Sagittarius A*: Milky Way central black hole woke up 200 years ago

Sagittarius A* is a gigantic black hole sitting at the heart of our Milky Way galaxy.

**What is the Difference between Sagittarius A* & Black Holes?**

When compared to black holes in the center of other galaxies we’ve observed, Sagittarius A* doesn’t shine as bright. This suggests that, unlike its counterparts, this black hole hasn’t been busily munching on the surrounding matter. However, recent data from NASA’s IXPE (Imaging X-ray Polarimetry Explorer) telescope indicates that this sleeping giant had a snack about 200 years ago, munching on gas and other space scraps within its reach.

**Distance of Sagittarius A* with Other Black Holes**

Sagittarius A, the nearest massive black hole to Earth, sits 25,000 light years away. Despite its staggering distance from us, it’s truly mind-blowing to think this black hole is millions of times chunkier than our own Sun. Scientists often shorten it to Sgr A, “Sagittarius A* star.” It’s located in the Sagittarius constellation, smack in the middle of the Milky Way.
When earlier X-ray studies noticed that massive gas clouds near Sgr A* were recently giving off X-rays, scientists directed IXPE to look closer. Usually, these gas clouds in space, known as “molecular clouds,” are cold and dark, so their X-ray signals should have been weak. Instead, they were shining bright.

Frédéric Marin, a space scientist from the Astronomical Observatory of Strasbourg in France, shared:

“To explain why these enormous gas clouds are glowing, you could say they’re like a mirror reflecting a past burst of X-ray light,”

Marin took the lead in writing the new study, which was showcased in the journal Nature.

What is IXPE, and How it is Related to Sagittarius A*?

IXPE, which measures the direction and strength of X-ray light waves, studied these molecular clouds in February and March 2022. Astronomers found the origin of the reflected X-ray signal by mixing their findings with NASA’s Chandra X-ray Observatory’s images and comparing them with older snapshots from the European Space Agency’s XMM-Newton project.

“Think of the polarization angle like a compass. It guides us towards the source of the light that disappeared a long time ago,” explained Riccardo Ferrazzoli, a space scientist at the Italian National Institute of Astrophysics in Rome.

“And what do we find there? None other than Sgr A.”

X Rays Light Bounced Back from Huge Molecular Clouds

By examining the data, the team deduced that the X-rays from the huge molecular clouds were light bounced back from a bright, brief flare near or at Sagittarius A*. This flare might have been sparked by the black hole suddenly consuming nearby matter.
The data also gave scientists clues about how bright the original flare was and how long it lasted. This suggests that the event occurred around 200 Earth years ago, roughly at the start of the 1800s.

Our next challenge,” announced Steven Ehlert, a project scientist with IXPE at NASA’s Marshall Space Flight Center in Huntsville, Alabama, “is to verify what we’ve found and tighten the measurement’s wiggle room.

Imagery from NASA’s Imaging X-ray Polarimetry Explorer and Chandra X-ray Observatory have been combined to show X-ray data of the area around Sagittarius A*, the supermassive black hole at the core of the Milky Way galaxy. The lower panel combines IXPE data, in orange, with Chandra data in blue. The upper panel depicts a much wider field-of-view of the center of the Milky Way, courtesy of Chandra. The thin white lines layered onto the top panel frame the highlighted area, and indicate that the perspective in the bottom panel has been rotated approximately 45 degrees to the right. The combination of IXPE and Chandra data helped researchers determine that the X-ray light identified in the molecular clouds originated from Sagittarius A* during an outburst approximately 200 years ago.
**Credits: IXPE: NASA/MSFC/F. Marin et al; Chandra: NASA/CXC/SAO; Image Processing: L.Frattare, J.Major & K.Arcand**

The intensity of occurance of Flare, and its Height

Further data could refine estimates of when the flare occurred and how intense it may have been at its highest. It will also help us understand how the big molecular clouds around the black hole are spread out in 3D.

Most importantly, such studies will help scientists learn more about the physical processes that could awaken Sagittarius A* again, even if only briefly.

Ehlert stated, “IXPE is vital to helping us understand how long it takes for the black hole at the heart of our galaxy to shift.” “We know that busy galaxies and massive black holes can shift on a timeframe we can comprehend.

We’re learning more about this one’s behavior and history of bursts over time, and we’re eager to keep an eye on it to discern which changes are typical and which aren’t.”

IXPE, A Collaborative Project!

IXPE is a collaborative project between NASA and the Italian Space Agency. Scientists and partners from 12 countries are involved in this project.

Marshall oversees IXPE. Ball Aerospace, tucked away in Broomfield, Colorado, works hand in hand with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder to keep the aircraft running smoothly.