Somak Raychaudhury
Research Interests

Superclusters of galaxies

Even though the Universe is supposed to be homogeneous and isotropic on large scales, very large structures spanning ten of megaparsecs seem to be pretty common. Numerical simulations show that in the currently favoured cosmologies, the largest structures expected to exist today are supercluster-sized filaments.


I started work on the observational evidence of such large structures as early as the late-1980s. In a Nature paper in 1989,  I announced the discovery of  the largest nearby supercluster (z<0.1), named it the Shapley Supercluster [1], and discussed its importance in the motion of our own galaxy, following up with detailed X-ray and optical studies [2-5,7]. Since then, numerical simulations have revealed how clusters and groups of galaxies trace a network of such filaments.

Here are some references on the web to this work:

The Shapley Supercluster in An Atlas of the Universe and the Encyclopedia of Astronomy and Astrophysics

My Publications in this field           

  1. The distribution of galaxies in the direction of the `Great Attractor'
    Raychaudhury, Somak, 1989, Nature, 342, 251-255
  2. X-Ray and Optical Observations of the Shapley Supercluster in Hydra-Centaurus
    Raychaudhury, Somak, Fabian, A. C., Edge, A. C., Jones, C. & Forman, W., 1991, MNRAS, 248, 101-111.
  3. GINGA Observations of the Shapley Supercluster
    Day, C. S. R., Fabian, A. C., Edge, A. C. & Raychaudhury, Somak, 1991, MNRAS, 252, 394-402
  4. Einstein X-ray observations of the core of the Shapley Supercluster in northern Centaurus
    Breen, J., Raychaudhury, Somak, Forman, W., & Jones, C., 1994, ApJ, 424, 59-67
  5. Spectroscopic Observations in the Cluster A3558 (Shapley 8) and in the core region of the Shapley Supercluster
    Quintana, H., Ramírez, A., Melnick, J., Raychaudhury, Somak & Slezak, E., 1995, AJ, 110, 463
  6. The Shapley Concentration
    Raychaudhury, Somak, 2001, Encyclopedia of Astronomy and Astrophysics (, ed. P. Murdin, Nature and IoP publishing (Invited and refereed review article)
  7. Shock Acceleration and Intergalactic Magnetic Fields in a Large-Scale Filament of Galaxies ZwCl 2341.1+0000
    Bagchi, Joydeep, Ensslin, Torsten A., Miniati, Francesco, Stalin C.S., Singh, M., Raychaudhury, Somak and Humeshkar, N. B., 2002, New Astronomy, 7, 249-277 (astro-ph/0204389)
  8. FLASH redshift survey---I. Observations and Catalogue
    Kaldare Raven, Colless Matthew, Raychaudhury Somak, and Peterson B.A., 2003, MNRAS, 339, 652-662 (astro-ph/0109415)
  9. The Pisces-Cetus Supercluster:  a remarkable filament of galaxies in the 2dF Galaxy Redshift Survey and Sloan Digital Sky surveys
    Porter, Scott C. and Raychaudhury Somak, 2005, MNRAS, 364, 1387 (astro-ph/0511050)
  10. Star formation properties in supercluster filaments
    Raychaudhury Somak and Porter, Scott C. 2005, BAAS, 207, 177.15 ADS link

Full List of publications