Scientists may have solved the mystery of how the most massive black hole is formed.
Researchers at the University of Hawaii at Manoa, the University of Chicago, and the University of Michigan at Ann Arbor proposed that black holes of previously unexplainable mass may grow simultaneously with the accelerated expansion of the universe.
This phenomenon may be an example of what the team calls “cosmic coupling.”
Since the Laser Interferometer Gravitational Wave Observatory (LIGO) first detected gravitational waves from black hole merger events in 2015, scientists have been amazed at how large some of the black holes involved in these events seem to be.
Before they started measuring gravitational waves (the space-time ripples originally predicted by Albert Einstein in 1915 in General Relativity), the researchers had always believed that the black hole in the merger event should be no larger than 40 times the sun, or 40 suns. quality.
This is because the merged black hole is produced by the collapse of stars in the binary star system. In the binary star system, the stars form and evolve together, eventually forming a black hole.These double stars should not be able to gather themselves together with a large enough mass, when they experience complete Gravity collapse That gave birth to a black hole.
However, the LIGO Observatory and its gravitational wave detector VIRGO often observe black hole mergers, with black holes having masses of up to 50 solar masses, or even 100 solar masses.
And a series of formation scenes It has been proposed to explain the mass of these merging black holes, but none of them have successfully explained the diversity of black hole merging observed so far.
This new study A single formation path is proposed, which can lead to a small black hole mass and a larger mass.The research was published in Astrophysical Journal Letters, Link this formation path to the accelerated expansion of the universe, instead of simulating black holes in a static, non-expanding universe.
“This is a hypothesis that simplifies Einstein’s equations, because a non-growth universe has to track much less,” explained Kevin S. Croker, professor of the Department of Physics and Astronomy at UH Mānoa and the first author of the paper. “Although there is a trade-off: the forecast may only be reasonable for a limited time.”
In the context of gravitational wave detection, it makes sense to only consider the static universe, because the single event received by LIGO and VIRGO lasts only a few seconds. However, actual collision events in the universe take billions of years to occur.
This means that in the time required for these black holes to form and finally merge, the universe has greatly expanded. After studying some subtle elements of general relativity, the team concluded that the mass of black holes may increase simultaneously with this expansion of the universe.
Crocker and his colleagues call this “cosmic coupling.” This is not the only example of this coupling.
Perhaps the most famous example of cosmological coupling is the energy loss during the expansion of the universe. This leads to the so-called “red shift”. As the universe expands, it will extend the wavelength of light, pulling it from the high-energy blue region of the electromagnetic spectrum to the lower-energy red region.
This phenomenon increases as the galaxy moves further away, so the redshift becomes more extreme. Not only has it become a key measure for astronomers, it is also the key to Edwin Hubble’s discovery that the universe is expanding. This also led to the discovery that this expansion was accelerating in the 1990s.
“We want to consider the opposite effect,” said Duncan Farrah, UH Mānoa professor of physics and astronomy, co-author of the paper. “If black holes are cosmologically coupled and gain energy without consuming other stars or gas, what will LIGO-Virgo observe?”
To study this possibility, the team created a simulation of the birth, life, and gravitational collapse of millions of large stars in a binary star system.See the pair left by both stars Black hole, The team linked the size of these black holes to the size of the universe when they were formed.
They found that when the universe expands in their model, the mass of black holes also grows as they hover around each other. The result is an increase in merger events and an increase in events involving larger and larger black holes.
TonThen his team compared their simulation results with the data The data collected by LIGO and VIRGO found a good agreement between the two. This surprised some authors of the paper themselves.
Co-author and University of Michigan professor Gregory Tarlé said: “I have to say, I didn’t know what to think at first. This is such a simple idea, and I am surprised that it works so well.”
One advantage of this approach Black hole Compared with other competing models used to explain how massive black holes form and merge, evolution does not need to change our current understanding of star formation, life, and death.
As gravitational wave detectors become more and more sensitive, the team will further test this theory and provide further data to verify the connection between the expansion of the universe and the mass of black holes.
The researchers said that despite these positive findings, the mystery of the merger of massive black holes detected by gravitational waves may not be solved yet.
“Many aspects of merging black holes are unclear, such as the dominant formation environment and the complex physical processes throughout their lives,” the research co-author and NASA Hubble researcher Michael Zevin. “Although we used simulated star clusters that reflect the data we currently have, there is still a lot of room for maneuver.
“We can see that cosmological coupling is a useful idea, but we cannot yet measure the strength of this coupling.”
NASA
