New Understanding of the Origin of Galaxies Advanced

A new theory as to how galaxies were formed in the Universe billions of years ago has been formulated by Hebrew University of Jerusalem cosmologists. The theory takes issue with the prevailing view on how the galaxies came to exist. The new theory, motivated by advanced astronomical observations and based on state-of-the-art computer simulations, maintains that the galaxies primarily formed as a result of intensive cosmic streams of cold gas (mostly hydrogen) and not, as current theory contends, due primarily to galactic mergers. The researchers show that these mergers had only limited influence on the cosmological makeup of the universe as we know it reports Science Daily.

The results of the cosmology research group, led by Prof. Avishai Dekel, who holds the Andre Aisenstadt Chair of Theoretical Physics at the Racah Institute of Physics of the Hebrew University, appear in a recent issue of the journal Nature.

The galaxies are the building blocks of the Universe. Each of them comprises some hundred billion radiant stars, such as our sun, which extend across about 50,000 light years. Every galaxy is embedded in a spherical halo made of dark matter that cannot be seen but is detected through its massive gravitational attraction. The exact nature of this matter is still unknown.

The galaxies are composed into two major types: spiral and elliptical. The spiral galaxies, such as our Milky Way, are rotating disks, rich in hydrogen gas, and are constantly forming new stars. The young stars give the spiral galaxies a blue tint. In contrast, the elliptical galaxies have bodies with a larger, more rounded shape, and are made of old, red stars that are devoid of gas. They are therefore referred to as red and dead.

The attempt to understand the way in which these two types of galaxies form is the primarily challenge facing modern cosmological researchers. The formation of galaxies is an essential stage in the cosmological process that leads to the formation of life.

The accepted model until now has as its basis the idea of spherical gas infall into a central disk, followed by mergers between disks. The assumption is that the stars formed slowly within the gaseous disks, and that the disks converted into globes when they merged. In such a merger, the colliding gas clouds produce a big burst of new stars at a rate of hundreds of solar masses per year.

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