Galaxies like ours are the result of many, many mergers. It’s a mystery exactly how galaxies form, but we do know that these vast seas of stars often collide with each other and blend together to form something new and bigger.

Last week, scientists developed the first family tree of our original galaxy, but another paper published this week in the Monthly notices from the Royal Astronomical Society claims to have discovered a hitherto unknown “fossil galaxy” hidden in the inner depths of our Milky Way.

It is believed to have collided with the Milky Way around 10 billion years ago. The Milky Way is 13.5 billion years old, but this collision appears to have been responsible for the addition of a parcel of stars.

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The fossil galaxy, whose remains were found in the dense halo of stars at the center of our galaxy, was named “Heracles” by the discoverers. Heracles was an ancient Greek hero who, according to legend, received the gift of immortality during the creation of the Milky Way.

Heracles is believed to be twice the mass of the recently discovered Gaia-Enceladus-Sausage Galaxy, which merged with the Milky Way around 9 billion years ago, and is believed to have been the largest collision event.

How was this new fossil galaxy discovered? If it’s all around us, why haven’t we seen it before?

It all comes down to new data on the makeup of stars and their movement in the Milky Way.

“To find a fossil galaxy like this, we had to look at the detailed chemical makeup and motions of tens of thousands of stars,” said Ricardo Schiavon, a member of the John Moores University research team. Liverpool. “This is particularly difficult to do for the stars in the center of the Milky Way, as they are hidden from view by clouds of interstellar dust.”

They did this by looking at the entire Milky Way at once in infrared light.

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This was done using two telescopes in both hemispheres. The Apache Point Observatory Galactic Evolution Experiment (APOGEE), a program of the Sloan Digital Sky Survey III, has telescopes at the Apache Point Observatory in New Mexico, United States, and at the Observatory Las Campanas in Chile.

APOGEE examines stars in near infrared light, which is not obscured by dust, and over the past decade has compiled data on the chemical composition and velocities of half a million stars across the Milky Way.

Crucially including the stars in the center of the Milky Way, previously obscured by dust and densely populated. “APOGEE allows us to pierce this dust and see deeper into the heart of the Milky Way than ever before,” said Schiavon.

“Of the tens of thousands of stars we looked at, a few hundred had surprisingly different chemical compositions and velocities,” said lead author Danny Horta, a graduate student at John Moores University in Liverpool. “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. “

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Finding evidence of this ancient galaxy buried in the Milky Way was “like finding needles in a haystack,” Horta added.

As tempting as it may be, the collision between a smaller, younger Milky Way and this “Heracles Galaxy” must have been a major event since the stars originally belonging to Heracles make up about a third of the mass. across the Milky Way.

The stars of Heracles are therefore now considered a major component of our galactic halo.

The results, of course, were the massive spiral galaxy we know today – our home.

I wish you clear skies and big eyes.

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Al Worden

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