MACHO

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MACHOs (abbreviation for " M assive A strophysical C ompact H alo O bjects ", German : "massive, astrophysical, compact halo objects") are compact celestial bodies made of ordinary baryonic matter in the halo of a galaxy . They are an attempt to interpret dark matter , since its mass could help explain the rotation curve of the stars in the galaxies, which cannot be derived from the star's mass alone .

Since, by definition, MACHOs emit little or no light , they cannot be observed directly from Earth with telescopes . Objects of planetary mass , brown dwarfs , black holes , white or black dwarfs come into question . It is assumed that MACHOs have enough mass not to disintegrate due to tidal forces when they come near other celestial bodies.

Observation through the microlens effect

In 1986, the astrophysicist Bohdan Paczyński proposed that MACHOs be detected using the microlens effect. This leads to the fact that the brightness of a background star, while the MACHO passes in front of it, increases due to its effect as a weak gravitational lens . The increase in brightness is achromatic, i.e. independent of the wavelength of the starlight, and over time in accordance with the general theory of relativity . Until about 2007 about 20 events with stars in the Magellanic Clouds and 1000 in the direction of the Bulge were known.

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Various research groups (including MACHO, OGLE , EROS) have systematically observed a large number of stars to see whether they find a light intensification due to the microlens effect. The Macho Collaboration claims to have provided evidence for a number of MACHOs. Your extrapolation results in MACHOs with up to 0.5 solar masses , which could explain a fifth of the dark matter in the Milky Way . However, other researchers doubt it.

literature

  • Arnold Hanslmeier: Introduction to Astronomy and Astrophysics . 2nd Edition. Spectrum Academic Publishing House, Berlin / Heidelberg 2007, ISBN 978-3-8274-1846-3 , p. 419 ff .

Individual evidence

  1. ↑ The Hidden Lives of Galaxies - Hidden Mass. Retrieved February 27, 2017 .
  2. ^ Arnold Hanslmeier: Introduction to Astronomy and Astrophysics . 2nd Edition. Spectrum Academic Publishing House, Berlin / Heidelberg 2007, ISBN 978-3-8274-1846-3 , p. 421 .
  3. ↑ MACHOs . In: Lexicon of Physics . ( Spektrum.de [accessed on February 27, 2017]).