[ad_1]
Scientists working with data from Sloan Digital Sky Surveys’ Apache Point Observatory Galactic … [+]
getty
Galaxies like ours are the result of many, many mergers. Exactly how galaxies form is a mystery, but we know that these vast seas of stars often collide and mix to form something new and bigger.
Just last week, scientists developed our native galaxy’s first family tree, but another paper published this week on Royal Astronomical Society Monthly Notices claims to have discovered a hitherto unknown “fossil galaxy” hidden deep within our Milky Way.
It is thought to have collided with the Milky Way about 10 billion years ago. The Milky Way is 13.5 billion years old, but this collision appears to have been responsible for adding a very of stars.
The fossil galaxy, the remains of which were found in the dense halo of stars at the center of our galaxy, was called “Heracles” by the discoverers. Heracles was an ancient Greek hero who in legend received the gift of immortality when the Milky Way was created.
Heracles is estimated to have twice the mass of the recently discovered Gaia-Enceladus-Sausage galaxy, which merged with the Milky Way about 9 billion years ago, and was thought to be the largest collision event.
How was this new fossil galaxy found? If it’s all around us, why haven’t we seen it before?
It all comes down to new data on what stars are made of and how they move through the Milky Way.
An artist’s impression of what the Milky Way might look like seen from above. The colored rings show … [+]
Danny Horta-Darrington (Liverpool John Moores University), NASA / JPL-Caltech and SDSS
“To find a fossil galaxy like this we had to examine the detailed chemical composition and movements of tens of thousands of stars,” said Ricardo Schiavon, a member of the research team at Liverpool John Moores University. “This is particularly difficult for stars at the center of the Milky Way to do because 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.
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, USA and at the Las Campanas Observatory in Chile.
APOGEE observes stars in near-infrared light, which is not obscured by dust, and over the past decade has compiled data on both the chemical composition and velocities of half a million stars right across the Milky Way.
Crucially, this included the stars in the previously dusty and densely populated center of the Milky Way galaxy. “APOGEE allows us to penetrate through that dust and see deeper into the heart of the Milky Way than ever before,” Schiavon said.
A full-sky image of the stars in the Milky Way as seen from Earth. The colored rings show the … [+]
Danny Horta-Darrington (LJMU), ESA / Gaia and SDSS
“Of the tens of thousands of stars we looked at, a few hundred had surprisingly different chemical compositions and speeds,” said lead author Danny Horta, a graduate student at Liverpool John Moores University. “These stars are so different that they could only come from another galaxy. By studying them in detail, we could trace the exact location and history of this fossil galaxy. “
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 and younger Milky Way and this “Galaxy of Heracles” must have been a major event as the stars originally belonging to Heracles account for about a third of the mass of the entire Milky Way halo .
The stars of Heracles are therefore now believed to be a fundamental element of our galactic halo.
The result, of course, was the huge spiral galaxy we know today: our home.
I wish you clear skies and eyes wide open.
.
[ad_2]
Source link
