Astronomers have discovered a peculiar dwarf galaxy that does not have the characteristics of a normal dwarf galaxy. It neither generates novae nor interacts with neighboring galaxies, but simply spends itself alone in space. This completely upends astronomers' understanding of how galaxies form and evolve.
Arizona State University in the United States said in a press release on January 28 that a research team led by Tim Carleton, an assistant research scientist at the university, has discovered a strange dwarf galaxy named PearlSDG.
The team was originally observing a cluster of galaxies with the James Webb Space Telescope, but the PearlSDG happened to appear in the telescope's photograph. The PearlSDG is not an observation target at all, but it appears next to the main observation area, and the researchers did not expect to see anything here.
Galaxies are made up of stars and planets, bound together by gravity, and they also have massive clouds of dust, gas, and dark matter. Dwarf galaxies are the most numerous galaxies in the universe and are defined as galaxies with small mass and low brightness. They usually contain fewer than 100 million stars, but the Milky Way, which is also classified as a dwarf galaxy, has about 200 billion stars.
However, PearlSDG, a dwarf galaxy with very sparse internal stars, does not have the characteristics of ordinary dwarf galaxies. It neither generates novae nor interacts with neighboring galaxies. It's actually an isolated stationary galaxy.
"With very few exceptions, such isolated stationary dwarf galaxies have not been observed before," Carleton said. Based on what we know about the evolution of galaxies, we really don't expect them to exist, so this observation can help us improve our theory of galaxy formation. Generally speaking, dwarf galaxies that exist on their own will continue to generate novae. ”
Until now, astronomers have known the evolution of galaxies as a way for independent galaxies to continue to generate novae or interact with larger neighboring galaxies. But this theory does not apply to PearlSDG. It has ancient stars, but it does not generate new stars and does not interact with other galaxies.
Astronomers can observe individual stars of the PearlSDG through the Webb Space Telescope. These stars appear brighter in the telescope's wavelengths. Based on the brightness of these stars, the Pearl SDG is estimated to be about 98 million light-years away from Earth.
The discovery has changed astronomers' understanding of how galaxies form and evolve, which means that there may be many isolated stationary dwarf galaxies waiting for astronomers to identify, and the Webb Space Telescope can help them do just that.
The Webb Space Telescope's near-infrared camera (NIRCAM) has very high angular resolution and sensitivity, allowing astronomers to identify individual stars in distant galaxies. Like looking at individual cells under a microscope, such observations leave the PearlSDG's star invisible.
The findings were published in The Astrophysical Journal Letters.