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In a breakthrough study in Nature Astronomy, researchers have discovered a new origin for some of the fastest stars ever observed: hypervelocity white dwarfs—compact stellar remnants hurtling through space faster than 2000 km/s.

Led by Dr. Hila Glanz of the Technion—Israel Institute of Technology, the international team performed state-of-the-art three-dimensional hydrodynamic simulations of a merger between two rare hybrid helium–carbon–oxygen white dwarfs. The results reveal a dramatic sequence of events: as the lighter star is partially disrupted, the heavier one undergoes a double-detonation explosion, slingshotting the surviving remnants of its companion into space at hypervelocity speeds exceeding 2,000 kilometers per second—fast enough to escape the gravitational grip of the Milky Way.

"This is the first time we've seen a clean pathway where the remnants of a white dwarf merger can be launched at hypervelocity, with properties matching the hot, faint white dwarfs we observe in the halo," said Dr. Glanz. "This solves the mystery about the origin of these stellar runaways—and also opens up a new channel for faint and peculiar Type Ia supernovae."

Unlike previously proposed scenarios, the new model accounts for both the extreme velocities and unusual temperatures and brightness of known HVWDs, such as the stars J0546 and J0927. It also offers insight into underluminous thermonuclear explosions, which are crucial tools for measuring the universe's expansion and for understanding how elements are formed in galaxies.

"This discovery doesn't just help us understand hypervelocity stars—it gives us a window into new kinds of stellar explosions," said co-author Prof. Hagai Perets, also of Technion.

The study was conducted by researchers from the Technion, Universität Potsdam, and the Max Planck Institute for Astrophysics, combining high-performance simulations with new theoretical modeling.

The work has implications for upcoming transient surveys and Gaia data releases, which may uncover more of these elusive stellar cannonballs flying through the galaxy.