Structure in the Cosmos

structure in cosmosOrigins of Structure in the Cosmos


Dark Matter
Dark Matter, millenial simulation (Image credit: Millenium Simulation, MPA Garching, V. Springel, S. White et al.)

The origins of structure in the universe encompasses some of the most active research in astronomy and astrophysics. This theme addresses the formation of planets, stars, galaxies, and the largest scale structures in the universe, namely the filamentary organization of galaxies into the "cosmic web" including massive clusters of galaxies in regions where filaments meet. The force of gravity plays the dominant role on these scales, creating concentrations of dark matter that are the structures out of which galaxies form. The dark matter halos that dominate the mass of any galaxy gravitationally attracts the gas out of which stars are eventually made.  Dark matter on these scales can be detected using "gravitational lensing" which is the focusing of light by matter predicted by Einstein's theory of general relativity.


The first stars appeared about 400 million years after the Big Bang. Their radiation eventually ended the cosmic 'dark age' that set in as the universe expanded and cooled.  These stars are expected to be quite massive (a hundred times the mass of our Sun). Intense efforts over the coming decade using new observatories such as the James Webb Space Telescope to be launched in 2017 and a new generation of very large optical telescopes such as the Thirty Meter Telescope now under construction will be focused on the quest to have direct measurements of how such stars heat the universe at early times. .


Star formation
Artist's view of Star Formation in the Early Universe. Painting by Adolf Schaller. STScl-PRC02-02

The formation of galaxies is a central problem in modern astrophysics. The major question here is how gas is converted to stars in such a way as to reproduce the structure of galaxies that we observe. A central focus of current research is on how the intense radiation from massive young stars as well as the violent stellar winds and supernova explosions that such stars undergo at the end of their lives dumps energy and momentum into the gaseous clouds and interstellar medium of the host galaxy. These "feed back" processes  are critical in order to prevent the too rapid conversion of gas into stars allowing the formation of extended spiral galaxies rather than overly spherical ones. All the evidence indicates that star formation is highly inefficient.


The ALMA Observatory
Currently under construction in the thin, dry air of northern Chile's Atacama desert at an altitude of 5,000 meters above sea level, ALMA will initially be composed of 66 high-precision antennas working together at millimeter and submillimeter wavelengths.

The formation of stars is another vast area of research whose pace has been dramatically quickened by the advent of new observatories such as the Atacama Large Millimeter Array. Stars form within large (up to 300 light years across), cold (10 degrees above absolute zero), massive (up to a million times the mass of the Sun) clouds of molecular gas and dust. The most recent observations by the Herschel Space Observatory show that star forming gas is concentrated within filaments in these clouds. Overdense regions within such filaments collapse under their own weight to form gaseous disks, out of which both stars and their planetary systems form.  Thus star formation is a critical process in astronomy as it affects both galaxy structure and evolution, as well as setting the stage for and controlling aspects of planet formation.


Herschel image of the region of massive star formation in the molecular cloud, W3. This cloud is 6200 light years away from us in the Milky Way, and spans 200 light years in size. At the upper left, dense blue knots mark two regions in W3 where massive stars are formingwithin young star clusters. Extensive networks of filaments of cool dust and gasdominate the cloud structure. The intense radiation from the young stars is starting heat and push away the gas that is arriving at the clusters by filamentary flows.

The discovery in 1995 of the first planet around another star opened up an incredible new field of astronomical research. Over 1000 planets are now known around other stars with more than 3000 candidates under investigation. These discoveries have been made using a combination of ground based telescopes that can detect the presence of a planet around its star by measuring the star's "Doppler wobble" effect (a planet and its star revolve around their common centre of mass), as well as the Kepler space observatory that observes the slight dimming of stars as their orbiting planets pass across their disks.

These discoveries have opened up entirely new fields of research on the question of how planets form. Most planetary systems discovered are much more densely packed with planets in their innermost region than our solar system. Thus, entirely new types of planets such as "hot Jupiters"  - Jovian mass planets with closer orbits than that of Mercury in our solar system - and Super Earths (one to ten times the mass of our Earth) have been discovered. It is clear that massive planets probably started to form in the outer reaches of their host gaseous disks, and slowly migrated inwards to their present orbits.  

Finally, the origins of structure has a direct impact on the origins of life in the cosmos.  There are now a dozen exoplanets known that are Earthlike in mass, and that orbit within the "habitable zone" of their host star. The HZ around a star are those orbits for which a planet is warmed sufficiently that water remains liquid on its surface. This has enormous implications for the possibility of life on worlds beyond our solar system.

Research Opportunities:

Research among OI members and their collaborators addresses many aspects of this theme, from cosmological structure formation to galaxy formation, star formation and planet formation. This research involves the use of state of the art supercomputer simulations, as well as theoretical and mathematical modeling; and advanced observations at radio, optical, and millimetre telescopes and observatories both on the ground and in space. This includes CFHT, ALMA, JCMT, and Gemini and space observatories such as the Hubble Space Telescope, and Herschel.