The centers of our Universe’s myriad galaxies rage with brilliant, roiling fires that hide, within their blinding glare, the darkest of hearts. These hearts of darkness are supermassive black holes, and they wait in sinister secret for their dinner–screaming, shredded stars; doomed, wandering clouds of gas; and anything else that is unfortunate enough to travel too close to where these cosmic beasts lurk–lost as they are in the enveloping brilliance of a surrounding swirling, whirling accretion disk of incandescent gas. Many mysteries surround these strange beasts, inhabiting the Universe’s exotic zoo populated by some undeniably bizarre entities. In January 2018, a team of scientists proposed a new theory that may have solved one of them–the puzzling origins of molecules, dancing within destructive cosmic outflows, that blow around in the raging winds powered by these supermassive beasts. The existence of large numbers of these molecules has puzzled astronomers ever since they were first discovered more than a decade ago–the question is how could anything survive the extreme heat of these energetic outflows?
In 1916, Karl Schwarzschild derived the first modern solution of the Theory of General Relativity that could describe a black hole. But its definition as a region of space, from which nothing could ever return, was not truly understood for another forty years. For decades, black holes were considered to be a mere mathematical quirk, and it was not until the 1960s that theoretical studies revealed that black holes truly are a generic prediction of General Relativity.
Molecules trace out for astronomers the most frigid regions of space. However, the enormous black holes inhabiting the hearts of galaxies are far from cold, and are the most energetic phenomena in the Cosmos. Indeed, finding these molecules in black hole winds is a little like detecting ice in a camp fire. The new theory, proposed by researchers in Northwestern University’s Center for Interdisciplinary Research and Exploration in Astrophysics (CIERA) in Evanston, Illinois, now offers a solution to this mystery. The theory predicts that these molecules are not survivors of these searing-hot and raging winds at all, but are instead newborn molecules that have formed in these fierce winds, and now display some very unique attributes. These unique properties enable the newborn molecules to adapt and thrive in the extremely hostile environment of the supermassive beast’s raging, roaring, and searing-hot winds.
A paper describing this new theory, published in the March 1, 2018 issue of the Monthly Notices of the Royal Astronomical Society (MNRAS) in London, is the work of Lindheimer post-doctoral fellow, Dr. Alexander Richings. Dr. Richings is responsible for developing the computer code that, for the first time, modeled the detailed chemical processes that occur in interstellar gas that is accelerated by the radiation being emitted during the growth of supermassive black holes. Dr. Claude-Andre Faucher-Giguere, who is a researcher studying galaxy formation and evolution as an assistant professor in Northwestern’s Weinberg College of Arts and Sciences, is a study co-author.
“When a black hole wind sweeps up gas from its host galaxy, the gas is heated to high temperatures, which destroy any existing molecules. By modeling the molecular chemistry in computer simulations of black hole winds, we found that this swept-up gas can subsequently cool and form new molecules,” Dr. Richings explained in a January 30, 2018 Northwestern University Press Release.
Abandon Hope All Ye Who Enter Here
As astronomers look deeper and deeper into Space, they are also staring further and further back in Time. There is no way to locate an object in Space, without also locating it in Time. Hence, the term Spacetime. The more distant a luminous object is in Space, the longer it has taken its streaming light to at last reach telescopes on Earth. No known signal in the Universe can travel faster than light in a vacuum, and the light that travels out from very remote objects in the distant Universe can travel to us no faster than this universal speed limit will permit.
In astronomy, Time and Distance, as well as the wavelength of light–at which a remote object is being observed–are all inextricably linked to one another. Light travels at a finite speed, and as a result takes a finite amount of time to reach us. This means that remote objects are observed the way they were in the distant past, and they look exactly the same as they did very long ago–when they first sent their light streaming out into the Cosmos. Astronomers use what is called the redshift (z) to determine how ancient and how far away an incandescent celestial object is. The measurable quantity of 1 + z is the factor by which the Universe has expanded–between that ancient era when a distant object first sent its light out into the space between galaxies, and the present time, when it is finally being observed. It is also the factor by which the wavelength of light, currently wandering towards us, has been stretched by the expansion of Spacetime. The redshift is the shift of a shining object’s spectrum towards increasingly longer and longer electromagnetic wavelengths, as it speeds away from us–or, towards the red end of the electromagnetic spectrum.
The first black holes to form in the Cosmos were both creators and destroyers. These primeval black holes were gluttons, readily devouring anything unlucky enough to travel too close to where they lay hidden. However, the good news is that these black holes formed jets of high-energy particles and radiation as a result of their messy table manners. The jets produced by a black hole can be millions of light-years in length, and many astronomers propose that they are the trigger that gives rise to successive generations of sparkling new baby stars. This means that the first generation of black holes were the seeds of what would eventually grow into the galaxies that host them. These very ancient black holes were essential to galactic evolution–and they still are. In the long run, these primeval black holes can be considered responsible for the birth of our Sun, our planet, and our very lives.
Supermassive black holes and their surrounding accretion disks can be, at least, as vast as our entire Solar System. These gravitational beasts are characterized by their enormous weight, insatiable appetites, and sloppy eating habits–attempting to swallow more than they can chew. When their outside sources of energy ran out, the brilliant quasars that inhabited the ancient Cosmos switched off. It is generally thought that most galaxies experienced a quasar phase in the primordial Cosmos, and that they currently host a relic of their flamming youth in their secretive hearts, in the form of a mostly dormant supermassive black hole. The supermassive black holes that populate the Universe today display only a shadow of their former youthful greed.
Our own Milky Way Galaxy hosts its own resident, dormant dark-hearted beast. As supermassive black holes go, our Galaxy’s central monster is a small one. Our Milky Way’s heart of darkness is “only” millions of solar-masses–and not the billions of solar-masses displayed by many others of its bizarre kind. Long ago, our Galaxy’s elderly central black hole sent its brilliant light out into intergalactic space as an active, hot, and glaring young quasar. But it is a peaceful old celestial tiger now, except when it occasionally wakes up from its nap to enjoy an infalling buffet of shredded stars, clouds of gas, and other unlucky chunks of doomed material. At this point, our Galaxy’s dark heart goes on a feeding frenzy, greedily swallowing a large helping of celestial wreckage that traveled too close to its waiting maw. Our Milky Way’s supermassive black hole is named Sagittarius A*, or Sgr A*, for short (pronounced Saj-a-star), except when it awakens from its slumber to feast on its tragic prey with the insatiable greed of its youth–when it was a flaming quasar dazzling the ancient Universe.
In the 18th century, John Michell and Pierre-Simon Laplace made the first prediction that the Cosmos could play host to gravitational monstrosities like black holes. Albert Einstein’s Theory of General Relativity (1915) went on to predict the existence of weird entities possessing such deep gravitational wells that nothing, nothing, nothing at all–not even light–could escape from their gravitational clutches once they were captured. However, the concept of the real existence of such monstrosities seemed so outrageous at the time that even Einstein rejected the concept–even though his own calculations were correct when they showed otherwise.
Particles Born In A Black Hole’s Hostile Winds
The new theory, proposed by Northwestern University scientists, answers certain nagging questions raised by earlier observations conducted by researchers, using several cutting-edge astronomical observatories. These observatories include the Herschel Space Observatory and the Atacama Large Millimeter Array (ALMA), a powerful radio telescope located in Chile.
In 2015, astronomers confirmed that energetic outflows from supermassive black holes, exist in the secretive hearts of most galaxies. These outflows rampage through their galactic hosts, killing literally everything that is unlucky enough to be in their way–while also emitting the food (molecules) that fuel the birth of baby stars. Indeed, these powerful winds are so furious that they are thought to be the trigger behind the formation of “red and dead” elliptical (football-shaped) galaxies, in which no new sparkling baby stars can be born.
Finally, in 2017, astronomers observed swiftly moving stars forming in these ferocious winds–a phenomenon they once thought to be impossible because of the extreme environment of black hole-powered outflows.
New baby stars are born from molecular gas, so Dr. Richings and Dr. Faucher-Giguere’s new theory of molecular formation helps to solve the mystery of new stars forming in winds. It also strengthens earlier predictions that black hole winds destroy molecules when they first crash into one another, but it also predicts that new molecules–including hydrogen, carbon monoxide, and water–can form in the winds as well.
“This is the first time that the molecule formation process has been simulated in full detail, and in our view, it is a very compelling explanation for the observation that molecules are ubiquitous in supermassive black hole winds, which has been one of the major outstanding problems in the field,” Dr. Faucher-Giguere commented in the January 30, 2018 Northwestern University Press Release.
Dr. Richings and Dr. Faucher-Giguere predict that the new molecules formed in the winds are warmer and brighter in infrared radiation compared to pre-existing molecules. That theory will finally be tested when NASA launches the James Webb Space Telescope in the spring of 2019. If this theory is validated, the telescope will be able to map black hole outflows in detail using infrared radiation.