Pixels in each
of WISE’s four
of images WISE
takes per day
Black holes seen
dancing in pairs
Merging galaxies play host
to astrophysical pas de deux
often galaxy mergers occur
in the universe.
Observations have shown
that nearly every galaxy has a
supermassive black hole — a
black hole with a mass from a
million to a few billion times
that of the sun — at its cen-
ter and that galaxies often
collide and merge to create
larger galaxies. Astronomers
have expected to find many
galaxies in the midst of merg-
ing by focusing on the two
supermassive black holes,
which should be orbiting each other in
the middle. But so far, the dance floor has
been pretty much empty.
Using new techniques, Comerford
and her colleagues have now found 33
galaxies with dual supermassive black
holes. By determining whether each
black hole is moving toward or away
from Earth, one technique revealed 32
black hole pairs locked in step in the
DEEP2 Galaxy Redshift Survey, which
By Lisa Grossman
The universe may be one big dance party
for black holes. New observations from
the W.M. Keck Observatory in Hawaii
and the Hubble Space Telescope reveal
33 merged galaxies in which pairs of
supermassive black holes are “waltzing”
around the galactic centers.
“Our result shows that such waltz-
A Hubble telescope image of the galaxy COSMOS
ing black holes are much more common
than we previously knew,” reported Julie
Comerford of the University of California,
Berkeley on January 4. “We expect the
universe to be littered with these.... But
until recently, only a few had ever been
Finding pairs of black holes moving in
this way can help scientists estimate how
J100043.15+020637.2 shows two nuclei, possibly
black holes paired by a merger of two smaller galaxies.
was conducted at the Keck II Telescope
on Hawaii’s Mauna Kea.
The final black hole duo was found
serendipitously in a Hubble image of the
galaxy COSMOS J100043.15+020637.2.
That galaxy sports a tidal tail of stars,
gas and dust, a sign of a recent galaxy
merger. The galaxy also has two bright
nuclei, each of which could be a supermassive black hole surrounded by glowing dust and gas.
Where there’s smoke, supernovas
Gamma-ray burst may have illuminated ancient stardust
By Ron Cowen
Astronomers may have detected “smoke”
signals generated by supernovas that
blew up when the universe was less
than 1. 4 billion years old. If correct, the
find would be one of the earliest known
signs of supernova-produced dust in the
universe, and the earliest dust detected
thanks to a gamma-ray burst.
The supernovas are too faint and too
far away to be seen directly. But the
smoke, or stardust, they produced when
they erupted now appears to have been
revealed by the brilliant afterglow of a
much more powerful type of eruption, a
The new finding “is exciting because
gamma-ray bursts are showing them-
selves as a unique probe of the early uni-
verse that really hadn’t been considered,”
Joshua Bloom of the University of Cali-
fornia, Berkeley reported on January 4.
“We can now measure how matter in the
[young] universe converts from stars into
stardust,” the raw material for the next
generation of stars, he added. Bloom,
Daniel Perley of UC Berkeley and col-
leagues also posted the findings online.
When the astronomers examined visible and infrared afterglow of a gamma-ray burst discovered in 2007, dubbed GRB
071025, they found telltale light absorptions indicating the presence of dust.
Bloom said that the team tried several
models to explain the properties of the
afterglow light from the gamma-ray burst,
but only supernova dust fit the bill.
In nearby reaches of the universe,
including the Milky Way, most dust is
produced by mature, low-mass stars. But
at much earlier times, such as when GRB
071025 exploded (about a billion years
after the Big Bang), low-mass stars were
not yet common. Instead, Bloom noted,
supernovas were the dominant —and
perhaps only — source of dust.
The team suggests that light from this
gamma-ray burst passed through an
unusually dusty part of its galaxy, where
a series of supernovas had enriched the
surrounding space with dust grains.
January 30, 2010 | SCIENCE NEWS | 13