The supermasive black hole Sagittarius A* woke up 200 years ago

“No effect was felt on Earth, as the distance between Sgr A* and our planet is too great (about two billion times the distance from the Earth to the Sun). However, the  X-ray echo detected, which was emitted about 200 years ago, reveals that the original intensity was at least a million times greater than that currently emitted by Sgr A*.”

“ To get an idea of the increase in intensity of the X-ray emission when the black hole emerged from its quiescent state, it is as if a single glow-worm hidden in a forest suddenly became as bright as the Sun. These findings explain why galactic molecular clouds near Sgr A* are shining more brightly than usual: it is because they are reflecting the X-rays emitted by Sgr A* 200 years ago. To carry out their research, the scientists used NASA's IXPE (Imaging X-ray Polarimetry Explorer) satellite3, which was for the very first time able to detect the polarization of this X-ray light with great precision and also determine its source, something that had previously proved impossible.”

“Rather like a compass, the polarized X-ray light4 points directly to its source, Sgr A*, even though the latter is now virtually extinct. The scientists are continuing their work on Sgr A* to try to determine the physical mechanisms required for a black hole to switch from a quiescent state to an active one.”

Just last month, scientists from the Event Horizon Telescope (EHT) team revealed the first-ever image of Sagittarius A*. The EHT team noted that tens of millions of images taken by its worldwide network of radio telescopes were combined to provide the final image.

Study abstract:

The center of the Milky Way Galaxy hosts a ∼4 million solar mass black hole (Sgr A∗) that is currently very quiescent with a luminosity many orders of magnitude below those of active galactic nuclei. Reflection of X-rays from Sgr A∗ by dense gas in the Galactic Center region offers a means to study its past flaring activity on times scales of hundreds and thousands of years. The shape of the X-ray continuum and the strong fluorescent iron line observed from giant molecular clouds in the vicinity of Sgr A∗ are consistent with the reflection scenario. If this interpretation is correct, the reflected continuum emission should be polarized. Here we report observations of polarized X-ray emission in the direction of the Galactic center molecular clouds using the Imaging X-ray Polarimetry Explorer (IXPE). We measure a polarization degree of 31\% ± 11\%, and a polarization angle of −48∘ ± 11∘. The polarization angle is consistent with Sgr A∗ being the primary source of the emission, while the polarization degree implies that some 200 years ago the X-ray luminosity of Sgr A∗ was briefly comparable to a Seyfert galaxy.