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This image shows the Milky Way seen from Earth. The reddish rings highlight where Heracles’ stars linger in our galaxy.
Danny Horta-Darrington (John Moores University, Liverpool), ESA / Gaia and SDSS
Our own Milky Way galaxy had a dramatic childhood. Astronomers have unveiled a new chapter in his memoir with the discovery of a probable “fossil galaxy” hidden near his heart.
The proposed fossil galaxy is named Heracles for the Greek hero. It probably mingled with the Milky Way around 10 billion years ago, when our galaxy was a baby.
“The stars originally belonging to Heracles today make up about a third of the mass of the entire Milky Way halo – which means that this recently discovered ancient collision must have been a major event in history of our galaxy, ”the Sloan Digital Sky Survey (SDSS) said in a statement Thursday. SDSS participated in the research.
This illustration shows how Heracles fits into the heart of the Milky Way when viewed from above. The yellow dot indicates our sun.
Danny Horta-Darrington (John Moores University, Liverpool), NASA / JPL-Caltech and SDSS
A research team led by John Moores University, Liverpool (LJMU) graduate student Danny Horta this week published an article on Heracles in the Monthly Notices of the Royal Astronomical Society.
To find Heracles, the team spotted stars that didn’t match those in the Milky Way. “These stars are so different that they could only have come from another galaxy. By studying them in detail, we could trace the precise location and history of this fossil galaxy,” Horta said.
We have seen evidence of dramatic galactic fusions in the Milky Way’s deep past. Recent studies have looked at a time when our galaxy engulfed a dwarf galaxy called Gaia-Enceladus.
Heracles was particularly elusive, as the signs of his existence are obscured by clouds of interstellar dust. The research team used the SDSS Apache Point Observatory’s Galactic Evolution Experiment (APOGEE) to navigate this mess using near infrared light. “To find a fossil galaxy like this, we had to examine the detailed chemical makeup and motions of tens of thousands of stars,” said Ricardo Schiavon, study co-author and LJMU astrophysicist.
The Milky Way may not be over with its galaxy collision pathways. A Milky Way-Andromeda crash lurks billions of years in the future. It’s hard to be a galaxy. Sometimes you are the Milky Way eat them. Sometimes you are Heracles, the swallowed one.
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