(ORDO NEWS) — An analysis of the most energetic light in the galaxy has shown that we can be wrong about the rate of star formation in the Milky Way.
Gamma rays produced from the radioactive decay of isotopes produced during star formation show that stars form at a rate four to eight times the mass of the Sun per year.
That might not sound like much, but it’s two to four times the current estimate, which suggests our home galaxy isn’t as peaceful as we thought.
And this has important implications for our understanding. the evolution of our galaxy and those around us, because the rate at which stars are born and die can change the overall chemical composition of the galaxy.
Stars are factories that produce the more complex elements of our universe. Their nuclei are nuclear furnaces, slamming atoms against each other to turn them into ever larger atoms.
As they die, their violent death throes spew these heavier elements into interstellar space to drift in the clouds or be consumed by new forming stars.
Their supernova explosions are also high energy, creating even heavier elements that their cores could not support.
Like their deaths, the birth of stars is also energetic.
They form from dense clumps in clouds of interstellar dust and gas, collapse under the influence of gravity, and greedily consume material from their surroundings until there is enough pressure and heat in their cores to ignite fusion.
At the same time, they begin to radiate powerful stellar winds that carry particles into space, and jets launched from their poles of particles accelerating along the young star’s magnetic field.
It is known that one of the elements resulting from the death of a star is a radioactive isotope of aluminum called aluminum-26.
From a cosmic point of view, aluminum-26 does not last long; its half-life is 717,000 years. And when it decays, it produces gamma radiation at a certain wavelength.
But aluminum-26 is also present in significant amounts in the clouds of matter surrounding newly forming stars.
If the speed at which matter falls on a star exceeds the speed of sound, a shock wave is formed that generates cosmic rays.
When the beams collide with isotopes in the dust, such as aluminum-27 and silicon-28, they can produce an isotope of aluminum-26.
So, by looking at the universe’s budget for gamma radiation produced from the radioactive decay of aluminum-26, astronomers can estimate the rate at which stars producing this isotope form and die in the Milky Way, and use that to determine the overall rate of star formation.
Current ratings. since the rate of star formation in the Milky Way galaxy is about two Suns turning into stars every year.
Since most of the stars in the Milky Way are much less massive than the Sun, it is estimated that this averages out to about six or seven stars per year.
Siegert and colleagues conducted a census of aluminum-26 gamma radiation. in the galaxy and ran simulations to see the most likely mechanism for the observed abundance of this light.
They found that a star formation rate of four to eight solar masses per year works best; or up to about 55 stars per year.
This estimate can still be improved; the models did not quite reproduce the gamma radiation of the Milky Way as it is currently observed; and the distance from the gamma source can change the final estimate, but is difficult to measure.
That’s why the researchers could only give a range of star formation rates, not an exact mass.
However, the team’s method offers hope for a better understanding of how the Milky Way creates new stars.
Star formation is usually shrouded in thick gas and dust that is difficult to see; counting the gamma radiation it produces can be one effective way to look behind the scenes.
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