They are so small that they are almost non-existent. About the search for the ninth planet and Russell’s teapot
Prehistory of the ninth planet
The story of the discovery of Pluto is romantic, “tube” as they would say now. Lowell’s semi-imaginary planet came to light 14 years after his death. The name “Pluto” was coined by eleven-year-old Venetia Burney (1918-2009), and more coincidentally than deliberately, “PL” – the initials of Percival Lowell – were tucked into it. A tiny icy world seemed at last balance the whole system, although by the beginning of the 21st century it had exhausted itself. Pluto did not look like the core of a failed gas giant, much less like the planets of the terrestrial group – and now, with the improvement in the quality of telescopes in 2002, a trans-Neptunian object 50000 was discovered, named Quaoarin 2003 – object 90377 SednaJanuary 5, 2005 – object 136199 Erislater in 2005 – Makemake. There was an analogy with the situation at the beginning of the 19th century, when in 1801 a new dwarf planet was discovered by Giuseppe Piazzi (1746 – 1826). The orbit of this planet (Ceres) lay between Mars and Jupiter, and when searching for Ceres, Piazzi relied on calculations previously performed by Carl Friedrich Gauss. But even during the lifetime of Piazzi, Pallas (1802) Juno (1804) and Vesta (1807) were discovered, similar to Ceres in size, shape and configuration of the orbits. It became clear that Ceres is not a planet, but the largest representative of a new class of objects that form a wide belt and subsequently called asteroids.
Similarly, in 2006, Pluto was considered the first known representative of the trans-Neptunian objects (TNOs), and the entire population of these small icy bodies began to be studied collectively as the “outer asteroid belt.” The existence of such a region in the outskirts of the solar system was suggested as early as 1992, when the name “Kuiper Belt” appeared.
But the problem with the “ninth planet” has not disappeared anywhere, but only actualized. It’s not so bad that none of the trans-Neptunian objects could seriously affect the orbit of Neptune, since they are all much smaller than the ice giant. But so many of these objects became known that they began to be studied as a swarm – and modeling showed that entire groups of TNOs had orbits elongated as if they were being pulled by a massive body located 20-30 astronomical units from the Sun.
Such a strange configuration of orbits (as well as the shape of Neptune’s orbit) could be explained by the presence of a large planet, possibly an ice giant, beyond the orbit of Neptune. But the accumulated data on exoplanetary systems, as well as data received from Voyagers, such a giant can hardly form in the outskirts of the planetary system – there will not be enough residual hydrogen or the basis for a stone core. Theoretically, the Sun could in ancient times pick up the edge of the ecliptic orphan planet. But, despite the increasing accuracy of astronomical instruments, such a planet is also not observed.
But according to new study, the preprint of which was released in September 2019, the culprit of orbital anomalies in the Kuiper belt may not be a giant planet, but a miniature black hole. We are talking about an object belonging to a hypothetical class primordial black holes (PBH). Primordial black holes could appear in the first fractions of a second after the Big Bang, even before the beginning of the inflationary stage – when space was not yet completely isotropic, but “lumpy”, and tiny event horizons could form at some of its points. Primordial black holes themselves would not move anywhere, lying in their gravitational funnels, but at the stage of inflationary expansion they would be blown across the entire Universe by space itself. True, the existence of primordial black holes has not yet been confirmed.
If such a black hole is located near the solar system, then dozens of astronomical units separate it from the Sun, and it is comparable in size to an orange or a tennis ball. By mass, such a hole should be several times larger than the Earth.
The idea to look for PBHs in the immediate vicinity, apparently, first arose as part of the study of gravitational anomalies detected during the experiment OGLE (optical experiment on gravitational lensing). This is an astronomical Polish-American project in which events are searched through a telescope gravitational microlensing. Gravitational microlensing occurs when a massive object (such as a black hole) crosses the path of observation, passing between the telescope and a background object such as a star. If both the telescope and both of these objects are strictly on the same line, then the front object (in this case, a black hole) will work as a lens, distorting and amplifying the light from the star.
In the five years of OGLE’s operation, six strange events have been recorded. They could betray the presence of objects up to twenty times the mass of the earth. According to article with an analysis of OGLE observations, at a distance of about 8 kiloparsecs (26,000 light years) from us in the direction bulge In the Milky Way galaxy, there may be a whole population of objects that provoke microlensing, and this can be either a swarm of rogue planets or a population of primordial black holes. The article was published in 2019, and at that time the version dominated that in the outskirts of the solar system one should really look for an accidentally captured alien planet that was once wandering.
However, the famous American astronomer of Russian origin Konstantin Batyginsince 2016 actively promoting the idea of searching for a ninth planet, and not involved in the above analysis of the OGLE data, considered that a primordial black hole could definitely replace a rogue planet in the available models, but it is not yet possible to say which interpretation is more likely.
Accordingly, the idea is quite viable that in the near vicinity of the solar system there may be a population of primordial black holes, and one of these objects could be captured by our system like a wandering planet. Naturally, such an object would be invisible in optical observations.
Hawking radiation
In the 1970s, Stephen Hawking first suggested that black holes are actually not that black. At the event horizon, complex interactions occur due to gravity and quantum factors, therefore, according to Hawking, black holes can give a faint glow, while gradually disincarnating.
Hawking radiation is really very weak – a black hole the size of the Sun should emit about one photon per year. It is absolutely impossible to detect it with any detector.
However, if there is a relatively accessible black hole nearby, then it could be illuminated artificially. In 2021, French scientists from Paris and Lyon assumedthat the Hawking radiation of a hypothetical black hole would be easier to detect if a probe (or group of probes) was sent to fly around it. In addition, they believe, a black hole could be hurt by gravitational waves directed in its direction.
Ships and ice floes
A more convenient way to detect a black hole is to throw something into it, in which case the body that crosses the event horizon will throw out a flash of light. There is a projectBreakthrough Starshot”, within the framework of which it is planned to equip a fleet of lightweight spacecraft flying under solar sails. Such a fleet could reach the borders of the solar system in a few years. The trajectories of these ships could be distributed so that they diverge in a wide fan. As a result, one of these probes could either be captured by a black hole, or be affected by it and indicate where it is. The probe does not have to fall into a black hole – passing close to it, it would experience a strong relativistic time dilation, which would be easy to detect if high-precision clocks were installed on the probes.
A fundamentally different vector of the search for a primary black hole is also proposed, described in 2020 by Amir Siraj and Avi Loeb. You can not send a fleet of spaceships to the ends of the world, but look for anomalies in the distribution of icy bodies in the Kuiper belt or Oort cloud.
The primary black hole could not absorb a large object from these belts, but could destroy the trans-Neptunian bodies approaching it, tearing off pieces from them. In this case, in its vicinity, one could fix the destruction of one of these bodies, or find fragments that are held in the form of a small single conglomerate by secondary accretion forces.
Such a search assumes that a huge variety of trans-Neptunian objects will need to be considered separately. A telescope can be used for this purpose. LSST (Legacy Survey of Space and Time), which has been under construction since 2014 on Mount Cerro Pachon in Chile. The telescope is equipped with a 3200-megapixel camera and is intended for detailed mapping of the southern hemisphere of the sky for 10 years. It is assumed that this telescope will allow us to clarify the composition of 40,000 small objects in the solar system and, possibly, bring us closer to the localization of a primary black hole.
Conclusion
I decided to prepare this material, since the searches and versions described in it relate to completely hypothetical objects (primary black hole or unknown ninth planet). Indeed, if we were able to directly study a small and harmless black hole, this would greatly contribute to the development of the most important of the missing theories – quantum gravity. But the search described here also touches on a much more philosophical problem, since a miniature elusive black hole (and absolutely real) is surprisingly similar to the notorious Russell’s teapot. The described area of problems demonstrates that science is not satisfied with an explanation that could be formulated as follows: “We have something wrong with gravity in the outskirts of the solar system. A giant planet could cause perturbations, but for some reason it is not visible. Therefore, it is logical to assume that a black hole the size of an orange is to blame. It is almost impossible to detect it, so just believe she’s there“. But before our eyes, whole sequences of hypotheses and ideas are developing, designed not only to confirm or refute the presence of a mysterious source of gravity, but also to conceptualize its nature.
I think Bertrand Russell would be proud of us.
