Mini-jet found near Milky Way's supermassive black hole

Date:
December 9, 2021
Source:
NASA/Goddard Space Flight Center
Summary:
Our Milky Way's central black hole has a leak. This supermassive
black hole looks like it still has the vestiges of a blowtorch-like
jet dating back several thousand years. NASA's Hubble Space
Telescope hasn't photographed the phantom jet but has helped find
circumstantial evidence that it is still pushing feebly into a
huge hydrogen cloud and then splattering, like the narrow stream
from a hose aimed into a pile of sand.



FULL STORY ==========================================================================
Our Milky Way's central black hole has a leak. This supermassive
black hole looks like it still has the vestiges of a blowtorch-like jet
dating back several thousand years. NASA's Hubble Space Telescope hasn't photographed the phantom jet but has helped find circumstantial evidence
that it is still pushing feebly into a huge hydrogen cloud and then splattering, like the narrow stream from a hose aimed into a pile of sand.


==========================================================================
This is further evidence that the black hole, with a mass of 4.1 million
Suns, is not a sleeping monster but periodically hiccups as stars and
gas clouds fall into it. Black holes draw some material into a swirling, orbiting accretion disk where some of the infalling material is swept up
into outflowing jets that are collimated by the black hole's powerful
magnetic fields. The narrow "searchlight beams" are accompanied by a
flood of deadly ionizing radiation.

"The central black hole is dynamically variable and is currently powered
down," said Gerald Cecil of the University of North Carolina in Chapel
Hill. Cecil pieced together, like a jigsaw puzzle, multiwavelength
observations from a variety of telescopes that suggest the black hole
burps out mini-jets every time it swallows something hefty, like a gas
cloud. His multinational team's research has just been published in the Astrophysical Journal.

In 2013 evidence for a stubby southern jet near the black hole came
from X-rays detected by NASA's Chandra X-ray Observatory and radio
waves detected by the Jansky Very Large Array telescope in Socorro, New
Mexico. This jet too appears to be plowing into gas near the black hole.

Cecil was curious if there was a northern counter-jet as well. He first
looked at archival spectra of such molecules as methyl alcohol and
carbon monosulfide from the ALMA Observatory in Chile (Atacama Large Millimeter/Submillimeter Array), which uses millimeter wavelengths to
peer through the veils of dust between us and the galactic core. ALMA
reveals an expanding, narrow linear feature in molecular gas that can
be traced back at least 15 light-years to the black hole.

By connecting the dots, Cecil next found in Hubble infrared-wavelength
images a glowing, inflating bubble of hot gas that aligns to the jet at a distance of at least 35 light-years from the black hole. His team suggests
that the black hole jet has plowed into it, inflating the bubble. These
two residual effects of the fading jet are the only visual evidence of
it impacting molecular gas.



==========================================================================
As it blows through the gas the jet hits material and bends along multiple streams. "The streams percolate out of the Milky Way's dense gas disk,"
said co-author Alex Wagner of Tsukuba University in Japan. "The jet
diverges from a pencil beam into tendrils, like that of an octopus." This outflow creates a series of expanding bubbles that extend out to at least
500 light-years. This larger "soap bubble" structure has been mapped at
various wavelengths by other telescopes.

Wagner and Cecil next ran supercomputer models of jet outflows in a
simulated Milky Way disk, which reproduced the observations. "Like in archeology, you dig and dig to find older and older artifacts until
you come upon remnants of a grand civilization," said Cecil. Wagner's conclusion: "Our central black hole clearly surged in luminosity at
least 1 millionfold in the last million years.

That sufficed for a jet to punch into the Galactic halo." Previous observations by Hubble and other telescopes found evidence that the Milky
Way's black hole had an outburst about 2-4 million years ago. That was energetic enough to create an immense pair of bubbles towering above our
galaxy that glow in gamma-rays. They were first discovered by NASA's
Fermi Gamma-ray Space Telescope in 2010 and are surrounded by X-ray
bubbles that were discovered in 2003 by the ROSAT satellite and mapped
fully in 2020 by the eROSITA satellite.

Hubble ultraviolet-light spectra have been used to measure the expansion velocity and composition of the ballooning lobes. Hubble spectra later
found that the burst was so powerful that it lit up a gaseous structure,
called the Magellanic stream, at about 200,000 light-years from the
galactic center. Gas is glowing from that event even today.

To get a better idea of what's going on, Cecil looked at Hubble and
radio images of another galaxy with a black hole outflow. Located 47
million light- years away, the active spiral galaxy NGC 1068 has a
string of bubble features aligned along an outflow from the very active
black hole at its center. Cecil found that the scales of the radio and
X-ray structures emerging from both NGC 1068 and our Milky Way are very similar. "A bow shock bubble at the top of the NGC 1068 outflow coincides
with the scale of the Fermi bubble start in the Milky Way. NGC 1068 may
be showing us what the Milky Way was doing during its major power surge
several million years ago." The residual jet feature is close enough
to the Milky Way's black hole that it would become much more prominent
only a few decades after the black hole powers up again. Cecil notes that
"the black hole need only increase its luminosity by a hundredfold over
that time to refill the jet channel with emitting particles.

It would be cool to see how far the jet gets in that outburst. To reach
into the Fermi gamma-ray bubbles would require that the jet sustain for hundreds of thousands of years because those bubbles are each 50,000
light years across!" The anticipated images of the black hole's shadow
made with the National Science Foundation's Event Horizon Telescope may
reveal where and how the jet is launched.

Video of mini jet near the Milky Way's supermassive black
hole: https:// www.youtube.com/watch?v=zxqQ4G0NOhI&t=144s ========================================================================== Story Source: Materials provided by
NASA/Goddard_Space_Flight_Center. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Gerald Cecil, Alexander Y. Wagner, Joss Bland-Hawthorn, Geoffrey V.

Bicknell, Dipanjan Mukherjee. Tracing the Milky Way's Vestigial
Nuclear Jet. The Astrophysical Journal, 2021; 922 (2): 254 DOI:
10.3847/1538- 4357/ac224f ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209201656.htm

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