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. gettyGalaxies like ours are the result of many, many mergers. Exactly how galaxies form is a mystery, but we know these vast seas of stars often bump into each other and mix to form something new, and bigger. Just last week scientists developed the first family tree of our home galaxy, but another paper published this week in the Monthly Notices of the Royal Astronomical Society claims to have discovered a hitherto unknown fossil galaxy hidden in the inner depths of our Milky Way. Its 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 lot of stars. MORE FROM FORBESNASA's Hubble Spots 'Bizarre Glow' After An 'Impossible' Explosion In SpaceBy Jamie CarterThe fossil galaxy, the remains of which were found in the dense halo of stars at the center of our galaxy, has been named 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 figured to be twice the mass of the recently discovered Gaia-Enceladus-Sausage galaxy, which merged with the Milky Way some 9 billion years ago, and was thought to have been the biggest collision event.How was this new fossil galaxy found? If its all around us then why didnt we see it before?It all comes down to new data on what the stars are made of, and how theyre moving through the Milky Way. An artists impression of what the Milky Way might look like seen from above. The colored rings show ... [+] the rough extent of the fossil galaxy known as Heracles. The yellow dot shows the position of the Sun.Danny Horta-Darrington (Liverpool John Moores University), NASA/JPL-Caltech, and the SDSSTo find a fossil galaxy like this one we had to look at the detailed chemical make-up and motions of tens of thousands of stars, said Ricardo Schiavon, a member of the research team, from Liverpool John Moores University. 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.They did it by looking at the entire Milky Way at once in infra-red light. MORE FROM FORBESThis Week Jupiter Aligns With Saturn. What Happens Next Will Be A Once-In-A-Lifetime Sky EventBy Jamie CarterThat was done by 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 Apache Point Observatory in New Mexico, USA and at Las Campanas Observatory in Chile.APOGEE looks at stars in near-infrared light, which doesnt get obscured by dust, and in the last decade has compiled data on both the chemical make-up and the velocities of half a million stars right across the Milky Way. Including, crucially, stars in our galaxys previously dust-obscured, and densely populated, center of the Milky Way. APOGEE lets us pierce through that dust and see deeper into the heart of the Milky Way than ever before, said Schiavon. An all-sky image of the stars in the Milky Way as seen from Earth. The colored rings show the ... [+] approximate extent of the stars that came from the fossil galaxy known as Heracles. The small objects to the lower right of the image are the Large and Small Magellanic Clouds, two small satellite galaxies of the Milky Way. Danny Horta-Darrington (LJMU), ESA/Gaia, and the SDSSOf the tens of thousands of stars we looked at, a few hundred had strikingly different chemical compositions and velocities, said lead author Danny Horta, a graduate student at Liverpool John Moores University. 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.MORE FROM FORBESWhat Are Those Three Bright 'Stars' Visible At Dusk Each Night? This Is What You're SeeingBy Jamie CarterFinding the evidence for this ancient galaxy buried within the Milky Way was like finding needles in a haystack, added Horta. Tantalizing though it may be, the collision between a smaller, younger Milky Way and this Heracles Galaxy must have been a major event since stars originally belonging to Heracles account for about a third of the mass of the entire Milky Way halo. The stars of Heracles are hence now thought to be a major building block of our Galactic halo. The results, of course, was the massive spiral galaxy we know todayour home. Wishing you clear skies and wide eyes.