Nemesis (hypothetical star)
Nemesis is the name of a hypothetical companion of our sun, which is to circulate as a star or brown dwarf the sun at a distance of about one to three light years. Its existence was suspected due to a periodicity of cometary impacts and extinctions on Earth, can according to the available data in the 21st century of sky surveys but are largely excluded.
Nemesis has been postulated, among other things by Richard A. Muller. This was added, inspired by Walter Alvarez, the founder of the hypothesis that dinosaurs were extinct by the impact of a comet strike on Earth. Since the meteorite craters on the earth show a possibly matching Altersstufung, Alvarez relates this hypothesis, at least in its deliberations with a.
The name comes from Nemesis, the goddess of retribution and vengeance in Greek mythology, back.
Origin of the hypothesis
David M. Raup and J. John Sepkoski studied 1984, the previous extinctions on Earth and arranged these chronologically. They discovered that it regularly came to mass extinction, their temporal distances are 26-33 million years ago. As a starting point for most theoretical calculations is a period of about 27 million years ago. In about the same time interval increases occurred comets, so that a connection between these two events was suspected. In the following years was now looking for a cause for the periodic heaping comets. One explanation for this may be an existing companion of the Sun, which passes through the Oort cloud at regular intervals and throws located there comets from their orbits with its gravitational field. These comets will then move into the inner regions of the solar system, where there is also more likely to occur due to the increased number of comets statistically impacts on the planet. This hypothetical solar companion called Nemesis.
However, these results are challenged in principle, since in a measurement error of ten percent of the eligible period length is after 320 million years within the measurement error, and on the other hand has not the slightest reference to this star, which would be supported by verifiable direct observations.
Nemesis as a small star
If a star for the recurring comet increased number be responsible, this course also has physical parameters. Since the advent of the theory one has tried this narrow as much as possible using the known laws of physics and the existing observations.
Davis, Hut, and Muller describe the hypothetical companion of the sun as a brown dwarf in an orbit with an average eccentricity and perihelion in the Oort cloud. This is interfered with each run of Nemesis, which more than 109 are deflected on each comet orbits that lead them into the inner solar system, where strike about ten to 200 of them on earth.
The assumption that the increased impacts on Earth are caused by trapped from the sun comet, was discarded because it is very difficult with this model to achieve stable periods. In addition, the analysis of impact craters objects originating in the solar system suggests.
The model of Jackson and Whitmire is generally consistent with the above, but they receive an eccentricity e ≥ 0.9, which was even more than with Davis, Hut, and Muller occasion for criticism. Elliptical orbits require namely with increasing eccentricity always a better tuning of the angular momentum of the train, as they are usually not stable.
According to carried out by Weinberg, Shapiro and Wasserman numerical investigations have such a weakly coupled double star systems with the required properties, semi-major axis of ~ 105 astronomical units and 27 million years ago circulation time was small, but not negligible probability. These simulations take into account the interference caused by passing stars and interstellar gas clouds as well as the structure of gas clouds and the galactic tidal forces.
Varum Bhalerao and MN Vahia the question of the maximum mass of Nemesis have dedicated. Based on a correlation between the heaping comet hitting earth and an object that causes a disturbance in the Oort Cloud, this object has been assigned to an orbital period of 27 million years.
The cause of the faults occur, leading to an increased number of comets, it is assumed that the orbits of these small bodies are disturbed when they come near the first Lagrangian point located between the Sun and Nemesis. Assuming the luminosity of the star to be determined. For this purpose, it is assumed that Nemesis is about as old as the sun, thereby substantially heavier stars can be excluded, since these have a significantly shorter survival time and would have been already discovered due to their higher luminosity. Also, neutron stars and black holes can be excluded because they have a relatively high luminosity by accretion.
On the basis of these assumptions, numerical simulations were performed in order to investigate the parameters of Nemesis further. The resulted curves of the luminosity function of the mass were compared with the previous observations. Since the Tycho -2 catalog to m = 11.0 and the Guide Star Catalog II to J = 19.5 are complete, one can assume that Nemesis has a lower luminosity, since it was not observed until now. This leads to an upper mass limit, which is about 44 Jupiter masses. The effect of the period adopted this value is very low. However, could a highly elliptical orbit whose perihelion lies close to the sun, nor cause a deviation of up to 47 Jupiter masses, since the luminosity would once again fall by 0.045 L ☉, if the star is currently located at aphelion.
ER Harrison studied pulsars and their rotation period. These decreases with increasing age of the pulsar. He came across a group whose period decreases unusually slow. One explanation for this would be a companion of the sun, which speeds up the focus of the solar system. Harrison suspected it might be, now referred to a white, red or even a "black dwarf" as a brown dwarf, act.
Henrichs and Staller dealt with Harrison's hypothesis and found several arguments that disprove this. Firstly, such an object would interfere with the movement of the planets. Longitudinal variations in the orbit of Neptune can be, for example, not be explained by this theory and even contradict this. A brown dwarf can also be excluded, since, if he exists, in the infrared range have about the luminosity of Betelgeuse, and would have thus been discovered. The same applies to a red and a white dwarf. Another way to explain the effects that occurred, would be a black hole or a neutron star. However, this is assessed by all three scientists as very unlikely.
Alternative theory
According to Victor Clube (University of Oxford) and William Napier ( Cardiff University ), the model of Davis, Hut, and Muller in dominated by interstellar gas clouds is unstable environments. Consider one that is caused by the gas clouds gravitational disturbances of the highly elliptical Nemesisorbits, then the semi-major axis shortening after a few rounds to 100 astronomical units. Furthermore the model is out of phase, and there would be an additional periodicity of about 250 million years ago known.
Clube and Napier therefore proceed on the assumption that our solar system is moving periodically by a layer of extrasolar objects. This debris layer lies in the galactic ecliptic, ie the plane of the Milky Way. This assumption provides a period in the right order of magnitude, ie about 35 million years.
Davis, Hut, and Muller criticize on this hypothesis, in their turn, a phase shift: The sun is currently located near the galactic ecliptic, but the last extinction lie back about eleven million years so only a half period.
Observation
If Nemesis exists, it is very likely faint and has a low radial velocity.
Could be discovered nemesis with the help of Pan - STARRS ( Panoramic Survey Telescope and Rapid Response System ), a project for the continuous observation of the night sky. The four 1.8 - meter telescopes that were built in Hawaii on Mauna Kea and Haleakala, are able to observe objects with an apparent brightness up to the 24th magnitude. By comparing with previous observations, the discovery of many new asteroids, comets, variable stars and other celestial bodies is possible. Including the Nemesis with its large parallax, but radial velocity measurements at low speed.
In parallel with Pan - STARRS is planned LSST, a similar project with one stationed in Chile 8.4 -meter telescope.
In Nemesis it is not, as suggested by Whitmire and Jackson, a brown dwarf, since such would have been in the screening of the entire sky found by the 2009 launched by the NASA WISE mission, with its satellite-based infrared telescope.