S2 (star)

S2 , also S0-2 , is a star in the galactic center . It is in orbit around the radio source Sagittarius A * and orbits it once every 16.05 years. At its closest approach to the galactic center ( periapsis ), the star has a speed of up to 27 million kilometers per hour (approx. 2.55% of the speed of light), which makes S2 the fastest known ballistic orbit. It approaches Sagittarius A * to within 17 light hours (122 AU , or 18 billion kilometers ). This corresponds to 2.5 times the mean distance between the Sun and Pluto .

S2 is the first known star whose orbit around a supermassive black hole (Sagittarius A * is one of those with a probability bordering on certainty) could actually be measured. However, in order to be torn apart and swallowed up by the black hole (with a mass of 4.1 million solar masses ), it would have to approach it up to a distance of about 16 light minutes (slightly more than the distance between the sun and Mars ). According to previous observations, this will not happen in the foreseeable future.

In 2012 the star S0-102 was discovered, which at 11.5 years has an even shorter orbit around Sagittarius A *.

In the spring of 2018, S2 was closest to the black hole, a moment astronomers had been waiting for 16 years. It was expected that especially pronounced classical predictions of the general relativity theory ( gravitational redshift , perihelion rotation ) could be tested in the strong gravitational fields present here , including tests of alternatives such as the pseudo-complex gravitation theory of Walter Greiner and Peter O. Hess , as well special phenomena for black holes near the event horizon (e.g. Lense-Thirring-Effect due to the entrainment of spacetime around a rotating black hole ). In addition, it was hoped to gain knowledge about astrophysical phenomena such as the formation and dynamics of accretion disks ( jets , winds) and statements about whether smaller black holes exist in the vicinity of the supermassive black hole. Observation programs exist at the Keck Observatory and the Paranal Observatory (VLTI, Verly Large Telescope Interferometer), for the latter the GRAVITY consortium headed by Frank Eisenhauer . In July 2018, the Gravity Consortium announced that it had demonstrated a gravitational redshift in good agreement with general relativity. The combined effect of gravitational redshift and relativistic Doppler effect was . Another general relativistic effect is expected to be observed in the near future ( apsidic rotation of the orbit). ${\ textstyle {\ frac {\ Delta \ lambda} {\ lambda}} = 200 \, \ mathrm {km} \, \ mathrm {s} ^ {- 1} / \ mathrm {c}}$

Web links

S2 entry in the SIMBAD database
The star S2 ... Quarks & Co. In: wdr.de
Sgr A *: Fast Stars Near the Galactic Center - Astronomy Picture of the Day of December 20, 2000 (English).
ESO: A Full Orbit of the Star S2 (without annotations). In: eso.org
Searching for stars with radio telescopes? In: astronews.com , October 15, 2015
GRAVITY has a central black hole in its sights. In: astronews.com June 23, 2016

Individual evidence

↑ ^a ^b Markus Schmalzl: Race around Sgr A *: Pole position for S0-102. In: Sterne und Weltraum No. 2, 2013, pp. 24–25.
↑ R. Abuter, A. Amorim, N. Anugu, M. Bauböck, M. Benisty: Detection of the gravitational redshift in the orbit of the star S2 near the Galactic center massive black hole . In: Astronomy & Astrophysics . tape 615 , July 2018, ISSN 0004-6361 , p. L15 , doi : 10.1051 / 0004-6361 / 201833718 ( aanda.org [accessed July 29, 2018]).
↑ Nature 419, 694-696 (October 17, 2002) | doi: 10.1038 / nature01121 ; A star in a 15.2-year orbit around the supermassive black hole at the center of the Milky Way
↑ Jay Bennett, Einstein's Theory of Gravity Is About to Get a Test From a Star Passing by Supermassive Black Hole. In: Popular Mechanics , March 1, 2018, on observations at the Keck Observatory.
^ Gravity, ESO
↑ Gravity Collaboration, R. Abuter et al. a .: Detection of the gravitational redshift in the orbit of the star S2 near the Galactic center massive black hole. In: Astronomy & Astrophysics , Volume 615, 2018, L 15, Abstract

[SuW-1] Markus Schmalzl: Race around Sgr A *: Pole position for S0-102. In: Sterne und Weltraum No. 2, 2013, pp. 24–25.

[2] R. Abuter, A. Amorim, N. Anugu, M. Bauböck, M. Benisty: Detection of the gravitational redshift in the orbit of the star S2 near the Galactic center massive black hole . In: Astronomy & Astrophysics . tape 615 , July 2018, ISSN 0004-6361 , p. L15 , doi : 10.1051 / 0004-6361 / 201833718 ( aanda.org [accessed July 29, 2018]).

[3] Nature 419, 694-696 (October 17, 2002) | doi: 10.1038 / nature01121 ; A star in a 15.2-year orbit around the supermassive black hole at the center of the Milky Way

[4] Jay Bennett, Einstein's Theory of Gravity Is About to Get a Test From a Star Passing by Supermassive Black Hole. In: Popular Mechanics , March 1, 2018, on observations at the Keck Observatory.

[5] Gravity, ESO

[6] Gravity Collaboration, R. Abuter et al. a .: Detection of the gravitational redshift in the orbit of the star S2 near the Galactic center massive black hole. In: Astronomy & Astrophysics , Volume 615, 2018, L 15, Abstract