Shulou(Shulou.com)11/24 Report--

In the vast universe, collisions between celestial bodies occur from time to time, including giants such as galaxies. It can be said that our Milky way grew up in such collisions. Each collision will leave more or less traces on the galaxy, and even some major collisions still have traces to this day.

As mentioned last time, the outer edge of the disk of our Milky way galaxy is not flat, but a warped structure rolled up or down. Later, after analyzing the data from the Gaia Telescope, astronomers thought that the warping structure may have originated from the collision of a Milky way satellite galaxy (Sagittarius dwarf galaxy) with the Milky way.

In addition to the collision marks on the disk, astronomers have found that the galactic halo in the outer layer of the Milky way disk also seems to hold traces of a major collision.

A galactic halo is a roughly spherical part of a galaxy that expands to the outside, similar to the egg white of an egg, which wraps the "yolk" made up of a galactic disk inside. In addition to dark matter halos and interstellar gas, galactic halos are mainly composed of stars scattered outside the silver disk.

Although the stars in the halo occupy a lot of space as a whole, they are extremely scattered and sparse, with a small total mass, accounting for only 1% of the total mass of stars in the Milky way. They are mainly made up of stars with low metal content, including globular clusters.

Astronomers have thought for decades that the galaxy's stellar halo should be a relatively regular sphere, but in the last two years scientists have found that the halo may not be as round as we think, but a rugby-like ellipsoid.

Because the analysis is about the distribution of stars, data from the Gaia telescope are essential. In addition, the researchers used data from a high-resolution ground survey called H3.

Using these two sets of data, the researchers constructed a giant ellipsoid that surrounds the Milky way. Although stellar halos are based on stars, in theory, the entire galactic halo, including dark matter halos, should also be ellipsoidal.

As mentioned before, dark matter is like a skeleton, forming the general framework of the distribution of matter in the universe, while ordinary matter is like flesh and blood, attached to the skeletal framework. So usually, the overall distribution of the surrounding dark matter can be roughly inferred from the shape of ordinary matter.

Based on the stellar halo model, the researchers concluded that the ellipsoidal halo of the Milky way galaxy may be related to a galactic collision in ancient times.

The story starts 10 billion years ago. About three or four billion years after the Big Bang

At that time, the universe was like the warring States period, when the law of the jungle could be seen everywhere. At this time, the Milky way Galaxy is located in a more remote suburb because it is far away from the main battle field of the Virgo supercluster (the Virgo supercluster).

Although you can't take part in a "regiment war", it's okay to "fight a field" once in a while.

One day, a young galaxy called Gaia Sausage came to the challenge.

Yes, astronomers choose their names so casually. Here "Gaia", of course, refers to the Gaia telescope that found it; "sausage" is because it looks a bit like sausage when drawing patterns through Gaia data, hence the name "Gaia-sausage".

Although the young man is not as big as the Milky way, he is not very different in size. And this time it seems to have come prepared, while talking while the Milky way is not paying attention to cut into the sneak attack from the retrograde orbit. Although there is no carelessness in the Milky way, "any skill is in vain in the face of absolute power."

Soon, Gaia-sausage gave a "blood": its outer star cluster was stripped from the body under the powerful tidal forces of the Milky way. The Milky way came down with a knife, and the whole galaxy of Gaia-sausage was split in an instant, and the stars gushed out like blood. All of a sudden, blood spilled all over the Milky way, and the whole galaxy was shrouded in a halo of scattered stars.

The encounter between Gaia and sausages contributed at least eight globular clusters and 5 billion solar mass stars to the Milky way. At the same time, the Milky way also captured each other's gas and dark matter, which together formed the ellipsoidal galactic halo on the periphery of the galactic disk.

Since then, Gaia-sausage has been buried in the Milky way like Enceladus in Greek mythology, and the name "Gaia-sausage" has been renamed "Gaia-sausage-Enceladus", referred to as "GSE Galaxy".

After this war, except for some shrimp soldiers and crabs, the Milky way never met a decent opponent again. As a result, the Milky way dominates the local galaxy group, with at least 30 dwarf galaxies, including large and small Magellanic galaxies, bowing to each other in a radius of more than 1 million light-years.

Although large and small Magellanic galaxies later challenged the Milky way, they could not compete with the tidal forces of the Milky way. In the process of scuffling, they have all been torn and deformed by the Milky way. Today, although the outcome is uncertain, judging from the irregular shape of the Magellan galaxy and the star flow for several light-years, it seems that the outcome of this battle has been divided.

However, the Milky way is not the only dominant group of galaxies within a radius of 1000 light-years. More than 2 million light-years from the Milky way, a guy bigger than the Milky way has been watching us covetously. At the moment, it is already coming at us at a speed of hundreds of kilometers per second, and yes, it is the famous Andromeda galaxy (M31).

The Andromeda galaxy is more experienced than the Milky way. All the dwarf galaxies around it have been cleaned up by it, and now there are only a dozen left.

Even 5 billion years ago, M32, the predecessor of the third-largest galaxy in the local galaxy group, competed with it. However, after 3 billion years of protracted war, M32 was eventually beheaded by the Andromeda galaxy, leaving only the core to become what is now the M32 dwarf galaxy.

After killing the third, the next target is the Milky way, which ranks second.

But the battle for supremacy is at least 4 billion years away, and before that, the Milky way may first practice with the younger brothers of the Andromeda galaxy, such as the satellite galaxy of the Andromeda galaxy, the triangle galaxy (M33).

Although it is regarded as a satellite galaxy, the triangle galaxy is also something to be reckoned with. With its strength, it is now firmly in the third place in the local galaxy group.

However, when the final peak battle came, due to the addition of Andromeda galaxy, Milky way, Andromeda galaxy and Triangle galaxy formed an unstable three-body motion relationship. In this case, the triangle galaxy may be thrown directly out of the local galaxy group and no longer participate in the fight.

In this way, will it be the powerful and dominant Milky way or the larger and experienced Andromeda galaxy that will take the throne in the future?

As two evenly matched spiral galaxies, the result in the future may not be who loses and who wins. It is likely that billions of years after the war, the two galaxies will slowly merge into a new form of galaxies-elliptical galaxies. You can say that they both lose out, or you can say that the two of them break the ice. In short, the Galactic Fairy Galaxy, which merges into one, will become the real overlord of the local group in the future.

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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