4 big questions answered after the first photo of a black hole in the universe

For the first time in history, humans have seen a real image of a black hole. This result was achieved by the Event Horizon Telescope, a network of eight radio observatories around the world that has been dedicated to observing black holes since 2012.

This historic image will provide clues to answer four questions that have puzzled astronomers and physicists for years.

1. The real shape of a black hole

Black holes are exactly what their name suggests.These mysterious objects do not emit any light in the electromagnetic spectrum., so they themselves are almost invisible.

But astronomers know black holes exist by studying the gravitational pull they exert on all matter near them. As a black hole sucks in gas and dust, the matter settles down to form an orbiting accretion disk, with atoms jostling each other at extremely high speeds.

High speeds cause collisions and heat up matter, so they emit X-rays and other high-energy radiation. Black holes"voracious"Most of the disks in the universe have disks brighter than all the stars combined in their galaxy.

The first photo of a black hole ever taken by humans.

Previously, computer simulations and the laws of gravitational physics had allowed astronomers to visualize what they would expect to see in a real image. Because of the intense gravity near a black hole, light from the disk would be bent aroundevent horizon,So we can see the image of the bright disk behind the black hole.

When the actual image appears, it is not as symmetrical as it appears in movies. The gravitational force that bends light from the inner part of the disk toward Earth is stronger than the outer part, making one part of the circle brighter.

2. The accuracy of general relativity when applied to black holes

The precise shape of the resulting halo could help break one of the most vexing impasses in theoretical physics.

The two pillars of physics are Einstein's general theory of relativity, which governs massive, gravity-intensive things like black holes, and quantum mechanics, which governs the strange world of subatomic particles.

But these two theories are''don't play with each other'', each theory is only accurate for certain sizes of matter (Einstein's theory cannot be applied to quantum mechanics and vice versa).

General relativity is stuck in a black hole (singularity), so images from black holes can show where the theory needs to be completed, thereby combining the two great theories together.

Because black holes are the most extreme gravitational environments in the universe, they are ideal places to test theories about gravity. If general relativity holds, black holes will look one way; if it doesn't, black holes will look another way. Scientists learn all sorts of things.

Physicist Lia Medeiros of the University of Arizona (USA) and colleagues ran simulations of more than 12,000 different black hole shapes, different from Einstein's predictions.

“If the real image is somehow different from the simulation (ie there is a different hypothesis about the origin of gravity), consider the scientific community getting an early Christmas present,”she said

3. Do pulsars surround the Galactic black hole?

Another way to test general relativity around black holes is to look at the stars around them. As light escapes the extreme gravity in the vicinity of a black hole, its waves are stretched, making the light appear redder.

This process, called gravitational redshift, is predicted by general relativity and has been observed recently.SgrA* black holelast year. As of this writing, Einstein is still right.

The best test subject is a pulsar — ​​an extinct star that spins so rapidly and emits radiation at a regular rhythm that it gets its name.pulseGravitational redshift would disturb the pulsar's rhythm, so one examines the relativity predictions of this disturbance.

"Studying SgrA* also means trying to find a pulsar orbiting this black hole", said astronomer Scott Ransom of the National Radio Astronomy Observatory in Charlottesville.

Pulsar PSR J1745-2900 (left) was discovered in 2013 about 150 light-years from the black hole at the center of the galaxy.

Despite careful searches, no pulsars have been found near SgrA*, in part because gas and dust in the galactic center scatter their beams, making them difficult to detect.

But the EHT has the best imaging data yet of the black hole center across the entire spectrum of radio wavelengths, so Ransom and colleagues hope to spot some pulsars that have yet to be found.

"This is like a fishing expedition, and the chances of catching a big fish are very small", Mr. Ransom said.“However, if we dare to do it, the result will definitely be worth it."

4. Super-luminous gas streams of some black holes

Some black holes are voracious, aggressive monsters, sucking in large amounts of gas and dust, while others are picky eaters. No one knows why, but SgrA* seems to be one of the pickier ones, with an accretion disk that is not very bright despite its mass of 4 million times that of the Sun.

Another EHT target is the black hole in the galaxy M87. It’s a voracious eater, with a mass between 3.5 billion and 7.22 billion times that of the Sun. Not only does it have a bright accretion disk around it, it also shoots out a jet of charged subatomic particles that stretches 5,000 light-years.

This seems a bit misleading because people usually think of black holes as simply swallowing matter and not spitting anything out, says astrophysicist Thomas Krichbaum of the Max Planck Institute for Radio Astronomy in Bonn, Germany.

Many other black holes produce jets of light longer and wider than galaxies, which can extend billions of light years from their centers. The question arises:What energy is powerful enough to send these beams of light so far?

Previous simulations were done by computer, 3D algorithms, not real images.

EHT measurements of the M87 black hole will help estimate the strength of its magnetic field. Astronomers think this is related to the mechanism by which the jet is launched, and measurements of the jet's properties as it approaches the black hole will help determine where it originates — in the innermost part of the accretion disk, or from the black hole itself.

These observations could also reveal whether the jet of light was launched by something within the black hole or by fast-moving material in the accretion disk.

Because jets can carry matter away from the galactic center and into intergalactic space, they can influence how galaxies evolve, and even where stars and planets form within the galaxy.

This is a key to understanding the evolution of galaxies, from the early formation of black holes to the formation of stars, and then to the formation of life, according to Krichbaum.

“This is a very big story, of which studies of light from black holes are just a small piece.”, he said.