A controversial alternative to black hole theory has been bolstered by observations of an object in the distant universe, researchers say. If their interpretation is correct, it might mean black holes do not exist and are in fact bizarre and compact balls of plasma called MECOs.
Rudolph Schild of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US, led a team that observed a quasar situated 9 billion light years from Earth. A quasar is a very bright, compact object, whose radiation is usually thought to be generated by a giant black hole devouring its surrounding matter.
A rare cosmological coincidence allowed Schild and his colleagues to probe the structure of the quasar in much finer detail than is normally possible. Those details suggest that the central object is not a black hole. "The structure of the quasar is not at all what had been theorised," Schild told New Scientist.
A black hole, as traditionally understood, is an object with such a powerful gravitational field that even light is not fast enough to escape it. Anything that gets within a certain distance of the black hole's centre, called the event horizon, will be trapped.
A well accepted property of black holes is that they cannot sustain a magnetic field of their own. But observations of quasar Q0957+561 indicate that the object powering it does have a magnetic field, Schild's team says. For this reason, they believe that rather than a black hole, this quasar contains something called a magnetospheric eternally collapsing object (MECO). If so, it would be best evidence yet for such an object.
The researchers used gravitational lensing to make their close observation of the quasar. This technique exploits rare coincidences that can occur when a galaxy sits directly between a distant object and observers on Earth.
The gravity of the intervening galaxy acts like a lens. As the intervening galaxy's individual stars pass in front of the quasar, this bending varies, making the quasar appear to flicker.
Carefully scrutinising this flickering allowed the researchers to probe fine details of the quasar's structure that are normally far too small to be resolved by even the most powerful telescopes.
The researchers found that the disc of material surrounding the central object has a hole in it with a width of about 4000 Astronomical Units (1 AU is the distance between the Earth and the Sun). This gap suggests that material has been swept out by magnetic forces from the central object, the researchers say, and must therefore be a MECO, not a black hole.
"I believe this is the first evidence that the whole black hole paradigm is incorrect," says Darryl Leiter of the Marwood Astrophysics Research Center in Charottesville, Virginia, US, who co-authored the study. He says that where astronomers think they see black holes, they are actually looking at MECOs.
According to the MECO theory, objects in our universe can never actually collapse to form black holes. When an object gets very dense and hot, subatomic particles start popping in and out of existence inside it in huge numbers, producing copious amounts of radiation. Outward pressure from this radiation halts the collapse so the object remains a hot ball of plasma rather than becoming a black hole.
But Chris Reynolds of the University of Maryland, in College Park, US, says the evidence for a MECO inside this quasar is not convincing. The apparent hole in the disc could be filled with very hot, tenuous gas, which would not radiate much and would be hard to see, he says. "Especially if you're looking with an optical telescope, which is how these observations were made, you wouldn't see that gas at all," he told New Scientist.
Leiter says this scenario would leave other things unexplained, however. The observations show that a small ring at the inner edge of the disc is glowing, which is a sign that it has been heated by a strong magnetic field, he says. In Reynolds's scenario, one would expect a much broader section of the disc to be heated, he says.
In any case, says Reynolds, it is difficult to draw conclusions from the team's detailed comparisons of their observations with models of black holes because those models are far from definitive. "We know the accretion of gas into black holes is an extremely complex phenomenon," he says. "We don't know precisely what that would look like."
"It would be truly exciting if there was compelling evidence found for a non-black-hole object in these quasars," Reynolds adds. "I just don't think that this fits."
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