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

No effect was felt on Earth, as the distance between the celestial object and our planet is too great.
Loukia Papadopoulos
An illustration of the black hole's activity.jpg
An illustration of the black hole's activity.


Astrophysicists have discovered that Sagittarius A* (Sgr A*)1, the supermassive black hole at the center of the Milky Way, emerged from a long period of dormancy some 200 years ago. 

This is according to a press release from CNRS published on Wednesday. 

“The team, led by Frédéric Marin2, a CNRS researcher at the Astronomical Strasbourg Observatory (CNRS/University of Strasbourg), has revealed the past awakening of this gigantic object, which is four million times more massive than the Sun. Their work is published in Nature on 21 June. Over a period of one year at the beginning of the 19th century, the black hole gobbled up cosmic objects that got a little too close to it, before once more entering a state of quiescence,” noted the statement

“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.