Artist’s illustration of galaxy with jets from a supermassive black hole
Radio galaxy 3C 297
Radio galaxy 3C 454.1
Radio galaxy 3C 356
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Large Hubble survey confirms link between mergers and supermassive black holes with relativistic jets
Notes
[4] Other studies had shown a strong relationship between the merger history of a galaxy and the high levels of radiation at radio wavelengths that suggests the presence of relativistic jets lurking at the galaxy’s centre. However, this survey is much more extensive, and the results very clear, meaning it can now be said with almost certainty that radio-loud AGNs, that is, galaxies with relativistic jets, are the result of galactic mergers.
Fulldome clip showing animation of galaxy with jets from a supermassive black hole
Large Hubble survey confirms link between mergers and supermassive black holes with relativistic jets
In the most extensive survey of its kind
ever conducted, a team of scientists have found an unambiguous link
between the presence of supermassive black holes that power high-speed,
radio-signal-emitting jets and the merger history of their host
galaxies. Almost all of the galaxies hosting these jets were found to be
merging with another galaxy, or to have done so recently. The results
lend significant weight to the case for jets being the result of merging
black holes and will be presented in the Astrophysical Journal.
A team of astronomers using the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3)
have conducted a large survey to investigate the relationship between
galaxies that have undergone mergers and the activity of the
supermassive black holes at their cores.
The team studied a large selection of galaxies with extremely
luminous centres — known as active galactic nuclei (AGNs) — thought to
be the result of large quantities of heated matter circling around and
being consumed by a supermassive black hole. Whilst most galaxies are
thought to host a supermassive black hole, only a small percentage of them are this luminous and fewer still go one step further and form what are known as relativistic jets [1].
The two high-speed jets of plasma move almost with the speed of light
and stream out in opposite directions at right angles to the disc of
matter surrounding the black hole, extending thousands of light-years
into space. The hot material within the jets is also the origin of radio
waves.
It is these jets that Marco Chiaberge from the Space Telescope
Science Institute, USA (also affiliated with Johns Hopkins University,
USA and INAF-IRA, Italy) and his team hoped to confirm were the result
of galactic mergers [2].
The team inspected five categories of galaxies for visible signs of
recent or ongoing mergers — two types of galaxies with jets, two types
of galaxies that had luminous cores but no jets, and a set of regular
inactive galaxies [3].
“The galaxies that host these relativistic jets give out large amounts of radiation at radio wavelengths,” explains Marco. “By
using Hubble’s WFC3 camera we found that almost all of the galaxies
with large amounts of radio emission, implying the presence of jets,
were associated with mergers. However, it was not only the galaxies
containing jets that showed evidence of mergers!” [4].
“We found that most merger events in themselves do not actually result in the creation of AGNs with powerful radio emission,” added co-author Roberto Gilli from Osservatorio Astronomico di Bologna, Italy. “About
40% of the other galaxies we looked at had also experienced a merger
and yet had failed to produce the spectacular radio emissions and jets
of their counterparts.”
Although it is now clear that a galactic merger is almost certainly
necessary for a galaxy to host a supermassive black hole with
relativistic jets, the team deduce that there must be additional
conditions which need to be met. They speculate that the collision of
one galaxy with another produces a supermassive black hole with jets
when the central black hole is spinning faster — possibly as a result of
meeting another black hole of a similar mass — as the excess energy
extracted from the black hole’s rotation would power the jets.
“There are two ways in which mergers are likely to affect the
central black hole. The first would be an increase in the amount of gas
being driven towards the galaxy’s centre, adding mass to both the black
hole and the disc of matter around it,” explains Colin Norman, co-author of the paper. “But
this process should affect black holes in all merging galaxies, and yet
not all merging galaxies with black holes end up with jets, so it is
not enough to explain how these jets come about. The other possibility
is that a merger between two massive galaxies causes two black holes of a
similar mass to also merge. It could be that a particular breed of
merger between two black holes produces a single spinning supermassive
black hole, accounting for the production of jets.”
Future observations using both Hubble and ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) are needed to expand the survey set even further and continue to shed light on these complex and powerful processes.
Notes
[1] Relativistic jets travel at close to the speed of light, making them one of the fastest astronomical objects known.
[2] The new observations used in this
research were taken in collaboration with the 3CR-HST team. This
international team of astronomers is currently led by Marco Chiaberge
and has conducted a series of surveys of radio galaxies and quasars from
the 3CR catalogue using the Hubble Space Telescope.
[3] The team compared their
observations with the swathes of archival data from Hubble. They
directly surveyed twelve very distant radio galaxies and compared the
results with data from a large number of galaxies observed during other
observing programmes.
[4] Other studies had shown a strong relationship between the merger history of a galaxy and the high levels of radiation at radio wavelengths that suggests the presence of relativistic jets lurking at the galaxy’s centre. However, this survey is much more extensive, and the results very clear, meaning it can now be said with almost certainty that radio-loud AGNs, that is, galaxies with relativistic jets, are the result of galactic mergers.
Note for Editors
Image credit: NASA, ESA, M. Chiaberge (STScI)
Image credit: NASA, ESA, M. Chiaberge (STScI)
Contacts
Marco Chiaberge
Space Telescope Science Institute, USA
Johns Hopkins University, USA, INAF-IRA, Italy
Tel: +1 410 338 4980
Email: marcoc@stsci.edu
Roberto Gilli
INAF
Osservatorio Astronomico di Bologna, Italy
Tel: +39 051 2095 719
Cell: +39 347 4139847
Email: roberto.gilli@oabo.inaf.it
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500
Email: mjaeger@partner.eso.org
Space Telescope Science Institute, USA
Johns Hopkins University, USA, INAF-IRA, Italy
Tel: +1 410 338 4980
Email: marcoc@stsci.edu
Roberto Gilli
INAF
Osservatorio Astronomico di Bologna, Italy
Tel: +39 051 2095 719
Cell: +39 347 4139847
Email: roberto.gilli@oabo.inaf.it
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500
Email: mjaeger@partner.eso.org
Source: ESA/Hubble - Space Telescope
