On Wikipedia there is an article that says a star may have been expelled from the Milky Way because it interacted with Sagittarius A.

Sagittarius A* from Wikipedia: In July 2019, astronomers reported finding a star, S5-HVS1, traveling 1,755 km/s (3.93 million mph) or 0.006 c. The star is in the Grus (or Crane) constellation in the southern sky, and about 29,000 light-years from Earth, and may have been propelled out of the Milky Way galaxy after interacting with Sagittarius A*.[58][59]

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    $\begingroup$ Your title and the body of the question don't match. Please decide. You answer the title question yourself and should read the references linked in wikipedia. $\endgroup$ May 17 at 12:48
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    $\begingroup$ It often helps to follow the references in wikipedia. It is supposed to link to the primary sources - in science often research papers like here. They often are freely-accessible on arxiv or sometimes elsewhere. Regardless, it's always worth to take a look and read those. Having read those, your questions would profit - and you might be able to answer some of your questions even yourself, and quicker. And you learn and train a valuable skill: literature research and evaluation - and you gain the knowledge from those papers.informed. $\endgroup$ May 17 at 13:25
  • $\begingroup$ Additionally those primary references give you a good insight in how the knowledge is actually obtained, and you will understand much of the background on the fly while reading those papers as they often describe the methodogy and thus help to judge the confidence of the results and the constraints to knowledge. $\endgroup$ May 17 at 13:27
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    $\begingroup$ @planetmaker: As it happens, Wikipedia actually discourages relying on primary sources, because it's too easy for it to turn into original research and personal interpretation. That said, the primary sources are often linked at one remove through the (preferred) secondary sources. $\endgroup$ May 18 at 1:48

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The linked reference 59 in the wikipedia article you quote (Koposov et al (2019)) closes with the question

The fact that S5-HVS1 was ejected with a velocity almost twice that of all other known HVS potentially originating from the GC poses two questions: were all the known HVS produced by the same mechanism and has the HVS velocity spectrum been constant in time?

Thus at that time there seem to be no other known hypervelocity stars leaving the galaxy due to interaction with Sgr A*.

Searching through ADS with the keywords 'hypervelocity', 'milkyway' and 'ejected' gives me a paper from Evans (2022) which tries to come up with a likelyhood of finding these kind of stars. They state

Constraints from Gaia EDR3 and S5-HVS1 become slightly more vertical in κ − η space as we now expect more (fewer) HVSs for κ < −1.3 (κ > −1.3) when compared to a single power-law, but otherwise remain unchanged. For our fiducial model, this prescription would predict 14.2 +5.8 −5.0 total HVSs in Gaia DR4.

That leaves me to believe that they also don't know any further confirmed HVS accelerated by Sgr A* to velocities greater than the galactic escape velocity - but a careful analysis of Gaia DR4 data might reveal a few candidates.

  • $\begingroup$ I didn't know about the ADS astrophysics database . $\endgroup$
    – user50918
    May 17 at 14:53
  • $\begingroup$ From the references you quote a maximum of 1 in 100 interactions per year with Saggitarius A result in a hypervelocity star. And the true figure could be 1000 times lower .Even so, over millions of years there should be more HVS outside the milky way What is holding them back ? Collisions with other stars? $\endgroup$
    – user50918
    May 17 at 15:00
  • $\begingroup$ lifetime of the stars and our observational capabilities due to their large distance and possibly hidden behind molecular clouds. The milkyway has estimated 100...200 billion stars, with Gaia we know ~ 1...2 billion, thus approx. 1%. $\endgroup$ May 17 at 17:39

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