Observation of 26 cm radio signals, formed due to hyperfine transition of cosmic hydrogen offer an alternative tool to the study of early ulimwengu. As for neutral epoch of the infant ulimwengu when no light was emitted, 26 cm lines are perhaps only window. However, these redshifted radio signals emitted by cosmic hydrogen in the early ulimwengu are extremely feeble and have been elusive so far. In 2018, EDGE experiment reported detection of 26 cm signals but the findings could not be independently confirmed. The main issue was instrument systematic and contamination with the other signals from the sky. The REACH Experiment is to employ unique methodology to overcome the bottleneck. It is hoped that this research group will reliably be able to detect these elusive signals in near future. If successful, REACH Experiment may bring ‘26 cm radio astronomy’ to the forefront in the study of early ulimwengu and help us much in unravelling the mysteries of early ulimwengu.
When it comes to the study of ulimwengu wa mapema, name of recently launched Darubini ya Anga ya James Webb (JWST) pops up in our mind. JWST, a successor of hugely successful Hubble telescope, is a space-based, infrared observatory equipped to capture optical/infrared signals from the early stars and galaxies formed in the Ulimwengu soon after the Big Bang1. Hata hivyo, JWST has some limitation so far as picking up signals from the neutral epoch of ulimwengu wa mapema anahusika.
Table: Epochs in the history of ulimwengu since the Big Bang
(Chanzo: Falsafa ya Kosmolojia - usuli wa sentimita 21. Inapatikana kwa http://philosophy-of-cosmology.ox.ac.uk/images/21-cm-background.jpg)
Up to 380 k years after the big bang, the ulimwengu was filled with ionised gas and was fully opaque. Between 380k – 400 million years, the ulimwengu had become neutral and transparent. The epoch of reionisation started after this phase starting 400 million after the big bang.
During the neutral epoch of early ulimwengu, wakati ulimwengu was filled with neutral gases and was transparent, no optical signal was emitted (hence called dark age). Unionized material does not emit light. This poses a challenge in study of early Ulimwengu of neutral epoch. However, microwave radiation of 21 cm wavelength (corresponding to 1420 MHz) emitted by the cold, neutral cosmic hydrogen during this epoch as a result of hyperfine transition (from parallel spin to more stable anti-parallel spin) offers opportunities to researchers. This 21 cm microwave radiation would be redshifted upon reaching Earth and will be observed at 200MHz to 10 MHz frequencies as radio waves2,3.
21 cm unajimu wa redio: Observation of 21-centimeter cosmic hydrogen signals offers an alternative approach to the study of early ulimwengu especially of neutral epoch phase that was devoid of any light emission. This can also inform us about new physics such as distribution of matter over time, dark energy, dark matter, neutrino masses, and inflation2.
However, the 21-cm signals emitted by the cosmic hydrogen during early ulimwengu phase is elusive. It is expected to be extremely weak (about one hundred thousand times weaker than other radio signals also emanating from the sky). As a result, this approach is still in infancy.
Mnamo mwaka wa 2018, watafiti walikuwa wameripoti kugunduliwa kwa ishara kama hiyo ya redio kwa masafa ya 78 MHz ambayo wasifu wake ulikuwa sawa na matarajio ya ishara ya sentimita 21 iliyotolewa na hidrojeni ya kwanza ya ulimwengu.4. Lakini ugunduzi huu wa mawimbi ya awali ya redio ya 21-cm haukuweza kuthibitishwa kwa kujitegemea kwa hivyo kuegemea kwa jaribio hakuweza kuthibitishwa hadi sasa. Suala kuu linaonekana kuwa uchafuzi na mawimbi ya redio ya mbele.
Hatua ya hivi punde ni ripoti ya Majaribio ya Redio ya Uchambuzi wa Hydrojeni ya Cosmic (REACH) mnamo tarehe 21 Julai 2022. REACH itatumia mbinu mpya ya majaribio ili kugundua mawimbi haya ya redio ya angavu ambayo hayawezi kuepukika na hivyo kutoa tumaini jipya la uthibitisho wa mawimbi ya anga ya sentimeta 21.
Majaribio ya Redio ya Uchambuzi wa Haidrojeni ya Cosmic (REACH) ni jaribio la wastani la 21-cm. Hii inalenga kuboresha uchunguzi kwa kudhibiti masuala yanayokabili zana zinazohusiana na mabaki ya mawimbi ya utaratibu katika data. Inalenga katika kugundua na kuelezea kwa pamoja taratibu pamoja na mandhari ya mbele na mawimbi ya ulimwengu kwa kutumia takwimu za Bayesian. Jaribio linahusisha uchunguzi wa wakati mmoja na antena mbili tofauti, mfumo wa ukanda mpana zaidi (safu ya redshift takriban 7.5 hadi 28) na kirekebisha kipokezi kulingana na vipimo vya ndani.
This development is significant given its potential to be one of the best tools (and cost effective too vis-a-vis space-based observatories like James webb) for study of early ulimwengu as well as possibility of ushering in of new fundamental physics.
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Marejeo:
- Prasad U., 2021.Darubini ya Anga ya James Webb (JWST): Kichunguzi cha Kwanza cha Anga kilichotolewa kwa Utafiti wa Ulimwengu wa Awali. Kisayansi Ulaya. Ilichapishwa tarehe 6 Novemba 2021. Inapatikana kwa http://scientificeuropean.co.uk/sciences/space/james-webb-space-telescope-jwst-the-first-space-observatory-dedicated-to-the-study-of-early-universe/
- Pritchard JA na Loeb A., 2012. 21 cm cosmology katika karne ya 21. Ripoti za Maendeleo katika Fizikia 75 086901. Inapatikana kwa https://iopscience.iop.org/article/10.1088/0034-4885/75/8/086901. Preprint kwa arXiv inapatikana kwa https://arxiv.org/abs/1109.6012 pdf version https://arxiv.org/pdf/1109.6012.pdf
- Chuo Kikuu cha Oxford. Falsafa ya Kosmolojia - 21 cm background. Inapatikana kwa http://philosophy-of-cosmology.ox.ac.uk/21cm-background.html
- Bowman, J., Rogers, A., Monsalve, R. et al. Wasifu wa ufyonzwaji unaozingatia megahertz 78 katika wigo wa wastani wa anga. Nature 555, 67–70 (2018). https://doi.org/10.1038/nature25792
- de Lera Acedo, E., de Villiers, DIL, Razavi-Ghods, N. et al. Radiometer ya REACH ya kugundua ishara ya hidrojeni ya 21-cm kutoka kwa redshift z ≈ 7.5-28. Nat Astron (2022). https://doi.org/10.1038/s41550-022-01709-9
- Eloy de Lera Acedo 2022. Akifichua mafumbo ya Ulimwengu mchanga kwa kutumia radiometer ya REACH. Inapatikana mtandaoni kwa https://astronomycommunity.nature.com/posts/u
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