Bangalore: A team of astronomers from India, America and France led by of Pune The Inter-University Center for Astronomy and Astrophysics (IUCAA) has observed the formation of new stars in the outer regions of distant dwarf galaxies. These galaxies, known as ‘blue compact dwarf’ (BCD) galaxies, have also shown evidence of new stars migrating to their centres, which Galaxy’ mass and volume.
The team detected these star formation regions in eleven BCD using India’s AstroSat’s Ultra-Violet Imaging Telescope The first dedicated multi-wavelength space telescope for the purpose of studying astronomical sources. Their findings, which have been peer-reviewed, were published in scientific journal Nature Last week.
The findings indicate “expanded star formation” in the material that is coming together to form a dwarf galaxy. This is important, given that it is otherwise very difficult to observe the formation of these early BCD galaxies because they are so small and faint and distant.
AstroSat was able to observe these galaxies in both visible and ultraviolet (UV) light. According to the study, this is the first time a far-ultraviolet (FUV) disk has been observed in distant dwarf galaxies.
Astronomer and lead author Anshuman Borgohain from Tezpur University, Assam, said, “We are now able to see how dwarf galaxies in the comparatively early universe are gaining their stellar material and are currently on their way to evolve into dwarf galaxies.” Huh.” In an email to Paper, ThePrint, “This will help bridge the understanding gap in the diverse dwarf galaxy populations that we see around us at the present time.”
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BCD and star formation
AstroSat sees distant objects at the other end of the electromagnetic spectrum compared to NASA’s James Webb Space Telescope, the other space telescope making news, While Webb studies distant galaxies in different parts of the infrared wavelength, AstroSat observes objects in ultraviolet (UV), X-rays and visible light. NASA’s Hubble Space Telescope also uses the UV, visible and near-infrared regions.
Light from distant objects is ‘red-shifted’ due to the expansion of the universe Which means that the farther an object moves, the more visible light is shifted towards the red end of the spectrum.
In contrast, young stars that are just forming emit most of their energy in the UV. Thus, galaxies that contain large clusters of young, hot and massive stars appear blue, and are thus named blue compact dwarfs.
BCDs are difficult to study and understand because they are extremely compact and also very weak.
Like Webb, AstroSat has also been able to peek into the past; That is, seeing light sources as they were billions of years ago when the light was emitted. The galaxies observed in this study were a ‘Lookback Time’ 1.3-2.8 billion years.
The team also observed that the UV disk extending from the center of the galaxy was longer than the optically visible disk. material storage material.
“As we move from inner to outer regions, galaxies progressively decay. Therefore, to be able to detect emissions in such regions, we need long observation hours,” explained lead author Borgohain. . Even Hubble’s deep observations failed to yield data on star-forming regions in visible wavelengths.
“The detection of these star-forming regions in the UV suggests that they contain young stars because such stars are mainly emitted in the UV wavelength regime. Furthermore, since we see nothing in the optical, it means That there are no older stars in the outer regions,” Borgohain said, “the star formation observed in the outer low-density atmosphere is puzzling because gas in these regions is incapable of forming stars.”
missing reservoir of neutral gas
Only the most recent, outermost star-forming regions emit energy In far-ultraviolet.
“These extended FUV disks are the telltale signature of galaxy disks that are collecting neutral hydrogen gas from the surrounding environment, called the intergalactic medium,” explained Borgohain.
Another phenomenon that is likely to occur here is the inert current reservoir of neutral gas, According to borgohain, Over billions of years, instability in the outer parts of this gas disk leads to a localized collapse of the gas, igniting the region to form new stars.
But these large reservoirs of neutral gas around galaxies have not been detected, especially with the powerful telescopes of modern times that have been able to detect them. It’s likely that the current dwarf galaxies around us have evolved enough to exhaust the gas reservoir, or that interactions with nearby galaxies may have destroyed it, Borgohain speculated.
The lumpy structure of this less dense region also indicates that it is not gravitationally stable or uniform, and is having Drifted in the forces of the rotating galaxy and sucked towards its center.
The findings provide an important step in understanding the evolution of BCDs, and the next step will be to understand how the low-density star formation regions around these dwarf galaxies occur and what drives them.
“We don’t know whether our findings are special cases or a general phenomenon,” Borgohain said. “We are planning a survey for these types of galaxies to build up their statistical significance and also to find out if we may have missed something.”
(Edited by Gitanjali Das)
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