Funded Grants

Researcher: Christopher W. Stubbs, Ph.D.

Grantee: University of Washington, USA

Researcher: Christopher W. Stubbs, Ph.D.

Grant Title: Looking for Dark Matter through a Gravitational Lens: A Next Generation Microlensing Survey

Grant Type: Research Award

Year: 1999

Program Area: Centennial Fellowship

Amount: $1,000,000

Looking for Dark Matter through a Gravitational Lens: A Next Generation Microlensing Survey

Among the most profound questions confronting physical scientists are the nature and distribution of "dark matter". This mysterious substance dominates the mass of galaxies such as the Milky Way, but does not emit or absorb detectable amounts of fight. Its existence is inferred from determinations of galactic masses using the orbits of stars and gas. On a grander scale, whether the expansion of the Universe will continue forever, or will eventually reverse direction depends upon the overall cosmic density of dark matter. The fact that dark matter candidates range from exotic elementary particles to non-luminous astrophysical objects is evidence for how little we know about this hidden sector of the Universe.

I am engaged in an ambitious project that is searching for evidence of dark matter in the form of astrophysical objects, using the technique of gravitational microlensing. If the extensive dark matter halo of our Galaxy is made of such objects, then occasionally one of them will pass very close to the line of sight between the Earth and a distant star. The gravitational attraction of the dark object will deflect the fight from the star, acting as a gravitational lens. This produces a transient brightening of the star, with a very characteristic signature.

Our team has carried out one of the most ambitious observing programs to date in optical astronomy, measuring nightly the brightness of tens of millions of stars over many years. After sifting through this vast sea of data, we have found a handful of microlensing events that could be the first hint of the detection of the dark matter of the Milky Way.

We need to determine whether the signal we are seeing is the result of lensing by dark matter objects, or by ordinary stars in unexpected places. In order to make a conclusive distinction between these alternatives we need at least a tenfold increase in the rate of detected events. This is readily achievable with a next-generation survey, conducted from a superior astronomical site, using state-of- the-art instrument and telescope technology.

A next-generation microlensing survey is being assembled by a capable and experienced team, with the objective of ascertaining the whether the Galactic dark matter has in fact been found.