Supermassive black holes are mysterious entities that lurk hungrily in the hearts of probably every large galaxy in the observable Universe, where they hide in sinister, voracious secret, waiting for their dinner to come swirling down to their waiting maws. These in-falling buffets may consist of destroyed stars, clouds of disrupted gas, or any other unfortunate celestial object that has been wrecked by the big black hole’s gravitational snatching claws. Once a doomed object has passed the fatal point of no return, referred to as the event horizon, it can never return from the lair of this gravitational beast, and it is lost to the rest of the Universe forevermore. But, despite their bad reputation for being mercilessly destructive, one supermassive black hole that haunts the heart of a galaxy far, far away, has shown itself to have a nurturing character. This object has a maternal heart, and is aiding in the birth of bright new baby stars that are more than one million light-years away. One light-year is equal to 6 trillion miles.
The discovery of this motherly heart of darkness, that has managed to spark the births of stars over a mind-boggling distance–as well as across multiple galaxies–was made by astronomers using NASA’s Chandra X-ray Observatory and other telescopes. If confirmed, the black hole would represent the widest reach ever observed for such an object behaving as a nurturing stellar mother, kick-starting star-birth. This maternal heart of darkness has actually enhanced star formation.
“This is the first time we’ve seen a single black hole boost star birth in more than one galaxy at a time. It’s amazing to think one galaxy’s black hole can have a say in what happens in other galaxies millions of trillions of miles away,” commented Dr. Roberto Gilli in a November 26, 2019 Chandra Observatory Press Release. Dr. Gilli is of the National Institute of Astrophysics (INAF) in Bologna, Italy, and is lead author of the study describing the discovery.
Quoth the Raven, “Nevermore”
Supermassive black holes are greedy entities that weigh-in at millions to billions of times more than the mass of our Sun. Our own Milky Way Galaxy plays host to just such a gravitational beast, that resides in its secretive heart. Our resident supermassive black hole is named Sagittarius A*, and as supermassive beasts go, it is of relatively low mass. Sagittarius A* (pronounced saj-a-star) weighs a “mere” millions–in contrast to billions–of solar-masses. Our Milky Way’s dark heart is quiet now. It is an elderly beast, and it awakens only occasionally to feast on an unfortunate celestial object that has wandered too close to where it waits. Even though it is mostly dormant, when both Sagittarius A* and the Universe were young, it dined greedily, and glared brightly, as a quasar. Quasars are the brilliantly glaring accretion disks encircling active supermassive black holes haunting the centers of galaxies.
Despite their misleading name, black holes are not just empty space. Indeed, they come in more than one size. Besides the supermassive variety, there are black holes of stellar mass that form when an extremely massive star runs out of its necessary supply of nuclear-fusing fuel and violently explodes as a core-collapse (Type II) supernova. The gravitational collapse of an especially massive star heralds its natural “death”. When a doomed heavy star has no more nuclear-fusing fuel to burn, it has reached the end of the stellar road. Nuclear-fusion within a still-“living” roiling, broiling, brilliant star, creates radiation pressure that tries to push all of the stellar material outward. In the meantime, the star’s own gravity tries to pull everything inward. This creates a delicate balance that keeps a star bouncy. Alas, when a giant, massive star runs out of fuel, and contains a heavy iron-nickel core, it can no longer churn out pressure. Gravity wins in the end. The star’s core collapses and it goes supernova. Where once a star existed, there is a star no more.
Astronomers have also found convincing evidence of the existence of intermediate mass black holes that weigh less than their supermassive kin, but more than their stellar-mass “relatives”. Crush enough mass into a small enough space and a black hole will form every time. Some scientists have proposed that these intermediate mass objects met up with one another and merged in the early Cosmos. For this reason, it has been suggested that they served as the “seeds” that created the supermassive black holes that haunt the mysterious hearts of most, if not all, large galaxies, including our own.
The Milky Way’s resident supermassive black hole is not a lonely gravitational beast. Sagittarius A* has plenty of company. Indeed, theoretical studies indicate that a large population of black holes of stellar mass–possibly a many as 20,000–could be tripping the light fantastic around our own Galaxy’s resident central black hole. A study published in 2018, that was based on data acquired from Chandra, suggests the existence of a treasure trove of stellar mass black holes haunting the core of our Milky Way.
Some current theories propose that supermassive black holes already existed in the ancient Universe. During that very early era, clouds of gas and doomed stars whirled around and then down into the hungry beast’s waiting, greedy, gravitational snatching claws, nevermore to to return from the violently swirling maelstrom encircling this bizarre entity. As the captured, doomed material swirled down to its inevitable demise, it formed a brilliant, violent storm of glaring material around the black hole–its accretion disk (quasar). As this bright and fiery material became hotter and hotter, it hurled out a raging storm of radiation–especially as it traveled ever closer to the event horizon , which is the point of no return.
In the 18th-century, John Michell and Pierre-Simon Laplace proposed the possibility that there could really exist in nature such insults to our Earth-evolved common sense as black holes. In 1915, Albert Einstein, in his General Theory of Relativity, predicted the existence of objects bearing such powerful gravitational fields that anything unfortunate enough to wander too close to their pull would be consumed. Nevertheless, this concept seemed so outrageous at the time that Einstein rejected his own idea–even though his calculations proclaimed otherwise.
In 1916, the physicist Karl Schwarzschild formulated the first modern solution to General Relativity that described a black hole. However, its interpretation as an area of Spacetime, from which absolutely nothing could escape once snared, was not adequately understood until almost half a century later. Until that time, these gravitational beasts were considered to be only mathematical oddities. Finally, in the middle of the 20th century, theoretical physicists were able to demonstrate that these strange children of Mother Nature represent a generic prediction of General Relativity.
A Maternal Black Hole With A Midas Touch
The nurturing supermassive black hole resides in the center of a galaxy about 9.9 billion light-years from Earth. The galaxy is in the company of at least seven neighboring galaxies, according to observations conducted with the European Southern Observatory’s Very Large Telescope (VLT) and the Large Binocular Telescope (LBT).
Using the National Science Foundation’s (NSA’s) Jansky Very Large Array, astronomers had previously discovered radio-wave emission coming from a jet of high-energy particles that is about one million light-years in length. The jet can be tracked back to the nurturing supermassive black hole, which Chandra detected as a powerful source of X-rays. The X-rays are created by hot gas whirling around the supermassive black hole. Dr. Gilli and his colleagues also spotted a diffuse cloud of X-ray emission encircling one end of the radio jet. This X-ray emission is probably coming from an enormous bubble of gas being heated up by the dance being performed by the energetic particles in the radio jet with surrounding matter.
As the searing-hot bubble expanded and invaded the neighboring galaxies, it may have compressed the cool gas in these galactic neighbors. This would have given birth to fiery baby stars. All of the galaxies involved reside at about the same distance–approximately 400,000 light-years–away from the center of the expanding bubble. The scientists calculate that the rate of stellar birth is between two to five times greater than typical galaxies with similar masses and distance from our planet.
“The story of King Midas talks of his magic touch that can turn metal into gold. Here we have a case of a black hole that helped turn gas into stars, and its reach is intergalactic,” commented study co-author Dr. Marco Mignoli in the November 26, 2019 Chandra Press Release. Dr. Mignoli is also of the INAF.
Astronomers have observed many instances where a black hole influences its environment by way of “negative feedback.” This means that they have frequently observed a sinister black hole in the act of hindering the formation of new stars. This may occur when the jets emitted by the black hole send so much energy into the searing-hot gas of a galaxy–or cluster of galaxies–that the gas cannot cool down sufficiently to form a large number of baby stars. Although it may seem to defy common-sense, things have to get cold before a hot baby star can be born.
“Black holes have a well-earned reputation for being powerful and deadly, but not always. This is a prime example that they sometimes defy that stereotype and can be nurturing instead,” commented co-author Alessandro Peca in the Chandra Press Release. Peca, formerly of the INAF, is currently a doctoral student at the University of Miami.
The astronomers used a total of six days of Chandra observing time spread out over a five month period.
“It’s only because of this very deep observation that we saw the hot gas bubble produced by the black hole. By targeting objects similar to this one, we may discover that positive feedback is very common in the formation of groups and clusters of galaxies,” noted co-author Dr. Colin Norman in the Chandra Press Release. Dr. Norman is of the Johns Hopkins University in Baltimore, Maryland.
A paper describing these results has been published in the journal Astronomy and Astrophysics.