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First Star

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

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

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

has a 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

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

the whole universe. Further study is required to resolve the discrepancy.

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 HST),

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

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 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 distinguished from other sources of noise and emission.

Figure 08-02e First Stars Signatures as Infrared Blobs [view large image]

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.

Detection by 21 cm Radio Wave 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 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]

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