Journal of Physical Studies 28(1), Article 1902 [20 pages] (2024) DOI: https://doi.org/10.30970/jps.28.1902 ON THE POSSIBILITY OF DETECTING A GLOBAL SIGNAL IN THE LINE OF THE HYPERFINE STRUCTURE OF HYDROGEN FROM THE DARK AGES A. Konovalenko1 , V. Zakharenko1 , B. Novosyadlyj{2,3} , L. Gurvits4 , S. Stepkin1 , Y. Vasylkivskyi1 , P. Tokarsky1 , O. Ulyanov1 , A. Stanislavsky1 , I. Bubnov1  1Institute of Radio Astronomy NAS Ukraine, Kharkiv, Ukraine, 2Astronomical Observatory of Ivan Franko National University of Lviv, Ukraine, 3College of Physics, International Center of Future Science, Jilin University, Changchun, China, 4Joint Institute for VLBI ERIC, Dwingeloo, Netherlands Received 16 October 2023; in final form 27 November 2023; accepted 04 December 2023; published online 31 January 2024

We analyze the possibilities of detecting a signal in the hydrogen 21 cm line, which was formed in the early universe during the Dark Ages, using the Ukrainian radio telescopes UTR-2 and GURT of the National Academy of Sciences of Ukraine. As a result of cosmological expansion, this line is shifted to the decameter range of wavelengths ($λ_{\rm obs}≈18$ m, $ν_{\rm obs}≈16$ MHz) and is in the band of operating frequencies of these telescopes. The brightness temperature of the predicted sky-averaged global signal ranges from $\sim-0.08$ to $\sim0.02$ K, depending on the cosmological model. Such a weak signal is a big challenge even for the world's largest radio telescope in the decameter wavelength range UTR-2, since the signal level of the synchrotron radiation of the Galaxy at these frequencies is 20 000-40 000 K. The paper highlights the peculiarities of spectroscopy at decameter waves, interfering factors of natural and instrumental origin and ways to eliminate them in order to reliably detect the signal in the 21 cm line, which can become an important source of information both about the environment in which the first stars and galaxies were born, and about the nature of dark matter particles and the magnitude of primordial magnetic fields. It was concluded that the detection of such a signal using the most sensitive radio telescopes of the decameter wavelength range is quite possible (with a frequency accumulation of 25 MHz, the detection time will be $\sim50$ days) and can be implemented in the coming years of peace in Ukraine.

Key words: cosmological Dark Ages, hydrogen 21 cm line, radio spectroscopy, UTR-2 radio telescope.

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1. A. A. Penzias, R. W. Wilson, Astrophys. J. 142, 419 (1965);
   Crossref
2. Planck Collaboration: N. Aghanim et al., Astron. Astrophys. 641, A1 (2020);
   Crossref
3. Planck Collaboration: N. Aghanim et al., Astron. Astrophys., 641, A6 (2020);
   Crossref
4. B. E. Robertson et al., Nat. Astron. 7, 611 (2023);
   Crossref
5. E. Curtis-Lake, Four metal-poor galaxies spectroscopically confirmed beyond redshift ten; submitted to Nat. Astron.
6. L. Verde, T. Treu, A.G. Riess, Nat. Astron. 3, 891 (2019);
   Crossref
7. A. G. Riess et al., Astrophys. J. Lett. 934, 7 (2022);
   Crossref
8. V. Bromm, N. Yoshida, Ann. Rev. Astron. Astrophys. 49, 373 (2011);
   Crossref
9. J. R. Pritchard, A. Loeb, Rep. Prog. Phys. 75, 086901 (2012);
   Crossref
10. J. D. Bowman et al., Nature 555, 67 (2018);
    Crossref
11. S. Singh et al., Nat. Astron. 6, 607 (2022);
    Crossref
12. B. Novosyadlyj, Yu. Kulinich, V. Shulga, W. Han, Astrophys. J. 888, 27 (2020);
    Crossref
13. Yu. Kulinich, B. Novosyadlyj, V. Shulga, W. Han, Phys. Rev. D 101, id.083519 (2020);
    Crossref
14. B. Novosyadlyj, Yu. Kulinich, B. Melekh, V. Shulga, Astron. Astrophys. 663, A120 (2022);
    Crossref
15. B. Novosyadlyj, V. Shulga, Yu. Kulinich, W. Han, Physics of the Dark Universe 27, 100422 (2020);
    Crossref
16. B. Novosyadlyj, Yu. Kulinich, G. Milinevsky, V. Shulga, Mon. Not. Roy. Astron. Soc. 526, 2724 (2023);
    Crossref
17. K. Tauscher, D. Rapetti, J. O. Burns, E. Switzer, Astrophys. J. 853, 187 (2018);
    Crossref
18. D. Rapetti, K. Tauscher, J. Mirocha and J. O. Burns, Astrophys. J. 897, 174 (2020);
    Crossref
19. K. Tauscher, D. Rapetti, J. O. Burns, Astrophys. J. 897, 175 (2020);
    Crossref
20. K. Tauscher et al., Astrophys. J. 915, 66 (2021);
    Crossref
21. B. Novosyadlyj, Yu. Kulinich, O. Konovalenko, this issue; J. Phys. Stud. 28, 1901 (2024);
    Crossref
22. S. Ya. Braude, Antennas 26, 3 (Svyaz' Publ., Moscow, 1978).
23. O. O. Konovalenko et al., Radio Phys. Radio Astron. 26, 5 (2021);
    Crossref
24. A. Konovalenko et al., Exp. Astron. 42, 11 (2016);
    Crossref
25. V. Zakharenko et al., J. Astron. Instrum. 5, 1641010 (2016);
    Crossref
26. A. А. Konovalenko et al., Radio Phys. Radio Astron. 21, 83 (2016);
    Crossref
27. O. O. Konovalenko et al., Radio Phys. Radio Astron. 24, 3 (2019);
    Crossref
28. J. D. Kraus, Radio Astronomy (McGraw-Hill, 1966).
29. P. L. Tokarsky, A. A. Konovalenko, S. N. Yerin, IEEE Trans. Antennas Propag. 65, 4636 (2017);
    Crossref
30. P. L. Tokarsky, A. A. Konovalenko, S. N. Yerin, I. N. Bubnov, IEEE Trans. Antennas Propag. 67, 7312 (2019);
    Crossref
31. М. А. Sidorchuk et al., Radio Phys. Radio Astron. 26, 287 (2021);
    Crossref
32. V. V. Krymkin, Radiophys. Quantum Electron. 14, 161 (1971);
    Crossref
33. A. A. Konovalenko, L. G. Sodin, Nature 294, 135 (1981);
    Crossref
34. A. A. Konovalenko, S. V. Stepkin, in: Radio astronomy from Karl Jansky to microjanski. Vol. 15, edited by L. I. Gurvits, S. Frey, S. Rawlings (EAS publ., Budapest, 2005), p. 271;
    Crossref
35. S. V. Stepkin, A. A. Konovalenko, N. G. Kantharia, N. Udaya Shankar, Mon. Not. R. Astron. Soc. 374, 852 (2007);
    Crossref
36. A. A. Konovalenko, in: Radio recombination lines: 25 years of investigation. Proceedings of IAU colloq., edited by M. A. Gordon, R. L. Sorochenko, (Springer, Dordrecht, 1990), p. 175;
    Crossref
37. S. V. Stepkin, O. O. Konovalenko, Y. V. Vasylkivskyi, D. V. Mukha, Radio Phys. Radio Astron. 26, 314 (2021);
    Crossref
38. A. K. Vydula et al., Astron. J. 167, 2 (2024);
    Crossref
39. S. Ya. Braude, A. V. Megn, B. P. Ryabov, N. K. Sharykin, I. N. Zhouck, Astrophys. Space Sci. 54, 3 (1978);
    Crossref
40. E. P. Abranin, Yu. M. Bruck, V. V. Zakharenko, A. A. Konovalenko, Exp. Astron. 11, 85 (2001);
    Crossref
41. P. L. Tokarsky, A. A. Konovalenko, J. Modelski, IEEE Access 11, 75225 (2023);
    Crossref
42. А. А. Коноваленко, дисс. канд. физ.-мат. наук (ИРЕ АН УССР, Харьков, 1982).
43. A. А. Konovalenko, Pribory i tekhnika experimenta 6, 123 (1981);
44. S. V. Stepkin, Radio Phys. Radio Astron. 1, 255 (1996); http://rpra-journal.org.ua/index.php/ra/article/view/22/278 .\\