Observation of 26 cm radio signals, formed due to hyperfine transition of cosmic hydrogen offer an alternative tool to the study of early alheimurinn. As for neutral epoch of the infant alheimurinn when no light was emitted, 26 cm lines are perhaps only window. However, these redshifted radio signals emitted by cosmic hydrogen in the early alheimurinn 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 alheimurinn and help us much in unravelling the mysteries of early alheimurinn.
When it comes to the study of snemma alheimsins, name of recently launched James Webb geimsjónauki (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 Universe soon after the Big Bang1. Hins vegar, JWST has some limitation so far as picking up signals from the neutral epoch of snemma alheimsins er áhyggjufullur.
Table: Epochs in the history of alheimurinn since the Big Bang
(Heimild: Heimspeki heimspeki – 21 cm bakgrunnur. Fæst á http://philosophy-of-cosmology.ox.ac.uk/images/21-cm-background.jpg)
Up to 380 k years after the big bang, the alheimurinn was filled with ionised gas and was fully opaque. Between 380k – 400 million years, the alheimurinn 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 alheimurinn, þegar alheimurinn 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 Universe 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 útvarpsstjörnufræði: Observation of 21-centimeter cosmic hydrogen signals offers an alternative approach to the study of early alheimurinn 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 alheimurinn 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.
Árið 2018 höfðu vísindamenn greint frá uppgötvun slíks útvarpsmerkis á tíðninni 78 MHz sem var að mestu í samræmi við væntingar um 21 sentímetra merkið sem frumvetnið gefur frá sér.4. En ekki var hægt að staðfesta þessa uppgötvun frummerkja 21 cm útvarpsmerkis sjálfstætt og því var ekki hægt að staðfesta áreiðanleika tilraunarinnar hingað til. Aðalatriðið virðist vera mengun með útvarpsmerkjum í forgrunni.
Nýjasti áfanginn er skýrsla um útvarpstilraun fyrir greiningu á kosmískum vetni (REACH) þann 21. júlí 2022. REACH mun nota nýja tilraunaaðferð til að greina þessi veikburða geimræna útvarpsmerki og bjóða þannig upp á nýja von um staðfestingu á 21 sentímetra geimmerkjum.
Útvarpstilraunin fyrir greiningu á kosmískum vetni (REACH) er 21 cm tilraun með himinmeðaltali. Þetta miðar að því að bæta athuganir með því að stjórna vandamálum sem standa frammi fyrir tækjum sem tengjast leifum kerfisbundinna merkja í gögnunum. Það leggur áherslu á að greina og útskýra sameiginlega kerfisfræðina ásamt forgrunni og heimsfræðilegu merkinu með því að nota Bayesísk tölfræði. Tilraunin felur í sér samtímis athuganir með tveimur mismunandi loftnetum, ofur-breiðbandskerfi (rauðvikt á bilinu 7.5 til 28) og viðtakakvarðari sem byggir á mælingum á vettvangi.
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 alheimurinn as well as possibility of ushering in of new fundamental physics.
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Tilvísanir:
- Prasad U., 2021.James Webb geimsjónauki (JWST): Fyrsta geimstjörnustöðin tileinkuð rannsóknum á alheiminum snemma. Vísindaleg Evrópu. Sent 6. nóvember 2021. Fæst á http://scientificeuropean.co.uk/sciences/space/james-webb-space-telescope-jwst-the-first-space-observatory-dedicated-to-the-study-of-early-universe/
- Pritchard JA og Loeb A., 2012. 21 cm heimsfræði á 21. öld. Skýrslur um framfarir í eðlisfræði 75 086901. Fæst á https://iopscience.iop.org/article/10.1088/0034-4885/75/8/086901. Forprentun á arXiv fáanleg á https://arxiv.org/abs/1109.6012 pdf útgáfa https://arxiv.org/pdf/1109.6012.pdf
- Oxford háskóla. Heimspeki heimsfræði – 21 cm bakgrunnur. Fæst kl http://philosophy-of-cosmology.ox.ac.uk/21cm-background.html
- Bowman, J., Rogers, A., Monsalve, R. o.fl. Frásogssnið sem miðast við 78 megahertz í himinmeðalrófinu. Náttúra 555, 67–70 (2018). https://doi.org/10.1038/nature25792
- de Lera Acedo, E., de Villiers, DIL, Razavi-Ghods, N. o.fl. REACH geislamælirinn til að greina 21 cm vetnismerki frá rauðviku z ≈ 7.5–28. Nat Astron (2022). https://doi.org/10.1038/s41550-022-01709-9
- Eloy de Lera Acedo 2022. Afhjúpar leyndardóma ungbarnaalheimsins með REACH geislamælinum. Fæst á netinu á https://astronomycommunity.nature.com/posts/u
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