## Monday, April 10, 2006

### Elizabeth Lada: stars born in clusters

Elizabeth Lada from University of Florida is an astronomer who is most famous for defending the statement that most stars are born in clusters. This statement has brought two communities that studied star formation - those who only wanted the overall rate and those who investigated individual cases microscopically - closer together.

It was interesting to see a nice colloquium from an adjacent field - a field whose conclusions are slightly less theoretical, quantitative, universal, and principled than ours but one that can offer nicer pictures. Some of the main messages of the talk are the following:
• most stars are born in clusters
• most stars are born in embedded clusters
• the radius of the clusters is a few parsecs and their mass is a few dozens of the solar masses
• the mass distribution of the stars that are born is rather universal, peaked around "M = 0.3 solar mass": star creation is robust; the very light stars are exceptional

• star formation is an ongoing process that still occurs these days
• star formation is terribly inefficient: only roughly one percent of the matter ends up in stars
• infrared astronomy allows you to see things that are hidden from the visible spectrum astronomy: as you increase the wavelength, dark regions in the skies become increasingly transparent
• the observations have become much easier due to the technological progress - by Richard Wilson and others; some of her first major discoveries were deduced from pictures that were 60 x 60 pixels while today she works with a 4-megapixel arrays
• Orion is her (her son's) most favorite constellation
Back to my theme. Elizabeth Lada gave a nice and organized talk. Nevertheless, there is a cultural gap between physics - which includes condensed matter physics and experimental cosmology - on one side and astronomy on the other side. In physics, we are looking for patterns and laws that explain a whole class of phenomena and their details; something that allows us to predict the answers to new questions that were not used in creating our theories. Astronomy is a nice subject but from the viewpoint of the previous sentence, it is not a part of physics. In fact, I would say that the defining difference between astrophysics and astronomy is that astrophysics, as a part of physics, is predictive.

Incidentally, Josef Lada was a famous Czech artist whose pictures of a romantic Czech winter (and the good soldier Švejk) became one of the secondary national symbols of the Czechs. Recently, the musician Jaromír Nohavica recorded a song about the romantic "Ladian winter" (Ladovská zima) - combined with angry complaints about the upgef***ed snow that Nohavica has to remove every day at -30 degrees Celsius, and so forth.