An illustration of a blue swirling galaxy inside an amillary sphere. A black hole appears in the center.

Olena Shmahalo is a writer for the magazine.

The first image of the black hole at the center of the Milky Way was revealed at nine simultaneous press conferences. The image of the ring of light around the central pit of darkness seemed to prove that the black hole in the center of our galaxy is spinning and obeys Einstein.

Things don't stack up on closer inspection

Researchers estimate how much matter is falling onto Sagittarius A* from the brightness of the bagel of light. It's not quick at all. Natarajan compared the universe to a broken shower. It takes a thousandth of the matter from the surrounding universe to make it to the hole. Natarajan said that it was showing a huge problem. This gas is going somewhere. What is going on with the flow? Our understanding of black hole growth is questionable.

Over the past 25 years, astrophysicists have come to understand what a tight-knit, dynamic relationship exists between the black holes at their centers. There has been a huge change in the field of theoretical astrophysics. Black holes are important in shaping and controlling the evolution of the universe.

The giant holes, concentrations of matter so dense that gravity prevents even light from escaping, are like the engines of galaxies, but researchers are only beginning to understand how they work. The accretion disk around the black hole is formed when gravity pulls dust and gas into the center of the universe. When this matter is engulfed by the black hole, energy is sent back into the universe. The growth of a black hole is more efficient than any other process we know of in nature. The feedback affects star formation rates.

Researchers only have vague ideas about what happens when a black hole is active. The triggering mechanism is what I am wondering. The off switch is what I am wondering. The Harvard-Smithsonian Center for Astrophysics is trying to answer these questions.

AGN feedback on a smaller scale has the same effects as stellar feedback. The stellar engines are large enough to regulate small galaxies, while the giant engines of black holes can dominate the evolution of the largest elliptical galaxies.

The largest spiral galaxy is in the middle. Our universe was thought to be dominated by stellar feedback due to the lack of obvious activity at its center. Several recent observations show that AGN feedback shapes it. astrophysicists hope to figure out how galaxies and black holes coevolve by studying the details of the interplay between these feedback mechanisms. Natarajan said that the Milky Way is becoming the most powerful astrophysical lab. It may hold the key if it serves as a sample.

Galactic Engines

Astronomers accepted the existence of black holes in the late 1990s. They could see the invisible objects and figure out their mass from the stars' movements. It was found that the heavier the central black hole, the bigger it is. This was extremely tight and revolutionary. Tiziana Di Matteo is an astronomer at Carnegie Mellon University.

It is surprising that the correlation is not bigger than the black hole. TheSagittarius A* weighs around 4 million suns, while the Milky Way weighs 1.5 trillion suns. The black hole only pulls its gravity on the innermost part of the universe.

The United Kingdom's Astronomer Royal felt that AGN feedback could be used to connect the tiny black hole to the larger universe. The quasars were observed in the 1970s thanks to the hypothesis that black holes powered the jets. He proposed that a black hole explain why the center of the universe glows. It's possible that these are signs of a phenomenon that governs the size of black holes.

blurry orange ring of light encircles a black hole

The idea was that if a black hole swallows a lot of matter, the brighter it gets, and the more gas it creates. The gas falls into the black hole. It will end the growth. That was the reason in a hand-wavy way. The black hole eats and swallows. The black hole gets bigger before it swallows when a big galaxy puts more weight on it.

The energy of infalling matter was not thought to be ejected in such a dramatic way. Natarajan was a graduate student when he helped develop the first AGN feedback models. It was so radical that everyone had to be careful.

Confirmation of the feedback idea came from simulations developed by Di Matteo and others. The zoo of galaxies that we see in the real universe is what we wanted to reproduce. Galaxies are small and dense in the beginning of the universe. When gravity smashes these dwarfs together, they form rings, whirlpools, cigars and every shape in between. Galaxies grow in size and variety until they are large and smooth. It ends up in a blob. She and her colleagues were able to re-create elliptical galaxies using simulations. There was an issue.

There are many young stars that glow blue in the spirals of the Milky Way, but only a few old stars that glow red in the ellipticals. According to Springel, they are dead and red. The team ran their simulation and the ellipticals glowed blue. They didn't capture anything in their computer model.

Springel said that they had the idea to add black holes in the center. We let the black holes release energy and then let the whole thing fall apart. The elliptical galaxy stopped star formation and became dead.

He said his jaw fell. The effect was so extreme that we didn't think it was possible.

The black hole feedback theories were strengthened by reproducing red and dead ellipticals. A black hole can communicate with the entire universe through feedback. Over the last two decades, the computer models have been refined and expanded to mimic large swaths of the universe. The simulations show that the space between the galaxies is filled with hot gas that should have already cooled and turned into stars. Springel said that people are now convinced that black holes are engines. No one has come up with a model that works.

Mysteries of Feedback

The computer simulations are not always nice.

The amount of energy lost through trial and error is what the coders put into their simulations. The details are still hard to find. It is possible that we are getting the correct answer for the wrong reason. It is possible that we are not capturing what is the most important thing about black holes.

Astrophysicists don't know how AGN feedback works It is important to us. Di Matteo said that it's escaping us 888-609- 888-609- 888-609- 888-609- 888-609- We don't understand feedback very well.

The centers of active galaxies have a bright glow because of the radiation that is emitted. There are strong magnetic fields that cause matter to fly out of the accretion disk. The mechanism by which black holes are thought to launch jets, called the Blandford-Znajek process, was identified in the 1970s. The winds from the accretion disk are spherical and tend to interact with the galaxy more than the narrow jets. The billion-dollar question is how the energy is connected to the gas.

A thin beam extends in opposite directions from a bright point. The ends of the beam fan out into a pair of giant blobs.

There are huge blobs visible in radio waves from the black hole in the center of the Cygnus A.

The black holes in state-of-the-art simulations end up smaller than the real black holes in some systems. To switch off star formation and create red-and-dead galaxies, the simulations need black holes to choke off the inward flow of matter so that the black holes don't grow anymore. The feedback in the simulations is too aggressive.

Simulations predict that a galaxy of its size should have a black hole between three and 10 times larger than Sagittarius A*.

Researchers hope to get a better idea of how AGN feedback works by taking a closer look at the stars.

Milky Way Ecosystem

Researchers with the eROSITA X-ray telescope spotted a pair of bubbles stretching tens of thousands of light-years above and below the Milky Way. The bubbles of X-rays looked like bubbles of gamma rays that were detected a decade ago.

There were still two theories being debated. They were thought to be a relic of a jet that flew millions of years ago. The bubbles were thought to be generated by stars exploding near the center.

An image shows a side view of the Milky Way galaxy with two hourglass-shape structures emerging from it, one bigger than the other.

There are giant bubbles of X-rays and gamma rays in the sky that are thought to be related to a jet that came from the central black hole.

She started jumping up and down when she saw the eROSITA X-ray bubbles. If the same AGN jet were used to generate the X-rays, they could have the same origin. The X-rays would come from the stars, not the jet. She and her co-authors built a computer model. The results, published in Nature Astrophysics this past spring, reproduce the shape of the observed bubbles and a bright shock front, but predict that they formed over the course of 2.6 million years.

Researchers used to think that AGN feedback was unimportant in run-of-the-mill disk galaxies, but the finding shows that is not the case. The picture that is emerging is similar to that of an ecosystems, where AGN and stellar feedback are intertwined with the hot gas that surrounds the universe. There are different effects and flow patterns in different types of galaxies.

The interplay of these processes could be revealed in a case study. Europe's Gaia space telescope has mapped the precise positions and movements of millions of the Milky Way's stars. Merger events that shake matter into black holes can cause them to suddenly increase in size. There is a lot of debate about whether or not mergers are important. The data shows that the Milky Way did not undergo a merger at the time of the bubbles forming.

An illustration showing the Milky Way galaxy, along with nearby globular clusters and dwarf galaxies, and streams of stars flowing into it from different directions. (edited)

Accurately measuring the positions and velocities of millions of stars and other objects in and around the Milky Way has allowed scientists to understand the history of the merging of smaller and larger galaxies. There were streams of stars after these mergers.

S. Payne-Wardenaar is associated with K. Malhan.

The black hole could be activated by blobs of gas. It could switch between eating andlching out energy.

A new puzzle is presented by the recent image of Sagittarius A*, which shows its current trickle of infalling matter. Astrophysicists knew that not all of the gas drawn into a galaxy would make it to the black hole. The strength of the winds is not realistic. Narayan doesn't see a big wind when he does simulations. It isn't the kind of wind you need to explain what's happening.

Nested Simulations

There is a huge difference between the scales of stars and black holes and the scales of the whole universe. Researchers pick a scale and include relevant effects at it. Big and small effects are present in the universe.

Narayan said that the black hole is small compared to the big galaxy. The regimes don't know how to connect with the other guy.

Narayan, Natarajan and colleagues are launching a project that will use nested simulations to build a model of how gas flows through the Milky Way. The information from the black hole can be used to tell the galaxy what to do. There is a loop that goes around and around.

The simulations will clarify the flow pattern of the diffuse gas. Further observations of the circumgalactic medium will be helpful. That is a critical part of the entire system. How do you get the gas to go to the black hole?

The new scheme requires all inputs and outputs to be consistent. Narayan said that the simulation will determine how much gas should reach the black hole. Why didn't it consume all the gas? Why was it so difficult to get gas? The group wants to take pictures of the galaxies during different stages of their evolution.

There is still a lot of uncertainty about this. People are starting to think about the overlap of scenarios. I don't have a good answer, but I hope I will in a few years.

The scientific advisory board has a member named Priya Natarajan.