[tt] Hubble Finds a Mystery Object

[Christian Weisgerber]

http://www.skyandtelescope.com/community/skyblog/newsblog/28244844.html
Sky & Telescope
Alan MacRobert

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.
What was it?

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.

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/abs/0809.1648> with all the
details. The lead author is Kyle Barbary (University of California at
Berkeley).

-- 
Christian "naddy" Weisgerber                          naddy at mips.inka.de