LOCATED amidst the dolphin-shaped constellations Delphinus and the flying horse Pegasus, a pinwheel-like vortex hovers in space.
Quoting BBC News Indonesia, for billions of years the spiral arms of the UCG 11700 galaxy rotate peacefully, undisturbed by collisions and merging of objects in space that change the shape of other galaxies.
Spiral galaxies like UCG 11700 are fun to look at, but something horrific lies at the center of their swirls.
At the center of this beautiful cosmic wheel resides one of the most mysterious objects in the universe: a black hole supermasif (supermassive black hole).
Standard black holes generally range in size from about four times the mass of the Sun. Meanwhile, supermassive black holes can be millions, even billions, times larger.
Scientists believe that all large galaxies have a supermassive black hole at their center. But no one knows why this is so.
This is where the UCG 11700 comes in handy.
“The ideal galaxy for my study is the most beautiful and perfect spiral galaxy imaginable,” said Becky Smethurst, a young researcher at the University of Oxford who studies supermassive black holes.
“The most beautiful galaxies can help us solve the mystery of how black holes are born.”
How are black holes created?
Studying something that, by its nature, is so dense that not even light can escape it, is very difficult.
But new techniques that examine the effect these black holes have on nearby celestial objects, as well as examining the ripples they cause in the fabric of space and time, are providing new clues.
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There is a little secret about the formation and growth of conventional black holes.
Stars that die from exhaustion, explode in supernovae, are engulfed by themselves, then become so dense that not even light can escape its gravity.
The idea of black holes has been around for decades and was predicted in Albert Einstein’s Theory of General Relativity.
In pop culture, black holes are depicted as dark and always hungry. They glide through the Universe sucking up everything they have passed through and growing bigger because of it.
Because of this description, people think supermassive black holes are the oldest and hungriest kind.
In fact, black holes aren’t that bad.
They’re actually not very efficient at accreting (physical slang for “sucking up”) material around them, even in dense galactic nuclei.
Indeed, destroyed stars grow very, very slowly, they cannot become supermassive by simply absorbing new material.
“Let’s just say the first stars formed black holes about 200 million years after the Big Bang,” Smethurst said.
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“Once they disintegrate, it takes about 13.5 billion years to grow into a black hole billions of times the mass of the Sun. That’s too short a time to get that big, even by accretion alone.”
Even more confusing supermassive black holes existed when the Universe was very young.
Distant quasars, some of the brightest cosmic objects in space, are actually very ancient supermassive black holes, burning away the dead cores of galaxies.
Some giant quasars have been around since the Universe is at least 670 million years old, the same time some of the oldest galaxies formed.
Although the center of black holes is as yet unknown, supermassive black holes can shine brighter than a galaxy of stars and can even emit “burps” of ultraviolet radiation as they gobble up the matter around them.
Black holes have a curved boundary called the Event Horizon. Inside that fence, light, energy and matter are trapped and unable to escape.
Space and time have different rules there, so the laws of physics that explain much of how the Universe works don’t apply there.
However, just beyond the Event Horizon, a spinning black hole can shred nearby matter into a spinning, heated disk.
The disks inside quasars can reach temperatures in excess of 10 million degrees Celsius, allowing them to release blinding light across the entire electromagnetic spectrum.
“Black holes are the most effective and efficient machines in the Universe,” said Marta Volonteri, a black hole researcher at the Institut d’Astrophysique de Paris.
“They convert mass to energy with up to 40 percent efficiency. If you think about what we burn with carbon, or chemical energy, or even what happens to stars, that’s equivalent to a very, very small part of what is produced by the black hole.”
Trying to solve the mystery
But supermassive black holes are of interest to scientists not only because of their energy efficiency. Their formation and evolution is clearly related to the development of galaxies and, ultimately, to the entire history and structure of our Universe.
Solving the mystery of this cosmic giant represents a significant step in scientists’ quest to understand why things are the way they are.
The release of energy is one of the many ways black holes can reveal their secrets. When a black hole merges or collides with a less dense object like a neutron star, the event creates ripples in space-time called gravitational waves.
These waves then travel through the cosmos at the speed of light and were first detected from Earth in 2015.
Since then, large observatories such as the Laser Interferometer Gravitational-wave Observatories (Ligo) in the United States and the Virgo Facility near Pisa, Italy, have recorded waves resulting from collisions like these.
Although these observatories use instruments several kilometers wide, they can only detect waves from medium-sized black holes.
“Ligo can detect a merger down to about 150 solar masses,” said Nadine Meumayer, who leads the Galactic Nuclei research group at the Max Planck Institute for Astronomy.
“A medium-sized black hole could be the ‘seed’ of a supermassive black hole,” he said.
Intermediate-mass black holes, he said, may have formed in the early stages of the Universe when giant clouds of gas disintegrated or stars collided.
In the still restricted environment of the young Universe, collisions between medium-sized black holes, together with accretion from surrounding matter, could accelerate its growth to supermassive scales.
However, there’s a problem with this theory. The early universe was also very hot. The gas clouds must be enveloped in radiation, which gives them too much energy to break up. And even in the densest cosmos, the laws of physics limit the maximum suction power of black holes.
Volonteri said every explanation and theory about black holes that exists today has “weaknesses and problems,” leaving scientists lacking a definitive answer.
“Theoretically involving ‘dynamic processes’, in the sense that black holes are formed from many stars instead of one, it is possible. But this process has to happen under very specific conditions,” he said.
“There is also the ‘primordial black hole’ theory, which claims that black holes could have formed and enlarged before there were stars. But this is uncharted territory, because we have no observational evidence for this theory.”
Therefore, he believes that the real story of how black holes form has not been told.
“The more we dig, the more we find that there are problems with ideas we had previously understood. We are missing something important.”
The current generation of observing equipment is starting to fill this data gap. But scientists still need bigger detectors than they currently have.
In the 2030s, NASA and the European Space Agency (ESA) will launch the Space Laser Interferometer Antenna (LISA), which consists of three satellites flying in a triangular formation, with sides 2.5 million kilometers long.
Previously, there had been hints of how gravitational waves created by black holes engulf us.
In early 2021, astronomers announced they’d detected tiny differences in the radiation pulses of 45 pulsars, clusters of stars that periodically release beams of light.
While unconfirmed, the researchers imply that this could be due to a “gravitational background” that may have been created by merging supermassive black holes.
But there are more direct ways to observe black holes. The Event Horizon Telescope recently managed to take the first photograph of a black hole.
The telescope is revealing more about their properties and the gravitational and magnetic effects they have on the galaxies they inhabit.
Astrophysicists can also track the motion of stars orbiting black holes in galactic nuclei, extrapolating information about the massive objects at their centers.
“There is a close correlation, the more mass a galaxy has, the larger its central supermassive black hole,” Neumayer said.
“These objects evolve gradually.”
