Is the universe gravitationally dominated by nonbaryonic dark matter?

Makoto Hattori

Research output: Contribution to journalArticlepeer-review


A new method for deriving a lower limit of the mean density of the universe using the maximum temperature of the X-ray-emitting hot gas in clusters of galaxies is proposed. This method is applied to the present record holder for the highest temperature among X-ray clusters, A2163. I find that the probability that the observed volume, in which complete X-ray observations are performed, contains at least one cluster with a temperature as high as the temperature of A2163 is very small for a low-density universe. Even if we take the most conservative upper limit of the baryon density of the universe derived from big bang primordial nucleo-synthesis theories, the possibility that the universe is made from only baryonic matter can be rejected with more than 99.99% confidence. Applying the condition that the expectation of finding a cluster which has a temperature higher than A2163 in the observed volume is at least 1, the mean density of the universe must be more than twice the baryon density of the universe. I conclude that it is very probable that our universe is gravitationally dominated by non-baryonic dark matter.

Original languageEnglish
Pages (from-to)19-22
Number of pages4
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 1994 May 1
Externally publishedYes


  • Cosmology: dark matter
  • Galaxies: clustering
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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