In 1926, the famous astronomer Edwin Hubble developed a morphological classification of galaxies. This method divided the galaxies into three basic groups – elliptical, spiral and lenticular. Since then, astronomers have devoted a considerable amount of time and effort to discover how galaxies evolve over several billion years and why they acquire exactly the forms that ultimately acquire.
One of the most popular and widespread hypotheses on this subject is one that explains the change in the forms of galaxies as a result of their fusion, when more compact clusters of stars held together by mutual gravity merge together and thereby eventually form the shape and final form of galaxies. However, according to the findings of a new study conducted by an international group of scientists, the shape and size of galaxies can in fact be influenced by the appearance of new stars in their central regions.
The study was conducted under the guidance of the postdoctoralist Ken-Iti Tadaki in collaboration with the Max Planck Institute for Extraterrestrial Physics and the National Astronomical Observatory of Japan (NAOJ). To obtain a more complete picture of galactic metamorphoses, scientists conducted a series of observations of very distant galaxies.
Diagram of the evolution of galaxies
The study included the use of several telescopes, by which astronomers conducted observations of 25 galaxies located about 11 billion light-years from the Earth. At this distance, scientists actually observed the galaxies, when they looked exactly like 11 billion years ago, that is, about 3 billion years after the Big Bang. This time is considered by astronomers as a period of peak activity of galactic formation in the universe, when most galaxies were formed.
"It was believed that massive elliptical galaxies formed as a result of collisions of galactic disks. However, we are not sure that all the elliptical galaxies once touched such an intergalactic event. We believe that there is an alternative, "Tadaki said in a press release published on the website of the Japanese Astronomical Observatory.
The possibility of catching the subtle light of these distant galaxies turned out to be a very difficult task, and to solve it, scientists needed to use two terrestrial and one space telescopes. First, to search for 25 galaxies, they used the 8.2-meter Subaru telescope located in the Hawaiian Islands. Then, they monitored the detected objects with the help of the Hubble Space Telescope and the ground-based Atamak large antenna array of the millimeter range (ALMA) located in Chile.
Hubble allowed to catch the light of galaxies to determine their shape (which they had 11 billion years ago), with the help of ALMA scientists conducted a study of submillimeter waves emitted by cold clouds of dust and gas, the place where new stars were born. Comparing the results of both observations, astronomers were able to provide a detailed picture of how these galaxies looked 11 billion years ago, when their shape was still subject to change.
The observation of the galaxy located 11 billion light-years from us
What the scientists found was very revealing. Hubble images indicated that in the early galaxies the disk component predominated, and not the central bridge, which we were accustomed to associate with spiral and lenticular galaxies. At the same time, ALMA images showed that near the center of these galaxies there can be massive gas and dust reservoirs inside which a very active star formation takes place.
To exclude the possibility that such active star formation could have been caused by the fusion of galaxies, the researchers also used data from the Very Large Telescope of the European Southern Observatory, located at the Paranal Observatory in Chile, for verification.
"Here we have received convincing proof that dense galactic nuclei can be formed without galactic collisions. They can be formed due to a very active star formation in the very heart of the galaxy, "Tadaki reports.
The results of this study can force astronomers to reconsider the current models and theories of galactic evolution, as well as some aspects such as those of galaxies appear jumpers and spiral arms. The study can also lead to a revision of the cosmological evolution patterns, not to mention the history of our own galaxy.
Who knows, perhaps this will also cause astronomers to reconsider the predictions of what might happen when our Milky Way and Andromeda galaxy collide in a few billion years. The more and more scientists look into space, the more surprises he presents. And every time when the observed observations do not correlate with our expectations, it forces scientists to reconsider the accepted hypotheses concerning the evolution of the universe.