This simulation depicts how the Milky Way and Antlia 2 have interacted from 3 billion years ago to present day.
Structure and Composition:
The left panels show the gas distribution and the right panels show the stars. The top panels show the galaxies face on while the bottom panels show the galaxies edge-on. Chakrabarti et al. But not everybody agrees with this conclusion. Vasily Belokurov University of Cambridge, UK cites a series of less than probable assumptions required for the Antlia 2 scenario.
Moreover, he adds, the simulations where Antlia 2 can create ripples focus on the less likely scenario that Antlia 2 crashed relatively close to our galactic center, coming within roughly 30, light-years. The simulations also require a Milky Way on the more massive end of the spectrum.
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Chakrabarti acknowledges the difficulties of dealing with the uncertainties in the data provided by Gaia so far. Those difficulties extend to the question of whether the candidate Cepheid variable stars that she had discovered actually belong to Antlia 2. Fortunately, better data are forthcoming. The next two data releases from the Gaia mission, expected in and , will improve on the accuracy of earlier releases. I have asked this question before, and been ignored. I simply do not understand this obstinacy.
I agree, Jim. At least, allowing readers to click on the image to pop up a larger version would be good. Just a formatting error where a link is missing? Not an error, this is consistent policy across all articles. Habitable planets may certainly lie within the halo, and some clusters may escape the range of the Halo Effect given their distance from the galactic center.
A massive collision in the Milky Way's past
Optimal projection of the area covered by the Halo Array. Prior to approximately the year 97, B. However, encounters with a parasitic sentient species, the Flood , led to the Forerunner-Flood war , with the Flood consuming or killing the great majority of the galaxy's sentient species as the Forerunners first studied them, and then tried to stop them.
Eventually, the Forerunners were forced to construct the ultimate weapon, the Halo Array , in order to stop them - at the same time, killing its builders. The Forerunners built safe havens, including the Shield Worlds and the Ark , to save the remaining sentient species, before activating it, scouring the galaxy of all sentient life forms and killing the Flood except for samples kept on the Halos , then releasing the saved species from their havens to their home worlds. Almost , years afterward, the galaxy had recovered substantially, leading to the rise of two great forces: the UNSC , comprised of the majority of humanity and controlled from Earth , and the Covenant , a hegemony of many different species who worshiped the Forerunners as gods.
Contact between the UNSC and Covenant was not peaceful, leading to the Human-Covenant war , which destroyed hundreds of human colonies and killed billions of colonists and UNSC military personnel, since the Covenant had more advanced weaponry. The discovery of one of the Forerunners Halo installations set forth a series of events that would not only end the war, but also destroy the Covenant and begin the Covenant Civil War, or Great Schism.
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Triggered by the replacement of the Elites with the Brutes , the Elites left the Covenant, in the process that consumed a significant amount of the Covenant's populace and resources, creating the Separatist faction. The Separatists, realizing that the Prophets were conducting an unjustified war against humanity and planning a misguided activation of the Halo Array , allied with the UNSC to stop them, leading to the Battle of Installation The war would continue to rage until at least The first planet believed to be colonized is Mars , followed by the Jovian Moons.
The war was fought between the UN naval and infantry forces, the Neo-Communist Koslovics led by hardliner Vladimir Koslov , and the Frieden rebels Jovian secessionists. The development of the Shaw-Fujikawa Translight Engine in allowed humanity to leave the confines of its home star system for the first time and explore the wider galaxy, ushering in an age of rapid colonization and expansion. The first line of colony ships were unveiled in , and on January 1, , the Odyssey , the first colony ship capable of faster-than-light travel, was launched laden with troops and terraforming gear.
Over the next 28 years, the UNSC began terraforming and colonizing more than worlds, which would become the Inner Colonies. Colonial expansion continued and by , UNSC colonial space encompassed over worlds, large and small, in the Orion Arm. The success of colonization of the Outer Colonies made the Inner Colonies the primary stronghold, both military and economic, though they relied heavily on raw materials supplied by the Outer Colonies. During this period, the planet Reach orbiting Epsilon Eridani , right on Earth's metaphorical doorstep became the UNSC's primary naval yard and training academy.
The researchers backed up the finding by considering other suspects, like the other dwarf galaxies orbiting the Milky Way. It was found that the tidal strength of Sagittarius was too weak, and the Large and Small Magellanic Clouds are too far away to create the effects observed. Of course, the impact would have left a mark on Antlia 2 itself as well.
The researchers have also calculated what kinds of motions the stars in the ghostly dwarf galaxy would have after side-swiping the larger galaxy. These predictions can be tested in future Gaia data runs and, if they prove accurate, add even more weight to the idea. The research was published in the Astrophysical Journal Letters.
Source: Rochester University. An image from the simulation, showing the path of the ghostly dwarf galaxy Antlia 2 bottom cluster after it passed through the Milky Way middle Credit: Sukanya Chakrabarti.
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