Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........31m&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SANTA BARBARA, 1995.Source: Dissertation Abstracts International, Volume: 57-01, Sect
Astronomy and Astrophysics
Astrophysics
Dark Matter
Scientific paper
In the standard picture, only 1-10% of the mass of the Universe is accounted for by known distributions of stars, gas, and dust. Determining the nature and amount of the missing "dark matter" is perhaps the most important unsolved problem in astrophysics. The existence of dark matter is inferred on all scales larger than globular clusters, and there may be more than one form of dark matter required to explain the apparent distribution of mass in the Universe. Many dark matter candidates, especially hypothetical elementary particles, have been proposed to account for the unseen mass, but the least speculative option is that the dark matter consists of stellar or planetary mass objects that are not burning nuclear fuel. Examples include brown dwarfs, white dwarfs, and remnants of collapsed stars, and they are collectively known as MACHOs for MAssive Compact Halo Objects. If the halo of the Milky Way Galaxy contains MACHOs they can be detected by means of gravitational microlensing as first suggested by Paczynski (1986). When the path of a compact object (or a dim star) passes close to the line of sight to a distant star the light from the star is amplified so that a time history of the stellar brightness will have a peak with signatures that can be used to infer a microlensing event. By monitoring millions of stars in the Magellanic Clouds (LMC, SMC) and Galactic Bulge the Macho Project is carrying out a program to measure the content of MACHOs in the halo of the Galaxy. We have full time use of the 1.27 m telescope at Mt. Stromlo Observatory which images 0.5 square degrees of sky simultaneously in 2 color bands. The two foci are equipped with very large CCD cameras, each containing 4 Loral chips of 2048 x 2048 pixels. A custom photometry, database, and analysis system is used to construct stellar time histories and search for microlensing events. We have found more microlensing events than expected from known stellar populations suggesting that MACHOs are indeed present in the Galactic halo. However the observed event rate is too small to allow for a canonical halo dominated by these objects. Complimentary observations toward the Galactic Bulge have yielded substantially more microlensing events than expected from most Galactic models.
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