Black hole turns red giants into blue ones
Scientists have said that the shortage of red giants near the supermassive black hole in the center of the Galaxy is due to the “deflation” of their outer shells.
In the active center of the galaxy is a supermassive black hole. Its immediate surroundings are densely packed with dust and stars of all kinds, but among them there is a shortage of red giants – old, massive and bright stars with a “bloated” outer shell. Czech astrophysicists said that this shortage with the influence of the black hole itself. They write about it in an article that was published in the Astrophysical Journal.
Michal Zajacek and his co-authors studied space within 0.5 parsec of the center of the Galaxy (about 1.6 light years). The scientists noted that the Fermi bubbles emanating from here indicate a catastrophic event that occurred in the vicinity of a supermassive black hole about 4 million years ago.
According to astronomers, something very massive fell into it then, which led to the emission of streams of radiation and matter. The same processes could cause the ablation of red giants, “deflating” their outer shells. Because due to their size and “friability” such stars are especially sensitive to such influence.
Red giants arise in the late stages of the evolution of massive stars, in the center of which so much helium accumulates that the hydrogen fusion reaction here stops, but continues in the envelope surrounding the star’s core.
This causes it to expand and, consequently, cool down. As a result, the star turns into a “loose”, bright, but relatively cold giant. The diameter of red giants can be a hundred times the diameter of the Sun.
According to scientists, it is likely that about 4 million years ago, while the supermassive black hole in the center of the Galaxy was absorbing large volumes of matter, powerful plasma jets were ejected from its vicinity. As they rotated around the star, they could pass through these streams hundreds or thousands of times, and the red giants quickly lost their outer cold shells.
According to scientists, such a mechanism should have been particularly effective in the immediate vicinity of the hole, at a distance of up to 0.13 light years. At the same time, the deficit of red giants at a greater distance may arise for quite different reasons.