The "birth rate" for stars is certainly not easy to determine. Distances in the universe are far too great for astronomers to be able to count all the newly formed celestial bodies with the aid of a telescope. So it is fortunate that the emerging stars give themselves away by a characteristic signal known as "H-alpha" emissions. The larger the number of stars being formed in a particular region of the firmament, the more H-alpha rays are emitted from that region.
"H-alpha emissions only occur in the vicinity of very heavy stars" - Jan Pflamm-Altenburg of the Argelander Institute of Astronomy at Bonn University.
It has long been accepted that heavy and light stars are always born in a certain ratio to each other. One "H-alpha baby" is thought to be accompanied by 230 lighter stars with a mass too low for them to emit H-alpha rays. However, new observations make this theory untenable. On the edges of "disc galaxies" (like the Milky Way) the H-alpha radiation ceases abruptly. For a long time astronomers concluded from this finding that no stars are being born in this region.
"The explanation offered is simply that too little gaseous matter exists for it to collapse into balls and form stars. These theories largely inform our understanding of how galaxies developed from the Big Bang to the present" - Jan Pflamm-Altenburg.
