An international team of astrophysicists led by scientists at the University of California, Los Angeles, has confirmed the existence of the dimmest and most distant galaxy ever observed in the early universe. The JD1 galaxy is one of the most distant among those identified so far. This is reported in an article published in the journal Nature.

The ultra-faint galaxy JD1 was discovered using the James Webb Telescope. It arose during the transition from the era of the dark ages to the era of reionization, when neutral hydrogen atoms absorbed ultraviolet radiation from the first stars and ionized, which, in turn, made the universe transparent.

JD1 lies far beyond the galaxy cluster Abell 2744, which acts as a gravitational lens. The combined mass of the galaxies in the cluster creates a gravitational force that distorts and amplifies light from background galaxies, making JD1 appear larger and 13 times brighter. To observe the ultra-faint galaxy, the NIRSpec near-infrared spectrograph on the Webb telescope, as well as the NIRCam near-infrared camera, were used.

Image: Nature (2023). DOI: 10.1038/s41586-023-05994-w / Phys.org

To confirm that the JD1 galaxy is very distant, scientists have identified in its spectrum the so-called Lyman limit - a wave length of 91.15 nanometers generated by the transition of a hydrogen atom from the ground state to a hydrogen ion. The presence of a limit in the star's radiation indicates that it is predominantly hydrogen and thus very ancient.

If star formation occurs in the region, then the accumulations of neutral gas absorb a significant proportion of waves whose length is shorter than the Lyman limit, which is known as the Lyman gap. For a galaxy with a redshift of z = 3 or more (the travel time of light is more than 11 billion years), the wavelength of the break is significantly stretched due to the expansion of the Universe, which makes it possible to determine the distance to it.

The light emitted by the galaxy took 13.3 billion years to reach the Earth, but during this time the Universe managed to expand, so the galaxy is currently removed from the Earth by a distance (in cosmology called its own distance) of 31.3 billion light years. It arose just 480 million years after the Big Bang.

JD1 has a compact and complex morphology, and its mass is estimated at about 10 million solar masses. Its metallicity, that is, the content of elements heavier than helium, is lower than that of the Sun. This is because the first stars could only be made of hydrogen, but gradually produced heavy elements as stellar evolution progressed.