ASTRONEWS
Infalling dense, cold
1 molecular gasOutflowing hot
2 atomic gasGas returning
3 to the diskWWW.ASTRONOMY.COM 21GROWTH SPURT. Astronomers discovered a young star rapidly gobbling up material from the dusty,
gas-rich disk surrounding it. Only about a dozen such objects have been observed so far.Astronomers envision each supermassive black
hole with a doughnut-shaped torus of gas and
dust around it. New observations, published
October 30 in The Astrophysical Journal, are
now challenging that simplistic picture, find-
ing the doughnuts may more closely resemble
circulating fountains than solid ring-shaped
structures.
Researchers used the Atacama Large
Millimeter/submillimeter Array (ALMA) to
observe the supermassive black hole at the
center of the Circinus Galaxy, 14 million light-
years from Earth. Comparing their data to
detailed simulations, they found the material
around Circinus’ black hole is composed of sev-
eral moving components that resemble a recir-
culating fountain, such as in a plaza or park.
The fountain effect begins as cold gas falls
toward the black hole and forms the torus. As
the gas gets closer to the black hole, it heats
up and breaks apart into individual molecules
and then atoms, which become ionized (loseelectrons). Some of these atoms are absorbed
by the black hole, but some shoot out above or
below the disk in outflows. These atoms later
fall back onto the disk, creating a three-dimen-
sional structure that continuously circulates
hot gas.
The findings not only reveal where black
hole tori may come from, but also challenge
the relatively rigid properties astronomers
have assigned them for decades. “Previous
theoretical models set a priori assumptions of
rigid doughnuts,” team member Keiichi Wada
of Kagoshima University in Japan said in a
press release. “Rather than starting from
assumptions, our simulation started from the
physical equations and showed for the first
time that the gas circulation naturally forms
a doughnut.”
“Based on this discovery, we need to rewrite
the astronomy textbooks,” said lead author
Takuma Izumi of the National Astronomical
Observatory of Japan. — A.K., C.G.Black hole doughnuts resemble fountains
The number of years since the International
Astronomical Union was founded to promote
astronomical research, education, and100 development.
A team of astronomers led by University of
Leeds’ John Ilee uncovered a stellar surprise
while observing the massive infant star MM 1a.
In work published December 14 in The
Astrophysical Journal Letters, Ilee’s team found
that the star’s protoplanetary disk was so mas-
sive, it had formed a second star instead of a
system of planets. The much smaller compan-
ion, dubbed MM 1b, was detected just outside
the behemoth star’s dusty disk. Even more
bizarre, the smaller star may have a protoplan-
etary disk of its very own.
To shed light on the peculiar pair, the
researchers used the Atacama Large
Millimeter/submillimeter Array to probe the
star system, measuring the light emitted from
the disk’s gas and dust. They used this informa-
tion to calculate the mass of the stars, finding
that MM 1a is about 40 times the mass of the
Sun, while MM 1b has just half our Sun’s mass.
To account for this stark contrast, the
researchers think that MM 1b was actually
born in a fragment of MM 1a’s disk. Due to
the MM 1a’s hefty mass, they believe the disk
wasn’t able to hold up against its own gravity
and ended up breaking off into fragments.
One of those pieces housed enough dust and
gas to create the low-mass companion star.
Unfortunately, both stars will soon meet
a grim end. Despite the long life spans of
lower-mass stars like MM 1b, massive stars
like MM 1a are short lived; it will probably
destroy the whole system in a supernova
within about a million years.
Fiery futures aside, the discovery marks
one of the first times astronomers have seen
a star forming from the fragmented disk of its
companion. The finding could help research-
ers understand our universe’s strange star
systems, while also reminding us there are
plenty of stellar puzzles left to be solved. — A.J.Massive star births
its own companion
COSMIC FOUNTAIN. The dusty doughnuts astronomers have envisioned around supermassive black holes
appear to be dynamic fountains, rather than static rings. As cold infalling gas is heated, it shoots away from the
black hole in outflows, which then fall back onto the disk to repeat the process. NAOJMINI-ME. This image shows emission from dust
(green) and gas (reddish hues are receding, bluish
are approaching) around a strange pair of stars. The
smaller star, MM 1b, appears to have formed from a
fragment of the massive dusty disk surrounding the
much larger star MM 1a. J.D. ILEE/UNIVERSITY OF LEEDSMM 1aMM 1b