A ‘dark’ celestial object turns out to be a fertile young galaxy

Compact and with large amounts of interstellar dust, it is a young galaxy that forms stars at a rate of about 1,000 times that of the Milky Way.


A mysterious and very distant object, in a universe as it was 2 billion years after the Big Bang, has finally been characterized in a study published in The Astrophysical Journal .

An extremely remote celestial body in a still young universe, one sixth the size of the current one. An object so dark that it is almost invisible, even to the most sophisticated instruments. Its nature has been the subject of debate for a long time, but through surveys carried out with the ALMA interferometer, the research group at the International School of Advanced Studies (SISSA) in Italy, led by Professor Andrea Lapi, who investigates the formation and evolution of galaxies , has finally managed to identify their main properties.

What was discovered 

Compact and with large amounts of interstellar dust, it is a young galaxy that forms stars at a rate of about 1,000 times that of the Milky Way . The description of this galaxy will be useful to reveal more about this very distant object and indicate new approaches to the study of other ‘dark’ celestial bodies.

” Very distant galaxies are authentic mines of information about the past and future evolution of our universe,” explains first author Marika Giulietti, who studies Astrophysics and Cosmology at SISSA, in a statement.

“However, studying them is quite a challenge. They are very compact and therefore difficult to observe. Also, due to the distance, we receive very weak light from them. The cause of this dimming is the massive presence of interstellar dust, which intercepts visible light from young stars and makes it difficult to detect with optical instruments, and re-emits it at longer wavelengths, where it can only be observed with powerful interferometers in the (sub)millimeter and radio wave bands.”

These dark bodies are not especially rare: “In recent years,” Giulietti explains, “several particularly obscured distant galaxies have been discovered , which appear completely invisible even to the most powerful optical instruments, such as the Hubble Space Telescope.”

How could it be observed?

A tool used in these cases is the so-called gravitational lens, a solution with great scientific potential. The principle is simple: general relativity causes space objects closest to us that have a large mass to distort light from more distant sources that are perfectly aligned with them.

Giulietti continues: “In this way, large celestial bodies act as a kind of huge cosmic lens that makes ‘background’ galaxies appear larger and brighter, allowing them to be identified and studied.” Numerous observation programs have been carried out with this approach in the last decade. “About 100 have been discovered so far, but there could be many more.”

It was in one of these investigations, says Giulietti, that the main object of this current study was identified: “It was a very special celestial body. It is very bright and potentially subject to lensing, but this only happens at certain wavelengths.” accurate, probably due to the presence of large amounts of interstellar dust. Therefore, its study is very complex. Observations made with ALMA , a state-of-the-art submillimeter interferometer located in the Chilean Atacama desert, allowed us to determine its characteristics.”

“We studied this peculiar object by adopting particular codes that allowed 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 able to determine how it is distributed”.

“Our analysis showed that this object is very compact, presumably young, and is forming stars at an extremely high rate. In the future, the James Webb Space Telescope will reveal much more about this galaxy, something only it can do at the moment.” . (Europe Press)