Is the Milky Way… Normal?

It is difficult to study the large-scale structure of our universe. We don't have a good idea of the shape and features of the Milky Way because we live in it. Some advantages are available to us. We can conduct surveys of the stellar population and chemical composition from within. Researchers can use that information to compare our own galaxy to millions of others in the Universe.

A group of researchers from the USA, UK, and Chile published a paper this week. They searched through a catalogue of thousands of galaxies produced by the Digital Sky Survey, looking for similarities to our own.

They found that the Milky Way has many twins but only a few that are just as similar as the others. Implications for the future evolution of our own galaxy are what they discovered.

Analyzing the data.

To start their search, the researchers narrowed their sample size to only those galaxies that fit in with what we know about the Milky Way. They took the total mass of the galaxies and compared it to the total mass of the Milky Way. The size of the galaxy compared to the central core was ruled out. TheHubble type is a classification system that groups galaxies according to their shape. elliptical galaxies are shaped like fuzzy blobs and some are spiral-shaped. The idea was to use the classifications to find rough approximations of the Milky Way from which to start the more detailed work.

At the end of the process, the team was left with more than one similarity to our own. They could look into the details to see how close our cousins are to us.

They plugged the data into a model that predicts star formation, taking into account how stellar winds blow excess gas away from star systems, which can be pulled in towards the center of galaxies The model accounted for the chemical composition and metallicity of different parts of the universe.

They found what they were looking for.

It turns out that there are other universes that look similar to ours. The majority of the galaxies in the sample were close matches to their homes.

They have a long timescale in which star formation occurs in their outer regions, and they give new stars a leisurely time to form. A flow of gas being pulled inward towards the centre from the outer region caused a dramatic period of star formation in the inner region. The formation of stars in the core was slower due to the recycled gas blowing off older stars. The new stars, made of recycled material, have a higher level of metallicity with heavier elements added to them. This pattern is familiar to us in our own universe.

This isn't true for all of the stars. A lot of the galaxies that looked similar to the Milky Way ended up looking very different. There are two categories for these.

There are 55 galaxies that appear to have no difference between their inner and outer regions. The stars are forming uniformly in the galaxies without the burst in the core. The stars in the inner and outer regions look the same.

These are the strangest of the bunch, and are part of the second category. The radial inflow of gas from the outer regions of the Milky Way isn't happening in these outliers because they lack any recent star formation from recycled material.

The central-quenched galaxies appear to have completed most of their star formation in the past, suggesting that they may be older than the Milky Way.

Maybe we are looking at the Milky Way's own future. Our universe may one day end up with a quenched centre, which is a preview of the next phase of evolution.

The authors theorize that these are the evolutionary successors of the Milky Way.

An overly active galactic nucleus may be one of the possible explanations.

There is still a lot to learn about the evolution of the universe. It shows that we are not completely different. At least some of the different types in the Universe play by the same rules as the Milky Way and are at the same life stage. Studying these look-alikes can help us learn more about our home and give us the next best thing to look at our reflection.

Preprints of the paper can be found on ArXiv.

Alfonso Aragn-Salamanca, Shuang Zhou, Michael Merrifield, Niv Drory, and Richard R. Lane are some of the people who have worked there. Is there a similarity between the Milky Way and the Milky Way? There is a view from the SDSS-IV/ MaNGA.

The image was featured in theWikimedia Commons.