An international team of astrophysicists observed for the first time
that the jet of a quasar is less powerful on long radio wavelengths than
earlier predicted. This discovery gives new insights in the evolution
of quasar jets. They made this observation using the international Low
Frequency Array (LOFAR) telescope, that produced high resolution radio
images of quasar 4C+19.44 located over 5 billion light-years from Earth.
Supermassive black holes, many millions of times more massive than our
Sun reside in the central regions of galaxies. They grow even larger by
attracting and consuming nearby gas and dust. If they consume material
rapidly, the infalling matter shines brightly and the source is known as
a quasar.
Some of this infalling matter is not digested, but instead is
ejected in the form of so-called jets that punch through the
surrounding galaxy and into intergalactic space for millions of light
years. These jets, shining brightly at radio wavelengths, are composed
of particles accelerated up to nearly the speed of light, but exactly
how these particles achieve energies not attainable on the Earth is yet
to be completely solved.
The discovery on quasar 4C+19.44 gives new insights to the balance
between the energy in the field surrounding the quasar and that residing
in the quasar jet. This finding indicates to an intrinsic property of
the source rather than due to absorption effects. It implies that the
energy budget available to accelerate particles and the balance between
energy stored in particles and in the magnetic field, is less than
expected.
"This is an important discovery that will be used for the years to come
to improve simulations of jets. We observed for the first time a new
signature of particle acceleration in the power emitted of quasar jets
at long radio wavelengths. An unexpected behaviour that changes our
interpretation on their evolution." Said Prof. Francesco Massaro from
University of Turin. "We knew that this was already discovered in other
cosmic sources but it was never before observed in quasars."
The international team of astrophysicists had observed the jet of the
quasar 4C+19.44 at short radio wavelengths, in visible light, and X-ray
wavelengths. The addition of the LOFAR images allowed astrophysicists to
make this discovery. LOFAR is the first radio facility operating at
long radio wavelengths, which produces sharp images with a resolution
similar to that of the Hubble Space Telescope.
"We have been able to perform this experiment thanks to the highest
resolution ever achieved at these long radio wavelengths, made possible
by LOFAR." Said Dr Adam Deller, an astrophysicist of the Swinburne
University of Technology who contributed to the LOFAR data analysis and
imaging of 4C +19.44 while at ASTRON in the Netherlands, heart of the
LOFAR collaboration.
Dr Raymond Oonk, an astronomer at ASTRON and Leiden University and Dr
Javier Moldon, astronomer at the University of Manchester, explained
that "We have developed new calibration techniques for LOFAR and this
has allowed us to separate compact radio structures in the quasar jet
known as radio knots, and measure their emitted light. This result was
unexpected and demands to future deeper investigations. New insights and
clues on particle acceleration will come soon thanks to the
international stations of LOFAR."
The observation performed on the radio jet of 4C+19.44 was designed by
Dr D. E. Harris, supervisor of Prof. Francesco Massaro, while working at
the Harvard-Smithsonian Center for Astrophysics, several years ago. He
performed the observation in collaboration with Dr Raffaella Morganti
and his friends and colleagues at ASTRON. He only got the opportunity to
see preliminary results as he passed away on 2015 December 6th. This publication, published in the first March issue of the Astrophysical Journal, is in memory of a career spanned much of the history of radio astronomy.
