Despite its Swirly Nature, the Milky Way is not well mixed at all

Despite its Swirly Nature, the Milky Way is not well mixed at all

Our Milky Way galaxy is a massive spiral galaxy. Its swirly form may give the idea that it mixes well over time, but astronomers have discovered that the interstellar medium – the gas found between stars – is far less homogeneous than previously thought.

Three major factors influence a galaxy’s interstellar medium. The pure gas that condensed from the great bang is the first. This is mainly hydrogen, which was the lone element in the Milky Way at its birth. Gas from cosmic space continues to flood in.

Then there are the elements that were created by celebrities. Everything other than hydrogen and helium (referred to as metals in astronomical parlance) enriches hydrogen gas and is driven around the galaxy. Finally, some of those metals condense into dust, the essential ingredients that give rise to planets (and even us).

The Milky Way has known to feed on its neighbors for billions of years, slowly but surely merging with many dwarf galaxies that surround our galaxy. The remnants of such interactions can see today in the form of stellar streams wrapped around the galaxy like ribbons. A newly discovered "ribbon" is the Jhelum stellar Stream. Because of its location in the sky, astronomers considered the current to be part of a collision between the Milky Way and the Gaia-Enceladus-Sausage Dwarf galaxy, which thought to have occurred between 8 and 11 billion years ago. Now new observations have revealed that Jhelum does not come from the sausage dwarf galaxy above all. Astronomers were able to study the light spectrum of the stars in the Jhelum stream, which gave them an idea of ​​what the stars made of. The stars formed together will have a similar composition. It tracked using parts of the Apache Point Observatory Galactic Evolution Explorer (APOGEE) survey, Sloan Digital Sky Survey (SDSS). The combination, they have created and allows them to select related stars together by combining it with detailed information about their position and motion from the European Space Agency's Gaia has shown the team that the Jhelum stream does not match other evidence of sausage collisions. Its source was elsewhere. "Like fingerprints or tags, the chemical properties of the stars in a stream can be used to convey these exclusions to other streams - but more than that, the chemical makeup, position and speed are incredibly valuable to keep together and just to show off the benefits of a combination of APOGE and gear." Professor Alison Sheffield, a veteran author at LaGuardia Community College, said in a statement. The Jhelum stream is only observable from the Southern Hemisphere, so thanks to the Southern APOGEE instrument (APOGEE-2) coming online, the team was able to identify the right stars and then find out who the actual members of the stream were online. Co-author Aidan Subrahimovic, an astrophysics student at City University of New York added, "Measuring the tracks or orbits of the stars in the stream allows us to go almost behind the cosmic clock, and reveal where the flow itself came from." Researchers have not been able to link the Jhelum stream to any dwarf galaxy or globular cluster with any specific attachment and therefore its source is currently unknown. However, future work researchers can help us find the answer to the source of these and other stellar streams in the Milky Way.
Despite its Swirly Nature, the Milky Way is not well mixed at all

The zone around the Sun was thought to have nearly the same level of metal enrichment – known as metallicity – as our star. However, new measurements have revealed that this is not the case and that the gas found between stars in the Milky Way is highly variable. The findings were published in the journal Nature.

“Until now, theoretical models assumed that these three elements were homogeneously mixed and reached the Solar composition everywhere in our galaxy, with a slight increase in metallicity in the center, where stars are more numerous,” said co-author Patrick Petitjean of the Institut d’Astrophysique de Paris, Sorbonne University. “Using an ultraviolet spectrograph on the Hubble Space Telescope, we sought to investigate this in detail.”

It’s not straightforward to study the intergalactic medium, especially in the solar neighborhood. To estimate the enrichment of that particular location, the team used 25 brilliant stars and a long observation time.

Because this method does not account for dust, lead author Annalisa De Cia and her team had to devise a new method of observation.

“It entails simultaneously observing multiple elements such as iron, zinc, titanium, silicon, and oxygen to account for the complete composition of the gas and dust,” noted De Cia, who works at the University of Geneva. “Then we can calculate the total by adding the number of metals present in the dust to the amount already determined by prior observations.”

The findings demonstrate that there exist pockets of the interstellar medium that are one-tenth the metallicity of the Sun. According to the findings, models of our galaxy will need to be revised in order to be more accurate.

Jens-Kristian Krogager, also of the University of Geneva, noted, “This discovery plays a vital role in the building of theoretical models on the formation and evolution of galaxies.” “We will have to modify the simulations in the future by increasing the resolution so that we can include these changes in metallicity at different regions in the Milky Way,” says the researcher.

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