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The Net Advance of Physics: The Nature of Dark Matter, by Kim Griest -- Section 7I.

Next: Conclusions Up: Baryonic Dark Matter (Machos) Previous: Advantages of Many Events


Macho Conclusion


The microlensing experiments have given robust and strong limits

on the baryonic content of the halo. Much more data from the

LMC and SMC will be available soon, so we expect the statistics to

improve in the near future. The LMC events, if interpreted as due to

halo microlensing, allow a measurement of the baryonic

contribution to the halo, which is around 20% for a standard halo.

In this case, the most likely Macho contribution to the Milky Way

halo mass is about tex2html_wrap_inline214 , which is roughly the same as the disk

contribution to the Milky Way mass. However, the whole story has

been made more complicated (and exciting) by the much larger

than expected number of bulge microlensing events. These events

imply a new component of the Galaxy, and until the nature of this

new component is known, unambiguous conclusions concerning the

LMC events will not be possible. For example, if the Milky Way disk

is much larger than usually considered, a much smaller total halo

mass will be required, and so even an all-Macho halo might be

allowed. Alternatively, the new Galactic component which is giving

rise to the bulge events, may also be giving rise to the LMC events,

and the Macho content of the halo could be zero. Fortunately,

much more data is forthcoming, and many new ideas have been

proposed. Microlensing is fast becoming a new probe of Galactic

structure, and, beside the original potential to discover or limit dark

matter, may well produce discoveries such as extra-solar planetary

systems.

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Next: Conclusions Up: Baryonic Dark Matter (Machos) Previous: Advantages of Many Events

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