Numerous galaxies’ centers are home to supermassive black holes. Despite the fact that we know a lot about black holes (far from enough! ), the formation of the large ones is still unknown. It’s interesting that they are visible to astronomers in the early epochs of cosmic history. That begs the question of how they managed to grow to such a size when the Universe was still so young.
Astronomers in Taiwan are looking for solutions. The team, led by National Central University’s Chorng-Yuan Hwang and Academia Sinica’s Ke-Jung Chen, is investigating the genesis of supermassive black holes (SMBH). Giant molecular clouds were incorporated in complex models of galaxy mergers that were used to examine the development of these monstrosities. The findings of our study can help people comprehend galaxy development better, according to Lin. “We anticipate that more observational results will be available to confirm our conclusion.”
Giant Molecular Clouds and SMBH
The team hypothesizes that the accretion of the molecular clouds during mergers is principally responsible for the formation of black holes in early galaxies. These large clouds efficiently fall to the galactic center due to the gravitational forces at play. This accelerates the rate at which stars originate in the galaxy and gives a central SMBH the building materials it needs to grow quickly.
It is not a novel concept for molecular clouds to collapse. Although earlier works had made the suggestion, this work simulates their rapid development. It demonstrates how black holes can increase in size from a few million solar masses to billions of solar masses in a matter of a few hundred million years. That contributes to the explanation of why SMBH appears so early in cosmic history.
Supermassive Black Holes and Mergers
One of the difficulties in astronomy is comprehending the creation of SMBH in galactic cores. These monstrosities have the capacity to grow to have millions or billions of solar masses. You’d also be excused for thinking that something that large would take a very long time to create. After all, to support such a behemoth at its core, a galaxy needs at least that much mass—and much more. Timescales up to millions of years are involved in galaxy mergers.
For instance, the galaxies involved in the Mice collision (above) are about to join. A collision between the Milky Way and Andromeda is now taking place and will likely take 7 to 8 billion years to complete. Their primary black holes will also combine.
Since the late 1960s, astronomers have understood that most galaxies contain SMBH in their cores and that these objects are somehow related to the host galaxies. According to research, a galaxy’s bulge, stellar mass, and other features are related to the black hole’s mass. Additional research also indicated that it took time for all of this matter to accumulate into a black hole.
Think about how everyone was shocked when scientists first discovered them in galaxies that were more than 12 billion light-years away. As a result, they are situated during a period in cosmic history when the Universe is not nearly one billion years old. How is this even possible? Here is where simulations of enormous gas clouds in galaxies are useful.
Utilizing New Models of the Formation of Supermassive Black Holes
To explain the quick expansion of SMBH in the early Universe, the Taiwanese team developed simulations of merging galaxies. They had to account for several merger types, including small mergers and mergers between gas-rich and gas-poor galaxies. They also considered the function of those enormous molecular clouds during a merger.
The clouds create an intriguing issue. First, during a merger, they participate in increased star-formation rates, with the core areas accounting for at least half (if not more) of this activity. Star formation occurs in gas-poor galaxies as well, and it is accelerated at the core (albeit not as much as in a merger involving gas-rich galaxies). It goes without saying that star formation contributes to a galaxy’s bulge’s mass. In the course of the galaxy’s growth phase, a galaxy with a large bulge is likely to undergo a great number of small mergers.
The second characteristic of these enormous gas clouds is their high kinetic energy. However, because of dynamical friction during a merger, they lose that energy. They swiftly descend into the galaxy’s nucleus as a result of that. There, they participate in star formation as well as the development and expansion of a potential SMBH. According to the research team’s report, once a black hole generation scenario begins during a merger, it can increase from 100 million sun masses to over a billion solar masses in under 300 million years.
Implications for the Milky Way and Beyond
Our own Milky Way is the result of a merger. Even now, it is still fusing with other smaller dwarf spheroidal bodies. Additionally, it will undergo another shape change following its union with Andromeda. It’s highly likely that enormous molecular clouds contributed to the evolution of the Milky Way. The team actually looked into this possibility by analyzing how a small galaxy merger would affect one that resembled the Milky Way. The simulation revealed that the bulge of that hypothetical galaxy nearly doubled in size and mass. They came to the interesting conclusion that while there have been many tiny mergers in the Milky Way, there have not yet been any massive ones. As the Andromeda collision develops over the coming few billion years, that will change.
For continued modeling and simulation of galaxy mergers, new surveys of the Universe by JWST and the Vera C. Rubin Observatory during the following few years will add significantly more data. The development of supermassive black holes at the centers of early merging galaxies should become clearer as a result.
