We have found the fastest known star on the Milky Way. In the extreme environment at the center of our galaxy, a newly discovered star named S4714 orbits the supermassive black hole of Sagittarius A *.
On its orbital journey, the S4714 reaches a speed of about 8 percent of the speed of light – an absolute jaw that drops 24,000 kilometers per second (15,000 miles per second). But this is not the most amazing thing either.
S4714 is just one of a series of stars that have now been discovered descending Sgr A * into closer orbits than any other previously discovered star.
Not only does this discovery suggest that there are even more stars in daredevil orbits around the supermassive black hole of our galaxy, it has given us the first candidates for a star type originally proposed nearly 20 years ago ̵1; those that come so close to a black hole, they are ‘squeezed’ by its tidal forces. They are also known as ‘squeezars’.
The region at the center of the Milky Way may be quiet compared to the more active galactic centers, but even the environment around a soothing solid black hole can become quite wild.
Astronomers studying the region have identified a number of stars in long, looping, sharp elliptical orbits around Sgr A * – think of an oval, with a black hole at one end. These are called S stars, and we can use them to investigate the properties of the invisible gargantuan object they orbit.
For years, a star called S2 was considered the closest star to the black hole. With its closest approach, or periapse, its 16-year orbit brought it within about 18 billion kilometers of Sgr A *, the gravitational shock from this close approach that accelerated the star to 3 percent of the speed of light. Takenshte took the arduous work to observe and characterize this orbit.
But last year, a team led by astrophysicist Florian Peissker of the University of Cologne in Germany found a very weak but also much closer star: S62.
In a 9.9-year orbit, it practically grazes Sgr A * at a peripheral distance of 2.4 billion kilometers. This is closer than the average distance between Uranus and the Sun. As it surrounds, it reaches speeds of 20,000 kilometers per second (12,400 mps), or 6.7 percent of the speed of light.
But Peissker and his team did not. After many years of work, they have discovered five new S stars even closer than S2 – S4711, S4712, S4713, S4714 and S4715.
“I’m happy to have the opportunity to work and observe (with the Very Large Telescope) the Galactic Center for the last 7 years,” Peissker told ScienceAlert.
“Since then, I’ve been working on data SYNPHONY (roughly infrared). You need data reduction skills, a good eye, some luck and time. And of course a good knowledge of low filter and high. “
Of the young stars, S4711 and S4714 are the biggest positions.
S4711, a blue type B star, about 150 million years old, has an even shorter orbital period than S62; runs around Sgr A * once every 7.6 years, over a period of 21.5 billion kilometers.
Although it does not slide so close, its shortest orbital period means that it has the shortest average distance from the black hole in all of its orbit that we have yet to discover.
Meanwhile, the S4714 has a longer orbital period than the S4711 – 12 years – but its orbit is extremely eccentric, meaning the ellipse shape is elongated; as long as a steady orbit can be made, indeed. Orbital eccentricity is described in values from 0 to 1, with 0 being a perfect circle, and 1 being the rescue orbit. S4714 has an orbital eccentricity of 0.985.
On the periphery, it slides closer to the S62, reaching within about 1.9 billion kilometers (1.2 billion miles) of the Sgr A *. During this close approach, the star accelerates at speeds of up to 24,000 kilometers per second, slowing down as it accelerates as far as 250 billion kilometers from the black hole.
These extreme stars, Peissker said, are the first real candidates for crush, first theorized in 2003.
Astrophysicists Tal Alexander and Mark Morris proposed a class of stars in highly eccentric orbits around massive black holes. At each pass, tidal forces convert some of the star’s narrow orbital energy into heat. This, first, makes the star shine brighter than normal; and, secondly, contributes to the orbital decay of the star. In other words, extruders are dead stars that spin in orbit.
“At least the S4711 and S4714 are squeezing candidates,” Peissker said. “I would say, I’m sure about the S4711 as the orbital elements are in line with Tal Alexander ‘s predictions in 2003. In that sense, the S4711 is the first squeegee ever discovered.”
If confirmed, these stars can help us understand the interactions between black holes and the stars they (eventually) devour. But they offer other possibilities.
S2, for example, has recently been used to test overall relativity. Both the way starlight travels as it approaches the black hole and the way its orbit moves like a spirograph confirmed Einstein’s theory in some of the strongest evidence yet.
“We are actually one size closer to Sgr A * and almost four times faster than S2 during its peripheral passage,” Peissker explained. “With this, we find relatively stronger interactions with stars S62, S4711 and S4714 as with S2.”
These tests have yet to be done, and the SYMPHONY has since decomposed, so taking observations may still take some time. But it is certainly on astrophysical radar.
So, too, is the search for more of these close stars. It is possible that even the most extreme speeds and orbits could be hidden in the region around Sgr A * – and with the most powerful telescopes released in the coming years, including the extremely large Telescope, we should be able to find them. those.
Everything is just time.
“I’m constantly working on the galactic center and I’m pretty sure this was not our last edition,” Peissker said, with a wet-faced emoji. “The highly dynamic environment is to scientists like a children’s candy store.”
The research is published in Astrophysical Magazine.