http://www.skyandtelescope.com/community/skyblog/newsblog/28244844.html
Hubble Finds a Mystery Object
Don't get the idea that we've found every kind of astronomical object there is in the universe. In a
paper to appear in the Astrophysical Journal, astronomers working on the Supernova Cosmology Project
report finding a new kind of something that they cannot make any sense of.
http://media.skyandtelescope.com/images/What-Was-It.jpg
Now you don't see it, now you do. Something in Bootes truly in the middle of nowhere - apparently
not even in a galaxy - brightened by at least 120 times during more than three months and then faded
away. Its spectrum was like nothing ever seen, write the discoverers, with "five broad absorption
bands between 4100 and 6500 Angstroms and a mostly featureless continuum longward of 6500
Angstroms." Even the cause of the spectral features is unknown.
K. Barbary and others.
The project used the Hubble Space Telescope to monitor very distant galaxy clusters for supernovae.
On February 21, 2006, in the direction of a far-away cluster in Bootes named CL 1432.5+3332.8
(redshift 1.112, light travel time 8.2 billion years), Hubble began seeing something brighten. It
continued brightening for about 100 days and peaked at 21st magnitude in two near-infrared colors.
It then faded away over a similar timescale, until nothing was left in view down to 26th magnitude.
The object brightened and faded by a factor of at least 120, maybe more.
The mystery object did not behave like any known kind of supernova. It is not even in any detectable
galaxy. "The shape of the light curve is inconsistent with microlensing," say the researchers. They
recorded three spectra of it - and its spectrum, they write, "in addition to being inconsistent with
all known supernova types, is not matched to any spectrum in the Sloan Digital Sky Survey database"
of vast numbers of objects. "We suggest that the transient may be one of a new class."
What's its distance? That would certainly be a first step to figuring it out, but only the broadest
constraints can be put on its distance. Its lack of parallax motion means that it can't be closer
than about 130 light-years, and a lack of cosmic hydrogen absorption in its spectrum means that it
can't be farther than 11 billion light-years (when "distance" is defined by light travel time). That
leaves a lot of leeway.
Here is the group's paper [
http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.1648v1.pdf ]
with all the details. The lead author is Kyle Barbary (University of California at Berkeley).
Jan Rasmussen