Scientists use mismatch in telescopic data to get a handle on quasars and their ‘tails’

Scientists use mismatch in telescopic data to get a handle on quasars and their ‘tails’

Credit: MIPT

Scientists have determined the properties of ionized jets of
matter ejected by supermassive black holes in active galactic
nuclei. They analyzed unexpected discrepancies between the
data of high-precision observations conducted by an
international network of radio telescopes and that of Gaia—a
space observatory of the European Space Agency equipped with
optical telescopes.

Yuri Kovalev, who heads MIPT’s Laboratory of Relativistic
Astrophysics and a laboratory at the Lebedev Physical Institute
(LPI) of the Russian Academy of Sciences, says, “By comparing
the data from radio interferometers and , we can obtain information
about hot jets and the accretion disks surrounding black holes
at the center of galaxies in the visible part of the spectrum.
We have now gained a better understanding of what their
structure is and what processes occur inside them.”

Yuri Kovalev and Leonid Petrov from MIPT and LPI collaborated
on a research paper published in Monthly Notices of the
Royal Astronomical Society
analyzing the coordinates of
active nuclei of remote galaxies obtained independently by very
long baseline interferometry (VLBI) and Gaia.

In 2013, Gaia was launched with an aim of cataloging the
precise coordinates and velocities of 1 billion stars in our
galaxy. Hipparcos, its predecessor, gathered data on the
positions of some 1 million stars with a maximum precision of 1
millisecond of arc. In the near future, the accuracy of Gaia
will reach 24 microseconds of arc. In addition to stars in our
own galaxy, this telescope can observe objects outside the
Milky Way.

Earth-based radio interferometers, such as the Very Long
Baseline Array in New Mexico, U.S., enable imaging quasars and
determining their coordinates with an unparalleled — up until
recently — resolution of 1 millisecond of arc or better. However,
the launch of Gaia by the European Space Agency promised to make
measurements of stellar and galactic coordinates even more
precise. Is this true? Let us find out. Credit: MIPT

By now, Gaia has cataloged more than 1 billion objects. More
than 10,000 of these are extremely bright called quasars.
These have accretion disks of matter falling onto a
supermassive black hole that, in turn, ejects extended beams of
matter called jets. As matter falls onto the black hole, it is
heated to temperatures so extreme that it emits radiation
across almost the entire electromagnetic spectrum.

To study such objects, researchers use VLBI. It involves the
use of multiple positioned far from each other
but working as an integrated system. This technique bests the
angular resolution achieved by optical telescopes several
hundredfold. This is what made radio signals so useful for
resolving the structure of jets expelled by quasars.

“But there are things you can’t see in the radio spectrum,”
says Leonid Petrov. “Thus, for instance, an accretion disk
around a emits mostly
visible and ultraviolet light. So we decided to combine the
data from two sources.”

In contrast to the Hubble Space Telescope or similar
instruments, Gaia does not, by itself, produce an image.
Instead, it registers the coordinates of the center of the
luminosity of a celestial object. Together with MIPT student
Alexander Plavin, Kovalev and Petrov compared the data on the
coordinates of quasars obtained by Gaia and VLBI. They found
that for roughly 6 percent of objects, the positions did not
agree very well. Generally, the position of an object provided
by Gaia was shifted in the direction of jets.

This animation illustrates the expulsion of hot plasma in
remote quasars as seen in radio waves with a resolution better
than 1 milliarcsecond. The luminosity is reflected by the colors
used, with yellow corresponding to higher and blue to lower
levels. Graphic courtesy of Y. Kovalev and the MOJAVE
collaboration. Credit: 10.1093/mnras/stx1747

“We can now use the data on variable radiation output and
position of quasars provided by radio interferometry and Gaia
to recreate and study the structure of hundreds of very remote
quasars at the scale of parsecs, thousandths of a second of
arc. This precision is superior to what is possible with
ordinary optical telescopes and even with Hubble,” says
Kovalev. He adds that data analysis revealed the existence of
bright jets emitting in visible light in many quasars at
angular scales so fine that even the Hubble Space Telescope
cannot detect them. In order to see such a structure directly,
a space telescope with a mirror the size of a stadium would be
needed. The scientists suggested a method for revealing this
structure indirectly by means of combining the data from
existing telescopes.

The investigation of variations in source positions and
brightness will help researchers to determine what causes
bright flares in active galactic nuclei. This will improve
understanding of the physics of and supermassive black holes.

There is even a practical aspect to this discovery: VLBI-based
quasar observations are used in navigation to establish a
celestial frame of reference. This is necessary for tracking
the movement of continents and operating positioning systems,
including GPS and GLONASS. The comparison of the data provided
by VLBI and the Gaia space indicates the presence of a certain
source position “jitter” in the optical range. As a
consequence, caution is required when using the coordinates of
active galactic nuclei obtained by optical observations for
navigation.

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More information: L. Petrov et al, Observational
consequences of optical band milliarcsec-scale structure in
active galactic nuclei discovered by Gaia, Monthly Notices
of the Royal Astronomical Society
(2017). DOI: 10.1093/mnras/stx1747

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by:
Moscow Institute of Physics and Technology