New stars are still forming in our galaxy. According to observations, there are currently 1.65 to 1.9 solar masses of material that can warm up annually for nuclear fusion. For decades, however, models have yielded a completely different, much higher value for the star formation rate. According to this, there would be enough stellar raw material in our galaxy to reach 300 new solar masses per year. A team of researchers has now addressed this problem of slow star formation in the Milky Way and can announce that their theoretical calculated value matches the observations – finally. The study was published in The Astrophysical Journal Letters.
Why and why the Milky Way is rather sluggish when it comes to star formation, scientists have been puzzling for decades: Why is our galaxy so inefficient? It seems that she is not alone in this. Even in our neighboring galaxies, only a few new stars are formed per year, although there should be enough material for a much larger stellar fireworks display. At least that's what the theories of star formation say, which have also been spewing out much too high values for this galactic rate for decades.
Although it isn't related to the Milky Way, star formation models are to blame for it.
Neal J. Evans from the University of Texas at Austin and his research group have now started a new attempt to reconcile the observed star formation rate with the theoretically predicted values.
Stars develop from molecular clouds, which for the most part consist of molecular hydrogen. Since it is difficult to observe molecular hydrogen directly in order to infer the mass of the molecular cloud, researchers usually use a different value: they measure the brightness of a certain spectral line of carbon monoxide in the molecular cloud and then infer the total mass in this way. Evans and Co used a new conversion factor in this calculation. On the one hand, this takes into account how many massive elements beyond hydrogen and helium are in principle present in such clouds, since this is not the same for all molecular clouds. In addition, this factor depends on the distance of the molecular cloud from the galactic center: the further away from it, the fewer massive elements should be present in a cloud.
In a further step, the team around Evans dealt with how efficiently a molecules can form stars. In simpler models, a molecular cloud is as efficient or inefficient as any other molecular cloud: either it can form stars or not. Evans and Co, on the other hand, assumed that there could be a difference between clouds and that these differences would influence the efficiency of the star formation.
The theoretically calculated value for the average star formation rate in our galaxy was 1.46 solar masses per year. And this is actually more or less consistent with the observations. Certainly, the researchers will also have to refine this model a little, but it becomes clear: The Milky Way is not mysteriously inefficient at star formation, but the terrestrial models are too imprecise so far.
