Maisie, the oldest galaxy ever observed

After careful spectral analysis, an image captured by James Webb has identified the Maisie Galaxy, the oldest ever observed
This bright orange spot is the Maisie Galaxy, the oldest ever observed, and therefore one of the most significant discoveries in recent astronomical history. Credit: NASA

Well yes! That blurry orange spot in the photo, which seems to tell us nothing, is actually a galaxy. Its name is Maisie, and it’s the oldest galaxy ever observed by a human being. One of the first objects captured in the summer of 2022 by our new powerful cosmic eye: the James Webb Space Telescope. This simple blotch represents the dawn of a new era in astronomy, and the reason for all this is its age.

Scientists have officially confirmed exactly how old the universe was when we captured the image. Maisie has existed since the universe was only 390 million years old, which is 13.8 billion years ago. This makes it one of the four oldest galaxies ever seen by the human eye.

“The image of this galaxy captures a very remote moment in the universe. We couldn’t observe it without James Webb” said Steven Finkelstein, an astronomer at the University of Texas at Austin and the principal investigator of the CEERS project (Centre for Exoplanets and Extragalactic Research) (ref). “This was the cosmic period when we didn’t know how galaxies formed or what they looked like. Today, with James Webb, we’ve gone searching for them. When the first data arrived last summer, Maisie’s galaxy was one of the first galaxies to be identified”.

How was the name chosen?

Other galaxies identified by James Webb have rather dry and formal nicknames, such as CEERS 1019, CEERS 2782, and CEERS 746. The name Maisie clearly stands out among them. This remote celestial body is named after Finkelstein’s daughter. “We found the galaxy in James Webb’s data on my daughter’s ninth birthday. Her name is Maisie. Because of this coincidence, I started calling the galaxy by this name” explained Finkelstein.

“When it came time to write the article (ref.), we were discussing what to call it. Other researchers suggested simply using the name Maisie and seeing what would happen. We managed to get it approved, and we published it with that name”. While it’s impossible for Finkelstein to get his daughter’s age wrong, calculating the ages of galaxies in the primordial universe is much more complex.

This means that determining that the Maisie galaxy is the oldest ever seen required meticulous investigation. It might not seem like much, but this blurry image is one of the most important galaxies in recent astronomical history.

Redshift technique

To determine how far away a galaxy is, you need to know how long its light has traveled to reach us. In simple terms, this means determining at what point in the universe it was while we are observing it. Astronomers use a technique called “redshift”. Different wavelengths of light correspond to different colors in the visible spectrum. Light with a long wavelength and low frequency is red, while light with a short wavelength and high frequency is blue.

As light travels to us from a distant source, the expansion of the cosmos causes that source to move away from us simultaneously! This phenomenon causes the wavelengths of the light we are observing to stretch, making them lose energy and change frequency.

Astronomers call it redshift because the light is essentially shifted towards the red end of the electromagnetic spectrum. In some cases, the observed light can even end up in the infrared and become invisible to the human eye. Longer the journey, more extreme the redshift. In the case of early galaxies like the Maisie galaxy, the light has traveled for over 10 billion years. Consequently, its light has shifted well into the infrared section. This is why we designed a space telescope like James Webb, an extraordinary tool for hunting objects in the primordial universe in the infrared region.

Importance of James Webb

“We couldn’t really see it before James Webb” he explained. “The Hubble Space Telescope wasn’t large enough, and, more importantly, it doesn’t cover infrared wavelengths to observe a galaxy so distant and highly redshifted”.

Initial estimates of the redshift, and thus the age of the Maisie galaxy, were based on photometry. This technique works by analyzing brightness in images. These calculations suggested that the galaxy had a redshift of 11.8. But Finkelstein and the CEERS team wanted a much more accurate estimate.

To do this, they made observations with the Near Infrared Spectrograph (NIRSpec) on James Webb. This allowed Finkelstein and colleagues to observe the spectral lines dictated by the absorptions and emissions of chemical elements at specific wavelengths. From this data, they were able to determine the actual redshift of the Maisie galaxy, which is 11.4. And this confirms that Maisie is the oldest galaxy ever observed.

What was the universe like 13 billion years ago?

Finkelstein explained that the Maisie galaxy is very different from galaxies in the modern universe. “The universe was quite active when the Maisie galaxy existed. Its mass is concentrated in a very small volume” Finkelstein said. “Furthermore, galaxies were closer together and merged much more frequently. Since the universe was only about 400 million years old, all the stars around it are young. So there were many more bright and blue stars back then than we see in galaxies today”.

Maisie, the oldest galaxy ever seen, stands out from the “modern” galaxies because, during the time we are observing it, it seems to be rapidly giving birth to young, blue stars. We managed to capture it during the period astronomers call “starburst”. So, if its young stars are bright and blue, it means that this highly redshifted galaxy is actually much “bluer” than astronomers expected. “The Maisie galaxy is undergoing star formation at a much faster rate. It’s really like a compact ball of blue stars”.

For these reasons, Maisie is poor in heavy elements and has a primordial composition of hydrogen and helium. It is also much brighter than astronomers expected, a characteristic that has been found with other primordial galaxies observed with the James Webb.

Future Analyses

“Maisie Galaxy has provided us with the first hint that the early galaxies are brighter than we expected, making them easier to find” said Finkelstein. “Our understanding of how stars form in the early universe may require revision. It’s possible that galaxies were forming stars more efficiently than we think”.

Finkelstein will now continue to examine the Maisie Galaxy using the James Webb Mid-Infrared Instrument (MIRI), delving into the spectrum of light in an attempt to discover its heavy element richness and understand whether it hosts interstellar dust grains.

“Maisie certainly provides us with a good example of what a galaxy in the primordial universe looks like. And since it’s quite luminous, we can study it easily and measure many things like its stellar mass, its shape, and the amount of heavy elements” Finkelstein concluded. “In the end, it’s just the first of many galaxies we can use to explore the early universe”.

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