Nemesis is a hypothetical red dwarf star. The existence of this star has been proposed to explain a pattern observed in the periodicity of mass extinction events in geological ages.
Everyone has probably heard the story of Hou Yi shooting down the suns, but of course, myths and legends are fictional; it is impossible for there to be nine suns in the sky!
However, the Sun might have a twin brother named Nemesis. The relationship between it and the Sun is not straightforward; approximately every 26 million years, this star may return, leading to a risk of extinction for all living creatures on Earth. While it sounds unbelievable, this is actually an astronomical hypothesis aimed at explaining periodic extinction events on Earth and the activity of comets in the Solar System.
Based on data from NASA’s Chandra X-ray Observatory, it is estimated that over 80% of stars in the universe are found in binary or multiple star systems.
The hypothesis about the star Nemesis was first proposed by American astronomers Daniel Whitmire and Albert Jackson IV in 1984. They discovered that, during extinction events over the past 500 million years, Earth experiences a mass extinction approximately every 26 million years.
They believe that this periodic extinction event could be related to the activity of comets in the Solar System. They speculated that the Sun might have a “twin brother” that humanity has yet to discover, which is a companion star.
The orbit of this companion star is very stable, and it will return periodically about every 26 million years, bringing catastrophic consequences for life on Earth each time.
“The twin brother” of the Sun has been named the star Nemesis by astronomers – Nemesis is the goddess of vengeance in Greek mythology, thus Nemesis is also referred to as the avenging star and the dark companion star.
Nemesis is a red dwarf or brown dwarf star located approximately 50,000 to 100,000 astronomical units away from the Sun. According to Kepler’s laws, astronomers calculate that if its orbital period is 26 million years, then its semi-major axis is about 1.4 light years. Consequently, the relationship between the Sun and Nemesis is described as a binary star system in physics.
The binary star model for our Solar System is an intriguing perspective, as it could explain many “anomalous phenomena” in the single star hypothesis.
A binary star system (binary star system) is a celestial system consisting of two stars that appear very close to each other. Binary star systems can be divided into physical binaries and optical binaries.
If one star orbits another and they interact gravitationally, they are called physical binaries. If two stars appear to be close but are actually very far apart, they are called optical binaries.
In the Milky Way, where the Sun is located, more than 50% of stars are binary star systems. It is commonly believed that the structure of binary star systems is more stable than that of single star systems. In the field of physics, there are various opinions about the formation of binary star systems, with some suggesting that the formation is mainly influenced by gravitational forces.
Many stars have companion stars, including the closest triple star system to Earth, Alpha Centauri.
In any case, Nemesis, as the companion star of the Sun, could profoundly affect other stars in the Solar System. The star Nemesis approaches the Sun approximately every 26 million years on its orbit around the Sun.
Every time it comes close, it changes the orbits of asteroids and comets in the Oort Cloud due to its gravitational force. The Oort Cloud is a spherical shell believed to surround the Solar System. It contains countless comets and a small number of asteroids, located about 50,000 to 100,000 astronomical units from the Sun, with a maximum radius of about 1 light year.
It is estimated that the total mass of the Oort Cloud is about 3×10^25 kg, equivalent to about five times the mass of Earth. Under the immense gravitational influence of the star Nemesis, some comets and asteroids in the Oort Cloud will be “pulled” into the inner orbits of the Solar System, and they will travel on the orbits of the eight major planets. A small portion of these will be attracted by the gravitational pull of Earth.
In the Milky Way where the Sun is located, over 50% of stars are binary star systems.
After being captured by Earth’s gravitational force, smaller comets rub against the atmosphere and ignite as they enter the atmosphere, while larger comets and asteroids will collide directly with the surface of Earth, leaving large craters.
Moreover, the consecutive impacts will cause severe changes to the environment inside the Earth, with sudden increases in temperature, leading to disasters for living organisms on Earth. This hypothesis may explain several famous impact events in Earth’s history, such as the impact in Chile that wiped out the dinosaurs 65 million years ago and the impact in the Chesapeake Bay that killed mammals in North America 35 million years ago.
These impact events coincide with the times when Nemesis approaches the Solar System.
Additionally, this hypothesis may also explain the periodic changes in comet activity in the Solar System. Through observations and statistical analyses of astronomers regarding long-period and short-period comets, it was found that these two types of comets exhibit clear activity peaks and troughs over the past few thousand years. These peaks and troughs correspond to times when Nemesis moves closer to or farther from the Solar System.
An astronomical unit is the average distance between the Sun and the Earth (150 million km).
The analyses above are based on the assumptions of astronomers, assuming that the star Nemesis truly exists. So, does Nemesis exist? In 1986, astronomers from the University of California, USA, used infrared telescopes to scan the space near the Sun, hoping to find traces of the star Nemesis, but the results were unsuccessful.
From 1997 to 2001, astronomers used a 2-micron sky survey to comprehensively classify and measure stars surrounding the Solar System, but they found no evidence of the existence of the star Nemesis.
These observations indicate that the likelihood of Nemesis existing is very low, and it may even be excluded. However, this does not mean that there is no evidence of Nemesis’s existence at all.
In 2004, astronomer Michael Brown from Caltech discovered a dwarf planet named Sedna beyond the orbit of Pluto. The orbital eccentricity of this asteroid is extremely high, with its perihelion at 76 astronomical units and its aphelion reaching an astonishing 975 astronomical units.
This extreme eccentricity puzzled scientists because, under current theories, Sedna should not exist in such an orbit. Scientists speculate that Sedna may have been formed by an unknown celestial disturbance.
This unknown celestial body could be the star Nemesis. When the star Nemesis exists and moves close to the perihelion, Sedna could be influenced by the gravitational forces of both the Sun and the star Nemesis simultaneously, thereby greatly affecting its orbit and eccentricity.
Currently, Sedna is the only potential evidence that could support the existence of the star Nemesis, but it is not convincing. This is because Sedna’s eccentricity could also be caused by other reasons, such as disturbances from other stars or planets, instability within the inner Solar System, or other unknown physical mechanisms.
Therefore, more observations and research are needed to prove the existence of Nemesis.
