Okay, skeptical hats on. Ready? Let's go.
A paper has put forward a rather unusual theory about the suspected interstellar object Oumuamua. It suggests it may not be a comet or an asteroid as thought, but instead a clump of dark matter. Mmhmm.
Oumuamua, originally known as A1/2017 U1, tore through our Solar System last month, swinging past our Sun. It had astronomers the world over giddy with excitement as evidence mounted that it was an interstellar object, perhaps originating from a star cluster 200 or so light-years away, never to return again.
There has been some debate over whether it was an asteroid or a comet. The five co-authors of this paper (available on arXiv), however, suggest that some of the unusual properties of the object point to it being composed of “macro dark matter”.
The reason they think it may be composed of dark matter is due to some of its unusual properties. For example, it had a featureless red spectrum and was described as appearing “completely stellar”. These characteristics are also consistent with it being an asteroid, of course. Occam's Razor, anyone?
“Contrary to widely held misconceptions, dark matter need not be in the form of weakly interacting elementary particles, but might instead be found in much larger pieces with masses best measured in grams or kilograms,” the team writes.
If so, they note its mass may be a whopping 10^25 grams. That’s just slightly more than the mass of Earth, despite Oumuamua measuring a paltry 0.16 kilometers (0.1 miles) across compared to Earth’s diameter of 12,727 kilometers (7,908 miles).
"We would expect that if you had one [a chunk of macro dark matter] in front of you, it would look like an extremely dense, probably very spherical, dark and maybe shiny object," Glenn Starkman from Case Western Reserve University in Ohio, one of the paper's co-authors, told IFLScience.
It might sound a bit far-fetched, but the researchers say their theory is falsifiable. That is, they can prove if it is true or not.
“If Oumuamua is indeed dense macroscopic dark matter, then we would expect that its passage close to Mercury, the Earth and Moon would have had measurable gravitational effects on their orbits,” the team writes. “Such displacements should be detectable.”
It’s an interesting theory, but probably not one that’s going to be readily accepted any time soon. We don’t even have proof of the existence of dark matter, let alone macroscopic dark matter.
“The existence of macroscopic dark matter in asteroids in general and Oumuamua specifically remains hypothetical at the moment,” Andreas Hein from the Technical University of Munich, who was not involved in the paper, told IFLScience. “There doesn't seem to be much evidence for its existence in these objects.”
Nonetheless, the idea that we can actually prove the theory true or not is interesting. Starkman noted that the researchers were not planning to do the measurements themselves, but expected them to be done elsewhere.
“This is, as the authors admit, an unlikely possibility due to the constraints we have on the density of dark matter,” Marshall Eubanks, CEO of the company Asteroid Initiatives, told IFScience. “But it would be easy for the US spacecraft tracking networks to check, and I have already encouraged them to do so.”
Well, looks like some of them have checked at the very least. Davide Farnocchia from NASA's Center for Near-Earth Object Studies (CNEOS) was a bit more scathing in his reply to us.
“This paper seems highly speculative and, as far as I can tell, has neither been peer reviewed nor submitted to any scientific journal,” he said. “We do not see any significant perturbations on any of the planets, especially the Earth.”