A star of wonder could flash anytime now

From: http://www.msnbc.msn.com/id/16328694/

Dec 22, 2006

Images such as this one from the Hubble Space Telescope show that the white dwarf T Pyxidis is not disrupted by its violent eruptions and accumulates more matter from its companion, repeating the cataclysm some years later.

Recurrent nova is overdue for a show in southern skies

At this time of year it seems almost traditional for stargazers to ponder the age-old question of the origin of the Star of Bethlehem. The star’s appearance some 2,000 years ago is quite possibly one of the best-known celestial events in all of recorded history. 

Many planetariums are currently running sky shows interwoven with a Christmas theme.  Utilizing special-effects projectors, audiences are transported back in time to see the night sky as the Magi may have seen it and are then asked if perhaps an unusual gathering of planets might have been the fabled star (http://www.space.com/spacewatch/star_bethlehem_021220.html). Or was that “sign” a comet, a nova or something supernatural? 

The topic has universal fascination, and is why Christmas Star shows still play to packed planetarium houses.

Perhaps the simplest answer that can be offered is that the star might have been a nova: A “new star” suddenly blazing forth where no star had previously been seen.  While for the most part such objects are really dying stars (http://www.space.com/supernovas/) having a final fling of glory before descending the long road to ultimate extinction, there are some stars that go through such contortions more than once.

One such star is long overdue to “pop” and could do so at anytime. 

The star in question is T Pyxidis, in the constellation of Pyxis, the Mariner’s Compass, a dim southern constellation that never gets very high for skywatchers in the United States.  For instance: As seen from Philadelphia, Indianapolis and Denver, it reaches a maximum altitude of just 18 degrees above the southern horizon. (Your clenched fist, held at arm’s length, is roughly 10 degrees in width.) Currently, Pyxis is crossing the meridian around 2:30 a.m. By the end of January it will be there just after midnight, and by early March, just before 10 p.m.

T Pyxidis is about 6,000 light years away and belongs to a small and seemingly "exclusive" group of cataclysmic variable stars (http://www.space.com/scienceastronomy/060222_missing_stars.html) called recurrent novae — of which there are currently less than 10 confirmed members.  T Pyxidis is composed of a dense white dwarf and a close companion star. An outburst occurs when the temperature and density of the surge of matter dumped from the companion onto the surface of the white dwarf reach the nuclear flash point for hydrogen. While material is violently blown off in all directions (see comparison photos from both ground-based instruments and the Hubble Space Telescope here (http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=061222_nova_image_02.jpg&cap=Images+from+ground+telescopes+and+Hubble+show+that+the+white+dwarf+T+Pyxidis+is+not+disrupted+by+its+violent+eruptions+and+soon+begins+to+accumulate+more+matter+from+its+companion,+and+repeats+the+cataclysm+some+years+later.++)), the white dwarf itself is not disrupted and soon begins to accumulate more matter from its companion, and repeats the cataclysm some years later.