Conventional theory says that planet 9 – hypothetical of our external solar system 9e planet – is just a hitherto undetected planet, probably captured by our solar system at some point in its 4.6 billion year history.
But Harvard University astronomers now raise the possibility that planet 9’s orbital evidence could be the result of a missing link in the decades-long dark matter puzzle. That is to say a hypothetical primordial black hole (PBH) with a horizon size no larger than a grapefruit, and with a mass 5 to 10 times that of Earth.
How could it be detected?
In an article accepted for publication in The Astrophysical Journal Letters, the co-authors maintain that the observed grouping of extreme trans-Neptunian objects suggests a kind of massive super-terrestrial body based on the outer fringes of our solar system. Perhaps up to 800 astronomical units (Earth-Sun distances).
Thus, the authors propose that a single wide field investigation telescope, currently under construction in Chile, will soon allow them to set new limits to the possibility that planet 9 may indeed be a PBH instead of a simple ordinary planet. If they exist, such PBHs would require new physics and go a long way toward solving the mystery of the missing mass of the universe, or dark matter.
Our article shows that if planet 9 is a black hole, then comets residing on the periphery of the solar system (in the “Oort cloud”) would have an impact on it, Avi Loeb, president of the astronomy department of the Harvard University and co-contributor to the newspaper. author, told me. They would then be destroyed by its strong gravitational tide and in one second of accretion over the black hole, they would produce a visible rocket, he said.
For comets large enough, this stray light would be detectable by the 8.4-meter optical telescope of the LSST.
The idea is that once in the vicinity of a black hole, small cometary bodies would melt following the heating of the accumulation of background gas from the interstellar medium on the black hole, Amir Siraj, the first author of the article and an undergraduate student from Harvard University, noted in a statement.
The authors calculate that they would be able to detect the first accretion surge of this type in the few months following the operation of the LSST, which is now scheduled for the first light in 2021.
Why the LSST?
The LSST will be unique in its ability to probe the entire sky about twice a week at a remarkable level of sensitivity, Siraj told me. We have calculated that the eruptions from the accumulation of a small body on a black hole in Planet 9 would be the brightest near the optical strip, where the LSST operates, he said. And as the position of Planet 9 is unknown, Siraj notes that the LSST monitors the sky so quickly maximizes its chances of catching a flare.
The authors say that these brief accretion surges would be detected at a rate of at least a few per year over a distance of approximately 105 AU. And they expect to be able to exclude or confirm planet 9 as a primordial black hole during the first two years of LSST operation.
Why would our own solar system harbor such an exotic primordial black hole?
Quite simply by their number in the cosmos. The authors believe that it may be somewhat likely that our solar system will gravitate to capture a primordial black hole above the eons at least once.
What would the detection of such an exotic black hole mean for physics?
Loeb says that the formation of primordial black holes would certainly represent new physics. The process that made them in the first universe is not predicted by the standard model of particle physics and cosmology, he says.
If planet 9 is a primordial black hole, will there probably be others in the galaxy?
If it’s a black hole, there should be fifty quadrillion like this in the Milky Way alone, says Loeb.
Loeb says there is nothing to lose by using the LSST to search for such primordial black hole relics. Over the past four decades, laboratory research for dark matter research has consumed tens of millions of dollars, he says.
“Our article suggests using the LSST as a dark matter experiment, looking for primordial black holes at no additional cost,” said Loeb.