In search of the invisible galaxy

A mysterious and very distant being, in the universe as it was only two billion years after the Big Bang, hiding from even the most advanced machines. Its features were finally described by a team from SISSA in a recently published study published in Astrophysical Journal.

A very distant celestial body in a still young universe, one-sixth the size of the current universe. An object so dark that it is almost invisible, even to highly sophisticated devices. Their nature has long been a matter of debate, but through surveys conducted using the ALMA interferometer, the SISSA research group led by Professor Andrea Lappi who conducts research into galaxy formation and evolution has succeeded in identifying their key characteristics.

It is a small galaxy, contains large amounts of interstellar dust, and is forming stars at nearly 1,000 times the rate of the Milky Way. A description of this galaxy will be useful for revealing more about this particular galaxy distant object It points to new approaches to studying other “dark” celestial bodies. Research just published in Astrophysical Journal It will also provide new insights for developing advanced models of galaxy formation and evolution.

Far, dark and priceless: the galaxies farthest away

“Very distant galaxies are veritable mines of information about the past and future evolution of the universe,” explains first author Marika Golletti, who studies astrophysics and cosmology at SISSA.

However, they are very difficult to study. They are very compact and therefore difficult to observe. Also, because of the distance, we receive very weak light from them. This dimming is caused by the massive presence of interstellar dust, which intercepts the visible light from young starsand makes it difficult to detect using optical devicesand retransmits it at longer wavelengths where it can only be observed using powerful interferometers in the millimeter (sub) and radio wave bands.”

Such dark objects are not particularly rare: “In recent years,” Goleti explains, “many particularly distant, obscured galaxies have been discovered, which seem completely invisible even to the most powerful optical instruments, such as the Hubble Space Telescope.”

gravitational lens

The tool used in these cases is the so-called gravitational lens, a solution with great scientific potential. The principle is simple: general relativity It means that space objects that are closer to us and that have a lot of mass distort the light coming from distant sources are perfectly aligned with it.

Goleti continues: “This way, big spiral stars They act as a kind of massive cosmic lens that makes “background” galaxies appear larger and brighter, allowing them to be identified and studied. “Over the past decade, many monitoring programs have been implemented with this approach.” About a hundred galaxies have been discovered so far, but there could be more.”

A truly special being

In one such investigation, Giuletti says, the main target of this current study was identified: “This was a very special celestial body. It is very bright and is likely to be lensed, but this only occurs at specific wavelengths, probably due to the presence of large amounts of “Interstellar dust. It is therefore very complex to study. Observations made with ALMA, a very modern interferometer located in the Atacama Desert in Chile, have enabled us to identify its features.”

“We studied this strange object by adopting certain codes that enabled us to reconstruct the original shape of the background source and also to understand certain properties of the lens itself. The observations also provided valuable information about the gas content of this source, and we were also able to determine how it is distributed.”

“Our analysis showed that this object is very compact, presumably small, and is forming stars at a very high rate. In the future, the James Webb Space Telescope will reveal more about this galaxy, which is the only thing it can do at the moment.”

Professor Labe, co-author of the paper, concludes by stressing the importance of this study: “Small and compact distant galaxies, which have a strong star formation, are largely obscured by dust, and which possess very rich stores of gas molecules, are the forerunners of the enormous calm. galaxies that we see in the local universe, and thus provide very valuable insights into the processes that lead to the formation and evolution of these structures throughout the history of the universe. ”

“I would like to emphasize,” continues the professor, “that the success of this research was achieved through the synergy between the SISSA Astrophysics and Cosmology Group and the ALMA Regional Center located at INAF – Institute of Radio Astronomy in Bologna (in particular through the collaboration of Dr. Marcella Massardi , co-author of the study), allowing our students to access the ALMA data archive and learn how to use it effectively, a true gold mine for astrophysics research today.”