1 Million Habitable Planets Could (Theoretically) Orbit a Black Hole.

Here’s How

1 Million Habitable Planets Could (Theoretically) Orbit a Black Hole. Here's How

Huge numbers of potentially habitable planets could theoretically exist in stable orbits around a supermassive black hole, such as the fictional Gargantua from the 2014 film “Interstellar.”

Credit: Paramount Pictures

A black hole could have 1 million planets orbiting near it that are potentially capable of supporting life as we know it, an astrophysicist suggests.

Since there is life virtually everywhere liquid water exists on Earth, astronomers often judge a world as potentially habitable if it orbits within a zone where liquid water could survive on its surface. Our sun’s “habitable zone” hosts just one planet (Earth), but the story could be different for other stars. For example, the TRAPPIST-1 system has three Earth-size planets within its habitable zone.

Sean Raymond, an astrophysicist at the Observatory of Bordeaux in France, researches how planetary systems form and evolve. As part of a column Raymond writes called “Building the Ultimate Solar System,” he set out to see how many planets could orbit a black hole. [The Strangest Black Holes in Space]

“I think we can learn from the extremes … they are basically the boundaries of the box in which we are searching,” Raymond told Space.com. “This system is one extreme — the most packed imaginable. It’s a fun blend of imagination and science.”

There are currently two kinds of black holes that scientists know best, Raymond said. Stellar-mass black holes are equal in mass to a few suns, and form when giant stars die and collapse in on themselves. Supermassive black holes are millions to billions of times the mass of the sun, and are thought to exist in the hearts of most, if not all, large galaxies. (A third class, intermediate-mass black holes, is poorly understood.)

Black holes are extremely compact. A black hole with the mass of the sunwould be about only 3.7 miles (6 kilometers) wide. In comparison, Sagittarius A*, the supermassive black hole thought to lurk at the heart of the Milky Way, has a mass of about 4 million suns and a diameter of about 14.7 million miles (23.6 million km), or a little more than 40 percent the size of Mercury’s orbit around the sun.

Diagram of a hypothetical sun-black hole solar system.
Diagram of a hypothetical sun-black hole solar system.

Credit: Sean Raymond

A common question in physics classes is to imagine what would change if the sun were replaced with a black hole of the same mass, Raymond said. The answer is that nothing would change regarding the planets’ orbits — if the black hole had the same mass as the sun, the orbits would remain the same. (Life on Earth would obviously suffer from the lack of light and heat in such a scenario, Raymond added.)

If the sun had an equal-mass black hole companion orbiting near it — at, say, one-tenth of an astronomical unit (AU) — the orbits of the solar system’s planets would not change much, Raymond noted. (One AU is the Earth-sun distance — about 93 million miles, or 150 million km.)

Still, assuming these planets kept the same distance from the sun as they do now, the gravitational pull of the sun and its black hole partner would lead these worlds to complete their orbits a bit more quickly, with Earth’s year decreasing from 365 days to 258 days, he said.

In the above scenario, the sun and the black hole would complete an orbit with one another every 2.9 days. This means the amount of energy that Earth would receive from the sun would fluctuate between 90 percent and 110 percent of its average as the sun moved farther from or closer to Earth.

“That is like bouncing between New York and Miami and back every 2.9 days,” Raymond noted. [Black Hole Quiz: How Well Do You Know Nature’s Weirdest Creations?]

More than 500 Earth-like planets could circle a million-solar-mass black hole, given some fortuitous star placement, according to astrophysicist Sean Raymond.
More than 500 Earth-like planets could circle a million-solar-mass black hole, given some fortuitous star placement, according to astrophysicist Sean Raymond.

Credit: Sean Raymond

In addition to imagining life around a stellar-mass black hole, Raymond also calculated how many potentially habitable planets might fit around a supermassive black hole 1 million times the mass of the sun. “That’s almost as massive as the one in the center of the Milky Way,” he said. It would only be about the diameter of the sun, he added.

Around the sun, the orbits that planets travel can come only so close together before the effects of their gravitational pulls overwhelm those of the sun, leading to unstable orbits. Raymond noted that about six Earth-mass planets can fit in stable concentric orbits within the sun’s habitable zone.

In contrast, a supermassive black hole’s gravitational pull is extraordinarily strong, enough to easily overwhelm those of planets. If the sun were replaced with a million-solar-mass black hole, 550 Earth-mass planets could fit in stable concentric orbits in the habitable zone, Raymond calculated.

The supermassive black hole’s gravity would pull more strongly on the side of each planet closer to the black hole. This would stretch the habitable-zone planets out, although they would not be close enough to get ripped apart, Raymond said.

One way to create a habitable zone around this supermassive black hole is to place stars between it and the planets. A ring of nine sun-like stars 0.5 AU from a million-sun black hole would make each of the 550 Earth-mass planets in the above scenario potentially habitable, Raymond said.

“It would be pretty interesting to live on a planet in this system,” Raymond noted. “It would take just a few days to complete an orbit around the black hole — about 1.6 days at the inner edge of the habitable zone and 4.6 days at the outer edge.” [10 Exoplanets That Could Host Alien Life]

At the closest approach, or conjunction, between two such planets, the distance between these worlds would be “about twice the Earth-moon distance,” Raymond noted. “At conjunction, each planet’s closest neighbor appears about twice the size of the full moon in the sky.”

In addition, the next-nearest neighbors would be only twice as far away, and so would appear as big as the full moon during conjunction, Raymond said. Four more planets would be at least half the size of the full moon during conjunction, he added. “Conjunctions happen a little less than once per orbit, so every few days there is a gaggle of giant objects passing across the sky,” he said.

The nine suns “would also be a sight to behold,” Raymond said. Each would complete its orbit around the black hole every 3 hours.

“That means that every 20 minutes, one of the suns would pass behind the black hole,” Raymond said. “When a sun passes behind the black hole, the black hole’s gravity bends its light and can act like a lens. It focuses the sun’s light toward the planet. This distorts the shape of the sun into a ring … a pretty sweet light show.”

Furthermore, starlight would be stretched by the black hole’s gravity. “Stars closer to the black hole would appear redder, and those farther from the black hole would appear bluer,” Raymond said.

Given a million-sun black hole with an orbiting ring of nine sun-like stars, 1 million Earth-mass planets could orbit within the habitable zone, in 400 rings of 2,500 planets apiece, astrophysicist Sean Raymond has calculated that.
Given a million-sun black hole with an orbiting ring of nine sun-like stars, 1 million Earth-mass planets could orbit within the habitable zone, in 400 rings of 2,500 planets apiece, astrophysicist Sean Raymond has calculated that.

Credit: Sean Raymond

In the prior scenario, each planet was alone in its orbit around the supermassive black hole. Raymond also modeled what would happen if multiple planets shared an orbit around a million-sun black hole. Previously, Raymond calculated that 42 Earth-mass planets could orbit in a ring 1 AU from the sun.

To have a stable ring of planets, Raymond noted that planets in that ring must all have roughly the same mass. There must also be at least seven planets in such a ring, and they must be evenly spaced along a circular orbit.

Given a million-sun black hole with an orbiting ring of nine sun-like stars, Raymond calculated that a million Earth-mass planets could orbit within the habitable zone in 400 rings, each holding 2,500 planets spaced apart by about the same distance as that between Earth and the moon. In this scenario, planets would again take anywhere from 1.6 to 4.6 days to complete an orbit. [The Strangest Black Holes in the Universe]

Instead of placing nine sun-like stars between the black hole and the planets, Raymond also suggested one could place 36 sun-like stars in a ring 6 AU wide. In this scenario, “each planet is bathed in sunlight from all sides — the planets have no night side,” Raymond said. “It’s like Asimov’s permanent-daytime planet Kalgash.”

“You would never feel alone in these systems — the other planets would loom huge in the sky,” Raymond added. Neighboring planets would be about 10 times closer than the moon is to Earth, meaning they would appear “about 40 times larger in the sky than the full moon,” Raymond said. “That’s about the size of a laptop computer held at arm’s reach, only up in the sky.”

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In this latter scenario, the planets would be much closer to the black hole, each completing an orbit in just about 9 hours. This means they would orbit at extraordinary speeds — about 10 percent of the speed of light. According to Einstein’s theory of special relativity, time would appear to move noticeably more slowly the closer one gets to the speed of light, so “two babies born at the same instant on different rings would age at slightly different rates,” Raymond said. “The baby on the inner ring would age slightly more slowly.”

The differences in speed between the rings would be great enough to likely make it impossible for a spaceship to travel from one ring to another with any current technology, Raymond said. However, each world would share its ring with thousands of others, and the relative speed between neighboring planets would be almost zero. “A space elevator could connect planets,” Raymond said.

If each pair of neighboring planets along a given ring were connected, it would resemble a “Ringworld,” a gigantic alien megastructure in Larry Niven’s science-fiction epic of the same name. “The difference between this setup and the ‘Ringworld’ from Larry Niven’s book is that, in this case, there is no livable surface area in between the planets,” Raymond said.

Where might such million-planet systems come from? “I can imagine super-advanced aliens creating a system like the million-Earth solar system as a cosmic work of art, kind of like the art of skyscrapers or painted icebergs,” Raymond said. “A way to say, ‘Look how fancy we are,’ on the grandest scale.”

“Or maybe aliens would create this kind of system as a zoo,” Raymond said. “They could have a gradient in climates from the hottest to coldest, and stock the planets with all sorts of creatures they collect across the universe. Of course, they’d have to be careful not to put the wrong combinations of space creatures on the same ring of planets, because that wouldn’t end well.”

All in all, “it’s helpful to try to come up with all the possible planetary systems that might be out there,” Raymond said. “Some discoveries could have been anticipated by ‘going there’ and imagining possibilities that are far outside the norm. These systems are a combination of science fiction and ‘going there’ in that sense.”

“The main thing I go for is simply to try to push the limits of what we think is possible,” Raymond concluded.

Follow Charles Q. Choi on Twitter @cqchoi. Follow us @SpacedotcomFacebook and Google+. Original article on Space.com.

A Bone-Marrow Transplant to Treat Schizophrenia?

He Got Schizophrenia. He Got Cancer. And Then He Got Cured.

A bone-marrow transplant treated a patient’s leukemia — and his delusions, too. Some doctors think they know why.

Moises Velasquez-Manoff

By Moises Velasquez-Manoff

Mr. Velasquez-Manoff is a science writer.

CreditCreditJesse Jacobs

The man was 23 when the delusions came on. He became convinced that his thoughts were leaking out of his head and that other people could hear them. When he watched television, he thought the actors were signaling him, trying to communicate. He became irritable and anxious and couldn’t sleep.

Dr. Tsuyoshi Miyaoka, a psychiatrist treating him at the Shimane University School of Medicine in Japan, eventually diagnosed paranoid schizophrenia. He then prescribed a series of antipsychotic drugs. None helped. The man’s symptoms were, in medical parlance, “treatment resistant.”

A year later, the man’s condition worsened. He developed fatigue, fever and shortness of breath, and it turned out he had a cancer of the blood called acute myeloid leukemia. He’d need a bone-marrow transplant to survive. After the procedure came the miracle. The man’s delusions and paranoia almost completely disappeared. His schizophrenia seemingly vanished.

Years later, “he is completely off all medication and shows no psychiatric symptoms,” Dr. Miyaoka told me in an email. Somehow the transplant cured the man’s schizophrenia.

A bone-marrow transplant essentially reboots the immune system. Chemotherapy kills off your old white blood cells, and new ones sprout from the donor’s transplanted blood stem cells. It’s unwise to extrapolate too much from a single case study, and it’s possible it was the drugs the man took as part of the transplant procedure that helped him. But his recovery suggests that his immune system was somehow driving his psychiatric symptoms.

At first glance, the idea seems bizarre — what does the immune system have to do with the brain? — but it jibes with a growing body of literature suggesting that the immune system is involved in psychiatric disorders from depression to bipolar disorder.

The theory has a long, if somewhat overlooked, history. In the late 19th century, physicians noticed that when infections tore through psychiatric wards, the resulting fevers seemed to cause an improvement in some mentally ill and even catatonic patients.

Inspired by these observations, the Austrian physician Julius Wagner-Jauregg developed a method of deliberate infection of psychiatric patients with malaria to induce fever. Some of his patients died from the treatment, but many others recovered. He won a Nobel Prize in 1927.

One much more recent case study relates how a woman’s psychotic symptoms — she had schizoaffective disorder, which combines symptoms of schizophrenia and a mood disorder such as depression — were gone after a severe infection with high fever.

Modern doctors have also observed that people who suffer from certain autoimmune diseases, like lupus, can develop what looks like psychiatric illness. These symptoms probably result from the immune system attacking the central nervous system or from a more generalized inflammation that affects how the brain works.

Indeed, in the past 15 years or so, a new field has emerged called autoimmune neurology. Some two dozen autoimmune diseases of the brain and nervous system have been described. The best known is probably anti-NMDA-receptor encephalitis, made famous by Susannah Cahalan’s memoir “Brain on Fire.” These disorders can resemble bipolar disorder, epilepsy, even dementia — and that’s often how they’re diagnosed initially. But when promptly treated with powerful immune-suppressing therapies, what looks like dementia often reverses. Psychosis evaporates. Epilepsy stops. Patients who just a decade ago might have been institutionalized, or even died, get better and go home.

Admittedly, these diseases are exceedingly rare, but their existencesuggests there could be other immune disorders of the brain and nervous system we don’t know about yet.

Dr. Robert Yolken, a professor of developmental neurovirology at Johns Hopkins, estimates that about a third of schizophrenia patients show some evidence of immune disturbance. “The role of immune activation in serious psychiatric disorders is probably the most interesting new thing to know about these disorders,” he told me.

Studies on the role of genes in schizophrenia also suggest immune involvement, a finding that, for Dr. Yolken, helps to resolve an old puzzle. People with schizophrenia tend not to have many children. So how have the genes that increase the risk of schizophrenia, assuming they exist, persisted in populations over time? One possibility is that we retain genes that might increase the risk of schizophrenia because those genes helped humans fight off pathogens in the past. Some psychiatric illness may be an inadvertent consequence, in part, of having an aggressive immune system.

Which brings us back to Dr. Miyaoka’s patient. There are other possible explanations for his recovery. Dr. Andrew McKeon, a neurologist at the Mayo Clinic in Rochester, Minn., a center of autoimmune neurology, points out that he could have suffered from a condition called paraneoplastic syndrome. That’s when a cancer patient’s immune system attacks a tumor — in this case, the leukemia — but because some molecule in the central nervous system happens to resemble one on the tumor, the immune system also attacks the brain, causing psychiatric or neurological problems. This condition was important historically because it pushed researchers to consider the immune system as a cause of neurological and psychiatric symptoms. Eventually they discovered that the immune system alone, unprompted by malignancy, could cause psychiatric symptoms.

Another case study from the Netherlands highlights this still-mysterious relationship. In this study, on which Dr. Yolken is a co-author, a man with leukemia received a bone-marrow transplant from a schizophrenic brother. He beat the cancer but developed schizophrenia. Once he had the same immune system, he developed similar psychiatric symptoms.


The bigger question is this: If so many syndromes can produce schizophrenia-like symptoms, should we examine more closely the entity we call schizophrenia?

Some psychiatrists long ago posited that many “schizophrenias” existed — different paths that led to what looked like one disorder. Perhaps one of those paths is autoinflammatory or autoimmune.

If this idea pans out, what can we do about it? Bone marrow transplant is an extreme and risky intervention, and even if the theoretical basis were completely sound — which it’s not yet — it’s unlikely to become a widespread treatment for psychiatric disorders. Dr. Yolken says that for now, doctors treating leukemia patients who also have psychiatric illnesses should monitor their psychiatric progress after transplantation, so that we can learn more.

And there may be other, softer interventions. A decade ago, Dr. Miyaoka accidentally discovered one. He treated two schizophrenia patients who were both institutionalized, and practically catatonic, with minocycline, an old antibiotic usually used for acne. Both completely normalized on the antibiotic. When Dr. Miyaoka stopped it, their psychosis returned. So he prescribed the patients a low dose on a continuing basis and discharged them.

Minocycline has since been studied by others. Larger trials suggest that it’s an effective add-on treatment for schizophrenia. Some have argued that it works because it tamps down inflammation in the brain. But it’s also possible that it affects the microbiome — the community of microbes in the human body — and thus changes how the immune system works.

Dr. Yolken and colleagues recently explored this idea with a different tool: probiotics, microbes thought to improve immune function. He focused on patients with mania, which has a relatively clear immunological signal. During manic episodes, many patients have elevated levels of cytokines, molecules secreted by immune cells. He had 33 mania patients who’d previously been hospitalized take a probiotic prophylactically. Over 24 weeks, patients who took the probiotic (along with their usual medications) were 75 percent less likely to be admitted to the hospital for manic attacks compared with patients who didn’t.

The study is preliminary, but it suggests that targeting immune function may improve mental health outcomes and that tinkering with the microbiome might be a practical, cost-effective way to do this.

Watershed moments occasionally come along in medical history when previously intractable or even deadly conditions suddenly become treatable or preventable. They are sometimes accompanied by a shift in how scientists understand the disorders in question.

We now seem to have reached such a threshold with certain rare autoimmune diseases of the brain. Not long ago, they could be a death sentence or warrant institutionalization. Now, with aggressive treatment directed at the immune system, patients can recover. Does this group encompass a larger chunk of psychiatric disorders? No one knows the answer yet, but it’s an exciting time to watch the question play out.

Moises Velasquez-Manoff, the author of “An Epidemic of Absence: A New Way of Understanding Allergies and Autoimmune Diseases” and an editor at Bay Nature magazine, is a contributing opinion writer.

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