Just to add to this, there is no absolute simultaneity in General Relativity, and also no absolute way of saying, "This event happened T time ago." The only concepts that are rigorously defined are future, past and spacelike-separated (points in spacetime you could only reach by traveling faster than light). So if we try to define a reference frame that allows time comparisons between Earth and the Galactic Center, we have to be very careful, and keep in mind that it is just one of infinitely many possible coordinate systems, each of which will give a different answer to the question, "How long ago did this flare happen?"

One fun coordinate system is Cosmic Background Radiation time. The CMB redshifts as the Universe expands, so the temperature of the CMB can serve as a clock. Anyone anywhere in the Universe can measure the average temperature of the CMB, and use that as their clock.

About Mauna Kea, I urge everyone to look into the issue in more depth before forming an opinion. There is a huge amount of disinformation being spread on social media, and the basic picture most media is painting is wrong. The Thirty Meter Telescope project has gone to great lengths to try to listen to the community, and to take religious and cultural concerns into account. These concerns had a big impact on both the location and the design of the telescope. The telescope site is father below the summit than the previous telescopes, so that it cannot be seen from most of the island. The entire optical design of the telescope was made to be super compact (F/1), which was a very risky technical decision, just so the telescope wouldn't be as tall. The internal clearances of the telescope within the dome are just 20 inches, barely allowing it to be serviced, for the same reason.

The sacredness of Mauna Kea is also much more questionable, within traditional Hawaiian religion, than activists are claiming. There's actually surprisingly little evidence that it was historically held to be anywhere near as sacred as TMT opponents claim. The Hawaiian creation story, for example, doesn't mention Mauna Kea. It's important to realize that the Hawaiian traditional religion was suppressed by the Hawaiian monarchy in 1819, which means that it is not easy to reconstruct nowadays. Many of the anti-TMT activists belong to a movement trying to bring the religion back to life, but what they claim about the religion does not necessarily reflect ancient beliefs. One thing that undermines their claims is the fact that pre-contact, native Hawaiians excavated the largest quarry in Polynesia on Mauna Kea.

There are, however, culturally significant sites on Mauna Kea that clearly should be preserved. There are ancient shrines and burial grounds, for example. The TMT site was chosen to be as far removed from such sites as possible. There are also places where modern "cultural practitioners" (ironically enabled by the observatory access road) carry out their practices, and TMT does not significantly disturb these practices.