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Gaia reveals that most of the Milky Way galaxies are newcomers to the corners of our universe.

Our galaxy, the Milky Way, is surrounded by about 50 dwarf galaxies. Most of these galaxies can only be identified by a telescope and are named after the constellations that appear in the sky (for example, Draco, sculptor, Leo). However, the two most obvious dwarf galaxies, called the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), are easily visible to the naked eye. Traditionally, these dwarf galaxies have been considered satellites in orbit around the Milky Way for billions of years. But now, new data from ESA’s Gaia spacecraft show that most of the dwarf galaxies are passing through the Milky Way for the first time. This forces astronomers to rethink the history of the Milky Way and how it was formed, as well as the nature and composition of the dwarf galaxy itself. Credits: ESA / Gaia / DPAC, CC BY-SA 3.0 IGO

Data from ESA’s Gaia project rewrites the history of our galaxy, the Milky Way. What was traditionally thought of as the Milky Way’s companion galaxy has now become clear that most are newcomers to our galaxy environment.


Dwarf galaxies are a collection of thousands to billions of stars. For decades Dwarf galaxy The satellites that surround the Milky Way are satellites. That is, they have been trapped in orbit around our galaxy and have been our constant companion for billions of years.Now the movement of these dwarfs Galaxy Calculated with unprecedented accuracy thanks to data from Gaia’s early third data release, the results are amazing.

François Hammer, Paris Observatory—Paris University of Science and Retors in France, and colleagues across Europe and China used Gaia’s data to calculate the movement of 40 dwarf galaxies around the River of Heaven. They did this by calculating a series of quantities known as the three-dimensional velocities of each galaxy and using them to calculate the orbital energy and angular (rotational) momentum of the galaxy.

They found that these galaxies are moving much faster than the giants and clusters known to orbit the Milky Way. They were so fast that they still couldn’t get orbit around the Milky Way. There, the interaction of our galaxy with its contents robs them of their orbital energy, Angular momentum..

Our galaxies have cannibalized many dwarf galaxies in the past. For example, 80-100 billion years ago, a dwarf galaxy called Gaia Enceladus was absorbed by the Milky Way. The stars can be identified by Gaia data because of their eccentricity and the range of energy they have.

Recently, 4-5 billion years ago, the Sagittarius Dwarf Galaxy was captured by the Milky Way Galaxy and is now being dismembered and assimilated. The energy of the star is higher than that of Gaia Enceladus, indicating that it has a shorter time under the influence of the Milky Way.

In the case of new research dwarf galaxies that occupy most of the dwarf galaxies around the Milky Way galaxy, their energies are even higher. This strongly suggests that they have only arrived near us in the last billion years.

This discovery reflects what was made about the Large Magellanic Cloud (LMC), a larger dwarf galaxy that is so close to the Milky Way that it can be seen as a stain of light in the night sky from the Southern Hemisphere. The LMC was also considered a satellite galaxy of the Milky Way until the 2000s, when astronomers measured its speed and discovered that it was too fast to be bound by gravity. Instead of a companion, LMC will visit for the first time. Now we know that the same is true for most dwarf galaxies.

So will these newcomers settle down or just pass us? “Some of them are captured by the Milky Way and become satellites,” says François.

But it is difficult to say exactly which, as it depends on the exact mass of the Milky Way, and that is an amount that is difficult for astronomers to calculate with actual accuracy. Estimates are twice as different.

The discovery of dwarf galaxy energy is important because it forces us to reassess the nature of the dwarf galaxy itself.

As the dwarf galaxy orbits, the gravitational pull of the Milky Way tries to pull it apart. In physics, this is known as tidal force. “Because the Milky Way is a large galaxy, its tidal forces are simply huge, and it’s very easy to destroy a dwarf galaxy, perhaps after passing it once or twice,” says François.

In other words, being a member of the Milky Way is a death sentence for a dwarf galaxy.The only thing that can resist the destructive grip of our galaxy is if the dwarves had a significant amount. Dark matter.. Dark matter is a mysterious substance that astronomy thinks exists in the universe to provide extra gravity to hold individual galaxies together.

So, in the traditional view that there was a Milky Way dwarf Satellite galaxy Having been in orbit for billions of years, it was hypothesized that they must be dominated by dark matter in order to balance the tidal forces of the Milky Way and keep them intact. The fact that Gaia revealed that most of the dwarf galaxies orbit the Milky Way for the first time means that they do not necessarily have to contain dark matter, reaffirming whether these systems are balanced. Need to be evaluated. In the process of destruction.

“It is now clear that the history of the Milky Way is much more famous than previously understood by astronomers, mainly thanks to Gaia. By investigating these intriguing clues, we are in the galaxy. We hope to further tease the fascinating chapters of the past, “says Timo Trusti, Gaia Project Scientist at ESA.


Dwarf galaxies catch even smaller galaxies


For more information:
François Hammer et al., Gaia EDR3 Milky Way dwarf proper motion. II Velocity, total energy, and angular momentum, Astrophysical Journal (2021). DOI: 10.3847 / 1538-4357 / ac27a8

Quote: Gaia is a corner of our universe where most of the Heavenly Galaxy galaxies were acquired from https: //phys.org/news/2021-11-gaia-reveals-milky-companion-galaxies on November 25, 2021. Revealed to be a newcomer to (November 25, 2021) .html

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Gaia reveals that most of the Milky Way galaxies are newcomers to the corners of our universe.

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