[vsnet-alert 10525] Hubble Finds a Mystery Object

[LARRY KLAES]

http://www.skyandtelescope.com/news/home/28244844.html

Hubble Finds a Mystery Object

Posted by Alan MacRobert, September 11, 2008

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.

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

http://media.skyandtelescope.com/images/What-Was-It.jpg

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, distance 
8.2 billion light-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. That leaves a lot of leeway.

Here is the group's paper with all the details. The lead author is Kyle 
Barbary (University of California at Berkeley):

http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.1648v1.pdf