A research team led by Karim El-Badry, a post-doctoral student of Egyptian origin at Harvard University, discovered the existence of a very rare binary star system, which represented the solution to a decades-old problem in the realm of astrophysics.
Binary star systems consist of two stars orbiting around each other, and they are common in our galaxy, and represent about 40% of the stars we see in the sky, and because they are so far away, we see them as one star.
impossible star
But this binary star that Al-Badri and his team found is a special case, there is no doubt about that, in which a star called a "white dwarf with a very small mass" orbits with another star.
At the beginning of their lives, stars are as massive as the sun, but at the end of their lives they shake off their outer envelopes, leaving in the center a white dwarf with a mass equal to about a third of the mass of the sun.
However, this particular class of white dwarfs, which are called extremely low mass white dwarfs (ELM) for short, are less in mass than the usual white stars, and astronomical calculations indicate that the formation of a star with this very small mass It takes more time than the age of the universe itself, that is, more than about 13.8 billion years, and despite that, we are already observing these stars in the sky.
Some white dwarfs are so small that they resemble Earth (Space Telescope)
smart solution
A few decades ago, a hypothesis emerged saying that there is a solution to this problem, which is that this type of "white dwarf" exists in binary systems, if it meets with another star, this other star will withdraw its mass with time at a faster rate than astronomical calculations expect, and then They can exist with this very small amount of mass during the lifetime of the universe.
To confirm this hypothesis, El-Badri and his colleagues turned to new data from Gaia, the space observatory launched by the European Space Agency (ESA), and the Zwicky astronomical survey at CalTech, and this team narrowed down a billion stars. Possible to 50 candidates.
According to the study - published in the "Monthly Notices of the Royal Astronomical Society", and announced by Harvard University in an official statement on the first of this December - among the This group of stars, the research team found 21 binary stars in which the white dwarf is already close to reaching the very low mass stage.
This means direct observation of a transitional phase that confirms that white dwarfs with very little mass are already formed within the age range of the universe if they have a companion that withdraws from their mass.