Mysterious space blob discovered at cosmic
dawn
Wednesday, April 22, 2009
This image of the Himiko object
is a composite and in false color. The thick horizontal bar at the
lower right corner presents a size of 10 thousand light year.
Credit: This image is created by M. Ouchi et al, which is the
reproduction of Figure 2 in the article of The Astrophysical
Journal May 2009 - 10 v696 issue.
Using information from a suite of
telescopes, astronomers have discovered a mysterious, giant object
that existed at a time when the universe was only about 800 million
years old. Objects such as this one are dubbed extended Lyman-Alpha
blobs; they are huge bodies of gas that may be precursors to
galaxies. This blob was named Himiko for a legendary, mysterious
Japanese queen. It stretches for 55 thousand light years, a record
for that early point in time. That length is comparable to the
radius of the Milky Way's disk.
The researchers are puzzled by the object. Even with superb data
from the world's best telescopes, they are not sure what it is.
Because it is one of the most distant objects ever found, its
faintness does not allow the researchers to understand its physical
origins. It could be ionized gas powered by a super-massive black
hole; a primordial galaxy with large gas accretion; a collision of
two large young galaxies; super wind from intensive star formation;
or a single giant galaxy with a large mass of about 40 billion
Suns. Because this mysterious and remarkable object was discovered
early in the history of the universe in a Japanese Subaru field,
the researchers named the object after the legendary mysterious
queen in ancient Japan.
"The farther out we look into space, the farther we go back in
time, " explained lead author Masami Ouchi, a fellow at the
Observatories of the Carnegie Institution who led an international
team of astronomers from the U.S., Japan, and the United Kingdom.
"I am very surprised by this discovery. I have never imagined that
such a large object could exist at this early stage of the
universe's history. According to the concordance model of Big Bang
cosmology, small objects form first and then merge to produce
larger systems. This blob had a size of typical present-day
galaxies when the age of the universe was about 800 million years
old, only 6% of the age of today's universe!"
Extended blobs discovered thus far have mostly been seen at a
distance when the universe was 2 to 3 billion years old. No
extended blobs have previously been found when the universe was
younger. Himiko is located at a transition point in the evolution
of the universe called the reionization epoch—it's as far back as
we can see to date. And at 55 thousand light years, Himiko is a big
blob for that time.
This reionizing chapter in the universe was at the cosmic dawn, the
epoch between about 200 million and one billion years after the Big
Bang. During this period, neutral hydrogen began to form quasars,
stars, and the first galaxies. Astronomers probe this era by
searching for characteristic hydrogen signatures from the
scattering of photons created by ionized gas clouds.
The team initially identified Himiko among 207 distant galaxy
candidates seen at optical wavelengths using the Subaru telescope
from the Subaru/XMM-Newton Deep Survey Field located in the
constellation of Cetus. They then made spectroscopic observations
to measure the distance with the Keck/DEIMOS and Carnegie's
Magellan/IMACS instrumentation. Himiko was an extraordinarily
bright and large candidate for a distant galaxy. "We hesitated to
spend our precious telescope time by taking spectra of this weird
candidate. We never believed that this bright and large source was
a real distant object. We thought it was a foreground interloper
contaminating our galaxy sample," continued Ouchi. "But we tried
anyway. Then, the spectra exhibited a characteristic hydrogen
signature clearly indicating a remarkably large distance—12.9
billion light years!"
"Using infrared data from NASA's Spitzer Space Telescope and the
United Kingdom Infrared Telescope, radio data from the VLA, and
X-ray imaging from the XMM-Newton satellite, we were able to
estimate the star-formation rate and stellar mass of this galaxy
and to investigate whether it contains an active nucleus powered by
a super-massive black hole," remarked James Dunlop a team member at
Edinburgh. "We found that the stellar mass of Himiko is an order of
magnitude larger than other objects known at a similar epoch, but
we cannot as yet tell if the center houses an active and growing
black hole."
"One of the puzzling things about Himiko is that it is so
exceptional," said Carnegie's Alan Dressler, a member of the team.
"If this was the discovery of a class of objects that are ancestors
of today's galaxies, there should be many more smaller ones already
found—a continuous distribution. Because this object is, to this
point, one-of-a-kind, it makes it very hard to fit it into the
prevailing model of how normal galaxies were assembled. On the
other hand, that's what makes it interesting!"
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Carnegie Institution
Thanks to Carnegie Institution for
this article.