star and galaxy formation

Under current cosmological models, all matter created in the Big Bang was mostly hydrogen (75%) and helium (25%), with only a very tiny fraction consisting of other light elements such as lithium and beryllium.[7] When the universe had cooled sufficiently, the first stars were born as population III stars, without any contaminating heavier metals. This is postulated to have affected their structure so that their stellar masses became hundreds of times more than that of the Sun. In turn, these massive stars also evolved very quickly, and their nucleosynthetic processes created the first 26 elements (up to iron in the periodic table). [1]

Many theoretical stellar models show that most high-mass population III stars rapidly exhausted their fuel and likely exploded in extremely energetic pair-instability supernovae. Those explosions would have thoroughly dispersed their material, ejecting metals into the interstellar medium (ISM), to be incorporated into the later generations of stars. Their destruction suggests that no galactic high-mass population III stars should be observable.[2] However, some population III stars might be seen in high-redshift galaxies whose light originated during the earlier history of the universe.[3] Scientists have found evidence of an extremely small ultra metal-poor star, slightly smaller than the Sun, found in a binary system of the spiral arms in the Milky Way. The discovery opens up the possibility of observing even older stars.[4]

Stars too massive to produce pair-instability supernovae would have likely collapsed into black holes through a process known as photodisintegration. Here some matter may have escaped during this process in the form of relativistic jets, and this could have distributed the first metals into the universe.[5][6]

The explosion of these first stars and the subsequent formation of new stars and star clusters led to the creation of the first galaxies. Over time, these galaxies merged and interacted, forming the large, complex galaxies that we see in the universe today.

It is important to note that this is a simplified version of the process, and the exact details of how the first stars and galaxies formed are still the subject of ongoing research. However, this current understanding provides a broad picture of how the universe evolved from the Big Bang to the present day.

As those population II stars died, they returned metal-enriched material to the interstellar medium via planetary nebulae and supernovae, enriching further the nebulae, out of which the newer stars formed. These youngest stars, including the Sun, therefore have the highest metal content, and are known as population I stars.

14.2 Formation of the observed stars

The oldest stars observed thus far,[2] [12] known as population II, have very low metallicities;[9] [10] as subsequent generations of stars were born, they became more metal-enriched, as the gaseous clouds from which they formed received the metal-rich dust manufactured by previous generations of stars from population III.

Chronology

Formation of Population III stars: Approximately 500 million years after the Big Bang

Enrichment of the Intergalactic Medium: Over the next few hundred million years, population III stars exploded as supernovae and enriched the intergalactic medium with heavier elements
Formation of Population II stars: Approximately 300 million years after the formation of the first population III stars, or around 800 million years after the Big Bang.

Formation of Population I stars: Over the next few billion years, the gas and dust in galaxies continued to be enriched by successive generations of stars, leading to the formation of population I stars. These stars are the most metal-rich and are found in the disk of spiral galaxies.

A newfound galaxy dubbed GLASS-z13, by the James Webb Space Telescope, which is so far away that we see it as it appeared 300 million years after the Big Bang, now holds the record for the earliest known galaxy. [11]

[13]

M30 Cluster

[14]

Milky Way

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14.3 Organisation of our Visible Universe

14.3.1 Galaxy Clusters

Galaxy clusters, also known as clusters of galaxies, represent large structures encompassing hundreds to thousands of galaxies, bound by the gravitational pull. Their masses typically vary between 1014 to 1015 times that of the sun. These clusters are the second-largest gravitationally bound structures in the universe, surpassed only by galaxy filaments. Until the 1980s, they were considered the largest structures in the universe until the discovery of superclusters.

An important characteristic of these clusters is the intracluster medium (ICM), which is composed of heated gas situated between the galaxies. The peak temperature of the ICM, ranging from 2–15 keV, relies on the cluster's total mass. However, galaxy clusters must not be mistaken for galactic clusters (also referred to as open clusters), which denote star clusters within galaxies, or globular clusters that usually orbit galaxies. Smaller groupings of galaxies are identified as galaxy groups instead of galaxy clusters. These galaxy groups and clusters can further cluster together, leading to the formation of superclusters.

Some well-known galaxy clusters in the relatively nearby Universe are the Virgo Cluster, Fornax Cluster, Hercules Cluster, and the Coma Cluster. The Great Attractor, a significant aggregation of galaxies governed by the Norma Cluster, possesses enough mass to influence the local expansion of the Universe. Galaxy clusters like SPT-CL J0546-5345 and SPT-CL J2106-5844, located in the distant, high-redshift Universe, are among the most massive galaxy clusters identified in the early Universe. Over recent decades, these clusters have been recognized as important sites for particle acceleration, as evidenced by the observation of non-thermal diffuse radio emissions, such as radio halos and radio relics. Furthermore, the use of the Chandra X-ray Observatory has led to the discovery of structures like cold fronts and shock waves in numerous galaxy clusters.

The Virgo Cluster is the Cluster closed to our Local Cluster.

14.3.2 Local Group

The Local Group refers to the galaxy cluster which encompasses the Milky Way. It boasts an overall diameter of about 3 megaparsecs (equivalent to 10 million light-years or 9×10¹⁰kilometres) [15], with a mass roughly 2×10¹² times that of the sun (or around 4×10⁴² kg) [16]. It is made up of two galaxy clusters shaped like a “dumbbell”. The Milky Way and its satellite galaxies form one part, while the Andromeda Galaxy and its satellites form the other. These two clusters are approximately 800 kiloparsecs (3×106 light-years or 2×1019 km) apart and are drawing nearer to each other at a speed of 123 km/s. The Local Group is part of the larger Virgo Supercluster, which may in turn be part of the Laniakea Supercluster. The exact count of galaxies within the Local Group is unclear due to the Milky Way’s occlusion of some, but at least 80 known members exist, mostly dwarf galaxies.

The Andromeda and the Milky Way, the two largest members, are spiral galaxies with comparable masses of about 1012 solar masses each. Each of these has its distinct set of satellite galaxies:

Andromeda Galaxy’s satellites include Messier 32 (M32), Messier 110 (M110), NGC 147, NGC 185, Andromeda I (And I), And II, And III, And V, And VI (also called the Pegasus Dwarf Spheroidal Galaxy or Pegasus dSph), And VII (also known as the Cassiopeia Dwarf Galaxy), And VIII, And IX, And X, And XI, And XIX, And XXI, And XXII, as well as some additional ultra-faint dwarf spheroidal galaxies.

The Milky Way's satellites consist of the Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf Galaxy (its status as a galaxy is disputed), Ursa Minor Dwarf Galaxy, Draco Dwarf Galaxy, Carina Dwarf Galaxy, Sextans Dwarf Galaxy, Sculptor Dwarf Galaxy, Fornax Dwarf Galaxy, Leo I (a dwarf galaxy), Leo II (a dwarf galaxy), Ursa Major I Dwarf Galaxy, Ursa Major II Dwarf Galaxy, along with several other ultra-faint dwarf spheroidal galaxies.

The Triangulum Galaxy (M33) is the third-largest and third spiral galaxy in the Local Group, with an approximate mass of 5×1010 solar masses (or 1×1041 kg). It’s unclear whether it’s a companion of the Andromeda Galaxy since they are 750,000 light-years apart and experienced a close pass 2–4 billion years ago which spurred star formation across Andromeda’s disk. The Pisces Dwarf Galaxy is the same distance from both the Andromeda and Triangulum galaxies, so it could be a satellite of either.

The inclusion of NGC 3109 and its companions, Sextans A and the Antlia Dwarf Galaxy, is questionable due to their extreme distances from the Local Group’s center. The remaining members are likely gravitationally isolated from these major subgroups: IC 10, IC 1613, Phoenix Dwarf Galaxy, Leo A, Tucana Dwarf Galaxy, Cetus Dwarf Galaxy, Pegasus Dwarf Irregular Galaxy, Wolf–Lundmark–Melotte, Aquarius Dwarf Galaxy, and Sagittarius Dwarf Irregular Galaxy.

14.3.3 Our Milky Way [18]

The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλακτικὸς κύκλος (galaktikòs kýklos), meaning "milky circle" [19] [20]

]. From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe.[21] Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis,[22] observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.

The Milky Way is a barred spiral galaxy with a D25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,590 light-years), but only about 1,000 light-years thick at the spiral arms (more at the bulge). Recent simulations suggest that a dark matter area, also containing some visible stars, may extend up to a diameter of almost 2 million light-years (613 kpc).[23] [24] The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster.[24] [25]

It is estimated to contain 100–400 billion stars [26] [27] and at least that number of planets.[28] [29] The Solar System is located at a radius of about 27,000 light-years (8.3 kpc) from the Galactic Centre,[30] on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The Galactic Centre is an intense radio source known as Sagittarius A*, a supermassive black hole of 4.100 (± 0.034) million solar masses.[31] [32] Stars and gases at a wide range of distances from the Galactic Centre orbit at approximately 220 kilometres per second (136 miles per second). The constant rotational speed appears to contradict the laws of Keplerian dynamics and suggests that much (about 90%)[33] [34] of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter".[35] The rotational period is about 212 million years at the radius of the Sun.[36]

The Milky Way as a whole is moving at a velocity of approximately 600 km per second (372 miles per second) with respect to extragalactic frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang.[37]

14.3.4 Our Solar System [39]

The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. The largest of such objects are the eight planets, in order from the Sun: four terrestrial planets named Mercury, Venus, Earth and Mars, two gas giants named Jupiter and Saturn, and two ice giants named Uranus and Neptune. The terrestrial planets have a definite surface and are mostly made of rock and metal. The gas giants are mostly made of hydrogen and helium, while the ice giants are mostly made of 'volatile' substances such as water, ammonia, and methane. In some texts, these terrestrial and giant planets are called the inner Solar System and outer Solar System planets respectively.

The Solar System was formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. Over time, the cloud formed the Sun and a protoplanetary disk that gradually coalesced to form planets and other objects. That is the reason why all eight planets have an orbit that lies near the same plane. In the present day, 99.86% of the Solar System's mass is in the Sun and most of the remaining mass is contained in the planet Jupiter. Six planets, six largest possible dwarf planets and many other bodies have natural satellites or moons orbiting around them. All giant planets and a few smaller bodies are encircled by planetary rings, composed of ice, dust and sometimes moonlets.

There are an unknown number of smaller dwarf planets and innumerable small bodies orbiting the Sun. These objects are distributed in the asteroid belt that lies between the orbits of Mars and Jupiter, the Kuiper belt, the scattered disc that both lies beyond Neptune's orbit and at even further reaches of the Solar System which they would be classified as an extreme trans-Neptunian object. There is consensus among astronomers to these nine objects as dwarf planets: the asteroid Ceres, the Kuiper-belt objects Pluto, Orcus, Haumea, Quaoar, and Makemake, and the scattered-disc objects Gonggong, Eris, and Sedna. Many small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between the regions of the Solar System.

The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region of the interplanetary medium in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The nearest stars to the Solar System are within the Local Bubble; the closest star is named Proxima Centauri and is at a distance of 4.2441 light-years away.

14.4 New map of space precisely measures nearly 400,000 nearby galaxies

Mapping the night sky is essential for understanding our universe. Both researchers and amateur astronomers can now access a new atlas with detailed information on more than 380,000 galaxies: the Siena Galaxy Atlas. The collection, which provides precise measurements of the locations, shapes and sizes of large nearby galaxies, promises to be a boon to future astronomical inquiry and is freely accessible online for all to use. The research was published in the Astrophysical Journal Supplement.

The Siena Galaxy Atlas compiles data from three surveys completed between 2014 and 2017 known as the DESI Legacy Surveys. These observations were carried out to identify galaxy targets for the Dark Energy Spectroscopic Instrument, an international project managed by the Department of Energy’s Lawrence Berkeley National Laboratory. Data were collected at Cerro Tololo Inter-American Observatory and Kitt Peak National Observatory, both programs of the National Science Foundation’s NOIRLab, and the University of Arizona’s Steward Observatory.

14.5 Literature

The First Galaxies. Abraham Loeb and Steven R. Furlanetto
The First Galaxies. Volker Bromm and Naoki Yoshida. (2011)
Discovery and properties of the earliest galaxies with confirmed distances. Robertson, B. E. e. o.
A Glimpse of the First Galaxies. Naveen A. Reddy (National Optical Astronomy Observatory) (2011)
The First Stars and Galaxies – Basic Principles. V. Bromm (2012)
Galaxy Formation and Evolution. Houjun Mo, Frank van den Bosch, Simon White

Interactive : The New York Times Magazine - The James Web Telescope

14.6 Recent Developments

Properties of host galaxies of submillimeter sources as revealed by JWST Early Release Observations in SMACS J0723.3-7327 - Haojing Yan a.o. (2022)
Finding Peas in the Early Universe with JWST. James E. Rhoads a.o. The Astrophysical Journal Letters (2023)
On the ages of bright galaxies ∼ 500 Myr after the Big Bang: insights into star formation activity at 𝑧 & 15 with JWST. Lily Whitler, Ryan Endsley, Daniel P. Stark, Michael Topping, Zuyi Chen and Stéphane Charlot (2022)
Schrodinger’s Galaxy Candidate: Puzzlingly Luminous at z ≈ 17, or Dusty/Quenched at z ≈ 5? Rohan P. Naido e.o. (2022)
Siena Galaxy Atlas 2020. The Astrophysical Journal Supplement Series, 269:3 (25pp), 2023 November

Our Sun and its 10 nearest neighbors [38]

[39]

[17]

Camera

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14.7 Online Library

References

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[11] Wikipedia GLASS z-13

[12] In the meantime, popluation III stars/galaxies have been discovered thanks to the James Web Space Telescope.

[13] Globular cluster M30 (credit NASA, Hubble Advanced Camera for Surveys )

[14] Our Milky Way. NASA

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[16] The mass of the Local Group is essentially accounted for by the mass of the Milky Way and the Andromeda Galaxy. Estimates for the mass of each galaxy are compatible with 1012 M☉, and Peñarrubia et al. (2014) estimate (2.3±0.7)×1012 M☉ for the Local Group, but Karachentsev and Kashibadze (2006) estimate the somewhat lower value of (1.29±0.14)×1012 M☉.

[17] Wikipeida - Local Group

[18] Wikipedia - Milky Way

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[30] Gillessen, Stefan; Plewa, Philipp; Eisenhauer, Frank; Sari, Re'em; Waisberg, Idel; Habibi, Maryam; Pfuhl, Oliver; George, Elizabeth; Dexter, Jason; von Fellenberg, Sebastiano; Ott, Thomas; Genzel, Reinhard (November 28, 2016). "An Update on Monitoring Stellar Orbits in the Galactic Center". The Astrophysical Journal. 837 (1): 30. arXiv:1611.09144. Bibcode:2017ApJ...837...30G. doi:10.3847/1538-4357/aa5c41. S2CID 119087402.

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[38] Astronomy Magazine. Roen Kelly. June 2023

[39] User:MotloAstro (Sun); NASA (Mercury, Venus, Earth, Moon, Jupiter, Saturn, Uranus, Neptune, Io, Europa (with color correction), Ganymede, Callisto (reprocessed by Kevin M. Gill), Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Miranda, Ariel, Umbriel, Titania, Oberon, Triton); ISRO / ISSDC / Justin Cowart (Mars) Dwarf planets + moons credit: NASA and ESA