Spying on neighbouring galaxies help astronomers understand distant ones

Studying the galaxy with Lyman Alpha light

According to the Niels Bohr Institute at the University of Copenhagen, one of the best way to study galaxies in the early universe is by using a type of ultraviolet light called “Lyman alpha.” This is a particular type of light emitted from by the gas around the hottest stars and it is particularly useful for observing galaxies that have a high rate of star formation.

But unlike many other types of light, the exact wavelength and direction Lyman alpha light travels in depends on many physical processes inside and outside the galaxies. This type of light does not just travel in a straight line to our telescopes but it takes a complicated path out of the galaxy where it originated.

On its way through the origin galaxy, Lyman alpha light travels through regions of different physical conditions. Not only does this affect the path taken by individual light particles, but it also changes their wavelength. This journey also absorbs an unknown amount of the light.

Lyman alpha light, a kind of ultraviolet light, is particularly useful for studying galaxies in the early universe. But the light usually takes a convoluted path from its origin to where we observe it, changing its properties. pic.twitter.com/AkB11xHbuI

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Some of these regions that the light travels through is hotter than others, some are more dusty, some have strong flows. These different physical conditions change the properties of the light in different ways. Due to this, it is very difficult to interpret the Lyman alpha light that our telescopes receive.

But at the same time, interpreting this light correctly can help us understand more about the physics of the galaxy and how it works.

Spying on our neighbours can help

Studying these faraway galaxies gets especially difficult when you consider the fact that they are quite faint and small from our vantage point. To compensate for this, the astronomers built a reference sample of galaxies in our vicinity.

These reference galaxies are still hundreds of millions of light years away but they are still near enough to be studied in detail with the many telescopes around the world and in space.

This reference sample of galaxies has helped reveal many interesting properties of galaxies that are quite helpful when observing the more distant ones. For example, in the latest study, the astronomers understood how much of the Lyman alpha light escapes the galaxy and whether or not this correlates to the physical properties of the galaxy.

“With the new observations, we have established a connection between how much Lyman alpha escapes the galaxies, and several of the physical properties of these galaxies. For instance, there is a clear correlation between the amount of cosmic dust a galaxy has, and how much Lyman it lets out. This was expected because dust absorbs light, but now we have quantified the effect,” explained Jens Melinder, lead author of the research article, in a press statement.

The researchers also found a connection between the escaping light and the total mass of all the stars in the galaxy.

But more importantly, the use of such a Lyman alpha reference sample taken from our galactic neighbourhood will allow astronomers to make better sense of distant galaxies observed using the James Webb Space Telescope, Hubble and other observatories.