Meet I Zw 18: A Dwarf Galaxy

The Center of Astrophysics of the University of Porto recently came up with an analysis that seriously calls into question the current model of galactic formation. Polychronis Papaderos represented the CAUP, and with his Swedish colleague Göran Östlin, Papderos examined data from the Hubble Space Telescope to better understand the I Zw 18 dwarf galaxy. That particular object has received a lot of attention, and it is one of the few places where star-forming activity can be readily observed.

I Zw 18 region. (Credit: Image courtesy of Centro de Astrofísica da

For a long time, astrophysicists have simply assumed that stars were emitting light from gas structures. These structures occupied the same region as the stars that were emitting the light. The research suggests that galaxies that undergo active starbursts don’t follow this rule. Instead, nebula gases might actually be emitting around half of the total light in question. Since star mass is often calculated from the galaxy’s total luminosity, the idea that nebular emissions account for so much light means that many of these calculations could be totally off. One could also surmise that since I Zw 18 is young, the galaxy is acting the way many objects did shortly after the Big Bang. Many of the stars there have been around for less than 1 billion years. It will be interesting to watch this galaxy in the years ahead.


Papaderos, P., & Östlin, G. (2012). I Zw 18 as morphological paradigm for rapidly assembling high-galaxies Astronomy & Astrophysics, 537 DOI: 10.1051/0004-6361/201117551

Izotov, Y., Chaffee, F., Foltz, C., Thuan, T., Green, R., Papaderos, P., Fricke, K., & Guseva, N. (2001). A Spectroscopic Study of Component C and the Extended Emission around I Zw 18 The Astrophysical Journal, 560 (1), 222-235 DOI: 10.1086/322494

Image Credit: Hubble

Post Navigation