This unusual tidal tail is 1000 light years or so away, so it is close as the observable universe goes, and also rather interesting. I wish 30-40 million years old counted as "ultra-young" for people as well.
As background, what is a tidal tail?
A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the Tadpole Galaxy and the Mice Galaxies. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the Antennae Galaxies, for example, nearly half of the observed gaseous matter is found within the tail structures. Within those galaxies which have tidal tails, approximately 10% of the galaxy's stellar formation takes place in the tail. Overall, roughly 1% of all stellar formation in the known universe occurs within tidal tails.
Some interacting galaxy pairs have two distinct tails, as is the case for the Antennae Galaxies, while other systems have only one tail. Most tidal tails are slightly curved due to the rotation of the host galaxies. Those that are straight may actually be curved but still appear to be straight if they are being viewed edge-on.
The phenomena now referred to as tidal tails were first studied extensively by Fritz Zwicky in 1953. Several astrophysicists expressed their doubts that these extensions could occur solely as the result of tidal forces, including Zwicky himself, who described his own views as "unorthodox". Boris Vorontsov-Velyaminov argued that the tails were too thin and too long (sometimes as large as 100,000 parsecs) to have been produced by gravity alone, as gravity should instead produce broad distortions. However, in 1972, renowned astronomer Alar Toomre proved that it was indeed tidal forces that were responsible for the tails.
This discovery comes from Gaia DR2 (data release two from the Gaia mission).
Gaia is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until c. 2022. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision. The mission aims to construct by far the largest and most precise 3D space catalog ever made, totalling approximately 1 billion astronomical objects, mainly stars, but also planets, comets, asteroids and quasars among others.
[Submitted on 23 May 2020]
Discovery of an ultra-young stellar "snake" with two dissolving cores in the solar neighborhood
In this Letter we report the discovery of an ultra-young (only 30-40 Myr) quasi-tidal tail (dubbed a stellar "snake") nearby the region of Orion complex from Gaia DR2. The average distance of this structure is about 310 pc from the Sun. Both the length and width are over 200 pc, but the thickness is only about 80 pc. Oddly it has only one tail. Its head includes two dissolving cores, which can be clearly distinguished in the 6D phase space. The two cores are probably broken from an open cluster of initially thousands of members with a total mass of larger than 2000M⊙ in the same stellar population. This population is so young (an order of magnitude younger than the ages of any previously known tidal tails) that it can not be well explained with the classical theory of tidal tails. In addition, we check the theory of mass segregation, but do not find any strong evidence for this theory within 125 pc from the cluster center. Our finding challenges the current theory of the formation and evolution of tidal tails. Its age is well consistent with the history of the Gould Belt. So it may fill the observational gap between the history of the Gould Belt and the star formation near the Orion complex.
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