Cosmic gas cloud blinks in sync with circling black hole

Date:
August 17, 2020
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
Scientists have detected a mysterious gamma-ray heartbeat
coming from a cosmic gas cloud. The inconspicuous cloud in the
constellation Aquila is beating with the rhythm of a neighbouring
precessing black hole, indicating a connection between the two
objects.



FULL STORY ========================================================================== Scientists have detected a mysterious gamma-ray heartbeat coming from a
cosmic gas cloud. The inconspicuous cloud in the constellation Aquila
is beating with the rhythm of a neighbouring precessing black hole,
indicating a connection between the two objects, as the team led by
DESY Humboldt Fellow Jian Li and ICREA Professor Diego F. Torres from
the Institute of Space Sciences (IEEC- CSIC) reports in the journal
Nature Astronomy. Just how the black hole powers the cloud's gamma-ray heartbeat over a distance of about 100 light years remains enigmatic.


==========================================================================
The research team, comprising scientists from Germany, Spain, China and
the U.S., rigorously analysed more than ten years of data from the US
space administration NASA's Fermi gamma-ray space telescope, looking at
a so-called micro quasar. The system catalogued as SS 433 is located some 15,000 lightyears away in the Milky Way and consists of a giant star with
about 30 times the mass of our sun and a black hole with about 10 to 20
solar masses. The two objects are orbiting each other with a period of
13 days, while the black hole sucks matter from the giant star.

"This material accumulates in an accretion disc before falling into
the black hole, like water in the whirl above the drain of a bath tub," explains Li.

"However, a part of that matter does not fall down the drain but shoots
out at high speed in two narrow jets in opposite directions above and
below the rotating accretion disk." This setting is known from active
galaxies called quasars with monstrous black holes with millions of solar masses at their centres that shoot jets tens of thousands of lightyears
into the cosmos. As SS 433 looks like a scaled-down version of these
quasars, it has been dubbed a micro quasar.

The high-speed particles and the ultra-strong magnetic fields in the
jet produce X-rays and gamma rays. "The accretion disc does not lie
exactly in the plane of the orbit of the two objects. It precesses,
or sways, like a spinning top that has been set up slanted on a table,"
says Torres. "As a consequence, the two jets spiral into the surrounding
space, rather than just forming a straight line." The precession of
the black hole's jets has a period of about 162 days.

Meticulous analysis revealed a gamma-ray signal with the same period
from a position located relatively far from the micro quasar's jets,
which has been labelled as Fermi J1913+0515 by the scientists. It is
located at the position of an unremarkable gas enhancement. The consistent periods indicate the gas cloud's emission is powered by the micro quasar.

"Finding such an unambiguous connection via timing, about 100 light years
away from the micro quasar, not even along the direction of the jets is
as unexpected as amazing," says Li. "But how the black hole can power the
gas cloud's heartbeat is unclear to us." Direct periodic illumination
by the jet seems unlikely. An alternative that the team explored is
based on the impact of fast protons (the nuclei of hydrogen atoms)
produced at the ends of the jets or near the black hole, and injected
into the cloud, where these subatomic particles hit the gas and produce
gamma rays. Protons could also be part of an outflow of fast particles
from the edge of the accretion disc. Whenever this outflow strikes the
gas cloud, it lights up in gamma rays, which would explain its strange heartbeat. "Energetically, the outflow from the disc could be as powerful
as that of the jets and is believed to precess in solidarity with the
rest of the system," explains Torres.

Further observations as well as theoretical work are required to fully
explain the strange gamma-ray heartbeat of this unique system beyond this initial discovery. "SS 433 continues to amaze observers at all frequencies
and theoreticians alike," emphasises Li. "And it is certain to provide
a testbed for our ideas on cosmic-ray production and propagation near
micro quasars for years to come."

========================================================================== Story Source: Materials provided by
Deutsches_Elektronen-Synchrotron_DESY. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Jian Li, Diego F. Torres, Ruo-Yu Liu, Matthew Kerr, Emma de On~a
Wilhelmi, Yang Su. Gamma-ray heartbeat powered by the microquasar
SS 433.

Nature Astronomy, 2020; DOI: 10.1038/s41550-020-1164-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200817123059.htm

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