Doesn’t our black hole have a jet? – Astronomers discover traces of a weak outflow from the Milky Way Center –

Telltale outflow: The black hole in the center of the Milky Way apparently has an active jet after all – a weak flow of radiation and particles reaching into space. After the first evidence of this was recently discovered south of the galaxy level, astronomers have now discovered traces of such a jet in the north as well. Just a few hundred years ago, this jet could have been ten thousand times brighter than it is today, as the team reports in the “Astrophysical Journal”.

At the moment, the supermassive black hole in the heart of the Milky Way is calm and largely inactive. But huge bubbles and “chimneys” made of high-energy radiation and hot gases show that this was not always the case: Around two to three million years ago Sagittarius A * experienced a huge eruption that could even have illuminated the earthly night sky and far extragalactic gas flows . This explosion left a large part of the structures detectable today in the galactic center.

Are there active outflows in the galaxy center?

The unanswered question, however, is whether the black hole is still active enough today to create a jet – cones made of fast particles and radiation perpendicular to the plane of the galaxy. In active galaxy nuclei, such jets can be seen for millions of light years, but in our native black hole there did not seem to be these outflows – at least that’s what people thought up to now.

In recent years, however, astronomers have detected radio and X-ray emissions near the galactic center that could have come from a jet. Especially south of the Milky Way plain, there seemed to be possible traces of a weak, short outflow. Gerald Cecil from the University of North Carolina and his colleagues have now investigated what this is all about and whether there is also evidence of a jet north of the galactic center.

For their study, the astronomers evaluated data from the ALMA observatory in Chile, the Hubble space telescope and several X-ray telescopes.

Glowing gases and galactic “octopus”

In fact, the analyzes revealed some abnormalities. “The ALMA images show a uniquely linear structure that lies amidst the otherwise complicated movements of the excited molecular gases in the galactic center,” report Cecil and his team. This narrow gas flow can be detected up to about 6.5 light years from the galactic center.

Evidence of a jet in the heart of the Milky Way. © NASA/ESA, Gerald Cecil/ UNC-Chapel Hill, Joseph DePasquale/STScI

This is followed by a zone in which the XMM-Newton X-ray telescope has also detected conspicuous structures. There are clouds of gas there, the brighter, glowing edge of which lies exactly in the extension of the gas flow mapped by ALMA. Infrared images from the Hubble Space Telescope, in turn, extend this cone-shaped zone of intensely excited gases to a distance of at least 35 light years from the black hole.

“The outflows seep out of the dense gas disk of the Milky Way,” explains Alex Wagner from Tsukuba University in Japan. “The jet then divides into tendrils by a pencil-thin stream, similar to the tentacles of an octopus.” These “tentacles” merge into a series of expanding bubbles that extend at least 500 light years out. These bubbles have been detected by various telescopes in the past, but the connection with potential jets is only now emerging.

Jet could still be active

According to the astronomers, these observations provide indications that the central black hole may still be producing jets – even if they are very weak. Some of the structures also indicate significantly more activity just a few hundred years ago. “Sagittarius is only faintly glowing today, but just a few centuries ago it was ten thousand times brighter,” says Cecil.

The currently largely invisible outflow also requires little to become clearly more noticeable again: “Even a hundred times greater brightness would be enough to fill the jet to such an extent that it would glow over its entire length,” explain the astronomers. (The Astrophysical Journal, 2021; doi: 10.3847 / 1538-4357 / ac224f)

Quelle: NASA/ Goddard Space Flight Center

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