be named GK Per according to this system. Since 1925, newly discovered stars have been designated as variable stars, using the index V followed by the order number of discovery in the constellation and the name of the constellation. For example, a star discovered in 1975 in the constellation Perseus would be designated as GK Per. A star discovered in the constellation Cygnus would be designated as V1500 Cyg.
Cataclysmic Variable stars (CV) have a subclass known as New stars. This subclass is further divided into two types: classical novae, which have long periods between outbreaks, and recurrent novae, which have frequent outbreaks.
- Na – rapid novae, also known as rapid novae, with GK Per as a representative example.
- Nb – slow novae, also known as slow novae.
- Nc – extremely slow novae, also known as extremely slow novae, with RT Ser as a representative example.
- NR – recurrent novae, also known as recurrent novae.
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Overview
Not all celestial bodies follow the tranquil course of their life cycle (the progression of a typical star), starting as a condensed mass of diminishing gas and dust nebulae and ending as an incredibly dense, frigid black dwarf in its advanced “elderly” stage. Occasionally, certain stars experience a cataclysmic burst during their final phase and transform into a spectacular cosmic spectacle. These extraordinary events are known as “supernovae.” A supernova can emit a luminosity equivalent to approximately 500 million suns.
“Normal” new stars should be distinguished from “supernovae” stars. The explosive power of these stars is thousands of times less than that of supernovae. New stars erupt relatively frequently (approximately 100 eruptions per year occur in our galaxy). New stars are characterized by repeated outbursts that do not significantly alter the structure of the stars. On the other hand, a supernova eruption represents a radical transformation and even partial destruction of the star’s composition.
Thus far, we are not aware of any catastrophes that surpass the scale of supernovae. (Although astonishing phenomena like exploding galactic nuclei, which are incomparably more breathtaking than supernovae, appear to have only been discovered recently.)
Within a matter of days, a supernova undergoes a rapid increase in luminosity by hundreds of millions of times. It so happens that a solitary star emits more light in a brief period than billions of stars within the galaxy in which the explosion transpires.
Naturally, a formidable cosmic explosion ultimately results in the demise of the star and catastrophic ramifications in its immediate surroundings. Nevertheless, the occurrence of a cosmic explosion within the framework of preserving and redistributing the energy equilibrium of galaxies is likely not coincidental, but rather a natural phenomenon.
Explosions of Supernovae in Our Galaxy
Unlike the bursts of “typical” newly formed stars, this occurrence is exceptionally uncommon. In our galaxy, there exist approximately 100 billion stars. It is estimated that around 1-10 new stars are generated annually. In contrast, supernovae erupt only once or twice per century on average. Consequently, such eruptions are infrequently observed in other galaxies. If several hundred galaxies are systematically “under surveillance,” it is highly probable that at least one of these galaxies will encounter a supernova outbreak within a year. Currently, approximately 20-30 extragalactic supernovae are identified each year. Their cumulative count reaches almost 600.
After the year 1054, two additional supernovae have been observed within our galaxy: one in 1572 by Tycho Brahe, a Danish astronomer, and the other in 1604 by Johannes Kepler. Following this, there was a 300-year period without any new discoveries. However, even after their initial explosion, the remnants and effects of supernovae on the interstellar medium can still be detected.
Nebula
The Crab Nebula
After the supernova explosion in 1054, which occurred seven and a half centuries ago, an astronomer from France named Charles Messier included a uniquely shaped object as number 1 in his well-known catalog of nebulae. This object was later given the name the Crab Nebula. Unfortunately, this nebula cannot be seen with the naked eye. However, its image was captured by exposing a photographic plate for an extended period of time at one of the most advanced astronomical observatories.
The bright object’s fiber structure bears resemblance to the crab nebula, which is why it was given the name the Crab Nebula. Astronomers interpret this structure as evidence of turbulent activity at the object’s core. This activity becomes even more apparent upon closer examination of the nebula. For instance, measurements of the luminous matter’s velocity within the nebula indicate that it is moving away from the object’s center at speeds of approximately 1000 km/s or higher. Recent studies utilizing radio and X-ray technology have revealed that the Crab Nebula also emits radio waves, X-rays, and gamma rays. It is believed that this extraordinary phenomenon is the aftermath of a stellar explosion that occurred many centuries ago, specifically in July 1054.
Additional observations have revealed that the Crab Nebula is undergoing a gradual expansion, almost as if it is spreading out across the expanse of the sky. Given that the distance to this nebula is approximately 2000 parsecs, the substantial increase in its size in the celestial sphere indicates that the gases within it are moving at an astounding velocity of 1500 kilometers per second, which is over 100 times faster than that of man-made satellites. In comparison, the typical speed of gas nebulae within our Milky Way galaxy rarely exceeds 20-30 kilometers per second. This suggests that only an immensely powerful explosion could have generated such a massive amount of gas, propelled at such an incredible velocity. Based on the observed velocity of the Crab Nebula, it can be deduced that approximately 900 years ago, the entire nebula was concentrated within an exceedingly small volume, and that what remains today is merely a fragment of a colossal cosmic catastrophe – a supernova detonation.
Originating from common nebulae.
In 1949, scientists made the groundbreaking discovery that the Crab Nebula emits a significant amount of radioactivity. The mechanism behind this phenomenon was quickly understood: highly energetic electrons, propelled by magnetic fields within the nebula, generate radiation. This same process accounts for the radio emission observed throughout the entire galaxy. Consequently, when a supernova occurs, it releases an immense quantity of ultra-high-energy particles known as cosmic rays. As the nebula expands and disperses, these cosmic rays escape into the vast expanse of interstellar space. Considering the frequency of supernova eruptions within the galaxy, the cosmic rays produced during these events are more than sufficient to saturate the galaxy at its current density.
This discovery provides the initial concrete proof that supernovae play a significant role in rejuvenating cosmic rays within the Milky Way galaxy, while also enriching the interstellar medium with heavier elements. This has profound implications for the development of stars and the overall evolution of our galaxy.
Furthermore, the Crab Nebula possesses another extraordinary attribute. Approximately 95% of its optical emissions originate from “synchrotron” radiation, which is also generated by super-energetic electrons. According to a novel hypothesis concerning the Crab Nebula’s optical emissions, it was predicted that this radiation would exhibit polarization. Subsequent observations by scientists have fully vindicated this theory. Since then, optical synchrotron radiation has been identified in numerous other celestial objects, predominately radio galaxies.
In 1963, a rocket equipped with instruments was able to detect strong X-ray radiation coming from the Crab Nebula. However, in 1964, when the Moon passed in front of the nebula, it was discovered that the source of the X-rays was actually the nebula itself and not a star that had previously undergone a supernova explosion. X-ray images of the Crab Nebula have also revealed synchrotron characteristics.
X-rays are completely absorbed by the Earth’s atmosphere, making it necessary to use rockets and satellites to observe them. The Einstein satellite, launched on the 100th anniversary of the famous scientist’s birth, provided particularly valuable data in this field.
Further observations have revealed that all nebulae, which are remnants of supernova explosions, emit radio waves of similar nature to those emitted by the Crab Nebula.
Nebula in the Cassiopeia constellation
The Cassiopeia Nebula is a highly radioactive celestial object. It emits radio waves at meter wavelengths that are ten times stronger than those emitted by the Crab Nebula, despite being located at a significant distance from it. In terms of optical emission, this rapidly expanding nebula appears very dim. The Cassiopeia Nebula is the remnants of a supernova explosion that occurred approximately 300 years ago. It is unclear why the star that triggered the explosion was not discovered during that time, considering that European astronomy was quite advanced.
The IC 443 Nebula and the Filament Nebula in the Swan constellation also emit radio waves, although they are ten times less intense than those emitted by the Crab Nebula.
The Great Nebula in the Orion constellation
This particular area within the Universe is believed to be experiencing active star formation in the present era. Situated approximately 1500 centauri away from our location, it hosts a significant number of protostars. Within these protostars, the internal temperature has not yet reached the level required for thermonuclear reactions to occur. However, the temperature is sufficient for the protostars to emit energy at an intense level, primarily in the infrared portion of the electromagnetic spectrum. Multiple sources of infrared radiation have been observed within the Orion Nebula, providing confirmation of ongoing star formation.
Two types of supernovae
Up until now, our primary focus has been on the nebulae that are created as a result of supernovae. However, let’s now turn our attention to the stars themselves. As we mentioned earlier, the information we have about supernovae comes from observing them in other star systems. In our own galaxy, the most recent supernova was recorded in 1604. This particular star was observed by Kepler, who made the discovery without the aid of a telescope, which had not yet been invented. It wasn’t until about 250 years later that spectral analysis, a highly valuable tool in astronomical research, was first utilized.
Type II supernovae occur in spiral galaxies and do not occur in elliptical star systems. These supernovae are often associated with young, massive stars and are typically observed in spiral arms where star formation is ongoing. It is likely that a significant percentage, if not a majority, of hot, massive stars of spectral class O end their lives with a Type II supernova explosion.
The reason behind stellar explosions
There are multiple theories regarding the cause of stellar explosions, which are observed as supernovae. However, a universally accepted theory based on established facts, capable of predicting new phenomena, is yet to be established. Nevertheless, it is undeniable that such a theory will be formulated in the immediate future. Most likely, the explosion occurs due to the rapid and catastrophic release of gravitational potential energy during the inward collapse of the star’s inner layers towards its core.
Stars’ Evolution: A Journey of Explosions and Fragments
Have you ever wondered why stars explode? Is it a universal phenomenon or do only certain stars experience such cataclysmic events? And what exactly happens to a star when it explodes? These burning questions can only be answered by delving into the intricate structure and evolution of these celestial bodies. An explosion signifies a disruption of the star’s internal equilibrium, but understanding the underlying causes and timing requires a deeper knowledge of how stars maintain equilibrium in the first place.
The immense gravitational force exerted by massive objects compels them to contract. However, when the internal pressure within these objects is insufficient to counteract this contraction, they collapse. The Sun’s ability to maintain its size without succumbing to collapse is a testament to the tremendous pressure it harbors within.
Stars are believed to form through the compression of a cloud of gas and dust in space, according to modern scientific theories. As this cloud compresses, it breaks apart into smaller pieces. Each of these fragments continues to shrink, growing hotter, particularly at its core. This initial phase of a star’s existence was extensively researched by Japanese astronomer K. Hayashi. Once the temperature at the center of the star reaches a certain point, fusion reactions occur, marking the star’s entry into the mature stage.
However, there is a challenge that arises during the early stages of star formation, which is linked to supernovae.
After a star starts functioning as a nuclear reactor, its progress can be described in the following way. Initially, hydrogen is converted into helium through nuclear fusion reactions, which produces energy that counteracts the star’s gravitational collapse. As long as these fusion reactions persist, the star remains in the main sequence phase. This phase is the most extensive in a star’s lifespan and its duration is determined by the star’s mass. High-mass stars have a shorter time in the main sequence as they consume hydrogen at a faster rate.
With each successive step, a chain of reactions occurs, resulting in the formation of increasingly larger atomic nuclei. Each atomic nucleus absorbs an additional nucleus of helium, causing its charge to increase by 2 and its mass number to increase by 4. However, once the nuclei become too massive, the fusion process comes to a halt. This leads to a weakening of the resistance to gravitational forces, causing the core of the star to undergo compression and its temperature to rise.
Once the temperature reaches a certain point, a new cycle of nuclear reactions begins, temporarily halting the compression of the star. These reactions propel the atomic nuclei further up the ladder, with one helium atom being added at a time. At extremely high temperatures, even larger nuclei can undergo fusion. Thus, this multi-step process of toggling nuclear reactions on and off continues.
What occurs to the star during nuclear reactions?
The star’s fate depends on its mass. Generally, the core of the star becomes more compressed and heated, while the outer shell expands and cools. As a result, the star appears larger and redder to an outside observer (due to the cooling of the outer layer). These stars are known as red giants. (While the Sun’s surface temperature is approximately 5500°C, the surface temperature of a giant star can drop to around 3500°C. This is why the Sun has a yellowish color, while giant stars appear more red.)
This phase in a star’s life is when it is on the verge of going supernova, provided it has a sufficient mass.
The Limitation of Size. A Catastrophic Event
However, there exists a threshold concerning the magnitude of the nucleus, beyond which nuclear fusion reactions become impracticable due to energy constraints. This threshold is found within the vicinity of the iron core (with a mass number of 56), in a group known as the iron group, which encompasses iron, cobalt, and nickel. Any additional particles appended to the iron core are no longer capable of releasing energy. At this juncture, the core temperature soars to approximately 10 billion degrees Celsius, thrusting the star into a catastrophic predicament. The gravitational force that once maintained equilibrium within the scorching star is rendered ineffective. Instabilities arise within the star, leading to the collapse of its outer shell. This catastrophic phenomenon is witnessed as a supernova explosion.
A celestial explosion
The shockwave propels the matter surrounding the star at speeds exceeding the escape velocity, causing the outer layer to detach from the star and venture into the vastness of interstellar space. This process ultimately leads to the star’s explosive demise.
From an external perspective, the explosion becomes evident through a dramatic surge in the star’s luminosity, followed by a gradual and extended decline. At its zenith, a supernova can emit energy equivalent to an entire galaxy comprising up to 100 billion typical stars!
Explosion Products and Their Impact
When a star explodes, it produces various elements such as atomic nuclei, electrons, neutrinos, and radiation. These atomic nuclei can form cosmic ray streams that travel vast distances within our galaxy.
If a supernova explosion were to happen relatively close to Earth, let’s say within 100 light-years, it would have catastrophic consequences. The high-energy cosmic rays emitted from the explosion could severely damage Earth’s atmosphere. One significant effect would be the destruction of the ozone layer, leaving all life on Earth exposed to harmful ultraviolet radiation from the Sun. Thankfully, supernova explosions are relatively rare occurrences. The likelihood of a supernova happening within a distance of 100 light-years from us within the next 1,000 years is only one in a million.
Is it possible for an entire star to undergo a supernova explosion? Pulsars
There is evidence to suggest that the central core of a star may be able to withstand such an explosion. However, if this is the case, what happens to the core? A surprising experimental finding in 1968 offered a compelling solution to this inquiry.
J. Bell, a graduate student at Cambridge University’s Cavendish Laboratory, utilized a large radio telescope to conduct measurements on flickering radio sources caused by the scattering of radio waves due to irregularities in the interplanetary medium. In addition to the expected radiation, the telescope also detected an unusual pulsed emission. This discovery was unexpected for two reasons. Firstly, the emitted radiation exhibited strict periodicity, and secondly, the period of the pulses was exceptionally short. The fact that the period of the pulses can be determined with accuracy to the seventh decimal place demonstrates the remarkable regularity of the detected emission. It is also noteworthy that the value of this period was incredibly small, as no astronomical objects capable of emitting radiation with such rapid variability were known at the time.
Scientists conducted research on this unique pulsed emission. Their analysis indicated that the pulses could not have originated from a planet circling a star. Consequently, the intriguing theory that an advanced civilization was transmitting signals to us was dismissed. Instead, radio astronomers deduced that the pulses emanated from a dense astronomical object known as a
Although the chance discovery of the first pulsar, now called object SR-1919 (SR stands for Cambridge Pulsar Catalog), led to its emission properties being so anomalous that it sparked a global search for more pulsars among radio astronomers. This search yielded fruitful results. The detection of a pulsar in the Crab Nebula caused immense excitement, as it was believed to hold the key to understanding the aftermath of a supernova explosion.
Over 300 pulsars have been found to date, and astronomers have successfully unraveled the enigma of these peculiar objects’ regular, short-period emission pulses.
A pulsar – A neutron star that forms from the explosion of a supernova.
According to data on pulsar numbers and lifespans, it appears that an average of 2-3 pulsars are born every century. This aligns with the frequency of supernova explosions in the Galaxy. These findings support the theory that pulsars are neutron stars formed from supernova explosions. The existence of a pulsar in the Crab Nebula and another near a supernova remnant in the Segel constellation further substantiate this claim.
However, it is important to note that the connection between pulsars and supernovae has not been definitively proven. For astronomers who rely solely on established observational facts, this evidence may not be entirely convincing.
Supernovae and the process of star formation
It is well established that every star goes through its own unique and lengthy lifespan. Each star is born at least once and will eventually meet its demise.
While a supernova event marks the end of a star’s life, it also has a significant impact on the formation of future stars. In fact, it can even trigger the formation of a new star from a nearby gas cloud. The composition of our solar system suggests that it may have formed as a result of a supernova explosion. When shock waves from these explosions collide with interstellar gas clouds, they can cause compression and potentially lead to star formation.
Interestingly, stellar catastrophes like supernovae can also have a creative role in addition to their destructive nature. The Sun and planets may have condensed out of a contracting gas cloud, thanks to the influence of these catastrophic events.
From the perspective of star formation theory, this phenomenon is intriguing because the shockwave caused by the release of matter from a supernova could potentially trigger the initial compression of the interstellar cloud, thereby initiating the subsequent stages of the star formation process. This concept has been recently substantiated by the examination of a supernova explosion remnant linked to the R1 region of the Canis Major constellation. By analyzing the diameter of the shell and the rate at which it is expanding, we were able to estimate its age, which is approximately 800 thousand years.
It appears that the stars in proximity to this shell are in the early stages of their development, as they have not yet reached the main sequence. This means that their internal thermonuclear “reactors” have not yet activated. Scientists estimate that the age of these stars is less than 300 thousand years, making them some of the youngest known stars. This suggests that these stars were formed within the expanding envelope of a supernova. Based on calculations, it is believed that the initial force that propelled the envelope must have been incredibly powerful, indicating that it could only have been generated by a supernova explosion.
The Allende meteorite
In 1969, a meteorite descended close to the Mexican village of Pueblito de Allende. Presently, it is recognized as the Allende meteorite. This unassuming piece of substance from our solar system has surprisingly been associated with a supernova. It all comes down to isotopic anomalies. (Isotopes of a specific chemical element are atoms whose nuclei contain the same specified number of protons but different numbers of neutrons.) Isotopic anomalies pertain to disparities in the relative content of diverse isotopes in the substance of a meteorite and in the average isotopic composition of matter observed in the solar system.
When a star bursts, it releases its outer layer of material (such as hydrogen, helium, carbon, and oxygen) into the surrounding space between stars. These impurities will temporarily contaminate the surrounding environment. However, over time, these impurities will disperse and blend with other material in space. Therefore, if new stars form in an area where a star burst occurred a long time ago, their isotopic composition should be uniform. On the other hand, if stars form shortly after a star burst, the “contamination” of the star burst environment will result in a diverse chemical composition among the stars (as well as planets, comets, meteorites, etc.).
The isotopic anomalies of the Allende meteorite provide clear evidence for a supernova explosion. Moreover, the presence of these variations in the composition of Solar System matter, as demonstrated by the Allende meteorite, strongly supports the idea that the Solar System originated shortly after a nearby supernova detonation.
Summary
Our discussion regarding stellar explosions and related occurrences has come to a close. The expulsion of the outer layer into space and the preservation of the star’s core during a supernova explosion are linked to various fascinating phenomena. These include the stimulation of star formation, the ejection of matter into the interstellar medium that undergoes a series of transformations through thermonuclear reactions in stars, the creation of neutron stars and potentially black holes, and the formation of pulsars and cosmic rays.
There are still numerous unanswered inquiries regarding the interaction between supernovae and their surroundings. It is certain that both theoretical and experimental investigations in this field will yield significant findings.
List of literature
- V.N.Demin “Secrets of the Universe”. Published by “Veche”, Moscow, 1999.
- J.Narlikar “The Unquiet Universe”. Published by “Mir”, Moscow, 1986
- I.S.Shklovsky “Universe. Life. Mind”. Published by “Nauka”, Moscow, 1988
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