Supercomputer simulations show that magnetic fields can strip angular momentum from gas surrounding pairs of protostars, bringing them closer together and allowing a stable binary system to form. A similar mechanism may also help understand the convergence of supermassive black holes.
Computer simulations suggest that magnetic fields may play a critical role in helping pairs of young stars form. The finding could explain why binary star systems are so common in the Milky Way and also offer clues about how supermassive black holes evolve.
Stars form when huge clouds of gas in space collapse under gravity, creating dense regions called molecular cloud cores. Often, many stars form in the same cloud, so some of them become gravitationally bound, forming binary star systems in which the two stars orbit each other.
Astronomers have long suspected that many binary systems begin to form very early in the star formation process, before the stars themselves have fully developed. But it has been difficult to explain how these young protostars get close enough to become a stable pair.
Magnetic fields bring protostars closer together
To investigate the problem, researchers ran advanced simulations using several supercomputers. The simulations revealed that interactions between magnetic fields in interstellar space and the gas surrounding young protostars can strip angular momentum from the pair. As the angular momentum decreases, the protostars can move closer together, allowing a binary system to form within a realistic time frame.
The importance of magnetic fields became particularly clear when the researchers ran a comparison simulation without magnetic fields at all. In this scenario, the two protostars moved apart rather than closer together, highlighting the important role of magnetism in the formation process.
Implications for binary black holes
The researchers also found evidence that a similar mechanism could operate on a pair of massive black holes.
In the gas-rich central regions of a new galaxy formed when two smaller galaxies merge, magnetic fields can help supermassive black holes lose angular momentum and move closer together. Such a process could explain how black holes eventually get close enough to merge to form a supermassive black hole.
It is still computationally difficult to directly simulate massive black holes over the vast amounts of time it takes for them to spiral in. Therefore, the researchers say that the effect of magnetic fields on binary black holes needs to be further studied in detail.
For the scientific article: DOI: 10.1093/mnras/stag669
Short FAQ:
What was the mystery that the study tried to explain?
Astronomers know that binary star systems are very common, but it is difficult to explain how two young protostars get close enough to each other to become a stable pair.
What did the simulations find?
The simulations showed that magnetic fields can remove gas and angular momentum from the system, thus allowing two protostars to move closer to each other instead of moving apart.
What is angular momentum?
Angular momentum is a physical quantity associated with rotational or orbital motion. When a system loses angular momentum, objects orbiting each other can move closer together.
What happened in the imaging without magnetic fields?
When the researchers removed the magnetic fields from the model, the two protostars moved apart and did not form a close binary system, reinforcing the hypothesis that magnetic fields play a central role.
How does this relate to black holes?
The researchers suggest that a similar mechanism may also operate in pairs of supermassive black holes at the centers of merging galaxies, helping them lose angular momentum and come closer until they merge.
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