Material has been discovered moving at nearly 10% the speed of light away
from the centre of the nearby quasar PDS456 – the most powerful object in
the local universe. Like all quasars, PDS456 is thought to be powered by
matter converting into energy when material is swallowed by a supermassive
black hole. New observations show that its energy output is so large that it
is “choking on its food” and radiation is literally blowing the top off the
inner region of the disc of in-falling material that surrounds the black
hole. The discovery is being announced on Wednesday 9th April at the
UK/Ireland National Astronomy Meeting in Dublin on behalf of a team from the
University of Leicester and the NASA Goddard Space Flight Center.
PDS456 was discovered in 1997 and lies at a redshift of only 0.184 (a mere
800 million light-years away – our backyard by quasar standards).Its energy
output is equivalent to that of 25,000 billion Suns requiring a black hole
of roughly a billion solar masses. Such objects are relatively common with
high redshifts in the distant universe, but nearby ones are scarce.
“Fortunately, PDS456 is sufficiently close that we can study it in great
detail and thereby learn about the structure of these extraordinary
objects,” says Dr Paul O’Brien of the University of Leicester, who will
present the findings.
Members of the research team have been studying PDS456 for several years.
Their previous work has measured the large power output and other basic
properties of PDS456, but now, using X-ray data from the XMM-Newton X-ray
satellite and ultraviolet data from the Hubble Space Telescope, they have
discovered the new and unexpected twist. The team had suspected that PDS456
is accumulating matter at almost the maximum rate allowed for feeding a
black hole. Theory suggests that a black hole may “choke” under these
circumstances, expelling matter outward.
Before being sucked into the black hole, accreting material generally forms
a flattened, rotating disc which allows matter to move inwards while
radiating energy away. However, the energy output of PDS456 is so large that
even the enormous gravitational pull of the black hole cannot capture it
all. Instead the radiation blows the top off the inner disc. The material
travels at close to the speed of light because this process happens very
close to the black hole – within a region about the same size as the solar
system. “It appears that PDS 456 is expelling matter at the rate of many
times the mass of our sun every year” comments Dr James Reeves. “This
massive outflow may tip the balance of power in this quasar, implying that a
large fraction of its total energy output is involved in driving the flow.
Such high mass, high velocity flows pose a real problem for current models
of quasars.”
In one respect, PDS456 is similar to 3C273, the very first quasar discovered
back in 1962. “Our observations show that PDS456 looks remarkably similar to
3C273, though brighter, right across the spectrum from the ultraviolet
through to the infrared,” comments Paul O’Brien. “But 3C273 is a harder
object to study in X-rays because it has a powerful jet pointing almost
directly at us. The jet beams radiation, including X-rays, at us,
contaminating our view of the centre. It is like trying to see a light bulb
next to the glare of a searchlight. In the case of PDS456, any jet is
pointing away from our line of sight so we get a much clearer view of its
disc.”
The clear view to the centre of PDS456 means the researchers can use it as a
template object to determine what all powerful quasars are like,
particularly those accreting matter at a high rate. In the early universe,
when galaxies were young, their central black holes were growing rapidly and
may have been accreting matter at a high rate. Today only a few, like PDS
456, continue to do so.
CONTACTS
Dr. Paul O’Brien,
Department of Physics & Astronomy,
University of Leicester
(+44) (0)116 252 5203
pto@star.le.ac.uk
Will be present at the NAM 8-11 April; giving presentation
Dr. James Reeves
NASA Goddard Space Flight Center
(+1) 301 286 1592
jnr@milkyway.gsfc.nasa.gov
Will be present at the NAM 8-11 April
Professor Martin Ward
Department of Physics & Astronomy,
University of Leicester
(+44) (0)116 252 3540
mjw@star.le.ac.uk
Will be present at the NAM 8-11 April
Professor Ken Pounds
Department of Physics & Astronomy,
University of Leicester
(+44) (0)116 252 3509
kap@star.le.ac.uk
NOTE
Artist’s impressions of the centre of a galaxy containing a supermassive
black hole may be found at
http://hubblesite.org/newscenter/archive/1990/29/image/a
and
