Cosmology: Milky Way gobbles up satellites (Introduction)

by David Turell , Friday, November 20, 2020, 22:46 (1254 days ago) @ David Turell

Another fossil galaxy is found in the central Milky Way:

https://phys.org/news/2020-11-astronomers-fossil-galaxy-deep-milky.html

"Scientists working with data from the Sloan Digital Sky Surveys' Apache Point Observatory Galactic Evolution Experiment (APOGEE) have discovered a "fossil galaxy" hidden in the depths of our own Milky Way.

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"The proposed fossil galaxy may have collided with the Milky Way ten billion years ago, when our galaxy was still in its infancy. Astronomers named it Heracles, after the ancient Greek hero who received the gift of immortality when the Milky Way was created.

"The remnants of Heracles account for about one third of the Milky Way's spherical halo. But if stars and gas from Heracles make up such a large percentage of the galactic halo, why didn't we see it before? The answer lies in its location deep inside the Milky Way.

"'To find a fossil galaxy like this one, we had to look at the detailed chemical makeup and motions of tens of thousands of stars," says Ricardo Schiavon from Liverpool John Moores University (LJMU) in the UK, a key member of the research team. "That is especially hard to do for stars in the center of the Milky Way, because they are hidden from view by clouds of interstellar dust. APOGEE lets us pierce through that dust and see deeper into the heart of the Milky Way than ever before."

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"'Of the tens of thousands of stars we looked at, a few hundred had strikingly different chemical compositions and velocities," Horta said. "These stars are so different that they could only have come from another galaxy. By studying them in detail, we could trace out the precise location and history of this fossil galaxy."

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"Stars originally belonging to Heracles account for roughly one third of the mass of the entire Milky Way halo today—meaning that this newly-discovered ancient collision must have been a major event in the history of our galaxy. That suggests that our galaxy may be unusual, since most similar massive spiral galaxies had much calmer early lives.

"'As our cosmic home, the Milky Way is already special to us, but this ancient galaxy buried within makes it even more special," Schiavon says."

Comment: We have to be a giant galaxy to find a safe place for the Earth to avoid all the nastiness of radioactive waves that can destroy life.