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Cosmology
The field of my research is cosmology, a young and rapidly developing branch of physics and astronomy. While cosmology was something people were always thinking about, it was only in last few decades that scientist have approached it with a characteristic rigor and methodology. Initially driven by a few enthusiasts only, cosmology grew bigger and bigger, becoming a science where very basics physical questions are expected to unfold. With increasing popularity and raised expectations, good thing came along. Now one can do cosmology as a full time job, and not as a hobby in a free time; multi-million dollar missions are being regularly funded. Because of all this, in last 10 years or so, we have seen a real avalanche of observational data which in some aspects confirmed expectations, but in some aspects have turned the understanding of the universe up side down. In any case, a lot of data is present now, and even more is on the way, and that data have to be respected and accounted for by theories. Only some thirty years ago cosmologists were people that could afford to themselves to come up with a theory while having leisure walk with their hand on the back. But these almost philosophical times are past now, and like in all other areas of physics, cosmologists are now busy fitting models, estimating errors, finding distributions, profiles... For bad or for good, it became a real science. It became a precision physical cosmology.
So what are the things we have learned by now?
While we knew from the early 20th century that the universe expands, as
the theory of general relativity explains it,
it came as a big surprise that it actually
accelerates, an impossible scenario if the universe consists of matter only. The
main constituent of the universe today is still a mystery - called
dark energy.
While from observations we can quantify its amount, evolution and some basic properties
(equation of state), and using theory calculate its effects on say, structures or expansion,
it is still lack physical understanding on what it really is. Simply parametrizing
something is not the same as understanding it. I am a member of a
recently formed team
of scientists from several institutions and led by Los Alamos with a goal of
understanding the nature of dark energy. Likely, it will be a long and interesting journey.
The other extra ordinary component is the dark matter, but today it is understood much better.
It is still unclear from which elementary particle(s) it is made of, but there are plenty
of candidates in particle physics. It is 'dark' because it does not carry a charge and thus
do not interact via electromagnetic interaction (does not emit light), but it has a mass
and therefore leaves gravitational signature of its presence. There are several independent
proofs of its existence, and a few ground experiments are after dark matter particles now.
Finally,
the remaining approximately 4% of the universe is in the well known form of matter made of
protons, electrons, and other particles whose behavior early twentieth century physics
have already explained in detail.
More about evolution of the universe, and formation of all known structures can be found
on structure formation page here, and of course throughout
the web ...
Extragalactic Astrophysics
Studying cosmology necessarily includes studying clusters of galaxies; they are the biggest
and most massive objects in the universe.
They are good probe of cosmology because they are
the youngest objects most recently formed, carrying a lot of information about underlying
evolution of the universe which leads to their creation. Since they are so big (on color
composite image on the right, red and blue dots around the center are galaxies, likely
of the similar size as Milky Way) they are also a reasonably fair samples of the
content of the universe.
However, they are interesting from astrophysical perspective alone, even without any
cosmological perspective or predictiveness. They have large amount of very hot and
rarefied gas which gets stirred by galactic motion in the cluster. While the gas
temperature reflects the depth of gravitational potential, the recent observations
of intracluster gas in central regions do not show expected cooled cores nor cooling flows;
some other heating mechanism must be present there.
Usually having
hundreds of galaxies, they have very complicated dynamics with lot of galaxy stripping,
and even their complete destruction. This leads to a population of stars floating
throughout the cluster and changing its chemical composition.
They often host specific kind of very large elliptical
galaxies with extended envelopes of stars which are not seen as stand alone in the field.
In some clusters cavities have been
observed, often filled with radio emitting gas. Finally, clusters form through inflow of
surrounding material, but also from mergers of groups and/or smaller clusters, and these are
by far the most energetic events in the universe.
This is certainly not the complete list
of extragalactic topics involving clusters of galaxies, but is here just to give a flavor
of ongoing research. My advisor Paul Ricker
and I are attacking some of them using computer simulations. Stay tuned for the break-through
results ... :))
Simulations
Computer simulations are laying in the core of my research, and
they are in some way a substitute for an experiment;
instead of isolating a physical system and study its evolution under
different circumstances, one might model the system and important physics
through a system of equations which can then be evolved on a computer. The
reason for taking such an approach might be because it is cheaper
(often the case in industry), safer (e.g. nuclear stockpile program), or
because it is impossible to reproduce and/or manipulate the phenomena of
interest in the lab - which is exactly the case when one studies the
evolution of the universe.
On the other hand,
there is a theoretical underlining of computer simulations as well.
The change of some physical quantity in time and/or space is mathematically
shown through a
differential equation
or through a set of such equations if there are more coupled variables. In general,
these do not have an analytical solution, but have to be solved numerically. The
engine which is performing such a numerical evolution, step by step, is simply called
a simulation.
Besides using simulations as tools, I am interested in understanding and improving
their algorithms. Even though simulation development is often very tedious job, it is
a very rewarding in the end to be able to predict code's behavior on certain task, or
to quickly throw some changes.
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My Universe > Science |
© Zarija Lukic 2006 |