Galaxies are groups of stars held together by gravitational forces. Most galaxies originated in the first 200 million years after the Big Bang and have transformed over approximately 14 billion years. Early galaxies formed as aggregates of stars that clustered around the center of mass. In the youth of the universe, galaxies were in close proximity, exerting gravitational pull on one another. As the universe expands, the distances between galaxies have grown, reducing their interactions. They have remained far apart, allowing for internal development over billions of years.
Astronomers categorize galaxies based on their current shapes. Those resembling the Milky Way are termed spiral, while circular or oval-shaped ones are called elliptical. Galaxies that fall between spiral and elliptical forms are referred to as lenticular, and any that do not fit into these categories are labeled irregular. Over 75% of galaxies identified by astronomers are spiral in nature. If a spiral galaxy features prominent bars of stars and dust through its center, researchers classify it further as a barred spiral galaxy.
About 60% of spiral galaxies, including the Milky Way, exhibit galactic bars, designating them as barred spiral galaxies. These bars also serve as nurseries for star formation and are catalysts for the galaxy’s evolution. However, astronomers understand that galaxies do not inherently begin with these bars, prompting further investigation into the formation processes and timelines of these features.
This diagram illustrates the galactic classification system developed by 20th-century astronomer Edwin Hubble. The galaxy marked with the “E” label represents elliptical galaxies, while S0 indicates lenticular galaxies. The other “S” labels refer to spiral galaxies, with those labeled “SB” denoting a spiral structure. “Hubble tuning fork diagram” by cosmogoblin is licensed under CC0 1.0.
An international team of scientists researched the formation of bars in 20 galaxies near the Milky Way using advanced analytical techniques developed over the last four years. They gathered data from the TIMER space investigation, focused on the light emission patterns known as spectra from stars near the centers of these galaxies. The TIMER survey utilized the Very Large Telescope in Chile, equipped with a multi-unit spectroscopic explorer called MUSE.
The team initially struggled to obtain spectra for individual stars within these galaxies. As a reference, the closest galaxy studied was 7 megaparsecs away, approximately 23 million light years, or 130 million miles. Individual stars are too diminutive to distinguish at such distances, even with the most precise instruments.
To overcome this challenge, the team analyzed the spectra of stars within two concentric rings representing different regions at the centers of these galaxies. The inner ring comprised stars strictly within the bars of the galaxy, corresponding to an area known as the nuclear disk, while the outer ring included both inner and outer stars of the bar, referred to as the main disk.
They subtracted the spectrum of the stars in the inner ring from that of the outer ring, yielding two distinct light patterns: one for stars within the bar and another for stars outside of it. By treating the combined patterns of each ring as representative of typical stars in those regions, they could estimate the age of individual stars and ascertain when they formed. Past astrophysical models suggest that galaxy bars enhance the star formation rate around their centers. Hence, the team inferred the formation timing of galaxy bars as stars began to form more rapidly within those structures.
With this innovative approach, they estimated the age range for the 20 galaxies studied, with an error margin of approximately 1.5 billion years. Among their sample, the galaxy that formed bars most recently was 800 million years old. Out of the 20 galaxies, 14 formed bars approximately 7.5 billion years ago or later, while the remaining six galaxies established bars around 9.5 billion years ago, with the oldest estimates dating back 13.5 billion years. In contrast to earlier predictions, they found that larger galaxies do not necessarily possess older bars.
From the diverse ages of the bars observed, the team concluded that the formation of galaxy bars is an ongoing process in the cosmos. Their methodology provides astrophysicists with a means of gaining deeper insights into the dynamics of the early universe and the interactions between ancient galaxies, which connect to their present forms. By doing so, future research teams can establish a refined timeline for the universe and identify changes in how dominant forces have shaped galaxies, from their interactions to their internal structuring.
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Source: sciworthy.com
