Milky Way's 'Ageless' Silicon Suggests Galaxy Is Efficient At Mixing Things Up

The universe as we see it today is populated with the end results of a series of violent cataclysms — the birth and death of innumerable stars.

Each explosion seeded the cosmos with elements, which, in turn, became the raw materials for the next generation of stars. When these stars exploded into supernovae, they spread much heavier elements through space, and so on and so forth until heavy elements like oxygen, carbon and silicon were created.

Read: Astronomers Map The Elements Of Life Across The Milky Way

“Massive stars are the cauldrons in which heavy elements like silicon are fabricated,” Ed Young, a scientist at the University of California at Los Angeles, explained in a statement released Wednesday. “First-generation stars make silicon 28 — an isotope with 14 protons and 14 neutrons in its nucleus. Over billions of years, later generations of stars are able to create the heavier silicon 29 and 30 isotopes. When these later-generation stars explode as supernovas, the heavier isotopes are blasted into the interstellar medium, subtly altering the chemical profile of the galaxy.”

However, a new survey of the Milky Way (the galaxy we live in) conducted using the Green Bank Telescope (GBT) in West Virginia, which looked for signs of heavier isotopes of silicon, has revealed something surprising — the galaxy appears “ageless” insofar as the distribution of this particular element is concerned.

The concentration of stars increases as one moves closer to galactic center, and, as a consequence, more massive stars end their lives as supernovas near the center than at the outskirts. If this is true, one would expect to find an increase in gradient of heavier isotopes among the elements as one moves toward the center.

Although past radio telescope surveys of carbon and oxygen atoms have given some indication that there is in fact a steady progression from light to heavy isotopes the closer one moves toward the galactic center, these observations have been far from conclusive.

This is why, for this particular survey, the researchers — who describe their observations in a study published in the Astrophysical Journal — looked for the spectral signature of silicon, which is more distinctive and thus easier to detect than carbon and oxygen.

“There was no evidence of a gradient,” study lead author Nathaniel Monson, a graduate student at University of California, Los Angeles (UCLA), said in the statement. “That was a bit surprising. We may have to reassess what we think we know about our galaxy.”

According to the authors of the study, the most likely explanation for this unexpected finding is that the galaxy is more “efficient” than previously believed in mixing things up. It is possible that molecules and atoms from the galactic centre are being dispersed outward and vice versa — a phenomenon that would even out the proportion of heavy and light isotopes across the galaxy.

“There’s a lot about the galaxy we don’t understand yet,” study co-author Edward Young, also from UCLA, said. “It’s possible that further studies with the GBT will teach us a bit more about the Milky Way.”