take a good look in the latest image provided by the Hubble Space Telescope. It shows a huge elliptical galaxy called NGC 474 that is about 100 million light-years away from us. About two and a half times larger than our Milky Way, it is indeed a giant. Note its strange structure – mostly featureless and almost round, but with layered shells surrounding the central core. Astronomers want to know what caused these shells. The answer may lie in what this galaxy represents: a view of the future Milky Way and the Andromeda Galaxy.
The Milky Way’s Fate: When Galaxies Collide!
Galaxies change over long timescales. More than thirteen billion years ago, the first were tiny bits of matter. They came together to form larger and larger structures. This process of fusion and cannibalization continues to this day. It influences the “look” of a galaxy and adds variety to its stellar populations. Our own Milky Way is part of this process. It is currently cannibalizing the Sagittarius Dwarf Galaxy. He also merged with or swallowed between five and 11 minors during his lifetime.
Astronomers already know that the Milky Way will continue to be part of the process of merging galaxies. In about 4.5 to 5 billion years, it will begin to merge with the nearby Andromeda Galaxy (M31). Of course, the M31 will have gotten very close to us in the meantime. As an added bonus, the Triangle Galaxy (M33) can also participate in this galactic dance. For those keeping track of these things, this will happen when the Sun runs out of hydrogen in its core and starts evolving into a red giant. So it will be an interesting time. Mark your calendars.
NGC 474 predicts the future of the Milky Way
NGC 474 looks a lot like what astronomers think the Milky Way and Andromeda will look like after merging. It will no longer be two beautiful spirals. Instead, their gravitational interaction will produce an almost featureless elliptical galaxy. How will this happen? As the two galaxies get closer, the strong gravity of each will distort their shapes. Giant streamers of gas and dust will be pulled from each galaxy. There may even be central shells of material, just like in NGC 474.
In addition to all this activity, there is another hallmark of a merger: we starburst. They are sites of star formation that occur following a merger. The activity gathers clouds of gas and dust, eventually creating mounds of hot, young stars. This will happen as long as there is enough material available for star birth nurseries.
Eventually, the burst of star birth will slow down and stop. The resulting new galaxy will assume a rather flat-looking elliptical shape. That, in a nutshell, is what happened to NGC 474. And, that’s Milkdromeda’s fate: a (probably) featureless elliptical that was once two beautiful spiral galaxies.
Explaining these projectiles in NGC 474
In the case of NGC 474, astronomers have a few theories about why it has these strange shells. One idea is that it interacted with another galaxy billions of years ago. This created the shells in a process similar to throwing a stone into a pond and watching the ripples move away from it. NGC 474 is not the only one to have projectiles caused by collisions. About q0 percent of all ellipticals have these characteristics. This could be a clue to their formation and merger histories that astronomers will investigate.
There’s another interesting thing about these shell galaxies. While most ellipticals are in clusters, these oddities occupy relatively empty swaths of space. It is possible that they cannibalized nearby galaxies and thus cleared their neighborhoods of any galactic competition.
Other theories about NGC 474
It is also possible that NGC 474 is taking gas from a nearby galaxy called NGC 470. Another idea is that the shells could be caused by a collision with a very gas-rich galaxy. Not only did they meet once, but they had a second collision that led to their final merger. The shells are evidence of this long-merged galaxy. The Hubble view gives a closer look at this central region and these mysterious shells.
This article was originally published on universe today by Carolyn Collins Peterson. Read the original article here.