The Pea Galaxy is a celestial body discovered and named by volunteers participating in the “Galaxy Zoo” in 2009. Citizen scientists participated in the resolution of Sloan Digital Sky Survey (SDSS) observation data images to help classify galaxies. The Pea Galaxy is a distinct green dot, a new type of bright blue compact galaxy with an unusually high star formation rate. The Pea Galaxy is very rare, accounting for only 0.1% of nearby galaxies, and its color is unusual because a significant proportion of the light comes from brightly glowing clouds of gas that emit light of specific wavelengths (emission lines). The entire galaxy is also very small, typically about 5,000 light-years across and about 5% the size of the Milky Way.
In July 2022, astronomers published the farthest and clearest infrared image so far observed by Webb, capturing a galaxy cluster called SMACS 0723 and thousands of galaxies behind it. The mass of galaxy cluster SMACS 0723 makes it a gravitational lens, magnifying and distorting the appearance of background galaxies. Astronomers have found 3 faint infrared celestial objects (circled in the figure below), which are very similar in appearance to the nearby Pea Galaxy.
▲ The deep-space image of the galaxy cluster SMACS 0723 taken by Weber captured 3 faint celestial bodies (circled), which are very similar in nature to the Pea galaxy found closer to the earth. (Source: NASA, the same as the picture below)
Not only did Webb image galaxy clusters, the Near Infrared Spectrometer (NIRSpec) also observed galaxy spectra. When the research team checked the measurements and corrected for the wavelength stretching caused by the expansion of the universe, they saw signatures of oxygen, hydrogen and neon gas that were also strikingly similar to the nearby Pea Galaxy. The team believes that these suspected early pea galaxies existed 13.1 billion years ago, and the age of the universe is only 5% of its current age. The galaxy on the left of the picture above has an oxygen abundance of only 2% of the Milky Way, and may be the most primitive galaxy ever discovered in chemical composition. The research results were published in the journal “American Astronomical Society”.
▲ The near-infrared spectrometer observation data (red) of the Webb Space Telescope, after correcting for the red shift caused by the expansion of the universe, shows the characteristics of oxygen, hydrogen and neon, which are similar to the spectral characteristics of the nearby pea galaxy (green).
(This article is reproduced with the authorization of Taipei Planetarium; the first picture is a schematic diagram, source: Pixabay)
