Major Advances in Radio Astronomy: Some Key Questions Today

  • Govind Swarup


During the last six decades, several outstanding discoveries have been made in the field of radio astronomy. These have revolutionized our understanding of the mysteries of the Universe. Observations of radio galaxies and quasars that emit extremely powerful radio waves indicate presence of supermassive black holes at their centre. Discovery and detailed observations of the 2.7 K cosmic microwave background temperature have provided strong support to the Big Bang Model of the Universe, giving tight constraints on the relative contributions of baryons, dark matter and dark energy in the Universe. Observations of the emission line of neutral hydrogen from spiral galaxies provide information about the formation and evolution of galaxies. Over 150 molecules have been discovered in the interstellar medium, giving details about the physics and chemistry of the interstellar space; these are also ingredients of life in the Universe. Discovery of Pulsating Radio Sources (Pulsars) have provided strong support to the models of neutron stars that are end products of a star when its ‘nuclear fuel’ runs out. Observations of Pulsars also provide tests of the General Theory of Relativity. I also summarize some of the investigations that are being carried out currently with the Ooty Radio Telescope in South India and with the Giant Metrewave Radio Telescope near Pune; these are amongst the largest radio telescopes in the world. Finally, I describe some of the Key Questions today.


Radio galaxies Quasars Cosmology Big Bang Model Synthesis radio telescopes GMRT SKA 



I thank Dr. Nimisha Kantharia for discussions. This review article is based on the Krishna-Ji lecture based on the award given to the author by the National Academy of Sciences, India, on 7th April 2015.


  1. 1.
    Jansky K (1933) Electrical disturbances apparently of extraterrestrial origin. Proc Inst Radio Eng 21:1387Google Scholar
  2. 2.
    Reber G (1940) Cosmic static. Astrophys J 91:621–624CrossRefADSGoogle Scholar
  3. 3.
    Hey JS (1946) Solar radiations in the 4–6 metre radio wave-length band. Nature 157:47–48CrossRefADSGoogle Scholar
  4. 4.
    Southworth GC (1945) Microwave radiation from the Sun. J Frankl Inst 239:285CrossRefGoogle Scholar
  5. 5.
    Appleton EV, Hey JS (1946) Solar radio noise. Philos Mag 37:73–84CrossRefADSGoogle Scholar
  6. 6.
    Pawsey JL, Payne-Scott R, McCready LL (1946) Radio-frequency energy from the Sun. Nature 157:158–159CrossRefADSGoogle Scholar
  7. 7.
    Pawsey JL (1946) Observation of million degree thermal radiation from the Sun at a wavelength of 1.5 metres. Nature 158:633–634CrossRefADSGoogle Scholar
  8. 8.
    Wild JP, McCready LL (1950) Observations of the spectrum of high-intensity solar radiation at metre wavelengths I, the apparatus and spectral types of solar bursts observed. Aust J Sci Res A 3:387–394ADSGoogle Scholar
  9. 9.
    Wild JP (1950) Observations of the spectrum of high-intensity solar radiation at metre wavelengths. II. Outbusrsts. Aust J Sci Res A 3:399–408ADSGoogle Scholar
  10. 10.
    Boischot A (1957) Caractères d’un type d’émission hertzienne associé à certaines éruptions chromosphériques. Comptes Rendus de l’Académie des Sciences, Paris 244:1326–1329ADSGoogle Scholar
  11. 11.
    Wild JP, Sheridan KV, Trent GW (1959) The transverse motions of the sources of solar radio bursts. In: Bracewell RN (ed) Paris symposium on radio astronomy. Stanford University Press, Stanford, pp 176–185Google Scholar
  12. 12.
    Maxwell A, Swarup G (1958) A new spectral characteristic in solar radio emission. Nature 181:36–38CrossRefADSGoogle Scholar
  13. 13.
    Christiansen WN, Warburton JA (1955) The distribution of radio brightness over the solar disk at a wavelength of 21 centimetres. III. The quiet Sun-two-dimensional observations. Aust J Phys 8:474–486CrossRefADSGoogle Scholar
  14. 14.
    Bastian TS, Benz AO, Gary DE (1998) Radio emission from solar flares. Ann Rev Astron Astrophys 36:131–188CrossRefADSGoogle Scholar
  15. 15.
    Bastian TS, Gary DE (2012) Observing the Sun at radio wavelengths: current status and future prospects, science with large solar telescopes. In: Proceedings of IAU special session 6 held 22–24 August 2012.
  16. 16.
    Manoharan PK (2010) Ooty interplanetary scintillation—remote-sensing observations and analysis of coronal mass ejections in the heliosphere. Sol Phys 265:137–157CrossRefADSGoogle Scholar
  17. 17.
    Hey JS, Parsons SJ, Phillips JW (1946) Fluctuations in cosmic radiation at radio-frequencies. Nature 158:234CrossRefADSGoogle Scholar
  18. 18.
    Smith FG (1951) An accurate determination of the positions of four radio stars. Nature 168:551–553CrossRefADSGoogle Scholar
  19. 19.
    Baade W, Minkowski R (1954) Identification of radio sources in Cassiopeia, Cygnus A, Puppia A. Astrophys J 119:206–214CrossRefADSGoogle Scholar
  20. 20.
    Condon JJ et al (1998) The NRAO VLA sky survey. Astron J 115:1693–1716CrossRefADSGoogle Scholar
  21. 21.
    Perley RA, Dreher JW, Cowan JJ (1984) The jet and filaments in Cygnus A. Astrophys J 285:L35–L38CrossRefADSGoogle Scholar
  22. 22.
    Schmidt M (1963) 3C 273: a star-like object with large red-shift. Nature 197:1040CrossRefADSGoogle Scholar
  23. 23.
    Antonucci R (1993) Unified models for active galactic nuclei and quasars. Ann Rev Astron Astrophys 31:473–521CrossRefADSGoogle Scholar
  24. 24.
    Urry CM, Padovani P (1995) Unified schemes for radio loud AGN. Pub Astron Soc Pac 107:803–845CrossRefADSGoogle Scholar
  25. 25.
    Hubble E (1929) A relation between distance and radial velocity among extra-galactic nebulae. Proc Natl Acad 15:168–173zbMATHCrossRefADSGoogle Scholar
  26. 26.
    Lemaître G (1927) Un Univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques. Annal. Société Scientifique Bruxelles, A. Société Scientifique Bruxelles A 47:49–56ADSGoogle Scholar
  27. 27.
    Hoyle F (1948) A new model for the expanding universe. Mon Not R Astron Soc 108:372–383zbMATHCrossRefADSGoogle Scholar
  28. 28.
    Bondi H, Gold T (1948) The steady-state theory of the expanding universe. Mon Not R Astron Soc 108:252–271zbMATHCrossRefADSGoogle Scholar
  29. 29.
    Ryle M, Clarke RW (1961) An examination of the steady-state model in the light of some recent observations of radio sources. Mon Not R Astron Soc 122:349–362CrossRefADSGoogle Scholar
  30. 30.
    Swarup G, Sharma NVG, Joshi MN, Kapahi VK, Bagri DS, Damle SH, Ananthakrishnan S, Balasubrahmanya V, Bhave SS, Sinha RP (1971) Large steerable radio telescope at Ootacamund, India. Nat Phys Sci 230:185–188CrossRefADSGoogle Scholar
  31. 31.
    Swarup G (1975) Angular size-flux density relation for extragalactic radio sources. Mon Not R Astron Soc 172:501–512CrossRefADSGoogle Scholar
  32. 32.
    Kapahi VK (1975) Cosmology from angular size counts of extragalactic radio sources. Mon Not R Astron Soc 172:513–533CrossRefADSGoogle Scholar
  33. 33.
    Swarup G, Kapahi VK, Velusamy T, Ananthakrishnan S, Balasubramanian V, Gopal-Krishna, Pramesh Rao A, Subrahmanya CR, Kulkarni VK (1991) Twenty-five years of radio astronomy at TIFR. Curr Sci 60:79–94Google Scholar
  34. 34.
    Manoharan PK (2006) Evolution of coronal mass ejections in the inner heliosphere: a study using white-light and scintillation images. Sol Phys 235:345–368CrossRefADSGoogle Scholar
  35. 35.
    SkA Saiyad, Bharadwaj S (2014) Prospects for detecting the 326.5 MHz redshifted 21-cm HI signal with the Ooty Radio Telescope (ORT). J Astrophys Astron 35:157–182CrossRefADSGoogle Scholar
  36. 36.
    Hawking S (1988) A brief history of time. Bantam Books, New York. ISBN: 0-553-38016-8Google Scholar
  37. 37.
    Penzias AA, Wilson RW (1965) A measurement of excess antenna temperature at 4080 Mc/s. Astrophys J 142:419–420CrossRefADSGoogle Scholar
  38. 38.
    Mather JC et al (1990) A preliminary measurement of the cosmic microwave background spectrum by the Cosmic Background Explorer (COBE) satellite. Astrophys J Lett 354:L37–L44CrossRefADSGoogle Scholar
  39. 39.
    Mather JC et al (1994) Measurement of the cosmic microwave background spectrum by the COBE FIRAS instrument. Astrophys J 420:439–444CrossRefADSGoogle Scholar
  40. 40.
    Smoot GF (1992) Structure in the COBE differential microwave radiometer first-year maps. Astrophys J Letts 396:L1–L5CrossRefADSGoogle Scholar
  41. 41.
    Bennett CL et al (2004) First-year Wilkinson microwave anisotropy probe (WMAP) observations: preliminary m maps and basic results. Asrophys J Suppl 148:1–27CrossRefADSGoogle Scholar
  42. 42.
    Bennett CL et al (2013) Nine-year Wilkinson microwave anisotropy probe (WMAP) observations final maps and results. Astrophys J Suppl Ser 208:20CrossRefADSGoogle Scholar
  43. 43.
    Spergel DN et al (2003) First-year Wilkinson microwave anisotropy probe (WMAP) observations: determination of cosmological parameters. Astrophys Suppl 148:175–194CrossRefADSGoogle Scholar
  44. 44.
    Rubin VC, Ford WK (1970) Rotation of the andromeda nebula from a spectroscopic survey of emission regions. Astrophys J 159:379–403CrossRefADSGoogle Scholar
  45. 45.
    Roberts MS, Whitehurst RN (1975) The rotation curve and geometry of M31 at large galactocentric distances. Astrophys J 201:327–346CrossRefADSGoogle Scholar
  46. 46.
    Bosma A (1978) The distribution and kinematics of neutral hydrogen in spiral galaxies of various types. Ph.D. Theses, University of GroningenGoogle Scholar
  47. 47.
    Riess AG et al (1998) Observational evidence from supernovae for an accelerating universe and a cosmological constant. Astron J 1009:1009–1038CrossRefADSGoogle Scholar
  48. 48.
    Perlmutter S et al (1999) Measurements of Ω and Λ from 42 high-redshift supernovae. Astrophys J 517:565–586CrossRefADSGoogle Scholar
  49. 49.
    Ewen HI, Purcell EM (1951) Observation of a line in the galactic radio spectrum: radiation from galactic hydrogen at 1420 Mc/sec. Nature 168:356CrossRefADSGoogle Scholar
  50. 50.
    Lah P (2007) The HI content of star-forming galaxies at z = 0.24. Mon Not R Astron Soc 376:1357–1366CrossRefADSGoogle Scholar
  51. 51.
    Weinreb S et al (1963) Radio observations of OH in the interstellar medium. Nature 200:839–841CrossRefADSGoogle Scholar
  52. 52.
    Baan WA, Wood PAD, Haschick AD (1982) Broad hydroxyl emission in IC 455. Astrophys J 260:L49–L52CrossRefADSGoogle Scholar
  53. 53.
    Kanekar N, Chengalur JN, Ghosh T (2010) Probing fundamental constant evolution with redshifted conjugate-satellite OH lines. Astrophys J 716:L23–L26CrossRefADSGoogle Scholar
  54. 54.
    Hewish A et al (1968) Observation of a rapidly pulsating radio source. Nature 217:709–713CrossRefADSGoogle Scholar
  55. 55.
    Gold T (1968) Rotating neutron stars as the origin of the pulsating radio sources. Nature 218:731–732CrossRefADSGoogle Scholar
  56. 56.
    Golreich P, Julian WH (1969) Pulsar electrodynamics. Astrophys J 157:869–880CrossRefADSGoogle Scholar
  57. 57.
    Hulse RA, Taylor JH (1975) Discovery of a pulsar in a binary system. Astrophys J 195:L51–L53CrossRefADSGoogle Scholar
  58. 58.
    Taylor RA, Weisberg RH (1989) Further experimental tests of relativistic gravity using the binary pulsar PSR 1913 + 16. Astrophys J 345:434–450CrossRefADSGoogle Scholar
  59. 59.
    Christiansen WN, Hogbom JA (1985) Radio telescopes. Cambridge University Press, CambridgeGoogle Scholar
  60. 60.
    Ryle M, Neville AC (1962) A radio survey of the North Polar region with a 4.5 minute of arc pencil-beam system. Mon Not R Astron Soc 125:39–56CrossRefADSGoogle Scholar
  61. 61.
    Swarup G, Ananthakrishnan S, Kapahi VK, Rao AP, Subrahmanya CR, Kulkarni VK (1991) The Giant Metrewave Radio Telescope. Curr Sci 60:95–105Google Scholar
  62. 62.
    Swarup G (2010) Growth and development of radio astronomy in India. In: Padmanabhan T (ed) Astronomy in India: a historical perspective. Springer, New York, pp 129–178Google Scholar
  63. 63.
    Roy S, Pal S (2013) Discovery of the small diameter young supernova remnant G354.4 + 0.0. Astrophys J 774:150–157CrossRefADSGoogle Scholar
  64. 64.
    Roy S, Rao AP (2004) Sgr A* at low radio frequencies: Giant Metrewave Radio Telescope observations. Mon Not R Astron Soc 349:L25–L29CrossRefADSGoogle Scholar
  65. 65.
    Basu A, Mitra D, Wadadekar Y, Ishwara-Chandra CH (2012) GMRT 333-MHz observations of six nearby normal galaxies. Mon Not R Astron Soc 419:1136–1152CrossRefADSGoogle Scholar
  66. 66.
    Begum A, Chengalur JJ, Karachentsev ID (2005) A dwarf galaxy with a giant HI disk. Astron Astrophys 433:L1–L4CrossRefADSGoogle Scholar
  67. 67.
    Bagchi J, Sirothia SK, Werner N, Pandge MB, Kantharia NG, Ishwar-Chandra CH, Gopal-Krishna, Paul S, Joshi S (2011) Discovery of the first giant double radio relic in a galaxy cluster found in the PLANCK Sunyaev-Zel’dovich cluster survey: PLCK G287.0 + 32.9. Astrophys J Lett 736:L8-1–L8-6CrossRefADSGoogle Scholar
  68. 68.
    van Weeren RJ, Röttgering HT, Intema HT, Rudnick L, Bruggen M, Hoeft M, Oonk JBR (2012) The “toothbrush-relic”, evidence for a coherent linear 2-Mpc scale shock wave in a massive merging galaxy cluster. Astron Astrophys 546(A124):1–21Google Scholar
  69. 69.
    Sirothia SK, Gopal_Krishna, Witta PJ (2013) Discovery of giant relic radio lobes straddling the classical double radio galaxy 3C452. Astrophys J Lett 765:L11–L16CrossRefADSGoogle Scholar
  70. 70.
    Machalski J, Koziel-weirzbowska D, Jamrozy M (2007) Giant radio galaxies as a probe of the cosmological evolution of the AGM, preliminary detections and low resolution spectroscopy with SALT. Acta Astron 57:227–248ADSGoogle Scholar
  71. 71.
    Lal DV, Rao AP (2007) Giant Metrewave Radio Telescope observations of X-shaped radio sources. Mon Not R Astron Soc 374:1085–1102CrossRefADSGoogle Scholar
  72. 72.
    Paciga G et al (2011) The GMRT epoch of reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z ≈ 8.6. Mon Not R Astron Soc 413:1174–1183CrossRefADSGoogle Scholar
  73. 73.
    Carrili C, Rawlings S (2004) Science with the square kilometer array. New Astron Rev 48:979–1563CrossRefADSGoogle Scholar

Copyright information

© The National Academy of Sciences, India 2015

Authors and Affiliations

  1. 1.National Centre for Radio AstrophysicsTIFRPuneIndia

Personalised recommendations