even before the first stars, there
were molecular clouds with just
the right conditions to collapse
straight away into singularities.
The James Webb Space Telescope
might be able to shed some light
on this dark topic when it comes
online this year. It was designed
especially to see the first galaxies
and stars, and those primordial
formations could help us to
understand the initial distribution
of potential collapsible matter.
And that’s not all ...
It’s tempting to picture accretion
as a peaceful, gradual, and
constructive process, like erosion
in reverse. It can certainly
take time to get going. But the
methods by which an accretor
gains mass can be quite quick
and chaotic. Recently, observers
have seen what they call accretion
bursts around protostars —
instances of extreme instability
in a disk, where large amounts
of material suddenly plunge into
the star. Hunter recently observed
this on NGC 6334 I, a protostar
cluster in the Cat’s Paw Nebula
(NGC 6334) in the constellation
Scorpius, using the Stratospheric
Observatory for Infrared
Astronomy (or SOFIA). He
theorizes that a high proportion
of the total accretion of some
stars — up to 50 percent — may
actually happen in this way.
Furthermore, accretion is not
always a constructive process —
accretion in one place mightactually preclude the process else-
where. There is a rare kind of
supernova, called Type 1ax, where
the accretion disk around a white
dwarf explodes. The accretion
disks around quasars have power-
ful magnetic forces which shoot
material out in supersonic jets.
And there is evidence that winds
from the jets of actively feeding
SMBHs can actually quench, or
turn off, star formation in their
host galaxies.
These are exciting times for
those who study accretion.
Astronomers finally have the
capability to compare their math-
ematical predictions to actual
astrophysical objects at key stages
of their lives. Whether their theo-
ries ultimately measure up to
reality, or whether new ones will
need to be invented to account for
observations, only time — and a
lot more data — will tell.Supercomputer
simulations
reveal the turbulent
and hierarchical
dynamics of
collapsing infrared
dark clouds (IRDCs),
forming filaments
within filaments. In
the densest regions
of this simulation,
shown in red,
molecular clouds are
forming cores that
will become massive
stars. RICHARD KLEIN,
LAWRENCE LIVERMORE NATIONAL
LABORATORY; PAK SHING LI,
UNIVERSITY OF CALIFORNIA,
BERKELEY; TIM SANDSTROM, NASA
AMES RESEARCH CENTERIRDCs appear
as shadows
splayed across the
bright mid-infrared
background of the
Milky Way, as seen in
this false-color image
from NASA’s Spitzer
Space Telescope.
Though they are
some of the darkest
objects in the sky,
these ultracold and
dense clouds give
birth to the brightest,
most massive stars in
the galaxy. NASA/
JPL-CALTECHWWW.ASTRONOMY.COM 23
Arwen Rimmer is a writer and
musician in Cambridge, England.