[Spitzer News] Rare 'Star-Making Machine' Found In Distant Universe In this issue: 1) Rare 'Star-Making Machine' Found In Distant Universe 2) Stellar Lightweight Causes a Mysteriously Massive Explosion ----------------------------- RARE 'STAR-MAKING MACHINE' FOUND IN DISTANT UNIVERSE Astronomers have uncovered an extreme stellar machine -- a galaxy in the very remote universe pumping out stars at a surprising rate of up to 4, 000 per year. In comparison, our own Milky Way galaxy turns out an average of just 10 stars per year. The discovery, made possible by several telescopes including NASA's Spitzer Space Telescope, goes against the most common theory of galaxy formation. According to the theory, called the Hierarchical Model, galaxies slowly bulk up their stars over time by absorbing tiny pieces of galaxies -- and not in one big burst as observed in the newfound "Baby Boom" galaxy. "This galaxy is undergoing a major baby boom, producing most of its stars all at once, " said Peter Capak of NASA's Spitzer Science Center at the California Institute of Technology, Pasadena. "If our human population was produced in a similar boom, then almost all of the people alive today would be the same age." Capak is lead author of a new report detailing the discovery in the July 10th issue of Astrophysical Journal Letters. The Baby Boom galaxy, which belongs to a class of galaxies called starbursts, is the new record holder for the brightest starburst galaxy in the very distant universe, with brightness being a measure of its extreme star-formation rate. It was discovered and characterized using a suite of telescopes operating at different wavelengths. NASA's Hubble Space Telescope and Japan's Subaru Telescope, atop Mauna Kea in Hawaii, first spotted the galaxy in visible-light images, where it appeared as an inconspicuous smudge due to is great distance. It wasn't until Spitzer and the James Clerk Maxwell Telescope, also on Mauna Kea in Hawaii, observed the galaxy at infrared and submillimeter wavelengths, respective! ly, that the galaxy stood out as the brightest of the bunch. This is because it has a huge number of youthful stars. When stars are born, they shine with a lot of ultraviolet light and produce a lot of dust. The dust absorbs the ultraviolet light but, like a car s

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Thu Jul 10 15:50:38 PDT 2008


In this issue:

1) Rare 'Star-Making Machine' Found In Distant Universe
2) Stellar Lightweight Causes a Mysteriously Massive Explosion

-----------------------------

RARE 'STAR-MAKING MACHINE' FOUND IN DISTANT UNIVERSE

Astronomers have uncovered an extreme stellar machine -- a galaxy in  
the very remote
universe pumping out stars at a surprising rate of up to 4,000 per  
year. In comparison,
our own Milky Way galaxy turns out an average of just 10 stars per year.

The discovery, made possible by several telescopes including NASA's  
Spitzer Space
Telescope, goes against the most common theory of galaxy formation.  
According to the
theory, called the Hierarchical Model, galaxies slowly bulk up their  
stars over time by
absorbing tiny pieces of galaxies -- and not in one big burst as  
observed in the newfound
"Baby Boom" galaxy.

"This galaxy is undergoing a major baby boom, producing most of its  
stars all at once,"
said Peter Capak of NASA's Spitzer Science Center at the California  
Institute of
Technology, Pasadena. "If our human population was produced in a  
similar boom, then almost
all of the people alive today would be the same age." Capak is lead  
author of a new report
detailing the discovery in the July 10th issue of Astrophysical  
Journal Letters.

The Baby Boom galaxy, which belongs to a class of galaxies called  
starbursts, is the new
record holder for the brightest starburst galaxy in the very distant  
universe, with
brightness being a measure of its extreme star-formation rate. It was  
discovered and
characterized using a suite of telescopes operating at different  
wavelengths. NASA's
Hubble Space Telescope and Japan's Subaru Telescope, atop Mauna Kea  
in Hawaii, first
spotted the galaxy in visible-light images, where it appeared as an  
inconspicuous smudge
due to is great distance.

It wasn't until Spitzer and the James Clerk Maxwell Telescope, also  
on Mauna Kea in
Hawaii, observed the galaxy at infrared and submillimeter  
wavelengths, respectively, that
the galaxy stood out as the brightest of the bunch. This is because  
it has a huge number
of youthful stars. When stars are born, they shine with a lot of  
ultraviolet light and
produce a lot of dust. The dust absorbs the ultraviolet light but,  
like a car sitting in
the sun, it warms up and re-emits light at infrared and submillimeter  
wavelengths, making
the galaxy unusually bright to Spitzer and the James Clerk Maxwell  
Telescope.

To learn more about this galaxy's unique youthful glow, Capak and his  
team followed up
with a number of telescopes. They used optical measurements from Keck  
to determine the
exact distance to the galaxy -- a whopping12.3 billion light-years.  
That's looking back to
a time when the universe was 1.3 billion years old (the universe is  
approximately 13.7
billion years old today).

"If the universe was a human reaching retirement age, it would have  
been about 6 years old
at the time we are seeing this galaxy," said Capak.

The astronomers made measurements at radio wavelengths with the  
National Science
Foundation's Very Large Array in New Mexico. Together with Spitzer  
and James Clerk Maxwell
data, these observations allowed the astronomers to calculate a star- 
forming rate of about
1,000 to 4,000 stars per year. At that rate, the galaxy needs only 50  
million years, not
very long on cosmic timescales, to grow into a galaxy equivalent to  
the most massive ones
we see today.

While galaxies in our nearby universe can produce stars at similarly  
high rates, the
farthest one known before now was about 11.7 billion light-years  
away, or a time when the
universe was 1.9 billion years old.

"Before now, we had only seen galaxies form stars like this in the  
teenaged universe, but
this galaxy is forming when the universe was only a child," said  
Capak. "The question now
is whether the majority of the very most massive galaxies form very  
early in the universe
like the Baby Boom galaxy, or whether this is an exceptional case.  
Answering this question
will help us determine to what degree the Hierarchical Model of  
galaxy formation still
holds true."

"The incredible star-formation activity we have observed suggests  
that we may be
witnessing, for the first time, the formation of one of the most  
massive elliptical
galaxies in the universe," said co-author Nick Scoville of Caltech,  
the principal
investigator of the Cosmic Evolution Survey, also known as Cosmos.  
The Cosmos program is
an extensive survey of a large patch of distant galaxies across the  
full spectrum of light.

"The immediate identification of this galaxy with its extraordinary  
properties would not
have been possible without the full range of observations in this  
survey," said Scoville.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the  
Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science  
operations are
conducted at the Spitzer Science Center at the California Institute  
of Technology, also in
Pasadena. Caltech manages JPL for NASA. For more information about  
Spitzer, visit
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .

http://www.spitzer.caltech.edu/Media/releases/ssc2008-12/release.shtml

-----------------------------

STELLAR LIGHTWEIGHT CAUSES A MYSTERIOUSLY MASSIVE EXPLOSION

When amateur astronomer Ron Arbour spotted an enormous explosion from  
17 million
light-years away in the Fireworks Galaxy (NGC 6946), many  
professional scientists believed
that it was the final death throes of a massive dying star. However,  
observations from
NASA's Spitzer Space Telescope unexpectedly showed that a relatively  
lightweight star was
the source of this spectacular blast.

The explosion, called SN 2008S, was first spotted in February 2008.

"This finding was quite a surprise -- the exploding star was only  
about 10 times the mass
of our Sun. Typically, we see this kind of outburst from stars that  
are at least 30 times
more massive than our Sun," says Jose Prieto, a graduate student at  
Ohio State University
in Columbus, Ohio, who searched for the source of the blast in  
archive data taken by
professional optical and infrared telescopes.

Now astronomers are wondering, did this star really go supernova? Or  
is it an impostor?
Either way, they hope this finding will provide some insights into  
how a relatively small
star could cause such huge explosion.
The Flash

When astronomers see a bright flash of light indicating a possible  
nearby supernova, their
first instinct is to find the star before it died, or progenitor, in  
archived
visible-light observations of the region. But when Prieto and  
collaborators from Ohio
State searched for the source of the NGC 6946 flash in optical  
observations previously
taken by the Large Binocular Telescope Observatory (LBT) in Arizona,  
they found nothing.

"If this was indeed a core-collapse supernova, we should have seen a  
progenitor in the
optical observations, since the LBT observations were very deep,"  
says Prieto.

Out of curiosity, he also sifted through archived infrared  
observations of the galaxy that
Spitzer had taken three years before, and it was there that Prieto  
discovered the source
of the flash.

"The original star could only be seen at three infrared wavelengths  
of 4.5, 5.8 and 8.0
microns, this clearly indicates the presence of warm dust around the  
star, probably dust
formed in the wind flowing off the star," says Prieto. "This is the  
first time a
progenitor has only been spotted in Spitzer images."

This dust explains how the progenitor eluded the LBT's prying eyes --  
the blanket of dust
actually absorbed almost all of the star's optical and ultraviolet  
light. However, because
the dust re-radiates the absorbed starlight in the infrared, Spitzer  
could locate the
star. He notes that the total infrared brightness of the star  
indicates that it was only
10 times more massive than our Sun.

According to Prieto, the initial optical observations of the blast  
suggest that the event
was possibly a type IIn supernova. Like celestial chemical factories,  
stars spend most of
their lives fusing hydrogen atoms in their core. The energy produced  
by this fusion causes
an outward pressure that counters the force of gravity. When the  
hydrogen runs out, the
outward pressure ceases and the core begins to shrink. This causes  
the star's density and
temperature to increase, igniting further fusion of heavier chemical  
elements in its core.

For stars with several times the mass of our Sun, this process occurs  
again and again
until the core turns to iron. At this point the core collapses on  
itself at about 70,000
kilometers per second, smashing everything together into a super- 
dense mass. Protons and
electrons merge into neutrons, producing a shock wave of neutrinos.  
This is called a core
collapse, identified by scientists as a supernova of type II.

Type IIn supernovae are a subclass of core-collapse events that show  
an abundant amount of
hydrogen associated with a dense gas cloud surrounding the star  
before the explosion,
probably created by a strong wind.

Another possibility is that the explosion was a "fake supernova," or  
the super-outburst of
a luminous blue variable star. These stars eject an enormous amount  
of material in
occasional outbursts, as they near the end of their lives. The  
brightness of these
outbursts may be mistaken for a supernova explosion. Luminous blue  
variables are extremely
rare, as they are thought to be stars with more than 30 times as  
massive as our Sun. The
most famous example of a luminous blue variable in our galaxy is Eta  
Carina.

"Either way, the result is interesting because astronomers currently  
think that type IIn
supernovae and luminous blue variables are associated with very  
massive stars - tens of
solar masses - and not with the smaller 10 solar mass star we found  
with Spitzer. This is
a very unusual case, and more work definitely needs to be done to  
figure out exactly what
happened here," says Prieto.

Shortly after Prieto's paper was accepted, a similar bright outburst  
was spotted in the
nearby galaxy NGC 300. Again, researchers did not see anything when  
they scoured optical
archives for the source of the explosion. However, when they turned  
to archived Spitzer
observations team members were able to identify a dust-obscured star  
as the progenitor,
similar to the progenitor of the NGC 6946 outburst.

"These two luminous outbursts may be a new class of violent  
explosions in dusty massive
stars," says Prieto, whose paper on SN 2008S's progenitor will be  
published in the July
1st issue of the Astrophysical Journal Letters.

Co-authors on his paper include Matthew Kistler, Todd Thompson, Hasan  
Yuksel, Chris
Kochanek, Krzysztof Stanek, John Beacom, and Paul Martini, of Ohio  
State University. Anna
Pasquali, of the Max-Planck Institute for Astronomy in Germany. Jill  
Bechtold, of the
University of Arizona.

The LBT is an international collaboration among institutions in the  
United States, Italy
and Germany. LBT Corporation partners are: The University of Arizona  
on behalf of the
Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT
Beteiligungsgesellschaft, Germany, representing the Max-Planck  
Society, the Astrophysical
Institute Potsdam, and Heidelberg University; The Ohio State  
University, and The Research
Corporation, on behalf of The University of Notre Dame, University of  
Minnesota and
University of Virginia.

http://www.spitzer.caltech.edu/Media/happenings/20080623/

-----------------------------



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