SRON_Spectrum_2016

ters of galaxies, and how do black holes grow
and influence their surroundings? However,
they will need to be patient because the
launch of the space observatory is planned for
2028.
Matryoshka dolls
One of the researchers is SRON astronomer
Peter Jonker. Last year Jonker and his colleagues
caught a supermassive black hole
tearing a star apart. The black hole was quite
bright in the radio spectrum – there was
already an accretion disk with the flow of
matter moving towards the black hole –
but not so bright in the X-ray spectrum.
“Until a star passed that was being torn
apart,” explains Jonker. “Due to the new
flow of matter into the black hole, it entered
an entirely different mode.”
After this powerful injection of gas, Peter
Jonker and his team observed a strong in -
crease in X-rays and visible light, while the
radio emission became weaker. The radio
emission most likely originates from a jet,
a fast gas flow emitted by the black hole.
This fits exactly in the pattern that is observed
in much smaller stellar black holes. In general,
these are quiet and occasionally experience
an eruption during which they first become
brighter in the X-ray and radio spectra until
the flow of matter is so large that the X-ray
spectrum becomes dimmer, whereas the radio
spectrum decreases by factor of more than 50.
Jonker: “And that pattern was also found for
a supermassive black hole. We call this the
Matryoshka principle, which predicts that all
compact objects in universe that attract
matter behave the same with a correction
based on their mass.”
Medium-sized black holes
To gain a better understanding of this pro -
cess es Jonker wants to use ATHENA to start
hunting for black holes that are not extremely
heavy but are also not stellar, so-called
medium -sized black holes. Up until now the
masses of the candidate medium-sized black
holes are all based on rough estimates. Only
a handful of good candidates are known
but these are located so far away that as -
tronomers cannot determine how large the
orbits of the stars around the black hole are
and therefore cannot calculate the mass of
the black hole.
If we can find a white
dwarf that is being torn
apart then the perpetrator
has to be a medium-sized
black hole
Jonker: “Medium-sized black holes (a thousand
to ten thousand solar masses) can also
tear stars apart but that only happens if a star
comes relatively near. And then the time scales
are much shorter, so you have little time to
make your observation.” Jonker is mainly interested
in white dwarfs that are engulfed by
such medium-size black holes. “Supermassive
black holes can also do that but that only
occurs after such a star has passed the observation
horizon. Therefore we do not see it.”
If we can find a white dwarf that is being
torn apart then the perpetrator must be a
medium-sized black hole. As soon as a radio
or optical telescope has observed such an
event we can then immediately observe it in
the X-ray spectrum using ATHENA. Jonker
also hopes that the intended wide-angle
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SRON Spectrum
From top to bottom: Hot gas cloud as a consequence
of the Tycho supernova (NASA/CXC/SAO);
Black hole (NASA); supermassive black hole blows
bubbles in the hot gas of the Perseus cluster
(NASA/CXC/SAO/E. Bulbul, et al.).