While quantum physics continues to raise new questions concerning Einstein’s theory of general relativity, a recent analysis of a giant black hole at the center of the Milky Way demonstrates that general relativity continues to prove itself under more extreme conditions than initially expected.
Space.com spoke with Andrea Ghez, an astronomy professor at the University of California Los Angeles and co-lead author of a research paper that investigated gravitational redshift occurring near the massive black hole known as Sagittarius A* (abbreviated as Sgr A*), about what the results mean for Einstein’s theory:
Einstein’s right, at least for now. Our observations are consistent with Einstein’s theory of general relativity. However, his theory is definitely showing vulnerability. It cannot fully explain gravity inside a black hole, and at some point we will need to move beyond Einstein’s theory to a more comprehensive theory of gravity that explains what a black hole is.
Gravitational redshift is a phenomenon caused by gravity over distance, similar to how the Doppler effect changes characteristics of a wave in motion relative to its observer. We’re more accustomed to noticing Doppler shifts in audio, like when a police siren’s pitch changes as it speeds past our ears, but the same effect can be seen in other types of waves—such as those produced by photons. While relative position and motion create Doppler redshift, gravity can also produce redshift when it causes a reduction in frequency in blue light.
Image credit: Keck/UCLA Galactic Center Group
While we’ve proven gravitational redshift on Earth, it remained unclear if the same phenomenon occurred with black holes. Ghez’ team tracked the star S0-2 in its complete orbit in three dimensions using multiple telescopes in different locations. Combined with measurements taken over the last 24 years, the scientists were able to show redshifting as S0-2 passed near Sgr A*’s extreme gravitational field.
Tracking S0-2 is just the beginning of the investigation into gravitational redshift. Sgr A* already provides other candidates to track but future results still may take a while. Out of 3,000 stars near Sgr A*, S0-102 has the shortest orbit of 11.5 years. Nevertheless, future efforts now have more of an expected outcome and it will require thorough analysis to discover additional detail about one of the universe’s biggest mysteries.
Einstein’s theory of general relativity predates the discovery of black holes, which makes these results all the more impressive. While the party won’t last forever, it’s amazing to see how far an idea can reach across spacetime.
Top image credit: NASA
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