Bewitching, bewildering, and bizarre, supermassive black holes weighing millions to billions of times more than our Sun, lurk secretly, hungrily in the mysterious hearts of probably every large galaxy in the Cosmos–including our own. Our Milky Way Galaxy’s heart of darkness is relatively light-weight compared to others of its kind–weighing “only” millions, Black Travel as opposed to billions, of solar masses. In November 2014, an international team of astronomers analyzing decades of observations derived from numerous facilities–including the W.M. Keck Observatory poised atop Mauna Kea, the Pan-STARRS-1 telescope on Haleakala and NASA’s Swift satellite–has discovered what seems to be a supermassive black hole that has been unceremoniously booted from the center of its home galaxy. However, alternatively, this exotic object may be the relic of a massive star that suffered through a record period of eruptions before blasting itself to smithereens in a supernova conflagration. The study is published in the November 21, 2014 edition of the Monthly Notices of the Royal Astronomical Society.
The team of astronomers was led by Dr. Michael Koss, who was a postdoctoral fellow at the Institute for Astronomy (IfA) at the University of Hawaii at Manoa during most of the time the study was conducted. The source, dubbed SDSS1133, is both exotic and bewildering.
“With the data we have in hand, we can’t yet distinguish between these two scenarios. One exciting discovery made with NASA’s Swift is that the brightness of SDSS1133 hasn’t changed in ultraviolet light for a decade, which is not something typically seen in a supernova remnant,” Dr. Koss explained in a November 2014 IfA Press Release. Dr. Koss is now an astronomer at ETH Zurich, the Swiss Federal Institute of Technology. This trend, if maintained, would strengthen the black hole interpretation.
This bewitching object of mystery is part of the dwarf galaxy Markarian 177, which is situated in the bowl of the Big Dipper, a famous star pattern within the constellation Ursa Major. Although supermassive black holes usually lurk hungrily in the centers of their galactic hosts, SDSS1133 is located at least 2,600 light-years from its galaxy’s heart. The team was able to spot it in astronomical surveys that date back over 60 years.
In June 2013, the astronomers obtained high-resolution near-infrared images of the strange object using the 10-meter Keck II telescope at Keck Observatory. “When we analyzed the Keck data, we found the emitting region of SDSS1133 is less than 40 light-years across, and that the center of Markarian 177 shows evidence of intense star formation and other features indicating a recent disturbance that matched what we expected for a recoiling black hole,” explained Chao-Ling in a November 19, 2014 Keck Observatory Press Release. Chao-Ling is a University of Hawaii at Manoa graduate student performing the analysis derived from the Keck Observatory imaging the study.
Anything But Empty Space
In the 18th century, John Michell and Pierre-Simon Laplace predicted the existence of black holes, and Albert Einstein’s General Theory Of Relativity (1915) famously predicted the existence of weird objects that possessed such deep gravitational wells that anything unlucky enough to travel in too close to their gravitational snatching claws would be devoured. However, the concept of black holes was considered to be a mere mathematical oddity for decades, and even Einstein for a time doubted their real existence in Nature–even though his own calculations indicated otherwise. In fact, it was not until the 1960s that theoretical calculations demonstrated that these massive beasts are a generic prediction of General Relativity. Einstein’s equations demonstrated that when a massive star has finished burning its necessary supply of nuclear fuel and “dies,” it leave behind a relic small, dense core. If the core weighs more than about three times solar mass, the force of gravity overwhelms all other forces and creates a black hole.
Despite their name, black holes are anything but empty space. In fact, a black hole is an enormous amount of matter squeezed into a small area. Imagine a very heavy star that weighs ten solar-masses packed into a sphere the size of Chicago. The weird result is a gravitational field so powerful that absolutely nothing–not even light–can escape from its strong gravitational embrace.
Supermassive black holes lurk secretively and hungrily in the hearts of perhaps every large galaxy in the Universe, and they gain their impressive weight by eating their surroundings. They are also sloppy, and try to swallow more than they can, hurling out into space a small amount of what was once a wandering gas cloud or a passing star–or whatever else had the misfortune to travel in too close to their powerful gravity.
Smaller black holes of stellar mass are born when a very heavy star collapses in the rage of a supernova blast that completely destroys the star. The brilliant supernova conflagration marks the end of the sparkling, active “life” of an ordinary main-sequence (hydrogen burning) normal star.
After a black hole has formed from the ruins of a massive star, it can continue to put on additional weight by devouring anything that it can snatch up with its ferocious, powerful gravity. Many scientists theorize that by consuming stars, gas, and by merging with other black holes, the most massive of all gravitational beasts in the Cosmos–supermassive black holes–are born.
Supermassive black holes are mysterious and weird denizens of the Cosmic Zoo. Stars and gas whirl into the maelstrom that surrounds these hungry beasts, and this tumbling banquet creates a huge accretion disk. This doomed feast becomes progressively hotter and hotter and spews out an enormous amount of radiation–particularly when it approaches the “point of no return” termed the event horizon. The event horizon is located at the innermost region of the accretion disk, and it keeps the interior of a black hole of any size effectively cut off from everything that exists outside of it. However, it is not a material boundary. Travelers unlucky enough to to tumble into the gravitational snare of a black hole would not experience anything especially bizarre as they entered this point of no return. However, once having done so, they would never again be able to communicate with anyone on the outside. Neither would they ever be able to return to the outside. An observer outside of the event horizon would only be able to receive messages dispatched by the doomed travelers before they crossed this point of no return.
Astronomers cannot observe black holes directly with telescopes designed to spot X-rays, visible light, or other forms of electromagnetic radiation. But it is possible for them to infer their existence by watching how they influence matter that is close to them. For example, if a stellar mass black hole travels through a cloud of interstellar matter it will sip the matter inward in a process termed accretion. Similarly, if a normal star wanders in too close to a voracious black hole, the beast can literally tear the star to shreds as it sucks it inward. As the doomed material–that was once a normal star–heats up and accelerates, it tosses out X-rays that radiate into space. Black holes can exert a very powerful and dramatic influence on their environment–creating gamma-ray bursts, ravenously feasting on tragic nearby stars, and causing the birth of brilliant new baby stars in some regions–while preventing star-birth in others.