Editing 2783: Ruling Out

Most science studies are intended to discover new knowledge. In astronomy, the goal is often to find different types of objects in space, or learn how astronomical objects are formed and behave. But often from studying things that exist, we also learn about limits of the kinds of things that ''can'' exist; when this happens, we say that we've "ruled out" the excluded phenomena.

[[Cueball]] lists five obviously impossible objects.{{Citation needed}}

* "Earthlike stars": A play on "Earth-like planets" which scientists are very interested in finding. The [https://solarsystem.nasa.gov/planets/earth/overview/ Earth] is not a {{w|star}}, hence stars cannot be Earthlike.

* "Habitable-zone quasars": {{w|Quasar}}s in the {{w|habitable zone}}s of stars are only theoretically feasible for relatively small {{w|black hole}}s with active {{w|accretion disk}}s in a star's habitable zone, visible from the Earth and brighter than the Sun, because of the technical criteria for classifying them in terms of their {{w|apparent magnitude}} relative to that of their galaxy.[https://iopscience.iop.org/article/10.1088/0004-637X/728/1/26] None such have ever been observed.{{fact}} While typical galaxies usually have only one quasar in their center, merging galaxies often have two far apart. Perhaps in 4-5 billion years, when the {{w|Andromeda Galaxy}} merges with our {{w|Milky Way}}, its [https://www.sci.news/astronomy/article00779.html microquasar] might qualify, but that is extremely unlikely.

:While not certain, habitable zones around some quasars have not been ruled out.[https://iopscience.iop.org/article/10.3847/1538-4357/ab1b2f/meta][https://iopscience.iop.org/article/10.1088/1742-6596/2364/1/012057/meta]

* "Stars with subsurface oceans": Because the temperatures inside stars are higher than that which can support the existence of liquids as we understand them, stars cannot have subsurface oceans. After many billions of years, a {{w|white dwarf}} will cool to the point where it no longer emits significant heat or light, becoming a {{w|black dwarf}}, eventually cooling to the point where it might develop subsurface liquids.{{acn}} However, the universe is not old enough for any black dwarfs to exist yet,[https://iopscience.iop.org/article/10.1086/375341/pdf] and sufficiently cool black dwarfs might not even be considered stars, but rather {{w|rogue planet}}s.

: The possibility of subsurface oceans within various planets and moons is an {{w|Extraterrestrial liquid water|active subject of study}}, and was previously mentioned 10 comics ago in [[2773: Planetary Scientist]].

: There are theories that neutron stars can exhibit {{w|Quake (natural phenomenon)#Starquake|tectonic-like movements}} (as some of the more typical rocky bodies certainly do), but the physics of the 'inside' of a black hole are thought to involve {{w|Black hole#Singularity|strange physics}} incompatible with any form of geology, and cannot be observed anyway – it is believed that the only externally-observable properties of black holes are mass, electric charge, and angular momentum, poetically called the '{{w|no-hair theorem}}'.

Some studies are also done to confirm the results of previous studies, to ensure that the conclusions were not mistaken or a fluke. The title text describes a study that was done to confirm the existence of a moon orbiting Earth, even though any sighted person can walk outside and see the Moon, the existence of the Moon has been known for at least as long as humanity has existed, and the fact that it orbits the Earth has been assumed or known for upwards of 3,000 years. The ancient Greeks and Babylonians, for example, thought that the Moon orbited the Earth, though they lacked a detailed physical understanding of the system (they also believed, erroneously, that {{w|Geocentric model|everything else in the universe orbited the Earth too}}). {{w|Anaxagoras}} (c. 500–428 BC) is credited with the correct explanation of lunar eclipses, and reportedly was the first to explain that the Moon shines due to reflected light from the Sun. However, it was not until the work of {{w|Nicolaus Copernicus}} in the 16th century that a detailed and accurate model of the Moon's orbit around the Earth was developed.  Regardless, at this stage, a study to confirm the validity of Copernican orbits would contribute nothing to the scientific process, much less a study confirming the mere existence of the Moon.