Thin break on a star family portrait

Thin break on a star family portrait

The ESA Mission Gaia has unveiled the richest star map of our galaxy today.

A thin slit was found on the Hertzsprung-Russell (HRD) diagram. This is the most fundamental of all star astronomy maps, providing information about the internal structures of low-mass stars in the Milky Way.

Astronomers compare stars using their luminosity and temperature. HRD plays the role of a “family portrait” of stars in the galaxy, where you can match the Sun, Altair, Alpha Centauri, Betelgeuse, the North Polar Star and Sirius. The newly discovered gap shrinks diagonally across HRD and indicates where the critical internal change occurs in the star structures. The gap delineates the moment when the stars go from larger and convective ones with a thin radiation layer to tiny and completely convective.

Radiation and convection are two ways to transfer energy inside a star to its surface. Radiation transfers energy through space, and convection - by the movement of fluid. The analysis shows that the stars above the gap contain more than 1/3 of the solar mass, and below - a smaller mass. Different types of stars are massive, so the feature shows where different types of internal structures are located on the HRD. The gap is located in the middle of the region of red dwarf stars, which are much smaller and cooler than the Sun, but constitute 3 out of 4 stars in a solar neighborhood. In 2013, ESA launched the Gaia mission to conduct a census of stars in the Milky Way and create a 3D map. In April 2018, the results of the mission were published, showing an unprecedented map of more than a billion stars of the galaxy. Now the team is trying to figure out why this gap exists. Using data from a theoretical model that simulates activity inside stars, the gap appears to be caused by a slight decrease in size if the star is convective all the way.

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