UNC-Chapel Hill physics professor Laura Mersini-Houghton has proven mathematically that black holes don't exist. (Source: unc.edu)
That’s the conclusion reached by one researcher from the University of North Carolina: black holes can’t exist in our Universe — not mathematically, anyway.
“I’m still not over the shock,” said Laura Mersini-Houghton, associate physics professor at UNC-Chapel Hill. “We’ve been studying this problem for a more than 50 years and this solution gives us a lot to think about.”
In a news article spotlighted by UNC the scenario suggested by Mersini-Houghton is briefly explained. Basically, when a massive star reaches the end of its life and collapses under its own gravity after blasting its outer layers into space — which is commonly thought to result in an ultra-dense point called a singularity surrounded by a light- and energy-trapping event horizon — it undergoes a period of intense outgoing radiation (the sort of which was famously deduced by Stephen Hawking.) This release of radiation is enough, Mersini-Houghton has calculated, to cause the collapsing star to lose too much mass to allow a singularity to form. No singularity means no event horizon… and no black hole.
Artist’s conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
So what does happen to massive stars when they die? Rather than falling ever inwards to create an infinitely dense point hidden behind a space-time “firewall” — something that, while fascinating to ponder and a staple of science fiction, has admittedly been notoriously tricky for scientists to reconcile with known physics — Mersini-Houghton suggests that they just “probably blow up.” (Source)
According to the UNC article Mersini-Houghton’s research “not only forces scientists to reimagine the fabric of space-time, but also rethink the origins of the universe.”
Hm.
The submitted papers on this research are publicly available on arXiv.org and can be found here and here.
Don’t believe it? I’m not surprised. I’m certainly no physicist but I do expect that there will be many scientists (and layfolk) who’ll have their own take on Mersini-Houghton’s findings (*ahem* Brian Koberlein*) especially considering 1. the popularity of black holes in astronomical culture, and 2. the many — scratch that; the countless — observations that have been made on quite black hole-ish objects found throughout the Universe.
So what do you think? Have black holes just been voted off the cosmic island? Or are the holes more likely in the research? Share your thoughts in the comments!
Want to hear more from Mersini-Houghton herself? Here’s a link to a video explaining her view of why event horizons and singularities might simply be a myth.
Black holes are a spot in the universe where you won’t see the sun shine in, to paraphrase that 1960s rock-musical Hair. But speaking of “hair”, a group of scientists says these singularities may have matter (sometimes referred to as “hair”) that could affect how they appear.
This is a tangled concept to figure out (so to speak), so let’s unpack what the new study in Physical Review Letters means.
When black hole understanding was still in its infancy in the scientific literature, physicist John Wheeler wrote a phrase that is now famous among scientists in that field: “Black holes have no hair.” His phrase referred to how black holes are defined, which he believed came down to only two factors: their mass, and their angular momentum, or the rotation velocity of the hole. (Some sources also say electric charge was included as a third factor.)
Say you have a black hole that was created out of a huge star that imploded. Even though the star itself had distinctive properties, this theory says they would vanish in a black hole. So to take that to a generality, Wheeler’s phrase said all black holes are essentially the same.
Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)
This understanding of black holes dates back to 1963, arising back to a “clean” black hole model first published by Roy Kerr. The new study agrees that Kerr’s work from 50 years ago works with general relativity, a theory from Einstein that (in very simple terms) says the laws of nature are consistent throughout the universe. (More at this past Universe Today article.) As the theory pertains to black holes, strong sources of gravity bend space and time.
Kerr’s theory, however, does not agree with extensions of Einstein’s work, the scientists said. These extensions are known as scalar-tensor theories and there are several variations on this topic. The physics deals with the interactions between two different types of fields, scalar and tensor. Scalar fields, according to this Massachusetts Institute of Technology paper, assign values for every point of space observed. (Think a temperature map of Mars). Tensor fields measure these variables with relation to each other.
This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Credit: ESO/M. Kornmesser
The science team included Thomas Sotiriou, a physicist at the International School for Advanced Studies in Italy.
His team, Sotiriou said in a statement, “focused on the matter that normally surrounds realistic black holes, those observed by astrophysicists. This matter forces the pure and simple black hole hypothesized by Kerr to develop a new ‘charge’ (the hair, as we call it) which anchors it to the surrounding matter, and probably to the entire universe.
“According to our calculations,” he added, “the growth of the black hole’s hair is accompanied by the emission of distinctive gravitational waves.”
Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
Ever since scientists first discovered the existence of black holes in our universe, we have all wondered: what could possibly exist beyond the veil of that terrible void? In addition, ever since the theory of General Relativity was first proposed, scientists have been forced to wonder, what could have existed before the birth of the Universe – i.e. before the Big Bang?
Interestingly enough, these two questions have come to be resolved (after a fashion) with the theoretical existence of something known as a Gravitational Singularity – a point in space-time where the laws of physics as we know them break down. And while there remain challenges and unresolved issues about this theory, many scientists believe that beneath veil of an event horizon, and at the beginning of the Universe, this was what existed.
Definition:
In scientific terms, a gravitational singularity (or space-time singularity) is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. In other words, it is a point in which all physical laws are indistinguishable from one another, where space and time are no longer interrelated realities, but merge indistinguishably and cease to have any independent meaning.
This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. Credit: ESA/Hubble, ESO, M. Kornmesse
Origin of Theory:
Singularities were first predicated as a result of Einstein’s Theory of General Relativity, which resulted in the theoretical existence of black holes. In essence, the theory predicted that any star reaching beyond a certain point in its mass (aka. the Schwarzschild Radius) would exert a gravitational force so intense that it would collapse.
At this point, nothing would be capable of escaping its surface, including light. This is due to the fact the gravitational force would exceed the speed of light in vacuum – 299,792,458 meters per second (1,079,252,848.8 km/h; 670,616,629 mph).
This phenomena is known as the Chandrasekhar Limit, named after the Indian astrophysicist Subrahmanyan Chandrasekhar, who proposed it in 1930. At present, the accepted value of this limit is believed to be 1.39 Solar Masses (i.e. 1.39 times the mass of our Sun), which works out to a whopping 2.765 x 1030 kg (or 2,765 trillion trillion metric tons).
Another aspect of modern General Relativity is that at the time of the Big Bang (i.e. the initial state of the Universe) was a singularity. Roger Penrose and Stephen Hawking both developed theories that attempted to answer how gravitation could produce singularities, which eventually merged together to be known as the Penrose–Hawking Singularity Theorems.
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
According to the Penrose Singularity Theorem, which he proposed in 1965, a time-like singularity will occur within a black hole whenever matter reaches certain energy conditions. At this point, the curvature of space-time within the black hole becomes infinite, thus turning it into a trapped surface where time ceases to function.
The Hawking Singularity Theorem added to this by stating that a space-like singularity can occur when matter is forcibly compressed to a point, causing the rules that govern matter to break down. Hawking traced this back in time to the Big Bang, which he claimed was a point of infinite density. However, Hawking later revised this to claim that general relativity breaks down at times prior to the Big Bang, and hence no singularity could be predicted by it.
Some more recent proposals also suggest that the Universe did not begin as a singularity. These includes theories like Loop Quantum Gravity, which attempts to unify the laws of quantum physics with gravity. This theory states that, due to quantum gravity effects, there is a minimum distance beyond which gravity no longer continues to increase, or that interpenetrating particle waves mask gravitational effects that would be felt at a distance.
Types of Singularities:
The two most important types of space-time singularities are known as Curvature Singularities and Conical Singularities. Singularities can also be divided according to whether they are covered by an event horizon or not. In the case of the former, you have the Curvature and Conical; whereas in the latter, you have what are known as Naked Singularities.
A Curvature Singularity is best exemplified by a black hole. At the center of a black hole, space-time becomes a one-dimensional point which contains a huge mass. As a result, gravity become infinite and space-time curves infinitely, and the laws of physics as we know them cease to function.
Conical singularities occur when there is a point where the limit of every general covariance quantity is finite. In this case, space-time looks like a cone around this point, where the singularity is located at the tip of the cone. An example of such a conical singularity is a cosmic string, a type of hypothetical one-dimensional point that is believed to have formed during the early Universe.
And, as mentioned, there is the Naked Singularity, a type of singularity which is not hidden behind an event horizon. These were first discovered in 1991 by Shapiro and Teukolsky using computer simulations of a rotating plane of dust that indicated that General Relativity might allow for “naked” singularities.
In this case, what actually transpires within a black hole (i.e. its singularity) would be visible. Such a singularity would theoretically be what existed prior to the Big Bang. The key word here is theoretical, as it remains a mystery what these objects would look like.
For the moment, singularities and what actually lies beneath the veil of a black hole remains a mystery. As time goes on, it is hoped that astronomers will be able to study black holes in greater detail. It is also hoped that in the coming decades, scientists will find a way to merge the principles of quantum mechanics with gravity, and that this will shed further light on how this mysterious force operates.
