Are black holes a figment of our imagination, or are they real?
In 1972 I bought my first book on black holes. It contained a lot of high level math so I didn’t understand everything in it, but one thing was clear – these monsters were the new wonder of the universe and there was a lot we didn’t understand about them. (There was even a chapter by a relative unknown at the time: Stephen Hawking!)
Since then, there has been a lot of research and thinking on black holes but they remain one of the great wonders of the universe.
The standard understanding is that black holes form when a star 5 times the size of our Sun or greater blows off its outer layers in a supernova and the remaining mass contracts from the compact gravity. So much matter is concentrated into such a small area that it creates a “singularity,” which creates around it an “event horizon,” such that anything that is attracted into the event horizon cannot escape, including light – which is why it’s called a “black” hole.
At first, black holes were mostly theoretical. Eventually, astronomers began spotting evidence of black holes using x-ray sensitive telescopes. Black hole candidates have been spotted in our own galaxy (such as Cygnus X-1), and now it is suspected that supermassive black holes – in sizes of millions of our own Sun – exist at the center of every galaxy. There is even evidence of one at the center of our own Milky Way, including evidence by tracking the movement of stars at the galactic center.
But more recently, theoretical physicists are questioning if black holes actually do exist.
Laura Mersini-Houghton, a physics professor at UNC-Chapel Hill in the College of Arts and Sciences, has shown mathematically that as a star sheds its mass it no longer has the density to become a black hole. According to her calculations, a singularity can’t form and neither can an event horizon – the result: no black hole.
Astrophysicists at the University of California, Santa Cruz (UCSC) and the University of Minnesota ran a number of supercomputer simulations of primordial (first generation) stars whose masses were 55,000 and 56,000 times the mass of our Sun and found that they died a very unusual death. They went supernova but burned up completely, leaving behind no black hole!
Math and computer simulations are no guarantee of reality, of course, but they are suggestive and deserve further investigation. So, do black holes really exist and do they always develop when a star dies?
Back in the spring, astronomers had an excellent opportunity to test the viability of that supermassive black hole at the center of our Milky Way. A huge plume of gas roughly three times the mass of Earth was about to pass right through the center of our galaxy and astronomers were going to get to watch that black hole shred it to pieces. They began watching it through various light filters, including the x-ray, from 2004 until the present. If there was no black hole, the gas would pass through with little effect. But every evidence from 2004 through July of 2014 showed the gas accelerating and elongating and shredding, just as it should if a black hole was there.
Are there other explanations? Possibly. Perhaps there is something in the mass at the center of the galaxy, although the mass in the galaxy doesn’t affect the structure of the galaxy as once thought.
Update: Astronomers studying the “plume of gas” now think it wasn’t a plume of gas at all but more likely “a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust—its movements choreographed by the black hole’s powerful gravitational field.” (Phys.org)
The evidence presented here may beg a different question. Not “do black holes exist,” but more, under what conditions might black holes exist and when are they not likely to exist? Are they the beasts we think they are, or are they sometimes more figments of our imaginations and our mathematics? More study will ferret out the answers.
The universe is an amazing place. The more we explore it the more amazing it becomes.