Stars are not static: they all revolve in the arms of their galaxies, around their centers; Well, in the center of our galaxy, the Milky Way, there is a black hole called Sagittarius A, about which scientists have theorized for years that it has stars that rotate very close to it, accelerating at incredible speeds during their orbital periods, as if they were in a big juicer. The closer to the black hole, the faster its orbital speed.
There is a group of stars, belonging to this great high-speed cosmic sink, known as S stars (due to their proximity to Sagittarius). Two studies recently published in The Astrophysical Journal describe how several of them travel at the fastest speeds ever observed in any other stellar body.
For a time it was believed that the star S2 was probably the closest to Sagittarius A, and at its closest point to the black hole, it was measured to be traveling at about 3% of the speed of light. However, in 2019, researchers found another star that was spinning closer to the black hole and therefore traveling even faster, at about 6.7% of the speed of light. Since then, the team has continued to study fast-moving stars and found five more that appear to travel even faster.
For now, according to the conclusions of this team, there are two stars who hold the record for the fastest. They are S62 and S4714. They both travel at about 8% of the speed of light. However, their orbits are very different.
S4714 has a longer orbit; but it is elliptical, which means it is elongated. This gives it time to gain more speed as it approaches the black hole – up to 15,000 miles per second. For its part, S62 has the smallest orbit; it is its approach to the black hole that causes it to move at these incredible speeds. S62 orbits Sagittarius A every 10 years.
Time dilation
8% of the speed of light is unimaginable for humans: it means traveling so fast that time dilation would come into play: according to General Relativity, no object can travel faster than the speed of light. This physical law implies that, when a body accelerates near these speeds, an external observer would measure that the time elapsed in these stars passes more slowly. For example, as a result of this time dilation we have that, what would be one minute on Earth (60 seconds), would be the equivalent of 100 seconds on the star S62.
Thus, observing these unusual stars allows astronomers to test the effects of relativity with more precision than any other stellar body has ever done.
Referencias:
Florian Peißker et al. S62 and S4711: Indications of a Population of Faint Fast-moving Stars inside the S2 Orbit—S4711 on a 7.6 yr Orbit around Sgr A*, The Astrophysical Journal (2020). DOI: 10.3847/1538-4357/ab9c1c , arxiv.org/abs/2008.04764
Florian Peißker et al. S62 on a 9.9 yr Orbit around SgrA*, The Astrophysical Journal (2020). DOI: 10.3847/1538-4357/ab5afd
