why is she so fast?

It is the fastest star detected to date. It draws its speed from the supermassive black hole at the center of the Milky Way.

The Sun moves at 720,000 km / h. This is nothing, compared to a category of stars which greatly surpass this speed: hypervelocity stars. They move faster than normal. In 2019, astrophysicists had discovered a star moving faster than usual hyperveloc stars: S5-HVS1. It travels at 1,700 kilometers per second, which translates to 6 million kilometers per hour. This was already more than the travel speed of the Milky Way itself (2 million km / h), which meant that the star could end up ejecting.

The record has just been broken in an absolutely flamboyant manner by the star S4714: it travels at 24,000 kilometers per second. At this point, let’s not even try to convert to km / h, we have to move up a notch: this represents 8% of the speed of light. The reasons for this extraordinary speed are detailed in a study that has just been published, on August 11, 2020, in The Astrophysical Journal.

The reason: the Milky Way’s supermassive black hole

Usually, hypervelocity stars are associated with black holes. One of the hypotheses is that when a binary star system gets too close to a black hole, one of the two stars is snapped up, while the other is ejected at super-fast speed. For individual stars, there is also a theory, that of squeezars : stars captured in the orbit of a supermassive black hole. The latter could immediately be hypervelocity stars.

In the case of our star S4714 moving at 8% of the speed of light, its position is not insignificant: it was precisely discovered in the area surrounding Sagittarius A *, the supermassive black hole which is at the center of the Milky Way. It is in orbit around him. The team behind the discovery was looking for stars near the black hole, so far few have been detected. As their research progressed, they discovered stars ever closer to Sgr A *.

Up to S4714. Its periapsis (minimum point of the orbit of a celestial object with respect to the source of the orbit) is 1.9 billion kilometers from Sgr A *. It might sound like a lot to you, but on the cosmic scale of a supermassive black hole, it’s an important proximity. It is when it “grazes” the black hole of the Milky Way that it reaches its maximum speed of 24,000 kilometers per second, then it slows down when it moves away from it.

Improvements in observational instruments increasingly allow scientists to explore an area as mysterious as the one surrounding our galaxy’s supermassive black hole. One of the authors of the find entrusts : « I am constantly working on the galactic center and am pretty sure this is not our last post. This highly dynamic environment is for scientists like a children’s candy store. »