Origin of supersonic stars in the Milky Way discovered

The Technion Institute of Technology (Israel) has just announced the discovery of the origin of some of the fastest stars ever observed - supersonic white dwarfs, some even located in our own Milky Way Galaxy.

White dwarfs are extremely hot and dense cores, about the size of Earth, that remain after a star begins to die. When these white dwarfs move at extremely high speeds through space, they are called “hypersonic white dwarfs.” What causes them to reach such speeds was a mystery before this latest research.

Led by Dr. Hila Glanz from the Technion, the international team performed 3D simulations of the merger of two rare white dwarfs – those containing helium, carbon and oxygen (HeCO WDs). Using hydrodynamic models, the scientists simulated the interactions of subatomic particles and dark matter – the component that makes up about 86% of the mass of the universe.

These simulations show that when two HeCO white dwarfs collide, a powerful explosion occurs, causing the smaller star to be ejected at a velocity high enough to escape the Milky Way's gravitational pull.

Specifically, the small white dwarf is deformed as it approaches the larger star, then collides and explodes the outer shell of the larger star, followed by an explosion at the core. This process turns the main white dwarf into a type Ia supernova, simultaneously ejecting the core of the secondary star at a speed of more than 2,000 km/s - four times faster than the speed needed to escape the Milky Way.

“For the first time, we demonstrate a clear pathway for a white dwarf merger remnant to reach hypersonic speeds, with characteristics that match those of hot, dim white dwarfs observed in the galactic halo,” Dr. Glanz emphasized.

The discovery not only helps decode the phenomenon of "runaway stars" - stars fast enough to escape the galaxy, but also opens up new perspectives on unusual type Ia supernovae, which are dimmer than standard brightness.

Because type Ia supernovae are used as “cosmic lighthouses” to measure the distance and expansion rate of the universe, a better understanding of the variations in this phenomenon will help scientists calculate more precisely about the universe and the formation history of the elements.

The phenomenon of “redshift” – when the wavelength of light is stretched because the object emitting the light is moving away – is an important tool in measuring the expansion rate of the universe, and type Ia supernovae are the standard measuring tool for this.

Co-author Professor Hagai Perets said: “This discovery not only helps explain the origin of supersonic stars, but also opens the door to observing previously unknown types of stellar explosions.”

Unlike previous studies that used only 2D simulations, this is the first time a 3D model has been applied to track the entire process of star mergers and ejections. This allows the team to more accurately describe the process of creating supersonic white dwarfs, especially known stars like J0546 and J0927 - which have unusual temperatures, brightness and velocities.

Dr. Glanz asserts that this research not only solves the mystery of “runaway” stars, but also opens a new channel for the formation of faint and unusual Type Ia supernovae.

The research results were published in the scientific journal Nature Astronomy./.

(TTXVN/Vietnam+)

Source: https://www.vietnamplus.vn/phat-hien-nguon-goc-nhung-ngoi-sao-lao-voi-toc-do-sieu-thanh-trong-dai-ngan-ha-post1059911.vnp