February 15th 06, 10:34 PM
http://www.news.cornell.edu/stories/Feb06/ULIRGs.Spoon.lg.html
Distant inferno: Cornell astronomer finds galaxies that contain
massive young stars in compact, cosmic globs
Feb. 15, 2006
By Lauren Gold )
The discovery makes the fiery environment within a typical spiral or
starburst galaxy look almost pastoral. Cornell researchers using the
Spitzer Space Telescope say distant galaxies contain an inferno of
very young, massive and violently evolving stars, packed together in
tiny but extremely powerful cosmic globs.
The key to the discovery, paradoxically, is in the presence of
delicate, glittery crystalline silicates called Forsterite. These are
glassy particles that exist in the debris disks of young stars and in
the stellar wind of very old stars, but which have never before been
observed in the mass of gas and dust known as the interstellar
medium, or ISM, in the Milky Way or in any other galaxy.
The research, led by Cornell astronomer and Spitzer Fellow Henrik
Spoon, will appear in the Feb. 20 issue of the Astrophysical Journal.
Using Spitzer's infrared spectrograph (IRS), an instrument developed
by a team led by Cornell professor of astronomy James Houck and built
at Cornell, Spoon and colleagues observed dozens of distant galaxies
known as ultra-luminous infrared galaxies (ULIRGs). First discovered
in large numbers in 1982, most ULIRGs are thought to form as two or
more spiral galaxies collide (as our galaxy will, in a few billion
years, with the nearby Andromeda galaxy), and their leftover hydrogen
gas fuels the fierce, rapid formation of massive stars.
ULIRGs are relative runts in galactic terms (though some have
sweeping tidal tails), with the source of their luminosity coming
from an area as small as one-hundredth that of typical galaxies. Seen
with an optical telescope, they look dusty, chaotic and
unspectacular. But in the mid-infrared spectrum, said Spoon, "they
are booming," appearing up to 100 times more luminous than a spiral
or starburst galaxy.
Silicates are the most common types of minerals in the Milky Way, so
their presence in ULIRGs is not surprising. But among the silicates,
most (95 percent in the immediate vicinity of rapidly evolving stars
and at least 99 percent in the general ISM) are amorphous in
structure.
Spoon and his team saw the expected broad absorption features of
amorphous silicates in the infrared spectra of the ULIRGs they
observed. But they also saw signature narrow dips within the broad
bumps indicating the presence of silicates in crystalline form in the
general ISM. The concentration of crystalline silicates in at least
21 ULIRGs, Spoon found, is seven to 15 times greater than in any
other known environment.
In our galaxy, crystalline silicates have only been observed close to
active new stars, which inject them into their immediate environment
as they evolve, and in the exhaled winds of dying stars. Subject to
heavy pummeling by destructive cosmic and shock-accelerated ions, the
silicates quickly lose their ordered, crystalline structure and take
an amorphous shape.
"We were surprised to find such delicate little crystals in the
centers of some of the most violent places in the universe," said
Spoon. "Given the rapid transformation of crystalline silicates to an
amorphous state, the injection rate of freshly produced crystalline
silicates must be far higher than in our galaxy. We're probing exotic
circumstances."
Spitzer's IRS, which can record infrared spectra from objects fainter
and farther away than ever before, has allowed astronomers to study
ULIRGs and other stellar nurseries in new detail.
"Now we can take a good look at what these characteristics are," said
Spoon. "It's like, for the first time, you put on a pair of glasses,
and -- wow."
The Spitzer Space Telescope is the last of NASA's Great
Observatories. The Jet Propulsion Laboratory, a division of the
California Institute of Technology, manages the Spitzer mission for
NASA's Science Mission Directorate, Washington. Science operations
are conducted at the Spitzer Science Center at Caltech.
##
Media Contact: Press Relations Office
(607) 255-6074
Distant inferno: Cornell astronomer finds galaxies that contain
massive young stars in compact, cosmic globs
Feb. 15, 2006
By Lauren Gold )
The discovery makes the fiery environment within a typical spiral or
starburst galaxy look almost pastoral. Cornell researchers using the
Spitzer Space Telescope say distant galaxies contain an inferno of
very young, massive and violently evolving stars, packed together in
tiny but extremely powerful cosmic globs.
The key to the discovery, paradoxically, is in the presence of
delicate, glittery crystalline silicates called Forsterite. These are
glassy particles that exist in the debris disks of young stars and in
the stellar wind of very old stars, but which have never before been
observed in the mass of gas and dust known as the interstellar
medium, or ISM, in the Milky Way or in any other galaxy.
The research, led by Cornell astronomer and Spitzer Fellow Henrik
Spoon, will appear in the Feb. 20 issue of the Astrophysical Journal.
Using Spitzer's infrared spectrograph (IRS), an instrument developed
by a team led by Cornell professor of astronomy James Houck and built
at Cornell, Spoon and colleagues observed dozens of distant galaxies
known as ultra-luminous infrared galaxies (ULIRGs). First discovered
in large numbers in 1982, most ULIRGs are thought to form as two or
more spiral galaxies collide (as our galaxy will, in a few billion
years, with the nearby Andromeda galaxy), and their leftover hydrogen
gas fuels the fierce, rapid formation of massive stars.
ULIRGs are relative runts in galactic terms (though some have
sweeping tidal tails), with the source of their luminosity coming
from an area as small as one-hundredth that of typical galaxies. Seen
with an optical telescope, they look dusty, chaotic and
unspectacular. But in the mid-infrared spectrum, said Spoon, "they
are booming," appearing up to 100 times more luminous than a spiral
or starburst galaxy.
Silicates are the most common types of minerals in the Milky Way, so
their presence in ULIRGs is not surprising. But among the silicates,
most (95 percent in the immediate vicinity of rapidly evolving stars
and at least 99 percent in the general ISM) are amorphous in
structure.
Spoon and his team saw the expected broad absorption features of
amorphous silicates in the infrared spectra of the ULIRGs they
observed. But they also saw signature narrow dips within the broad
bumps indicating the presence of silicates in crystalline form in the
general ISM. The concentration of crystalline silicates in at least
21 ULIRGs, Spoon found, is seven to 15 times greater than in any
other known environment.
In our galaxy, crystalline silicates have only been observed close to
active new stars, which inject them into their immediate environment
as they evolve, and in the exhaled winds of dying stars. Subject to
heavy pummeling by destructive cosmic and shock-accelerated ions, the
silicates quickly lose their ordered, crystalline structure and take
an amorphous shape.
"We were surprised to find such delicate little crystals in the
centers of some of the most violent places in the universe," said
Spoon. "Given the rapid transformation of crystalline silicates to an
amorphous state, the injection rate of freshly produced crystalline
silicates must be far higher than in our galaxy. We're probing exotic
circumstances."
Spitzer's IRS, which can record infrared spectra from objects fainter
and farther away than ever before, has allowed astronomers to study
ULIRGs and other stellar nurseries in new detail.
"Now we can take a good look at what these characteristics are," said
Spoon. "It's like, for the first time, you put on a pair of glasses,
and -- wow."
The Spitzer Space Telescope is the last of NASA's Great
Observatories. The Jet Propulsion Laboratory, a division of the
California Institute of Technology, manages the Spitzer mission for
NASA's Science Mission Directorate, Washington. Science operations
are conducted at the Spitzer Science Center at Caltech.
##
Media Contact: Press Relations Office
(607) 255-6074