Research Areas: Michael Bolte
Part of the incredible image of NGC 602 obtained with the Advanced Camera for
Surveys on the Hubble Space Telescope
Globular Clusters and the Age of the Universe: Research from the Past
For many years my research involved observations of stars in Galactic
globular clusters. These beautiful objects are part of the halo
of the Galaxy and, based on the comparison of stellar evolution
models to the observed color-magnitude diagrams, they are ancient relics
of the early formation period of the Galaxy. A very lively controversy
in astronomy circles in the 1990s revolved around the ages derived
for globular cluster stars. At the time the best ages were around 15 billion
years which was older than the favored "expansion" age of the Universe based
on the value of the Hubble Constant and a "flat" Universe with no Dark Energy.
One day I will add my version of the history of this topic. For now, here is
a Nature paper I wrote with Craig Hogan on the controversy in 1995.
Note the prediction
of Dark Energy and the call to use Type 1a supernovae to observationally
confirm the prediction!
Bolte & Hogan Nature paper
Extremely Metal-Poor Stars, White Dwarfs and Supernovae: Current Research
My more recent research has concentrated in two areas. The first is
the study of stars that are very deficient in the elements with higher
atomic number than helium (that is everything but hydrogen and helium).
Like globular clusters, these stars are relics from the earliest times
in Galactic history. They are a laboratory for testing equilibrium
and explosive nucleosynthesis in stars, they allow us to trace
the early epoch of chemical evolution of the Galaxy and Universe, and
the pattern of chemical abundances in these stars may be our best clue
identifying the nature of the first stars to form in the Universe.
This work started with Jennifer Johnson's
(now at Ohio State University) dissertation,
David Lai has
just finished up his dissertation (June 2008) in the same field and we have
been fortunate to work with
and it is a privilege to sometimes
Chris Sneden and
two of the most important pioneers in this field.
The second area is based on observations of white dwarf (WD) stars in
young open clusters. The princpal question we are addressing here is
"what is the mass for main-sequence stars above which they explode
as core-collapse supernovae and below which they evolve into WDs". This
is an important question for understanding the early history
of galaxies, particularly low-mass galaxies. SNII insert a significant
amount of kinetic energy into the ISM and the lower limit on galaxy
mass may be set by the gravitational potential required to stay
bound during the initial star-formation epoch during which the stars
about this critical mass rapidly evolve and explode. The brains behind this
program is Kurtis Williams (now at U Texas, Austin). Santa Cruz
graduate student Kate Rubin has made a nice contribution and long-time
WD experts Detlef Koester and Jim Leibert (U. Arizona) are on-going
- EMP Stars:
these are my pages about that program including links to Keck data that
we have made publicly available.
- This will be a link to the page sumarizing our results soon!
I also have a long-standing program with Eric Sandquist and students at
San Diego State University analysing large samples of stars in globular
clusters. We use wide-field CCD images, a battery of "artifical star"
experiments and generate very accurate luminosity functions for essentially
all the evolved stars in each cluster. This allows very precise
tests of stellar evolution for stars with around 1 solar mass.
Messier 5 CMD
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Michael Bolte- email@example.com