Great Diamond of Virgo (Asterism)      Arcturus  Spica   Denobola  Cor Caroli

Thus, during this stargazing, I had gazed at 57 different stars one by one while uttering their names simultaneously.

Example 2

On 15 October 2021, around 4:20am, I had done Stargazing as given below.

Thus, during this stargazing, I had gazed at 60 different stars one by one while uttering their names simultaneously.

Example 3

On 16 October 2021, around 8:20pm, I had done Stargazing as given below.

Thus, during this stargazing, I had gazed at 37 different stars one by one while uttering their names simultaneously.n

Galaxies: A galaxy is a collection of around 1 billion stars.

There are four basic kinds of galaxies: spirals, ellipticals, lenticulars, and irregulars.

1. Spiral galaxies are disk-shaped, with a brighter bulge at the center of the disk and contain the spiral arms. The central bulge consists primarily of red stars, whereas the spiral arms contain a mixture of red and blue stars.

1a. Some spiral galaxies have a 'bar' going across their central bulge, and are referred to as 'barred spiral galaxies'. Barred spiral galaxy represented by SB and unbarrred spiral galaxy is represented by S.

1b. Spiral galaxies can also be classified based on the ratio of bulge size to disk size.

Type a spiral galaxies have a very large central bulge in comparison to their disk. Their spiral arms are tightly wound.

The Sombrero galaxy (M104) in the constellation Virgo is a Type a spiral galaxy (Sa).

Type c spiral galaxies have a very small central bulge in comparison to their disk. Their spiral arms are wide open.

The Whirlpool galaxy (M51) in the constellation Canes Venatici and the Pinwheel galaxy (M101) in the constellation Ursa Major are Type c spiral galaxies (Sc).

 Intermediate between these two is type b spiral galaxy (Sb).

The Bode’s Galaxy (M81) in  the constellation Ursa Major is a type b spiral galaxy (Sb).

M91 in Coma Berenicis is a barred type b spiral galaxy, so it is classified as SBb.

Millky Way is thought to be a barred type b spiral galaxy,

The Andromeda galaxy (M31) is also a type b spiral galaxy (Sb), similar to the Milky Way in overall shape.

M31 is the biggest, brightest and nearest galaxy visible in the Northern Hemisphere. M31 (NGC 224) is around 2.5 million ly away and 200000 ly across.

M31 is only one of the few extra-galactic objects that is blue-shifted that is it is approaching our galaxy. Virtually all other galaxies are red-shifted that is they are moving away from us and from each other due to the expansion of the universe. .

1c. Spiral galaxies can also be classified based on the structure of their spiral arms.

Those galaxies whose spiral arms can be traced continually from the core to the periphery are called ‘grand design spiral galaxy’. 

The Whirlpool galaxy (M51) in the constellation Canes Venatici and the Bode’s Galaxy (M81) in the constellation Ursa Major are grand design spiral galaxies.

M74, M83 are also grand design spiral galaxies. M51 is type c spiral galaxy and M81 is type b spiral galaxy.

Those galaxies whose spiral arms cannot be traced continually from the core to the periphery are called ‘flocculent’ spirals.

The Sunflower galaxy (M63) in the constellation Canes Venatici is a flocullent galaxy.

2. Elliptical galaxies are those whose basic shape as projected on the sky is an ellipse. They contain no spiral arms.

Elliptical galaxies are designated by “E” followed by a number from 0 to 7.

A perfectly rounded elliptical galaxy is classified as E0, whereas a highly 'stretched' elliptical galaxy is classified as E7.

At the center of the Virgo cluster, there is a giant elliptical galaxy M87 (E0 to E01) located on the line segment connecting Vindemiatrix (Virgo) and Denebola (Leo).

M87 (NGC 4486) is about 55 million ly away and 132000 ly across. It contains over one trillion stars and about 15000 globular clusters. M87 has a supermassive black hole at its core – Powehi, which is responsible for a large jet structure emanating from the nucleus of M87.

M32 and M110 are satellite galaxies of M31. M32 (class E2) and M110 (class E6) are both dwarf elliptical galaxies. M110 and M32 are found above and just below the bulge of M31 respectively.

M32 and M110 are ~2.57 million ly away and 6500 ly and 16000 ly across respectively.

Cygnus A in the constellation Cygnus is an elliptical galaxy. It is about 600 million light years away.  Cygnus A is a radio galaxy, one of the strongest radio sources in the sky.

3. Lenticular galaxies often appear much like an E7 elliptical, but they have a definite disk and a central bulge surrounded by a flattened disk. However, they contain no trace of spiral arms.

Lenticular galaxies are designated by S0. M84 in Virgo and M85 in Coma Berenices are lenticular galaxies.

4. Irregular galaxies don’t have a distinct regular shape, unlike a spiral or elliptical gakaxy. They generally have no central bulge.

Irregular galaxies are subdivided into (at least) two subclasses.

Irr-l galaxies are those which do have some trace of spiral structure, but not enough to be classified as a true spiral.

Irr-ll galaxies are those which do not have any trace of spiral structure. They are very rare.

Large Magellanic Cloud (LMC) crossing the border of constellations Dorado and Mensa, and Small Magellanic Cloud (SMC) in the constellation Hydrus are both dwarf irregular galaxies in the southern hemisphere. They are both Irr-l galaxies.

For Northern Hemisphere observers, M31 is the only easy naked-eye galaxy. For Southern Hemisphere observers, LMC and SMC are two naked-eye galaxies.

LMC and SMC are satellite galaxies to the Milky Way.

LMC is 163000 ly away and 14000 ly across. us

SMC is 206000 ly away and 7000 ly across. us.

Milky way is 100000 light years across.

LMC was the host galaxy to Supernova 1987 A.   

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There are many types of double stars or binary stars.

Optical double means the two stars only appear to be close together in the sky, but are in fact at different distances.

Visual or true binary means the two stars can be separated in a telescope.

Eclipsing binary shows a change in brightness as one star eclipses the other.

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Location of some constellations and stars

1. In winter evening sky (mid-January, 9:00pm), the constellation Orion is high in the south.
Orion’s belt asterism consists of three bright stars: Alnitak, Alnilam, Mintaka, in a straight line, relatively close together at equal distances. Mintaka is at the western end of the Orion’s Belt in winter sky when viewed facing south. Alnitak is at the eastern end of the Orion’s Belt in winter sky. Alnilam is between them.
Four stars forming a rough rectangle surround Orion’s Belt. Upper east star is Betelgeuse (red supergiant, claa M2Ib), upper west star is Bellatrix (blue giant, class B2III), lower west star is Rigel (blue supergiant, class B8I) and lower east star is Saiph (blue supergiant, class B0.5Ia).

Just below Orion’s belt lies Orion’s sword. It consists of three stars, fainter and closer together than the belt stars, and is oriented more vertically (in a roughly north-south fashion). The middle star of this sword is the combined light of the Trapezium and the Orion Nebula.

A cosmic cloud called the Orion Nebula (M42) is primarily composed of hydrogen, helium, and other ionized gases, as well as dust particles. 

The Orion Nebula is a stellar nursery or star-forming region, meaning it's where new stars are being born.

Orion Nebula includes a group of four young bright hot massive stars near the center called the Trapezium or Theta¹ Orionis.

The four stars of the trapezium are called  Theta¹ Orionis A, Theta¹ Orionis B, Theta¹ Orionis C and Theta¹ Orionis D.

Theta¹ Orionis A is a triple star system including eclipsing binary.

Theta¹ Orionis B is a 5-star system including eclipsing binary.

Theta¹ Orionis C is a Spectroscopic binary.

Theta¹ Orionis D is also a double star.

Theta-1 Orionis C is the brightest and most massive star of the Trapezium open cluster within M42 Orion Nebula

It is the hottest naked eye star. Its apparent visible magnitude is 5.1.

Theta¹ Orionis C is blue main squence, class (Spectral type) O6V. Primary component C1 is O-type main sequence, other component C2 is B-type main sequence.

Trapezium Cluster is responsible for heating the Orion Nebula and causing it to glow.

UV light from Theta¹ Orionis C1 is the primary cause of the glow that illuminates the Orion Nebula.

The Trapezium stars are very young, only about 0.3 to 1 million years old whereas the sun is 4.5 billions years old.

To the east, the line of the Orion’s Belt points towards Sirius, the brightest star. To the west, the line of Orion’ Belt point towards Aldebaran

The brightest star in Taurus is Aldebaran (red giant, class K5III).
Aldebaran is located amongst a cluster of much fainter stars forming a 'V' shape. The left end point of this 'V is Aldebaran. The 'V' is a true cluster of stars called the Hyades cluster. Aldebaran is not actually part of the Hyades cluster.
The Pleiades (M 45), one of the best naked eye open star clusters containing hot B-type stars is located in the Constellation Taurus. Pleiades is just west of the Hydaes. M45 consists of a few hundred stars but only six or seven are visible to the unaided eye. They form a shape resembling a tiny little dipper.

The constellation Auriga is directly north of Orion, and looks like an uneven Pentagon. The brightest star in Auriga is Capella. Capella (in Auriga) is a double binary star system which includes a yellow giant binary star. Two stars of binary pair are G0lll and G5lll respectively and are the brightest stars of the system.

The constellation Perseus is west of Auriga and north of the Pleiades  The second brightest star in Perseus is Algol.
Algol is an eclipsing binary. Every 2.87 days, the faint star passes in front of the bright one, blocking some of its light. Thus every 2.87 days, Algol drops in brightness down to magnitude 3.4 for a few hours, and then goes back to its normal brightness of magnitude 2.1.

The constellation Gemini is east of Auriga. Two brightest stars in Gemini are Pollux (orange giant) and Castor (multiple star system). Pollux is the one farther south.
 
The small constellation Canis Minor is in between Sirius and Pollux. The brightest star in Canis Minor is Procyon (white main sequence, class F5V).
 
Sirius (in Canis Major), Procyon (in Canis Minor) and Betelgeuse (in Orion) form the astersim called Winter Triangle.
Winter Triangle: Sirius, Procyon, Betelgeuse
Rigel (in Orion), Aldebaran (in Taurus), Capella (in Auriga), Pollux (in Gemini), Procyon (in Canis Minor) and Sirius (in Canis Major) form the astersim called Winter Hexagon.
Winter Hexagon: Rigel, Aldebaran, Capella, Pollux, Procyon, Sirius.

2. In spring evening sky (mid-april, 10:00pm), the constellation Leo is very high in the south.
The brightest star in the constellation Leo is Regulus. East of Regulus is a group of three stars, which form a right triangle. The eastern vertex of this triangle is the star Denebola.
Regulus is a widely separated main sequence binary star. Two components are separated by 177 arc-seconds. Regulus A is class B7V. Regulus B is class K2V.
M65, M66, GC3628 are spiral galaxies and form a triangle called Leo Triplet. These three are near chort in the constellation Leo.

The faint constellation Cancer is west of Leo. It lies just about halfway in between Gemini and Leo. It has the shape of an upside down letter 'Y'.
 
The constellation Coma Berenices is east and slightly north of Leo. It consists of only faint stars.
Black Eye galaxy (M64) is located in Coma Berenices and is just north of the Virgo cluster.
Black Eye galaxy (M64) is famous because about half the spiral disk is obscured by dust giving the galaxy a very unusual appearance.
 
The constellation Bootes is just east of Coma Berenices. It is shaped like a kite. The brightest star in Bootes is Arcturus (red giant,class K2III). It forms the base of the kite.

Stars or constellations whose declination is greater than 90° minus your latitude never go below the horizon and are visible all night, year-round. These stars and constellations are called circumpolar.

The constellation Ursa Major is circumpolar for northeen latitudes. But it is highest in the north in late spring sky.
Ursa Minor is also circumpolar for northern latitude.
 

The astersim Big Dipper is a part of the constellation Ursa Major.

The seven stars of the Big Dipper in order of decreasing brightness are:

Alioth, Dubhe, Alkaid, Mizar, Merak, Phecda, Megrez.

Alkaid and Mizar are the last and middle stars respectively in the handle of the Big Dipper. The two stars (Dubhe and Merek) on the edge of the bowl of the Big Dipper point directly to the North star Polaris which is about five times the distance between Dubhe and Merek away from Dubhe.

The astersim Little Dipper is a part of the little constellation Ursa Minor.

The six stars of Little Dipper in order of decreasing brightness are:

Polaris, Kochab, Pherkad, Akhfa al Farkadain, Yildun, Anwar al Farkadain.

Polaris is the last star in the handle of the Little Dipper. The two stars (Kochab and Pherkad) on the edge of the bowl of the Little Dipper are only slightly fainter than Polaris. The rest of the stars in Ursa Minor are much fainter.

Bode’s galaxy (M81) and M82 are located just north of Ursa Major and they are circumpolar for mid-northern latitudes.
The constellation Draco winds up in between Ursa Major and Ursa Minor.

The constellation Canes Venatici is north of Coma Berenices. The brightest star in Canes Venatici is Cor Caroli.
Cor Caroli (in Canes Venatici) is the blue-white binary star. It is visible to the unaided eye as a single star. A small telescope resolves this binary star into two components which are 19.6 arc-seconds apart. The brighter star in Cor Caroli is class A0 whereas the fainter star is class F0V.
Whirlpool galaxy (M51) is located in Canes Venatici, and is very close to the Big Dipper. M51 is just northwest of Alkaid at about half the distance betweem Alkaid and Mizar.
The Whirlpool galaxy (M51) is actually two galaxies in the process of collision. The larger galaxy M51A is the grand design spiral, and is the brighter of the two. M51 (NGC 5194) is around 23 million ly away and 600000 ly across.
 
The fairly large constellation Virgo is south east of Coma Berenices. The brightest star in Virgo is Spica.
Spica (in Virgo) is one of the bluest bright stars in the southeastern sky, early in the spring evening, class B1V.
 
Sombrero Galaxy (M104) is located in Virgo and is just to the left of the line segment connecting Algorab (Corvus) and Porrima (Virgo), about one-third of the way up. It is west of Spica (Virgo).
The Sombrero Galaxy (M104) is famous because of the striking dust lane around the galaxy’s perimeter.
M104 (NGC 4594) is around 29 million ly away and 500000 ly across.

Arcturus (in Bootes), Spica (in Virgo), Denobola (in Leo) and Cor Caroli (in Canes Venatici) form the astersim called Great Diamond of Virgo.
Great Diamond of Virgo: Arcturus, Spica, Denobola, Cor Caroli
 

3. In summer evening sky (mid-july, 11:00pm), Bootes is high in the west.
The small constellation Corona Borealis is just east of Bootes. This constellation forms an almost perfect little half-circle of stars.

The constellation Hercules is just east of Corono Borealis. The stars Eta, Pi, Epsilon, and Zeta Herculis form a trapezoid. This trapezoid contains Hercules Globular Cluster (M13).This globular cluster is located one-third of the way down from Eta to Zeta Herculus.

Summer evening is the best time of the year to observe the constellation Scorpius, which is low in the south. The brightest star in Scorpius is Antares (red supergiant, class M1Ib). A number of star clusters are found in Scorpius. The Butterfly Cluster (M6) and the Ptolemy Cluster (M7) are two such examples.  
In the summer evening (Northern Hemisphere), the southern part of our sky is directed towards the galactic center. Thus, many open and virtually all globular clusters are visible in the summer evening sky in that direction.
The very large constellation Ophiuchus is north of Scorpius and south of Hercules. It consists of stars of magnitude 2 or more.

4. In late summer evening sky (mid-august, around 11:00pm), the Milky Way shines brightly ovehead and passes through the astersim Summer Triangle consisting of Vega Deneb Altair.
Vega and Deneb are on the north side of the triangle. Vega is west of Deneb. Altair is located at a greater angular distance to the south.

The brightest star in the small constellation Lyra is Vega. Lyra consists of about 6 easily visible stars.
Epsilon Lyrae is just east and slightly north of Vega.
Epsilon Lyrae, the famous “double double” is a visual (true) binary star. It is faint but two components are visible to the unaided eye but each of these two components is also a binary atar. A telescope resolves this double double into four stars. The two main pairs appear widely separated. However, the stars within each pair are split by just over 2 arc-seconds. One pair is “horizontal” and the other is 'vertical'.
 
The brightest star in the constellation Cygnus – the swan is Deneb. Deneb is the “tail of the swan.’ The wingtips of swan are represented by Geinnah Cygni and Rukh. Albireo the bottom star of Northern Cross is the ‘head of the swan.' This reflects the long neck and short tail of a swan.

Albireo (in Cygnus) is the bright blue-yellow binary star. It is easily visible to the unaided eye as a single star.
A telescope resolves this binary star into two components which are 35 arc-seconds apart. The brighter star in Albireo is blue main sequence (B8V), whereas the fainter star is yellow giant (K3ll).

The brightest star in the constellation Aquilla – the Eagle is Altair. Altair is the head of the eagle.’ Alshain and Tarazed are on the opposite side of Altair. The wingtips of the Eagle are represented by Tseen Foo and Deneb el okab Australis. Lambda Aquilae (V: 3.43) and the nearby stars mark the tail.

The Constellation Sagittarius is low in south and slightly west of Aquila. It consists of medium brightness stars (around magnitude 2). The central bulge of our galaxy is within the boundary of this constellation, 26000ly away, so it contains a lot of deep sky objects. Many bright patches of the Milky Way are visible to naked eye in Sagittarius. These are all star clusters and nebulae.
A number of Messier Objects including star clusters and nebulae are found along the Milky Way in and around the Constellations Sagittarius and Scorpius.
Messier Objects in Scorpius (4 MO) are: M4 (globular cluster), M6 (open cluster), M7(open cluster) , M80 (globular cluster)
Messier Objects in Sagittarius (15 MO) are: M8, M17, M20 (nebulae); M18, M21, M23, M25 (open clusters); M22, M28, M54, M55, M69, M70, M75 (globular clusters); M24 (Milky Way star cloud)
 
5. In autumn evening sky (mid-october, around 10:00pm), the constellation Pegasus is very high in the south to southeast.
The most recognizable part of the constellation Pegasus is the asterism called the Great Square of Pegasus. Three out of four stars of this asterism are in Pegasus.
The star on the northeast corner of the Great Square of Pegasus is Alpheratz – the brightest star in the constellation Andromeda.
Andromeda is shaped like a curved bull horn extending northeast from Alpheratz and curving north. This bullhorn is comprised of an upper and lower arc, both of which begin at Alpheratz. The lower arc contains the stars Mirach and Almaak.
Andromeda contains the brightest galaxy in the northern celestial hemisphere: M31.
To locate M31 hop over two stars northeast from Alpheratz to Mirach on the lower arc. Then hop up northwest to Mu Andromedae on the upper arc. Then hop up once more northwest to Nu Andromedae. M31 is located just over one degree west of Nu Andromedae. It is the farthest and largest object that can be (easily) seen with the unaided eye.
Cepheus and Cassiopea are both circumpolar constellations for mid-northern latitude. But they are highest in the sky during the autumn. Cassiopea is shaped like a 'W 'or 'M'.

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Protoplanetary disks or proplyds

Protoplanetary disks or proplyds (first discovered with the Hubble in 1992) are swirling disks of dense gas and dust around newly formed stars, and are believed to be the raw material for planets to form.

The dust particles collide and clump together within these disks so that these disks may eventually form planets, asteroids, and comets. 

The Orion Nebula is a famous star-forming region. This makes it a prime location for observing proplyds and studying the early stages of planetary system formation. 

Hubble Space Telescope observations have revealed nearly 200 proplyds in the Orion Nebula.

There are two different types of proplyds around young and forming stars.

The first type of proplyds are those which lie close to a bright star e.g. Theta-1 Orionis C. The bright star heats up the gas in the nearby discs, causing them to shine brightly.

The second type of proplyds are those which lie farther away from a bright star and hence do not receive enough energetic radiation from the star to set the gas ablaze. These discs that are farther away, can only be detected as dark silhouettes against the background of the bright nebula, as the dust that surrounds these discs absorbs background visible light.

Following are some Star-forming regions with proplyds.

1. Orion Nebula (M42 or NGC 1976): Ionizing stars include Theta1 Orionis C, and it's located 1344 light-years away.

2. NGC 1977: Ionizing stars include 42 Orionis, and it's located 1500 light-years away.

NGC 1977 is a nebula close to the M42 Orion nebula.

42 Orionis is B-type main sequence star,  class B1V. It excites and illuminates NGC 1977.

3. Lambda Orionis Cluster: Ionizing stars include Meissa, and it's located 1300 light-years away.

Meissa, designated Lambda Orionis is a multiple star approximately 1,300 ly away with a combined apparent magnitude of 3.33. The main components are an O8 giant star and a B-type main sequence star.

Huygens region

This bright region having the Trapezium stars at the center of the Orion Nebula and the Orion Bar to the south is called the Huygens region.

The Orion Bar is a ridge-like feature of gas and dust within Orion Nebula where energetic ultraviolet light from the Trapezium Cluster interacts with dense molecular clouds.

The most readily identifiable dusty realms of M42 lie between the bright central Huygens region and the neighboring De Mairan’s Nebula (M43). M43 is actually part of the same gas cloud that comprises M42 but it only appears isolated due to intervening lanes of cosmic dust blocking the light of bright nebulosity beyond.

Age and Size of Universe

About 13.7 billion years ago, our universe was an infinitesimally small region of space of infinite density. Due to some unknown reason, that point universe exploded (which is called the Big Bang) and began to expand and that was also the beginning of time.

Age of universe is 13.7 billion years (13 billion and 700 million years)

The observable universe is roughly 93 billion light years in diameter.

The observable universe is the portion of the universe that we can see, as light from more distant regions hasn't had time to reach us. 

The universe has been expanding since the Big Bang, stretching space and increasing distances between galaxies. Due to this expansion, the observable universe is larger than the age of the universe would suggest. 

There are regions of space that are expanding away from us faster than the speed of light, making them unreachable. The true size of the universe beyond the observable part is unknown and could be infinite. 

An object can not move faster than the velocity of light anywhere in the universe but the space between two points can expand faster than the velocity of light.

One second after the Big Bang, the observable universe was approximately 20 light years in diameter whereas light can travel only 1 light second in one second.

Imagine a balloon with dots drawn on its surface. As you inflate the balloon, the dots move further apart, not because the dots are moving across the balloon's surface, but because the rubber of the balloon (space) is stretching between them.

Similarly, the space between distant galaxies is stretching, causing them to move away from us at an accelerating rate. 

Due to the expansion of the universe, the distant objects are further away than their light travel time.

Suppose a star is 10000 light years away from the Earth today. Then the light emitted by the star today would reach the Earth after 10000 years. That is the light travel time would be 10000 years but by the time that light reaches to the Earth, due to the expansion of the universe, star would be say, 10200 light years away from the Earth which is more than its light travel time. 

During inflationary epoch (t = 10⁻³⁶ and t = 10⁻³²), hot microscopic universe expanded exponentially which is called inflation. During inflation universe became super cooled.

After the end of inflation, the supercooled universe reheated and reverted to the conventional hot Big Bang model.

During inflation, the volume of universe increased by a factor of at least 10⁷⁸ (i.e. an expansion of distance by a factor of at least 10²⁶ in each of the three dimensions).

Inflation smoothed out the universe and amplified quantum fluctuations into the large-scale structures we observe today.  

After inflation, cosmic expansion decelerated to much slower rates. However, around 9.8 billion years after the Big Bang (4 billion years ago) cosmic expansion began to accelerate and is still accelerating.

Proper distance

The actual, physically measured distance between an object and an observer, taking into account the expansion of the universe.

The amount of redshift indicates the galaxy's recessional velocity i.e. how fast it's moving away from us.

By measuring the velocity, astronomers can calculate the proper distance to the galaxy by using Hubble’s law.

Hubble’s law is as follows:

v = HοD

where,

v is the recessional velocity in km/s

Hο is is Hubble’s constant whose topical value is approximately 70km/s/Mpc.

D is the proper distance between the galaxy and the observer.

Light-travel distance

The distance the light has traveled from the object to the observer, essentially how far away the object was when it emitted the light.

Comoving distance

Comoving distance factors out the expansion of the universe, giving a distance that does not change in time except due to local factors, such as the motion of a galaxy within a cluster.

Redshift

When a distant object emitting light moves away from us due to the expansion of the universe, then the wavelength of its light is stretched, causing the wavelength to shift towards the red end of the spectrum. This shift is known as redshift. 

A higher redshift indicates that the object is moving away from us at a faster rate, and therefore is further away.

The redshift is a measure of both the distance to the object and the time since the light was emitted by the object. Higher redshift means greater distance and looking further back in time. 

Red shift z = (λ_received − λ_emitted) / λ_emitted.

The spectrum of a star is a combination of its continuous spectrum (emitted by the hot interior) and the absorption lines from its cooler outer layers. 

Each chemical element has a unique pattern of emission (bright) or absorption (dark) lines on the spectrograph. When you look at a red-shifted star, all the elements are there but the entire spectrum is shifted towards the red end.

Astronomers compare the position of these received wavelengths to where those wavelengths would be if the object were stationary. In this way, astronomers know the value of emitted wavelengths.

Continuous Spectrum

When white light passes through a prism and falls on a screen, then instead of white light, the different colours i.e. violet, indigo, blue, green, yellow, orange and red (VIBGYOR) are seen on the screen. This pattern of the colours on the screen is called the continuous spectrum of light.

Absorption Spectrum

Absorption spectra occur when electrons absorb photons to jump to higher energy levels. 

Suppose white light (containing all wavelengths of visible light and having continuous spectrum) passes through a cloud of hydrogen gas and then through a prism and then falls on the screen. Not all of the light will make through the cloud of hydrogen gas.

For example, each of the photons that has energy 1.89 eV and corresponding wavelength 656nm will be absorbed by particular electron of hydrogen atom in second energy level (n = 2) and such an electron will jump from n = 2 to n = 3. Thus, an absorption line would be created corresponding to the wavelength 656nm in the otherwise continuous spectrum of light.

Similarly, each of the photons that has energy 2.55 eV and corresponding wavelength 486nm will be absorbed by particular electron of hydrogen atom in second energy level (n = 2) and such an electron will jump from n = 2 to n = 4. Thus, an absorption line would be created corresponding to the wavelength 486nm in the otherwise continuous spectrum of light.

That is, the continuous spectrum of light will have dark lines corresponding to the wavelengths of light absorbed by the hydrogen gas. This is called absorption spectrum.

Absorption Spectrum is a continuous spectrum of light (like rainbow) with dark lines or gaps at the wavelengths of light that were absorbed. 

Absorption Spectrum shows which wavelengths of light a substance absorbs, which can be used to identify its composition and temperature. 

The absorption spectrum of hydrogen in visible region includes four lines of Balmer series I.e. 656 nm (red) corresponding to n = 2 to n= 3, 486 nm (blue-green) corresponding to n= 2 to 4, 434 nm (blue) corresponding to n = 2 to n= 5 and 410 nm (violet) corresponding to n= 2 to n = 6 and other lines in the UV region. Then shortest wavelength in Balmer series is 364nm corresponding to the transition of the electron from n = 2 to n = ∞. 364nm is in UV region (10nm – 400nm).

The Lymen series (transition from n = 1 to higher levels) includes lines in UV region from 121.6nm (corresponding to n = 1 to n = 2) to 91.15nm (corresponding to n = 1 to n = ∞).

For example, each of the photons that has energy 13.6 eV and corresponding wavelength 91.1nm will be absorbed by particular electron of hydrogen atom in first energy level (n = 1) and such an electron will jump from n = 1 to n = ∞. Thus, an absorption line would be created corresponding to the wavelength 91.1m in the UV spectrum.

The Paschen (transition from n = 3 to higher levels), Brackett (transition from n = 4 to higher levels), Pfund (transition from n = 5 to higher levels) and Humphreys (transition from n = 6 to higher levels) series includes lines in Infrared region.

Emission Spectrum

Emission spectra occur when excited electrons in an atom or molecule jump from a higher energy level to a lower one, releasing photons of specific energies.

Emission Spectrum is a series of bright, distinct colored lines against a dark background. 

The emission and absorption spectra for the same element are the exact inverse of each other, because the energy absorbed by an electron to move to a higher level is the same as the energy released when it returns to its original level.

The emission spectrum of hydrogen in visible region includes four lines of Balmer series i.e. 656 nm (red) corresponding to n = 3 to n= 2, 486 nm (blue-green) corresponding to n = 4 to 2, 434 nm (blue) corresponding to n = 5 to n= 2 and 410 nm (violet) corresponding to n = 6 to n = 2 and other lines in the UV region.

Active Galactic Nucleus (AGN)

AGN is a supermassive black hole surrounded by a rapidly rotating accretion disk. 

The core of Active Galactic Nucleus (AGN) is a supermassive black hole at the center of a galaxy that is actively accreting matter.

The gas and dust swirls around the spinning black hole before being pulled in beyond the event horizon and on to the black hole.  This swirling disk of gas and dust is called accretion disk. 

As the gas and dust from the accretion disk spirals into the spinning black hole, they experience friction with the other particles in the disk, causing the gas and dust to heat up (frictional heating) significantly.

Thus, the gas and dust falling into a supermassive black hole from the accretion disk emit electromagnetic radiation across the entire  electromagnetic spectrum, from radio waves to gamma rays.

Near the event horizon of a black hole, the accretion disk temperature may reach up to one hundred million kelvins. Matter at such high temperature emits high-energy thermal radiation, typically X-rays.

Quasars (QSOs), Blazars, Seyfert Galaxies, Radio Galaxies are galaxies having AGN at their core.

Quasar

Quasar is a galaxy which has the brightest or most luminous type of active galactic nucleus (AGN) at its core.

If the gas and dust falling into a supermassive black hole from the accretion disk emit significant electromagnetic radiation in visible spectrum, then the galactic core becomes far brighter than the rest of the galaxy. Thus, these galaxies look much like stars: point-like, without the fuzzy halo normally associated with a galaxy.

Since these galaxies look much like stars, they are called Quasi-Stellar Objects or QSOs.

QSOs are of two types: radio-quiet QSOs and radio loud QSOs.

Black holes at the center of some QSOs spew powerful jets of plasma from their poles, millions of light years across intergalactic space. The plasma gas is so hot that it’s essentially a soup of electrons moving with the velocity nearly equal to that of light.

The jets are created by the interaction between the spinning black hole's magnetic field and the material in the accretion disk. 

The relativistic electrons in the jets of QSOs emit synchrotron radiation. For relativistic electrons, the synchrotron radiation falls within the radio wave spectrum.

This synchrotron radiation is concentrated into a narrow cone in the direction of the electron's motion.

QSOs which are the strong sources of radio waves are radio loud and can be seen with a radio telescope. These radio loud QSOs are called Quasi-Stellar Radio Sources of Quasars. About 10% of the known quasars are radio loud.

It is common to use the term ‘quasar’ for both radio-quiet and radio loud QSOs.

Radio-quiet quasars lack powerful jets and are weak sources of radio waves, About 90% of the known quasars are radio quiet.

Quasars are small, blue objects which have enormous redshifts, suggesting that they are at great distancs from Milky Way which imply they had formed in the early universe and through the telescopes, we can see how they looked like in their early stages of development.

Quasars are young galaxies, located at vast distances from us.

Synchroton Radiation:

A magnetic field exerts Lorentz force on a moving charged particle that is always perpendicular to the direction of the motion of the particle and the magnetic field. 

Due to this force perpendicular to the direction of motion, electron continuously accelerates and moves in a circular or helical path in a magnetic field.

Any charged particle that is accelerated always emits electromagnetic radiation. 

Thus, the electrons, which continuously accelerates while moving in a circular or helical path in a magnetic field, continuously emits electromagnetic radiation. This electromagnetic radiation is called synchroton radiation.

Examples of Quasars: UHZ1, J0313-1806, J1601+3102, J0529-4351, TON 618, 3C 273

1. UHZ1 is the highest red shift, most distant and hence also the oldest known quasar. It is located in the constellation Sculptor.

The observed redshift of quasar UHZ1 is z = 10.1. This indicates the light travel time of the quasar UHZ1 is about 13.2 billion years.

This means the light we see from UHZ1 was emitted when the universe was 0.5 billion or 500 million years old,

Comoving distance of quasar UHZ1 from the Earth is 31.7 billion light-years. 

UHZ1 has a supermassive black hole (SMBH) at the center with a mass 40 million solar masses.

The black hole at the center of UHZ1 was detected using the Chandra X-ray Observatory which identified the X-ray emission from the black hole and its accretion disk, while the James Webb Space Telescope helped identify the galaxy itself. 

The discovery of UHZ1 suggests that some early supermassive black holes may have formed from massive gas clouds collapsing directly (a process known as direct collapse), rather than through the merging of smaller black holes. 

Before the discovery of UHZ1, J0313−1806 was the most distant quasar known.

2. J0313-1806 was the most distant and hence also the oldest known quasar at the time of its discovery. It is located in the constellation Eridanus.

The observed redshift of the quasar J0313-1806 is z = 7.642.  This indicates the light travel time of the quasar J0313-1806 is about 13.03 billion years. This means the light we see from the quasarJ0313-1806 today was emitted when the universe was 670 million years old,

J0313-1806 is a key object in understanding the very early universe, dating back to just 0.67 billion or 670 million years after the Big Bang.

Proper distance of the quasar J0313-1806 from the Earth is 30 billion light-years. 

J0313-1806 has a supermassive black hole (SMBH) at the center with a mass 1.6 billion solar masses. It is one of the most massive and largest SMBHs observed in the early universe.

3. The extremely radio-loud quasar J1601+3102 is located in the constellation Corona Borealis. 

The observed redshift of quasar J1601+3102 is z ~ 5. This indicates the light travel time of the quasar J1601+3102 is about 12.5 billion years.

This means the light we see from J1601+3102 was emitted when the universe was 1.2 billion years old.

J1601+3102  has a supermassive black hole (SMBH) at the center with a mass 450 million solar masses.

The quasar J1601+3102 has two-lobed radio jet that spans at least 200,000 lightyears, which is twice the width of our Milky Way galaxy, making it the largest ever radio jet found so early in the Universe.

The jet was first identified by the international Low Frequency Array (LOFAR) Telescope, a network of connected radio telescopes located

across Europe.

Black hole at the center of this quasar is smaller, weighing 450 million solar masses.

This suggests that an exceptionally massive black hole may not be necessary to generate such giant radio jets shortly after the Big Bang i.e. in the early Universe.

These large radio lobes have remained elusive at z > 4. However,  quasar J1601+3102 having z ~ 5 have large radio lobes.

4. J0529-4351 is the most luminous object in the known universe, with a luminosity over 500 trillion times that of our sun. It is located in the constellation Pictor.

The observed redshift of quasar J0529-4351 is z = 3.962.  This indicates the light travel time of the quasar J0529-4351 is about 12 billion years.

This means the light we see from the quasar J0529-4351 today was emitted when the universe was 1.7 billion years old,

J0529-4351 has a supermassive black hole (SMBH) at the center with a mass about 17 billion solar masses. 

The supermassive black hole at the center of this quasar is growing at an incredibly fast rate, consuming about one solar mass of material per day. 

The immense energy output of the quasar comes from a hot accretion disk surrounding the black hole. This disk is estimated to be seven light-years in diameter, making it the largest known accretion disk. 

5. TON 618 is one of the brightest quasars in the universe,140 trillion times more luminous than the Sun. TON 618 is a hyperluminous, radio-loud quasar. It is located near the border of the constellations Canes Venatici and Coma Berenices.

The origin of the name TON 618 is the Tonantzintla Observatory in Mexico. It was first observed and catalogued in 1957.

The observed redshift of quasar TON 618 is z = 2.219. This indicates the light travel time of the quasar TON 618 is about 10.8 billion years.

This means the light we see from the quasar TON 618 today was emitted when the universe was 2.9 billion years old,

Proper distance of the quasar TON 618 from the Earth is 18.2 billion light-years. 

TON 618 has a supermassive black hole (SMBH) at the center with a mass 66 billion solar masses. It is the most massive and largest SMBH observed in the early universe.

The combined mass of all the stars in the Milky Way galaxy is 64 billion solar masses.

Based on its mass, the Schwarzschild radius of the black hole of TON 618 is about 195 billion kilometers or 1300 AU.

The average distance between the Sun and Pluto is 39.5 AU (astronomical units). One AU is the average distance between the Sun and Earth.

The absolute magnitude of TON 618 is −30.7.

Due to the brilliance of the central AGN, the surrounding galaxy is outshone by it and hence is not visible from Earth.

It is not known how SMBHs like those at the center of the quasar J0313-1806, quasar J0529-4351, quasar TON 618, galaxy GN-z11 could have formed and grown so rapidly In the early universe.

6. 3C 273 was the first quasar to be discovered. It is located in the constellation Virgo.

This is the optically brightest quasar in the sky from Earth with an apparent visual magnitude of ~12.9.

Since it is radio-loud, 3C 273 is a true quasar.

The observed redshift of quasar 3C 273 is z = 0.158. It is one of the closest quasar.

Proper distance of quasar 3C 273 from the Earth is 2.4 billion light-years. 

3C 273 has a supermassive black hole (SMBH) at the center with a mass about 0.9 billion or 900 million solar masses. 

The quasar 3C 273 has a large-scale visible jet, which measures ~200,000 light-years long,

3C 273 is one of the most luminous quasars known, with an absolute magnitude of −26.7.

Since the Sun's absolute magnitude is 4.83, it means that the quasar is more than 4 trillion times more luminous than the Sun at visible wavelengths.

Luminosity refers to the total amount of energy a star radiates into space, while brightness (or apparent brightness) is how bright the star appears from Earth. Essentially, luminosity is an intrinsic property of the star, while brightness depends on both the star's luminosity and its distance from us. 

Blazar

Blazar is a galaxy like quasar and has AGN at its core but in blazar, one of the two relativistic jets of high-energy particles emitted from the poles of the supermassive black holes is pointed towards Earth. 

The jets from these blazars can extend millions of light-years in length.

Up until now, a little less than 3,000 blazars have been discovered but most are located closer to Earth than J0410-0139.

Blazars are rare and account for only a small fraction of all quasars.

Examples of Blazars: J0410-0139, OJ 287

1. J0410-0139 is the highest red shift, most distant and hence also the oldest known blazar.

The observed redshift of blazar J0410-0139 is z ~ 7. This indicates the light travel time of the blazar J0410-0139 is about 12.9 billion years. This means the light we see from the blazar J0410-0139 today was emitted when the universe was 0.8 billion or 800 million years old,

J0410-0139 has a supermassive black hole (SMBH) at the center with a mass 700 million solar masses.

2. Blazar OJ 287 is located in the constellation Cancer.

The observed redshift of blazar OJ 287 is z = 0.306. This indicates the light travel time of the blazar OJ 287 is about 3.5 billion years. This means the light we see from the blazar OJ 287 today was emitted 3.5 billion years ago i.e. when the universe was 10.2 billion years old.

Proper distance of blazar OJ 287 from the Earth is about 5 billion light years. 

OJ 287 has supermassive binary black holes (SMBBH) at the center. The primary, larger black hole has a mass of about 18 billion solar masses, while the smaller companion has a mass of approximately 150 million solar masses.   

The smaller black hole orbits the larger black hole, passing through the accretion disc of the larger black hole approximately every 12 years, causing flares. Thus, OJ 287 exhibits the phenomenon of two-peak outbursts after every 12 years period.

The jet from the smaller of the two black holes is ‘twisted like a jet of water from rotating garden hose,’ caused by its rapid motion around the larger one.

The orbital motion of the smaller black hole around the larger one is the source of the gravitational waves.

The gravitational waves that gravitational waves interferometers like LIGO, Virgo or KAGRA detect are caused by e.g. colliding black holes, merging neutron stars, exploding stars.

However, the gravitational waves from OJ 287 are at a low frequency (nanoHertz), making them too faint for these detectors to detect. 

Future space-based missions, such as the Laser Interferometer Space Antenna (LISA), are expected to be able to detect these waves.

OJ 287 is a blazar and also a BL Lacertae object.

On the basis of optical spectra, blazars are classified into two main types:

Flat Spectrum Radio Quasars (FSRQs) and BL Lac objects.

FSRQs have strong, broad emission lines with equivalent width (EW) greater than 5 Å.

BL Lacs have either no emission lines or weak emission lines with equivalent width (EW) less than 5 Å.

Both FSQRs and BL Lacertae exhibit strong and often rapid changes in their brightness across the electromagnetic spectrum, from radio waves to gamma-rays.

Seyfert Galaxy

Seyfert Galaxies are Galaxies with active galactc nuclei that are less luminous than quasars, but still significantly brighter than normal galaxies. They emit considerable infrared radiation.

Examples of Seyfert Galaxy: Markarian 231, NGC 4395

1. Markarian 231 is a Type-1 Seyfert galaxy that was discovered in 1969 as part of a search for galaxies with strong ultraviolet radiation.

The observed redshift of Markarian 231 is z = 0.04147. It is located about 581 million light years away from Earth, in the constellation of Ursa Major.

Hubble Space Telescope image reveals a bright starlike glow at the center of the Markarian 231,

Hubble spectroscopic observations infer the presence of two supermassive black holes whirling around each other. That is, the AGN of Markarian 231 is a binary black hole system.

Galaxy Markarian 231 has a supermassive black hole (SMBH) at the center with a mass 150 million solar masses. 

2. NGC 4395 is one of the least luminous Seyfert galaxies. It is a dwarf Seyfert galaxy.

The observed redshift of NGC 4395 is z = 0.00106. It is located about 14 million light years away from Earth in the constellation Canes Venatici.

AGN of NGC 4395 is the nearest known Active Galactic Nucleus.

Seyfert galaxies, like NGC 4395, are typically closer to Earth than more distant quasars, making them easier to study. The extremely bright central regions of Seyfert galaxies, often containing AGNs, can sometimes obscure the dimmer stars in the surrounding galaxy disks.

Radio Galaxy

Radio Galaxies are galaxies which spew powerful jets of plasma. These plasma jets glow at radio frequencies, so they can be seen with a radio telescope.

Like radio-loud quasars, radio galaxies have a radio-loud AGN but AGN of radio galaxy is not luminous.

The visible light from radio galaxies comes from the stars within them.   

Radio galaxies often display a core-jet-lobe morphology, with the core being the active nucleus, the jets being the visible manifestation of the outflow, and the lobes being the extended regions of radio emission. 

Lobes are not visible in optical light and are only observable with radio telescopes. 

Jets are the visible pathways of material being ejected from the AGN into the lobes. 

Examples of Radio Galaxy: Cygnus A, M87

1. Cygnus A is a radio galaxy, known for its powerful radio emissions and its double-lobed structure.

The observed redshift of Cygnus A is z = 0.0565. It is located 760 million light years away from Earth, in the constellation Cygnus.

Cygnus A has a supermassive black hole (SMBH) at the center with a mass 2.5 billion solar masses.

2. M87 is a radio galaxy with lobes extending 130,000 light-years.

The observed redshift of M87 is z = 0.00436. It is located about 53.5 million light years away from Earth, in the constellation Virgo.

M87 has a supermassive black hole (SMBH) Powehi at the center with a mass 6.5 billion solar masses.

In case of blazor, the observer's line of sight is aligned with the axis of the jet, making the central nucleus visible.

In case of Quasor and radio galaxy, the observer's line of sight is at an angle to the jet, obscuring part of the central nucleus.

There are lots of radio galaxies, some of which are also quasars. There are also lots of quasars, only a fraction of which are also sources of radio emission.

Some other popular galaxies

JADES-GS-z14-0, HD1, GN-z11, MACS0647-JD are some of the popular galaxies.

1. Galaxy JADES-GS-z14-0 is the most distant and earliest galaxy ever identified. It is located in Fornax.

The observed redshift of Galaxy JADES-GS-z14-0 is z = 14.32. This indicates the light travel time of the Galaxy JADES-GS-z14-0 is about 13.41 billion years.

This means the light we see from JADES-GS-z14-0 today was emitted when the universe was about 290 (from genuine pdf) million years old.

Proper distance of Galaxy JADES-GS-z14-0 from the Earth is 33.6 billion light-years. 

2. Galaxy HD1 is located in Sextans.

The observed redshift of Galaxy HD1 is z = 13.27. This indicates the light travel time of the Galaxy HD1 is about 13.4 billion years.

This means the light we see from HD1 today was emitted when the universe was about 0.3 billion or 300 million years old.

HD1 is one of the earliest and most distant galaxies ever observed, dating back to just 300 million years after the Big Bang.

Proper distance of Galaxy HD1 from the Earth is 33.3 billion light-years. 

If HD1 harbours a supermassive black hole, it would be the earliest example of such a structure.

3. Galaxy GN-z11 is located in Ursa Major.

The observed redshift of Galaxy GN-z11 is z = 10.6. This indicates the light travel time of the Galaxy GN-z11 is about 13.3 billion years.

This means the light we see from GN-z11 today was emitted when the universe was about 400 million years old,

GN-z11 is one of the earliest and most distant galaxies ever observed, dating back to just 400 million years after the Big Bang.

Proper distance of Galaxy GN-z11 from the Earth is 31 billion light-years. 

Galaxy GN-z11 has a supermassive black hole (SMBH) at the center with a mass 2 million solar masses. 

GN-z11 is very luminous because the black hole at its center is in a very active phase of consuming matter.

4. MACS0647 is a galaxy cluster, and its significance lies in its gravitational lensing capabilities. It acts as a cosmic lens, magnifying and bending the light from more distant galaxies, including the galaxy MACS0647-JD.

MACS0647-JD is located in Camelopardalis.

The observed redshift of Galaxy MACS0647-JD is z = 10.6. This indicates the light travel time of the Galaxy MACS0647-JD is about 13.28 billion years.

This means the light we see from MACS0647-JD is today was emitted when the universe was about 420 (from genuine pdf) million years old,

Proper distance of Galaxy MACS0647-JD from the Earth is about 30 billion light-years.  

Most massive black hole

Phoenix A is the most massive black hole and is located at the center of the Phoenix cluster of galaxies.

It is located 5.8 billion light-years away. It’s mass is 100 billion solar masses.

Based on its mass, the Schwarzschild radius of the black hole Phoenix A is 2000 AU, about 50 times the distance from the Sun to Pluto

The following list includes six quasars, two blazars, two radio galaxies, two Seyfert galaxies and four other galaxies in order of decreasing value of z.

Galaxy JADES-GS-z14-0, z = 14.32, light travel time = 13.41 billion years, proper distance = 33.6 billion light-years, constellation Fornex.

Galaxy HD1, z = 13.27, light travel time = 13.4 billion years, proper distance =  33.3 billion light-years, constellation Sextans.

Galaxy GN-z11, z = 10.6. light travel time = 13.3 billion years, pd = 31 billion light-years, SMBH mass = 2 million solar masses, constellation Ursa Major.

Galaxy MACS0647-JD, z = 10.6. light travel time = 13.28 billion years, proper distance = 30 billion light-years, constellation Camelopardalis.

Quasar UHZ1, z = 10.1, light travel time = 13.2 billion years, comoving distance = 31.7 billion light years, SMBH mass = 40 million solar maases, constellation Sculptor.

Quasar J0313-1806, z = 7.642, light travel time = 13.03 billion years, proper distance = 30 billion light years, SMBH mass = 1.6 billion solar maases, constellation Eridanus.

Blazar J0410-0139, z ~ 7, light travel time = 12.9 billion years, SMBH mass = 700 million solar maases

Quasar J1601+3102, z ~ 5, light travel time = 12.5 billion years, SMBH mass = 450 million solar maases, constellation Corona Borealis. 

Quasar J0529-4351, z = 3.962, light travel time = 12 billion years, SMBH mass = 17 billion solar masses, constellation Pictor. 

Quasar TON 618, z = 2.219. light travel time = 10.8 billion years, proper distance = 18.2 billion light years, SMBH mass = 66 billion solar maases, near the border of the constellations Canes Venatici and Coma Berenices.

Blazar OJ 287, z = 0.306, proper distance = 5 billion light years, SMBBH masses = 18 billion solar masses (primary SMBH) and 150 million solar masses (smaller SMBH), constellation Cancer. 

Quasar 3C 273, z = 0.158, proper distance = 2.4 billion light years, SMBH mass = 0.9 billion or 900 million solar masses, constellation Virgo.

Radio Galaxy Cygnus A, z = 0.0565. proper distance = 760 million light years, SMBH mass = 2.5 billion solar masses, constellation Cygnus.

Seyfert Galaxy Markarian 231, z = 0.04147, proper distance = 581 million light years, SMBH mass = 150 million solar masses, constellation Ursa Major.

Radio Galaxy M87, z = 0.00436. proper distance = 53.5 million light years away, SMBH (Powehi) mass = 6.5 billion solar masses, constellation Virgo.

Dwarf Seyfert Galaxy NGC 4395, z = 0.00106, proper distance = 14 million light years, constellation Canes Venatici.

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More About Black Holes

Types of Black Holes:

Stellar-mass black hole, Intermediate-mass black hole (IMBH), Supermassive black hole.

Stellar black hole has a mass 10 to 100 times the mass of the sun. 

Intermediate-mass black hole (IMBH) has a mass 100 to 10,000 times the mass of the sun.

Supermassive black hole has a mass millions or billions times the mass of the suns.

A stellar or stellar-mass black hole is a black hole that is formed when the core of the white dwarf collapses and explodes as Type I Supernova or when the core of the neutron star collapses and explodes as Type II Supernova.

If the core of a white dwarf or neutron star, after undergoing a supernova explosion, is massive enough (a few times the mass of our sun), then the core collapses under its own gravity into an infinitely dense point and becomes a black hole.

Thus, the stellar black holes are the remnants of the supernova explosions.

White dwarfs and neutron stars are the remnants of the stars after their death.

Intermediate-mass black holes (IMBHs) are thought to form through a combination of stellar collisions and merging.

1. In dense stellar clusters, stars can collide rapidly, leading to the formation of very massive stars (up to 400 solar masses).

These massive stars can then be swallowed by a stellar-mass black hole to form an IMBH.

2. Smaller black holes can merge to form an IMBH.

They can grow by consuming gas, planets, stars and other black holes. 

Formation theories of Supermassive black hole:

Many smaller black holes may have merged to form supermassive black holes. 

In the early universe, supermassive stars may have collapsed to form supermassive black holes. 

Supermassive black holes may have formed in the cores of starburst galaxies which are the galaxies that are vigorously forming stars.

To describe the characteristics of a supermassive black hole there are two important numbers to use. One is its mass and the other is its spin rate. Spin rates of some of the black holes are thought to be very close to the speed of light.

To measure the spin rate of a black hole, it is important to know the mass of the black hole and the structure of the accretion disk.

To separate the spin of a black hole from the spin of the accretion disk surrounding it, the key is to look at the innermost region, where the matter is falling into the black hole's event horizon. A spinning black hole drags that innermost material along for the ride.

Supermassive black holes formed by the mergering of the smaller black holes alone don’t spin too fast.

Supermassive black holes formed by steadily accreting gas and dust spin faster. Such black holes grow from the material falling in it. 

The most distant black holes seem to be spinning faster than the ones nearest to us. It's as if they spin faster in the early universe, and more slowly in more recent epochs.

The early fast spin rate implies that in the early universe, the supermassive black holes (like the one in our own Milky Way galaxy) had formed  by steadily accreting gas and dust.