The history of the black hearts of galaxies is almost completely told for the first time, when astronomers combined X-ray observations with detailed supercomputer models to record the growth of galaxies. supermassive black holes more than 12 billion years of cosmic history.
The scientists have shown that the black hole forms the core of our body galaxy reached its four million solar mass relatively late in its history.
Supermassive black holes range from millions of times more massive than our sun up to billions of times more massive, but their origins are unclear and how they grew to such enormous masses has been challenging for astronomers to understand.
Now, however, astronomers Fan Zou and W. Niel Brandt, both from Penn State University, have led a team that linked the two mechanisms of black hole growth through observations and simulations. The results may finally provide some answers.
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“A very big question is: how do these supermassive black holes become so massive?” Zou said briefly present their work at the 244th meeting of the American Astronomical Society in Wisconsin. “To address that, we need to track the overall growth history of these supermassive black holes.”
As mentioned, black holes grow via two main mechanisms. One of these is due to the accretion of cold gas from their host system. This gas forms an accretion disk around the black hole itself and matter from the disk gradually spirals toward the black hole’s core. The accretion disk can become so dense that friction between gas molecules causes it to heat up to millions of degrees, emitting X-rays. The other mechanism occurs during collisions between galaxies. When this happens, not only will galaxies merge, but their supermassive black holes will eventually merge and release a burst of energy. gravitational waves.
Cosmic voids follow
To assess the extent to which gas accretion contributes to the growth of supermassive black holes, the research team sifted through more than two decades of archival data. NASA‘S Chandra X-ray Observatoryof the European Space Agency XMM Newton mission and the eROSITA X-ray instrument on board the joint German-Russian Spektr-RG spacecraft. The researchers were able to identify X-ray signals coming from about 8,000 fast-growing supermassive black holes.
“When supermassive black holes suck in the surrounding gas, they emit strong X-rays, so by detecting them in the X-ray bands we can measure their accretion power,” says Zou.
Then they turned to the IllustristTNG cosmological supercomputer simulation to model galaxy mergers throughout cosmic history. From there, the team combined X-ray data showing growth through accretion with the results of the simulated mergers to gain insight into how and when supermassive black holes have grown over the past 12 billion years, starting 1.8 billion years after birth. Big bang until today.
These simulations “capture the overall large-scale structure [of the universe] but are also able to investigate individual galaxies,” said Zou.
Supermassive black hole stories
Zou and Brandt found that the X-ray data show that accretion has been the main driver of black hole growth throughout all epochs of cosmic history. Furthermore, the more massive the galaxy, the faster the supermassive black hole within it grows through accretion. Mergers, on the other hand, are a less prominent driver black hole growth according to the simulations, but can still have some influence.
“Accretion dominates supermassive black hole growth in most cases, and mergers make some notable secondary contributions,” Zou said.
These results also show that supermassive black holes grew faster earlier in the universe, and new ones appeared regularly. However, about 7 billion years ago, the total number of supermassive black holes was more or less established and few new supermassive black holes were formed. Mergers had more impact in later history, peaking in their importance for black hole growth about 4 billion years ago.
‘We found that once the universe reaches about 40% of its age, the overall demography of supermassive black holes is very similar to the demography of supermassive black holes seen in the local universe,” Zou said.
The astronomers even specifically modeled our Milky Way’s black hole, Sagittarius A*and concluded that most of its matter grew relatively late in the cosmos time. This growth is thought to be mainly due to accretion, with the majority of the Milky Way’s mergers with other galaxies occurring more than a year ago. 8 billion to 10 billion years ago. however, the European Space Agency‘S Gaia mission has recently found evidence for a dwarf galaxy that collided with the Milky Way just 2 billion to 3 billion years ago. Dwarf galaxies are thought to contain intermediate-mass black holes measuring tens to hundreds of thousands of times the mass of our Sun, and it is possible that one of these could have merged with Sagittarius A* to increase the mass of our black hole.
Because the results only take us back 1.8 billion years after the Big Bang, they don’t describe how the seeds for supermassive black holes first formed. This remains a dilemma for cosmologists, especially since the Hubble Space Telescope and the James Webb Space Telescope have found surprisingly large black holes very earlier in the history of the universe. How they grew It is currently unknown whether this will be millions of times the mass of our Sun in less than a billion years.
One paper describing the findings was published in March The Astrophysical Journalwith a second article in the pipeline.