When you go out and see the clear night sky, it feels like there is nothing more peaceful and calm. But many of those tranquil stars are proof of turbulent history - and now we're learning to unlock their secrets.
Using data from the Gaia Milky Way Mapping Survey, astronomers have discovered a vast array of stars, which they believe are the remnants of a massive dwarf galaxy that was dragged into the galactic disc before exploding. He called the Nix the stream after the Greek goddess of the night.
According to the standard model of the evolution of the universe, galaxies merge with smaller galaxies and grow - the process of accretion. There is a lot of evidence for this phenomenon in the Milky Way: many currents associated with dwarf galaxies and spherical clusters blocked by the tidal forces of the galaxy have been identified.
Then the Gaia satellite came along. It was launched in 2013 and is currently collecting data to create the most accurate 3D map of the Milky Way. A careful study of the optimal velocity, radial velocity and distance of stars to see where everything is and how it rotates.
It reveals the Milky Way transformation with other details such as Antilia 2, Sagittarius Dwarf Spherical Galaxy and Um, Gaia Sausage. Not to mention the Mean-Aridanus constellation, wondering what's left of the star cluster.
But all of this is marked by moving and searching for differently constructed objects. It is very difficult to find a truncated galaxy. Stars that move with the rotation of the galaxy disk and have chemical compositions similar to the stars formed here can be ignored.
So Caltech's theoretical physicist Leena Nakib and her colleagues have run a neural network since the release of the second Gaia data, creating a list of stars that have not collapsed in the galaxy.
"The network," the researchers point out in their paper, "takes the five-dimensional kinematics of each star (two angular coordinates, two optimal motions and parallax) as input and then gives the score associated with the growth potential of the star."
When they discovered the stars that the neural network was so sure of, the team discovered a group of 232 stars, all moving in one motion - that is, with galactic rotation - and similar chemical compositions. With. This group has never been associated with any other stellar flow.
When they orbited these stars 1 billion years ago, the team found that they had very different orbital features to the stars in both the Milky Way's thick disk and the thin disk.
"With this observation, Nyx k has a speed of 90 km and disk 1 and sufficient radial velocity component, giving a strong case that this is the result of satellite merger," the researchers wrote.
Constellations moving together can be caused by disturbances from galactic bars or by other means, such as echoes generated by density waves in the spiral arms, but are not suited to Nikes. Simulations of these events cannot produce Nyx's interval without generating other effects not detected in the data.
At some point in the Milky Way's long history, a dwarf galaxy sprawling with stars shrinking in the center of the Milky Way would fit their data.
When the researchers repeated their study with a little relaxed certainty, they found another constellation that almost matched the nexus flow. Prognostic galaxy orbit and chemical composition are similar - but in the second group, radial velocity is the opposite. This is also consistent with the dwarf galaxy model, since simulations show that the second cluster may be debris from a different path to the same dwarf galaxy.
Nikes appear to have unidentified stars in this study because they are out of the strict parameters given to the neural network. Future research can shed light on this phenomenon - how it happened and how massive the dwarf galaxy is.
Nyx helps us understand how the dark matter of such a merged galaxy contributes to the disk, as there is evidence that the entangled star populations are interconnected with the dark matter clusters that are thought to have merged with the stars.
"If Nix is in fact the result of such a merger, it will provide evidence of progressive progress stars, and possibly, a dark matter in the stream or disk," the researchers wrote.
"The existence of such dark matter components will significantly change our understanding of the local dark matter phase-space distribution and lead to significant changes to the terrestrial discoveries of the dark matter particle."
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