Astronomers spy on the Milky Way’s neighbors, assessing how much light is streaming out of it and how that relates to the physical properties of each galaxy.
This in-depth study of our local universe could help scientists better understand the first distant galaxies currently observed by the James Webb Space Telescope (JWST) and the Hubble Space Telescope.
Because the galaxies of primitive universe are incredibly faint and therefore difficult to observe, a team of astronomers led by Jens Melinder of Stockholm University in Sweden set out to create a reference sample of galaxies in the vicinity of our Milky Way.
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In particular, Melinder and his colleagues collected and collated data regarding a special wavelength of ultraviolet radiation from these local galaxies known as Lyman’s alpha light.
Lyman’s alpha light is found in the light gas surrounding the hottest stars, which means that it is found especially in star-forming galaxies. The peak period of star formation in the universe occurred about 10 billion years ago. Lyman’s alpha light is therefore a great way to study the galaxies that existed when the universe was only about four billion years old. (THE big Bang that created our universe happened about 13.8 billion years ago.)
But decoding the information carried by this light can be difficult, because the path it takes to instruments like Hubble and the JWST is complex.
Lyman’s alpha light takes the scenic route around the cosmos
The exact wavelength of Lyman alpha light and the direction from which it travels are factors influenced by the physical processes it encounters as it exits its source. galaxy. Regions of these galaxies with different physical conditions through which Lyman alpha light travels can change the path of the individual photons that make up the light, change their wavelength, and even absorb a fraction of the light.
The fact that Lyman’s alpha light can encounter hot regions, dusty areas, or sectors with high-flowing gas clouds in their source galaxy and during its journey means that by the time it reaches us, the information it carries can be difficult to interpret.
While an accurate interpretation of this light after its complicated journey is possible, it can, however, reveal substantial amounts of information about the physical properties of the galaxies from which it originated.
To better understand these emissions and build their Lyman Alpha Reference Sample (LARS), the team selected 45 local galaxies with strong star formation, observing them across the entire electromagnetic spectrum. This allowed the team to deduce how much Lyman alpha light escapes from each galaxy and how this fraction correlates with the physical properties of that galaxy.
One of the most important discoveries astronomers have made is the connection between the amount of gas, plasma (which is a super hot, electrically charged gas) and dust envelopes surrounding the galaxies they have studied and the amount of Lyman’s alpha light that escapes them.
“There is a clear correlation between the amount of cosmic dust in a galaxy and the amount of Lyman it lets out,” he added. Melinder said in a statement. “This was expected, as dust absorbs light, but now we have quantified the effect.”
Scientists have also been able to determine how this gas is distributed in galaxies and how it moves through them.
The team discovered a link between the total mass of the stars in a galaxy with the amount of Lyman alpha light that is able to leak out of it, though that connection is less clear than the connection between gas and that light leaking out.
What doesn’t seem to be related to Lyman alpha light leaking into galaxies, however, is the rate at which these galaxies form new stars.
Related: The Early Universe Was Filled With Stars 10,000 Times Larger Than Our Sun, New Study Shows
Lyman’s alpha light ‘shrinks’ galaxies
One thing the team found that could be particularly significant is the fact that when viewed in other wavelengths of light, these galaxies suddenly appear considerably larger. This is an effect that has already been observed by astronomers.
“We see the same effect in computer simulations of galaxies with calculations of how Lyman alpha moves through gas clouds in interstellar space,” said team member Peter Laursen and researcher at the Cosmic Dawn Center in Denmark, in the same statement. “It confirms that we have a pretty good theoretical understanding of the physics involved.”
This effect is important to consider when looking at old and distant galaxies, as the light from their periphery may be too faint to detect or may fall beyond the limits of the detectors observing them. This means that examining and quantifying this effect, as seen in LARS, could help astronomers better account for it, and thus more accurately determine the size of early galaxies.
“These results will help interpret observations of very distant, but similar galaxies seen with the Hubble and James Webb Space Telescopes,” Melinder concluded. “Understanding the detailed astrophysics of this type of galaxy is crucial for developing theories about the formation and evolution of early galaxies.”
The team’s research was published earlier this month in the Astrophysical Journal Supplement Series.