Our residence galaxy has a secret buried inside. A brand new examine revealed within the Month-to-month Notices of the Royal Astronomical Society means that the Milky Manner swallowed an historic dwarf galaxy billions of years in the past, and its stellar stays are nonetheless embedded inside ours.
Researchers have named this misplaced galaxy Loki, after the Norse trickster god, and the title is kind of becoming as a result of it remained hidden in plain sight for a really very long time.
How did astronomers discover Loki?
V. Belokurov primarily based on the pictures by Marcus and Gail Davies and Robert Gendler
The invention got here all the way down to star chemistry. The primary stars that fashioned after the Huge Bang have been made nearly completely of hydrogen and helium.
Over billions of years, later generations of stars fused these parts into heavier ones. Stars with little or no of these heavier parts are due to this fact thought-about historic, and astronomers name them metal-poor.
Researchers studied a gaggle of 20 metal-poor stars sitting contained in the Milky Manner’s galactic disk, which is the flat, spinning area the place most of our galaxy’s stars reside. That’s what made them stand out. Steel-poor stars usually flip up within the galaxy’s outer halo, not the disk. Their presence means that they got here from some other place completely.
The chemical proof backed that up. The staff discovered chemical traces of supernovas and neutron star mergers, however no proof of white dwarf explosions. White dwarfs take billions of years to kind, so their absence suggests Loki burned out lengthy earlier than it might produce them.
The orbits of Loki’s stars reveal a secret about our galaxy’s previous
Many colourful stars are packed shut collectively on this picture of the globular cluster NGC 1805, taken by the NASA/ESA Hubble House Telescope. ESA/Hubble & NASA, J. Kalirai
Right here’s the place it will get stranger. Of the 20 stars, 11 journey in the identical route because the Milky Manner, and 9 go in the wrong way. This implies an especially early merger, again when our galaxy’s personal orbits have been nonetheless chaotic and unsettled. Researchers consider all 20 stars got here from one system, not two.
In truth, Loki isn’t the one galaxy the Milky Manner consumed. A separate 2020 examine recognized an historic galaxy known as Kraken that merged with our galaxy round 11 billion years in the past. The Milky Manner, it seems, has all the time had an enormous urge for food.
