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EI2GYB > ASTRO 15.09.23 09:06l 102 Lines 5848 Bytes #999 (0) @ WW
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Subj: Dark matter halos measured around ancient quasars
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Dark matter halos measured around ancient quasars
Date:
September 12, 2023
Source:
University of Tokyo
Summary:
At the center of every galaxy is a supermassive black hole. Beyond a
certain size, these become active, emitting huge amounts of radiation, and are
then called quasars. It is thought these are activated by the presence of
massive dark matter halos (DMH) surrounding the galaxy, directing matter
towards the center, feeding the black hole. A team has now surveyed hundreds of
ancient quasars and found this behavior is very consistent throughout history.
This is surprising, as many large-scale processes show variation throughout the
life of the universe, so the mechanism of quasar activation could have
implications for the evolution of the entire universe.
At the center of every galaxy is a supermassive black hole. Beyond a certain
size, these become active, emitting huge amounts of radiation, and are then
called quasars. It is thought these are activated by the presence of massive
dark matter halos (DMH) surrounding the galaxy, directing matter towards the
center, feeding the black hole. A team including researchers from the
University of Tokyo have, for the first time, surveyed hundreds of ancient
quasars and found this behavior is very consistent throughout history. This is
surprising, as many large-scale processes show variation throughout the life of
the universe, so the mechanism of quasar activation could have implications for
the evolution of the entire universe.
Measuring the mass of DMHs is not easy; it's famously a very elusive substance,
if substance is even the right word to use, given the actual nature of dark
matter is unknown. We only know it exists at all due to its gravitational
impact on large structures such as galaxies. Thus, dark matter can only be
measured by making observations about its gravitational effects on things. This
includes the way it might pull on something or affect its movement, or through
the lensing (bending of light) of objects behind a suspected area of dark
matter.
The challenge becomes greater at large distances, given how weak the light from
more distant, and therefore ancient, phenomena can be. But this did not stop
Professor Nobunari Kashikawa from the Department of Astronomy, and his team,
from trying to answer a long-standing question in astronomy: How are black
holes born, and how do they grow? The researchers are especially keen to
explore this in relation to supermassive black holes, the largest kind, which
exist in the heart of every galaxy. These would be very difficult to study were
it not for the fact that some grow so massive they begin to output incredibly
powerful jets of matter or spheres of radiation that in either case become what
we call quasars. These are so powerful that even at large distances, we can now
observe them using modern techniques.
"We measured for the first time the typical mass for dark matter halos
surrounding an active black hole in the universe about 13 billion years ago,"
said Kashikawa. "We find the DMH mass of quasars is pretty constant at about 10
trillion times the mass of our sun. Such measurements have been made for more
recent DMH around quasars, and those measurements are strikingly similar to
what we see for more ancient quasars. This is interesting because it suggests
there is a characteristic DMH mass which seems to activate a quasar, regardless
of whether it happened billions of years ago or right now."
Quasars at great distances appear faint, as the light which left them long ago
has spread out, was absorbed by intervening matter, and has been stretched into
nearly invisible infrared wavelengths due to the universe expanding over time.
So Kashikawa and his team, whose project began in 2016, used multiple surveys
of the sky which incorporated a range of different instruments, the main one
being Japan's Subaru Telescope, located in U.S. state of Hawaii.
"Upgrades allowed Subaru to see farther than ever, but we can learn more by
expanding observation projects internationally," said Kashikawa. "The
U.S.-based Vera C. Rubin Observatory and even the space-based Euclid satellite,
launched by the EU this year, will scan a larger area of the sky and find more
DMH around quasars. We can build a more complete picture of the relationship
between galaxies and supermassive black holes. That might help inform our
theories about how black holes form and grow."
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