Astronomers studied three ultra faint dwarf galaxies located in a region of space isolated from the influence of larger objects. Turns out they only contain very old stars. This supports the theory that events in the early Universe may have interrupted star formation in the smallest galaxies.
Ultra faint dwarf galaxies are the most inconspicuous type of galaxies in the Universe. These are small diffuse structures that typically contain a few hundred to a thousand stars. Not surprisingly, they are almost invisible against the background of many much brighter inhabitants of the sky. Astronomers are more likely to find them in the vicinity of our own Milky Way galaxy for this reason.
But this poses a problem in studying them. The gravitational forces of the Milky Way and its hot corona can strip dwarf galaxies of gas and prevent their natural evolution. And more distant ultra faint galaxies are too weak and hard to see for astronomers and traditional computer algorithms to detect.
That’s why University of Arizona astronomer David Sand used a manual “by eye” search to find such objects. He said it was during the pandemic when he was reviewing images taken by the Dark Energy Camera as part of the DECaLS program. He drew attention to areas of the sky that had not been explored. After a few hours of random searching, he managed to find three ultra faint galaxies located in the constellation Sculptor. They are among the first known objects of this type, located in an isolated environment free from the influence of the Milky Way or other large structures.
Sand and his team subsequently used the Gemini South telescope to study the discovered galaxies in more detail. It turns out that they contain no gas and contain only very old stars. This indicates that their star formation was suppressed many billions of years ago. It also supports the existing theory that ultra faint dwarf galaxies are stellar “ghost cities” that have not formed new luminaries for a very long time.
This is what astronomers have come to expect from such tiny objects. Gas is the most important raw material needed for the formation of new stars. But ultra faint dwarf galaxies have too weak gravity to hold this important component, and it is easily lost.
However, galaxies in the constellation Sculptor are far away from larger galaxies, which means that their gas could not have been lost through gravitational interaction with their neighbors. An alternative explanation is an event called the Epoch of Reionization. This is the period shortly after the Big Bang, when high-energy ultraviolet photons flooded the cosmos, which may have caused gas to boil off in the smallest galaxies. A third possibility is that some of the earliest stars in dwarf galaxies turned into supernovae. Their explosions pushed gas from galaxies into outer space.
According to the researchers, they intend to continue their search for ultra faint galaxies. Increasing the sample will help to understand exactly how such objects lost gas and what role reionization may have played in this. This would provide an important clue to understanding what the early Universe was like and how the processes that took place in it affected star formation.
According to NOIRLab
