Astronomers’ estimates of the rate at which new stars form in the Milky Way have long suggested that this process happens very slowly. But a new study suggests the actual occurrence value is ten times faster than that. If this suggestion is correct, it could completely change the way we see our galaxy (galaxy) and how it compares to others.
Astronomers divide galaxies between those that are actively forming new stars and those that they classify as “dead.” Dead galaxies still produce plenty of light and may be where the existence of technological civilizations is most likely. However, they produce very few new stars. Unless something like a merger with another galaxy changes that, these galaxies are poised for a long and slow contraction. Also, supernovas and many other interesting events occur almost exclusively within a few tens of millions of years of star formation, so a dead galaxy is described as a boring galaxy in many ways.
The Milky Way still has star forming regions, the most famous of which is the relatively close Orion Nebula. Still, astronomers concluded that with a rate of star formation that could be classified as “mostly dead” (only one to two stars per year by some estimates, two to five stars in others), the Milky Way had long passed its best years. However, a recent paper accepted by Astronomy and Astrophysics mentions a rather high number.
Stars do not appear suddenly, in a day, this process takes millions of years. Therefore, it is difficult to estimate the number of new stars, especially in our own galaxy, where larger areas are hidden from view. From Universität Würzburg, Dr. Thomas Siegert and co-authors use a somewhat indirect bottom-up model, looking at gamma rays associated with the decay of the aluminum-26 and iron-60 isotopes, both of which have half-lives of about one million years.
Both of these are made up of very massive stars, forming both in supernova explosions and, in the case of aluminum-26, during the star’s lifetime. So their abundance offers a clue as to how common these events are. Because stars large enough to become supernovae have very short lifetimes, the frequency of supernova events is a strong indicator of the number of massive stars that have formed recently. Starting from this point, the authors estimate the total number of new stars, including most stars too small to reach this intriguing ending.
Because gamma rays are much better at penetrating dust than visible light, it gives us an idea of what’s going on in parts of the galaxy we can’t see directly.
The fact that there are 1.8-2.8 supernovas in the galaxy every century raises more questions for astronomers as we have not observed a supernova in our own galaxy since the invention of the telescope four centuries ago. The authors prefer to focus on stars of four to eight solar masses that form each year, predominantly in the spiral arms. Because smaller stars are much more common than larger ones, masses equal 10-20 new stars per year each year.
Of course, there are some questionable steps in the logic of the article. Some points, from the possibility of errors in isotope abundance calculations, to the fact that the authors generalize the mass in only a part of the galaxy, bring important questioning to this article.
However, the work has already garnered a lot of praise and raises the possibility that our galaxy may have more life years than we thought. On the other hand, it can be said with certainty that we are not on the same level as COS-87259, which was found to form more than a thousand stars a year last week.
The article has been accepted for publication in Astronomy and Astrophysics. The preprint is currently available on arXiv.
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