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First Star (+ 2018, 2022, 2023 Updates)

First Star First Star 2 The first stars appeared about 200 million years after the Big Bang. It formed in the denser regions of gas inside the protogalaxies. The protogalaxies in turn would be most likely located at the nodes of the filaments in the large structure. Since there was little metals present in the early universe, the production of nuclear energy is less efficient, the first stars were able to assemble more mass and still maintained a stable structure. The limit should be no more than 1000 solar mass. Figure 08-02a compares the calculated characteristics of the first stars with those for the Sun. The most iron-deficient star HE0107-5240 was discovered in late 2002. This primitive star has a

Figure 08-02a First Stars
[view large image]

Figure 08-02b First Stars 2 [view large image]

measured abundance of iron less than 1/200000 that of the Sun. It seems to have formed shortly after the Big Bang. Figure 08-02b offers further explanation (in 2014) for the large size of the first stars.
HE0107-5240 These oldest stars belong to the population III category opposing to the older population II objects in galactic halo and the young population I objects in galactic disk. It is not clear if the small trace of iron was generated within HE0107-5240 itself, or contaminated by materials from stars of later/earlier generations. Figure 08-02c compares the abundance of elements between the HE0107-5240 data (red circles) and those produced by the 25 Msun population III supernova model.

Meanwhile, measurements of quasar absorption spectrum indicate that there is neutral hydrogen (not re-ionized) billion years after the Big Bang in contradiction to the 200 million years derived from the observation of first star. Perhaps reionization was a slow process, which only gradually encompassed the whole universe. Further study is required to resolve the discrepancy.

Figure 08-02c HE0107-5240
[view large image]

Evolution of First Stars In the June 2011 issue of the Astronomy magazine, there is an article to describe a more detailed development of the first stars. Figure 08-02d is a pictorial summary of the birth and death of the first stars as presented in the article (with slight modification). Although the first stars have yet to be found in the future (may be by the James Webb Space Telescope - the successor to the

Figure 08-02d Evolution of First Stars [view large image]

HST), the first galaxy have already been detected with an estimated age of about 480 million years after the Big Bang.

Early Infrared Blobs Figure 08-02e presents the images of a portion of sky in the Hubble Deep Field North at two different infrared wavelengths, 3.6 m and 4.5 m, including an overlapping region as shown. The black pixels are bright sources (in the foreground) masked off leaving extended fuzzy blobs glowing in the background. It is claimed that these could be fluctuations, due to nascent cosmic structure, in a bright pregalactic infrared background. The brighter, uniform, non-fluctuating component of the background is not directly detectable in these data, because it cannot be

Figure 08-02e Signatures of First Stars as Infrared Blobs

distinguished from other sources of noise and emission. In short, these puffy blobs are just the signatures of the early stars (not the real thing). See "Angular-Size Redshift Relation" for an explanation of the large angular size of the blobs.

The dark age in cosmic history is not completely dark. The neutral hydrogens would undergo spin flip emitting 21 cm radio wave. It is in this epoch when hydrogen gas gradually clumped together and all the way helped by the cooling effect. Eventually, the gas cloud is dense enough to ignite nuclear burning - a star was born. The high energy radiation re-ionizes the hydrogen atom turning off the source of 21
Detection by 21 cm Radio Wave Early Universe cm radio wave. The process started with small holes around the stars, the holes enlarged and emerged and finally all the hydrogen atoms are re-ionized leaving no trace of 21 cm emission. An observational plan is to detect the turn-off time, which would be closely related to the birth of the first stars (Figure 08-02f). Currently, the Precision Array to Probe the Epoch of Re-ionization (PAPER) is dedicated to such search of first star via 21 cm radio emission.

Figure 08-02f First Star Detection by 21 cm Radio Wave [view large image]

Figure 08-02g Early Universe, 21 cm Radio wave [view large image]

Figure 08-02g depicts another view of the 21 cm line in the Early Universe.

[2022 Update]
Cosmic Timeline Schematic

Figure 08-02k Cosmic Timeline (Graphic) [view large image]


While early stars have not been observed, some galaxies have been observed from about 400 million years cosmic time at z ~ 10, at the beginning of reionization (see Figure 08-02k); these are currently our early observations of stars and galaxies. The James Webb Space Telescope (JWST), launched in 2021, is intended to push this back to z ~ 20 (~ 180 million years cosmic time), enough to see the first galaxies (~ 270 Myr) and early stars (~ 100 to 180 Myr) as shown in Figure 08-02k above (and "High Z Table" in the schematic version). [End of 2022 Update]

[2023 Update]

The JWST also detects three high red shifted galaxies designated by spectral ID (04590, 06355, 10612) and their red shift z as shown in Figure 08-02r,a. The "Spec ID" in JWST observation refers to certain class of objects with some characteristics of observed spectrum.
Green Pea Galaxy These three objects are cataloged in the Near Infrared Spectrograph (NIRSpec) with (red-shifted) wavelength range from 0.6 to 5 microns (= 10-4 cm) or red-shifted by ~ z 0, where 0 is the rest wavelength and z ~ 8. Figure 08-02r,b shows the identical profile of the emission spectrum of these objects to that for Green Pea (GP) galaxies located nearby with z ~ 0.01.

Figure 08-02r Green Pea Galaxy [view large image]

See original paper "Finding Peas in the Early Universe with JWST" published in January 1, 2023.

In spite of the high red shift in those three cosmic GP, they are mature galaxies (similar to the local GP) emerging from the "dark age" as shown in Figure 08-02k, which set the boundary between "dark age" and completed "re-ionization" at about z ~ 11.58. This spot is marked by the most distant galaxy UDFj-39546284. While those cosmic GPs are located between the most distant GRB 090429B (at z = 9.4) and most distant Quasar ULASJ1120+0641 (at z = 7.09).

BTW, Gamma-ray bursts (GRBs) are some of the most energetic events in the universe, producing intense bursts of gamma-ray. They are thought to be produced by the collapse of massive stars, or the collision of two neutron stars, resulting in the formation of a black hole; while Quasar is a supermassive black hole feeding on gas at the center of a distant galaxy.

Thus, it is legitimated to list the properties of the cosmic and local GP together as shown below : Based on such unique combination of characteristics, the GPs can be considered as a new type of galaxy beside the elliptical and spiral.

Alternatively, the GP can be identified to the low metallicity phase of the Universe at about 0.8 billion years after BB (Figure 08-02k).
Elliptical Galaxy This was when the galactic bulge of the present day elliptical galaxies assembled from stars + dust and Gas. It involved a series of violent mergers. The collisions of gas and dust triggered high star formation rate (SFR), which is one of the GP's characteristics. The size and mass of the GPs are also within ranges of the galactic bulge. It seems that the GPs are located in an environment with a lot of star clouds but no galaxies and hence getting stuck at the phase existing in 0.8 billion years after BB (see Figure 08-02u).

Figure 08-02u Elliptical Galaxy Evolution [view large image]

When the overall angular momentum was small, and star formation proceeded rapidly (thereby mopping up most of the gas early on in the evolutionary process), the end result would be an elliptical galaxy dominated by older stars and containing little, if any, gas (see Figure 08-02u).
The exact effect on the star formation rate (SFR) depends on several factors, including the masses of the colliding galaxies, the speed and trajectory of their collision, and the amount of gas and dust present in each galaxy. Generally speaking, the more massive the galaxies and the more gas they contain, the more significant the increase in star formation rate is likely to be. The increased star formation rate can continue for several hundred million years after the collision as the gas and dust settle into a new configuration. However, the increased star formation rate cannot be sustained over the long term. Eventually, the gas and dust will be used up, and the star formation rate will decline fading into a "dead galaxy" with SFR = 0.

MagellanicClouds As for the "local" GPs, they could be close to us but in old age. For example, the Magellanic clouds (a pair of irregular galaxies, see Figure 08-02v) are located in Milky Way's back yard about 60 kpc away, but they were born around 500 million years after Big Bang (with age ~ 13.2 billion years).

Figure 08-02v Magellanic Clouds

A sensational headline titled "Webb telescope makes a surprising galactic discovery in the distant universe" appeared on the morning of February 23, 2023. It goes on to report that : The space observatory revealed six massive galaxies that existed between 500 million and 700 million years after the big bang that created the universe. The discovery is completely upending existing theories about the origins of galaxies. The original paper titled "A population of red candidate massive galaxies ~600 Myr after the Big Bang" presented a more moderate assessment. Here's a summary of the investigation :
Early Galaxies JD1 The latest (May 17, 2023) addition to JWST's "High Z Treasure Trove" is JD1 with z ~ 9.79, M ~ 107 MSun and size D ~ 0.15 kpc (see "The nature of an ultra-faint galaxy in the cosmic dark ages seen with JWST"). Comparing to the Green Pea (GP) galaxies, its mass and size is at the low end of the group while the red-shift is somewhat higher; it implies that JD1 is a GP at its early formation stage. It has been placed in "JWST's "Glass" dataset" earlier with red-shift estimated to be around z ~ 11.

Figure 08-02x Early Galaxy JD1 [view large image]

See Figure 08-21m about the Giant Molecular Cloud (GMC) in an even earlier time with mass M ~ [0.001-0.1]x107 MSun, D ~ [0.005-0.1] kpc emerging from the Dark Age.

JD1 has been detected by the Atacama Large Millimeter/submillimeter Array (ALMA) and ESO’s Very Large Telescope (VLT) in 2018 with the early estimates of z ~ 9.11, M ~ 109 MSun, and D ~ 1.0 kpc (see "Onset of star formation 250 million years after the Big Bang").

[2023 October Update]

While JWST was observing the distant galaxy JADES-GS-z6-0, it detects a bump in the spectrum at 2175 A which is attributed to absorption by carbonaceous dust. It is found that if the absorbing medium is produced via the Asymptotic Giant Branch (AGB), there is no low mass stars (Pop II and I stars) yet to produce such dust grains. Other source such as supernova has to be considered for its source.