Finding Runaway Stars to Help Map Dark Matter in the Milky Way

Arthur T Knackerbracket writes:

https://phys.org/news/2025-12-runaway-stars-dark-milky.html

Hypervelocity stars have, since the 1920s, been an important tool that allows astronomers to study the properties of the Milky Way galaxy, such as its gravitational potential and the distribution of matter. Now astronomers from China have made a large-volume search for hypervelocity stars by utilizing a special class of stars known for their distinct, regular, predictable pulsation behavior that makes them useful as distance indicators.

The escape velocity of any planet, star or galaxy is the velocity required for a mass, leaving the object's surface, to coast completely and exactly out of the planet's gravitational well, going to infinity. Earth's escape velocity is 11.2 kilometers per second (km/s).

Any mass that leaves the surface having that immediate initial speed will, without further energy, leave Earth's gravitational grasp. Examples are rocks ejected from Earth by a colliding incoming asteroid (as happened with rocks exchanged between Earth and Mars) or the possible escape of a steel lid covering a blast hole from a 1957 underground nuclear explosion in Nevada (unless the lid vaporized as it ascended towards space at an estimated six times Earth's escape velocity).

The escape velocity from the sun is 618 km/s (but only 42 km/s from Earth's position), and about 550 km/s from the sun's position in the Milky Way. Hypervelocity stars (HVSs) have tangential speeds of 1,000 km/s or more, making them gravitationally unbound from the Milky Way.

A prominent way HVSs come about is from a gravitational slingshot interaction with the supermassive black hole, Sagittarius A*, at the Milky Way's center.

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