As astronomers chronicle the growth of galaxies by combining X-ray observations with detailed supercomputer models, the history of the dark hearts of galaxies has been told almost completely for the first time. supermassive black holes More than 12 billion years of cosmic history.
By doing this, scientists showed that there is a black hole at the center of our universe. Milky Way galaxy It reached four million solar masses quite late in its history.
Supermassive black holes have masses millions of times larger. our sun They have masses billions of times more, but their origins are unclear and understanding how they achieve such large masses has been a challenge for astronomers.
But now astronomers Fan Zou and W. Niel Brandt, both at Penn State University, have led a team that connects the two mechanisms of black hole growth through observations and simulations. The results may eventually provide some answers.
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“A very big question is how do these supermassive black holes have so much mass?” Zou said at this time I present your work “To address this, we need to follow the overall growth history of these supermassive black holes,” he said at the 244th meeting of the American Astronomical Society in Wisconsin.
As mentioned, black holes grow through two main mechanisms. One of these is the accumulation of cold gas from the host galaxy. This gas forms an accretion disk around the black hole, and matter from the disk slowly spirals towards the core of the black hole. The accretion disk can become so dense that friction between gas molecules causes the disk to heat up to millions of degrees, emitting X-rays in the process. The other mechanism occurs during galaxy collisions. When this happens, not only do galaxies merge, but their supermassive black holes eventually merge, creating an explosion. gravity waves.
Chasing cosmic voids
To assess how much gas accretion contributes to the growth of supermassive black holes, the study team examined more than 20 years of archival data. NASA‘S Chandra X-ray ObservatoryEuropean Space Agency’s XMM-Newton mission and eROSITA X-ray device on joint German-Russian ship Spektr-RG spacecraft. Researchers were able to detect X-ray signals from approximately 8,000 rapidly growing supermassive black holes.
“When supermassive black holes accrete surrounding gas, they emit strong X-rays, so by detecting them in X-ray bands we can measure their accretion power,” Zou said.
Then they returned to them IllustrisTNG cosmological Supercomputer simulation to model galaxy mergers throughout cosmic history. From there, the team combined X-ray data showing growth through mergers with the results of simulated mergers to gain an understanding of how and when supermassive black holes grew over the 12 billion years until 1.8 billion years after the explosion. Big Bang to today.
These simulations “capture the overall large-scale structure” [of the universe] but we can also study individual galaxies,” Zou said.
Supermassive black hole stories
Zou and Brandt found that X-ray data show that accretion was the dominant driver of black hole growth throughout all periods of cosmic history. Moreover, the greater the mass of the galaxy, the faster the supermassive black hole within it grew and multiplied. Mergers, on the other hand, are less prominent drivers. black hole growth according to simulations, but it could still have some impact.
“Accretion dominates supermassive black hole growth in most cases, and mergers provide some important secondary contributions,” Zou said.
These results also show that supermassive black holes grew faster earlier in the universe, and new ones appeared frequently. But by about 7 billion years ago, the total number of supermassive black holes had more or less stabilized, with a small number of new supermassive black holes forming. Mergers had a greater impact later in history, peaking in importance for the growth of black holes around 4 billion years ago.
“Once we found this Universe “The overall demographics of supermassive black holes that are around 40% of their age are very similar to the demographics of supermassive black holes that we see in the local universe,” Zou said.
Astronomers have even specially modeled our galaxy’s black hole. Spring A*and concluded that most of its matter grew relatively late in the cosmic age. time. This growth may have occurred primarily through accretion, with the majority of the Milky Way’s mergers with other galaxies occurring in numbers greater than 100. 8 billion to 10 billion years ago. However European Space Agency‘S Gaia mission have recently discovered evidence For a dwarf galaxy that crashed into the Milky Way just 2 billion to 3 billion years ago. Dwarf galaxies are thought to contain intermediate-mass black holes, tens to hundreds of thousands of times the mass of our sun, and it is possible that one of these could merge with Sagittarius A*, increasing the mass of our black hole.
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Since the results only take us back 1.8 billion years after the Big Bang, they do not explain how the seeds of supermassive black holes first formed. This remains a dilemma, especially for cosmologists. Hubble space telescope And James Webb Space Telescope we found surprisingly massive black holes much earlier in the history of the universe. How did they grow It is currently unknown whether it will reach millions of times the mass of our Sun in less than a billion years.
A paper describing the findings was published in March. Astrophysical JournalA second article is waiting in the queue.