A team of researchers has observed the fastest moving star ever recorded. Their deep H+K-band (SINFONI) and K-band (NACO) data showed that the S-cluster star S4711 is on a highly eccentric trajectory around Sagittarius A with an orbital period of 7.6 yr and a periapse distance of 144 au to the supermassive black hole (SMBH). The star has the shortest orbital period and the smallest mean distance to the SMBH during its orbit to date. They also describe study of faint S-cluster star candidates, S4712–S4715, circling close to the black hole at the center of the Milky Way galaxy.
Fig: This artist’s impression shows part of the orbit of one of the stars very close to the supermassive black hole at the centre of the Milky Way. Analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of these stars may show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of this star, called S2, is deviating slightly from the path calculated using classical physics. This close-up of the orbit of star S2 shows how the path of the star is slightly different when it passed the same part of its orbit for the second time, 15 years later, due to the effects of general relativity.
Space scientists have known for some time that there is a black hole situated near the center of the Milky Way galaxy (Sagittarius A*), and have theorized that there are stars that circle very close to it—known as “squeezars”, they are believed to orbit so closely to the black hole that they are accelerated to incredible speeds during parts of their orbits. In their work, the researchers have been studying a group of stars that exist close to the black hole, each starting with the letter “S” to indicate their closeness to Sagittarius A.
Fig: The distance of SgrA* stars at closest approach. Credit: Florian Peißker et al.
Prior research had identified a star called S2 as likely existing the closest to Sagittarius A, and at its closest to the black hole, was measured to be traveling at approximately 3% of the speed of light. Then last year, the researchers with this new effort found another star that circled more closely to the black hole and therefore traveled even faster, at approximately 6.7% the speed of light. Since that time, the team has continued studying the fast-moving stars and have found five more that appear to travel even faster: S4714, S4711, S4712, S4713 and S4715.
Fig: S4711 on its orbit around Sgr A*. Credit: arXiv:2008.04764 [astro-ph.GA]
Of these, two stand out from the others—S4714 and S4711. S4711 is a blue star with an orbit shorter than S2, suggesting it might be the closest of all the stars to the black hole. And S4714 has proven to be the speediest of them all—it has a longer orbit, but its orbit is elliptical, which means it is elongated, giving it time, perhaps, to pick up more speed as it moves closer to the black hole—up to 24,000 kilometers per second, or approximately 8% of the speed of light. The researchers suggest the stars are good squeezar candidates, particularly S4714 and S4711 and the short orbital time period of these stars in the dense cluster around the SMBH in the center of our Galaxy are perfect candidates to observe gravitational effects such as the periapse shift.
References: Florian Peißker, Andreas Eckart, Michal Zajaček, Basel Ali, and Marzieh Parsa, “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, Volume 899, Number 1.. Link: https://iopscience.iop.org/article/10.3847/1538-4357/ab9c1c/meta doi: DOI: 10.3847/1538-4357/ab9c1c (2) Florian Peißker, Andreas Eckart, Marzieh Parsa, “S62 on a 9.9 yr Orbit around SgrA”, arXiv, Volume 889, Number 1, Published 2020 January 24
DOI: 10.3847/1538-4357/ab5afd link: https://arxiv.org/abs/2002.02341