Why doesn’t a supermassive black hole devour
its entire galaxy?
There are several factors working against the black hole sucking in all
before it. The biggest one is probably the need to get material down
into the centre before it can be eaten. Since the stars and gas in the
galaxy are moving, either in circles in a galactic disc or in a wider
range of different directions in an elliptical one, they typically have
angular momentum, like a figure skater. If a skater brings in their
arms, this quantity cannot be destroyed, and so they spin faster,
making it tougher to bring their arms in further. The answer is not
dissimilar to why all the bathwater doesn’t disappear the moment
you pull out the plug – first it has to spiral in and down.
Another factor is that the loss of angular momentum required to
funnel matter into the very centre can be achieved by transferring
energy and momentum outward as the material spirals in on
progressively faster, tighter orbits. This is arranged by shearing
between different layers. The stretched and sheared material can
become hot enough that its radiation carries substantial momentum
to the point where the push of this radiation can match the
gravitational pull of the black hole, stopping the material from falling
in. If the amount of matter falling in rises then the push rises in
proportion, providing a feedback loop to slow the accretion of even
the material that has made its way in close enough.
Andrew Blain is professor of Observational Astronomy
at the University of Leicester, England
ASTROPHYSICS
Didyou know?
Theterm‘blackhole’was
firstcoinedin1967by
American astronomer John
Wheeler, and the first
one was discovered
in 1971.Within the Standard Model of particle physics
the Higgs boson is the only fundamental
particle without any intrinsic spin, allowing its
interactionwithitselfandtheotherparticlesto
generatethemassforotherfundamentalstuff
like electrons and quarks.
Going beyond the Standard Model, the
Higgs could hold the key to many important
mysteries in particle physics. For example,
theHiggscouplestovacuumfluctuationsthat
shouldgiveitamassnearthePlanckscale,
where gravity becomes strong. Instead, the
Higgsmassof125GeV(gigaelectronvolts)is
17ordersofmagnitudesmaller.Wesuspect
that some as-yet-undiscovered physical
mechanismisresponsible.Popularcandidates
likesimplesupersymmetryorextradimensions
have not yet been discovered at the Large
Hadron Collider.Thesetheoriescouldproduceunexpected
LHCsignaturessuchasneutrallong-lived
particles(LLPs)thatareonlyvisibleoncethey
decay to known particles. Luckily the LHC
cansearchfortheseLLPssincetheyshould
occasionally be produced in exotic decays of
the Higgs boson, and this possibility is coming
under increased experimental scrutiny.
Finally, these theories could also leave their
trace by modifying the cosmic microwave
background or the distribution of dark matter
in our Milky Way galaxy in subtle ways.
The future of particle physics may lie at
this interdisciplinary frontier, tying together
theresultsfromcolliderexperimentswith
cosmological and astrophysical observations.
David Curtin is assistant professor
at the Department of Physics,
University of Toronto, CanadaWhat’s the importance of the Higgs Boson?
ASTROPHYSICSA black hole’s
‘event horizon’
is the point
where material
cannot escape
the black hole’s
enormous
gravity“Going beyond the Standard Model, the
Higgs could hold the key to many important
mysteries in particle physics”
The Large
Hadron Collider
resides near Geneva,
Switzerland© NASA; Tobias Roetsch; Maximilien Brice; bobpaz00202Ask Space