Not all are "destroyers," and Hubble discovered that some black holes facilitate star formation

2022-03-01 08:45:01

In previous studies, the jets or outflows produced by the black hole system are very close to the speed of light, and the gas swept by the jets and outflows will be heated and the gas in its path will be dispersed, and these effects are obviously not conducive to star formation. The outflow of the central black hole of Henize 2-10 is very low, and it does not significantly heat the gas when it interacts with the gas, but its outflow directly produces the effect of triggering star formation through the compressed gas.

Black holes have long been thought of as the "King of Destruction," devouring everything close to it. However, the Hubble Space Telescope recently observed a black hole in the dwarf galaxy Henize 2-10, in stark contrast to the "temperament" of other known black holes, which is promoting, rather than inhibiting, the formation of stars nearby.

This is a disruptive discovery. Hubble Space Telescope imaging and spectroscopic analysis of Henize 2-10 clearly shows that a stream of gas extends from the black hole to the bright star-birth zone, acting like an umbilical cord, allowing dense clouds to form stars.

Not all are "destroyers," and Hubble discovered that some black holes facilitate star formation

Black holes that promote star formation

Henize 2-10 is located in the constellation of Compass (one of the southern constellations), about 30 million light-years from Earth, and contains only about one-tenth of the number of stars in the Milky Way. Lei Weihua, a professor at the School of Physics of Huazhong University of Science and Technology, introduced that the Milky Way is the product of the continuous growth and merger of primitive galaxies, and although Henize 2-10 has undergone a long period of cosmic evolution, it still retains its original form, is a small-scale galaxy, and can be regarded as the "living fossil" of the galaxy.

Does such a dwarf galaxy also have a supermassive black hole in the center of the galaxy like other galaxies?

"10 years ago, this issue was a point of contention. It is thought that the X-ray and radio activity in the core of the Henize 2-10 galaxy may be caused by the gas deposition of the central black hole, or it may come from the remnants of young supernovae. Lei Weihua said.

The Hubble Space Telescope observations put an end to the debate over the existence of massive black holes at the center of dwarf galaxies. The study reveals the peculiar structure of the bidirectional outflow from the galactic core to the star-forming region. By moving the doppler frequency of the spectral line, the researchers can measure the velocity of the outflow gas at different locations, further showing the outflow precession.

Previously, scientists have observed the precession of jets in many active galactic nuclei. Theoretically, the precessions of jets or outflows could come from a distorted black hole accretion disk. Lei Weihua believes that the observation of precessive outflow proves that the center of Henize 2-10 must be a black hole, and it is impossible to come from supernova remnants.

Meanwhile, Henize 2-10 has no nucleus sphere at its center, suggesting that supermassive black holes with about a million times the mass of the Sun at their centers existed before the nucleus formed, unlike supermassive black holes in normal and active galaxies experiencing growing growth along with their nucleospheres.

"The supermassive black hole at the center of Henize 2-10 may still be in its infancy, which is of great research value, and can be used to restore the original seed information similar to the supermassive black hole at the center of the Milky Way." Lei Weihua said.

For a nebula to collapse to form a star, it must be cold and dense enough. In previous observations and theoretical studies, it has been generally believed that jets or outflows from the black hole at the center of galaxies will continue to heat and disperse gas where they pass, which will inevitably inhibit star formation. For dwarf galaxies, although few samples of black hole activity have been observed, scientists still share the same view.

Lei Weihua said that observations of Henize 2-10 have found the complete opposite, and the outflow generated by the black hole activity at its center triggers star formation, which is greatly unexpected by scientists.

Black hole outflows like no other

With the development of multi-band astronomy, scientists have studied galaxies more and more deeply, and gradually accumulated evidence that normal galaxies and active galaxies generally have a supermassive black hole with a mass of one million to ten billion times the mass of the sun.

Lei Weihua introduced that the black hole itself does not emit light, but the strong gravitational field of the black hole will affect the surrounding stars or gas, such as the supermassive black hole will capture and tear the star near it, suck the star debris, and the black hole with a mass of more than 100 million times the mass of the sun can directly swallow the star or gas to form an accretion disk.

The black hole accretions the surrounding gaseous material to form an accretion disk. On the accretion disk, the material at different distances relative to the center of the black hole rotates at different speeds, and these materials release gravitational potential energy and heat the gas to form a hot plasma by poor rotation (rotating around the black hole at different angular velocities in different radii).

In addition to accreting matter, The black hole accretion disk system also throws plasma outward, producing jets or outflows, which are very common in active galactic nuclei and microquasars, Lei said.

There are three main mechanisms for the formation of jets or outflows: the low accretion rate accretion disk cannot be effectively cooled by radiating photons, and the hot accretion disk will throw plasma outward to form a disk wind (outflow); if there is an extremely strong ordered magnetic field in the accretion disk, the plasma on the disk is ejected outward through the magnetic field line to form an outflow or jet; the rotating black hole can extract the rotational energy of the black hole through the surrounding ordered magnetic field to accelerate the formation of a collimated jet along the direction of the black hole's poles.

"The mechanism by which the Henize 2-10 central black hole generates outflow may be one of them, and it is still unclear which of these mechanisms is dominant." Lei Weihua said.

In previous studies, the jets or outflows produced by the black hole system are very close to the speed of light, and the gas swept by the jets and outflows will be heated and the gas in its path will be dispersed, and these effects are obviously not conducive to star formation. As a result, scientists often believe that black hole jets and outflows inhibit star formation, at least for active galaxies.

As a dwarf galaxy, Henize 2-10 has a very low outflow from its central black hole, about hundreds of kilometers per second, which is very slow relative to the speed of light, and does not significantly heat the gas when it interacts with the gas, but its outflow directly triggers the effect of star formation through the compression of gas. Based on this, the Hubble Space Telescope observed that the two-way outflow of Henize 2-10 extends directly into the star-forming region.

Not all are "destroyers," and Hubble discovered that some black holes facilitate star formation

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