NASA, ESA, CSA, STScI; A. Ginsburg, N. Budaiev, T. Yoo / U Florida; A. Pagan / STScI
Infrared image of Sagittarius B2, a molecular cloud in the Galactic Center obtained with James Webb, which is of a similar type to the clouds studied by the University of Michigan team
Our Galaxy’s supermassive black hole is famous for being one of the faintest in the Universe. Results from a new space telescope show that this may not always have been the case.
The black hole Sagittarius A*located in the center of the Milky Way, seems to have flared up dramatically sometime in the last few hundred years, according to X-ray emissions observed by the XRISM space telescope.
It is surprising discoveries reveal new details about the evolution of supermassive black holes. They also teach astronomers lessons about the history of our cosmic home.
Stephen DiKerbya researcher at Michigan State University, USA, worked with an international team to measure X-rays coming from a giant gas cloud near the center of the Galaxy.
The team examined the cloud with a incredible detail thanks to XRISM’s ability to resolve the energy of each X-ray photon. The findings offer strong evidence that the cloud is glowing in response to an outbreak Sagittarius A* past.
The results of the , published in the journal The Astrophysical Journal Lettersenhance the laboratory precision of XRISM, effectively changing the game in X-ray astronomy.
The work was carried out in collaboration with Kumiko Nobukawa from Kindai University in Higashiosaka, Osaka, Japan, and Masa Nobukawathat of the Nara University of Education, also in Japan.
“Nothing in my professional training as an X-ray astronomer had made me prepared for something like this“, DiKerby, postdoctoral researcher in the laboratory of assistant professor of physics and astronomy Shuo Zhang.
“This is a new and exciting capability and a new toolbox to develop these techniques”, he added.
A supermassive black hole is exactly as the term describes it – a massive black hole, containing millions or billions of masses Solar panels of material so dense that not even light can escape. All large galaxies have one, although researchers still don’t know why.
Many supermassive black holes are bright because the gas around them heats up and emits highly energetic radiation. In contrast, Sagittarius A* almost does not shine. It is one of the faintest black holes known in the Universe, only visible because it is very close to Earth.
Several large molecular clouds float around Sagittarius A* and may act as cosmic mirrorsreflecting the black hole’s X-ray flashes. Previous space telescopes have been able to detect these flashes, but not with enough energetic resolution to examine their fine structure or determine what produced them.
XRISM changed that. The telescope was launched in 2023 through a partnership between NASA and JAXA.
Its first observations are highly anticipated because they represent a huge improvement over all existing space telescopes in terms of energy resolution. Most X-ray space telescopes can distinguish the energy of a photon up to about one part in 10, or even 100.
XRISM can solve one part in 1000. The new images are like going from a Polaroid to a high-definition Technicolor image.
Larger map of the Galactic Center showing Sgr A* (the supermassive black hole) and several notable molecular clouds.
DiKerby used this clear vision to zoom in on two emission lines of extremely narrow X-rays coming from one of the molecular clouds.
By measuring their energies and shapes with innovative precision, he was able to determine the cloud’s movement and compare it with previous radio observations. Also examined subtle features in the spectrum to test two different explanations for the cloud’s brightness.
These details excluded the ideathat cosmic rays were responsible and instead showed that the cloud is reflecting an outbreak Sagittarius A* X-ray – effectively an “echo of light” from the past.
By studying multiple clouds at different distances from the black hole, astronomers can reconstruct a timeline of these ancient eruptions, just as if using delayed echoes to map the shape of a cave.
“This remarkable measurement shows how powerful is XRISM “By resolving the iron lines with such clarity, we can now read the Galactic Center’s past activity in unprecedented detail.”
The data shows for the first time how XRISM’s energy resolution can measure extremely fine features in the Universe. The team hopes the telescope will open many new avenues of discovery.
“We’re just the lucky scientists who were able to solve the problems of handling this data in this completely new way,” said DiKerby. “One of the things I love most about being an astronomer is knowing that I am the first human being to see this part of the sky this way.”
