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Reading: Astronomers Await a Nova
[Source: Space.com]
The Star of Bethlehem

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.

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 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.

Stargazing

The star in question is T Pyxidis, in the constellation of Pyxis, the Mariner's Compass. T Pyxidis is about 6,000 light years away and belongs to a small and seemingly exclusive group of cataclysmic variable stars called recurrent novae (NR). Astronomers have been patiently waiting for T Pyxidis's next outburst for more than 20 years.

Normally this star shines at magnitude 14: that's about a thousand times dimmer than the faintest star that can be perceived by most human eyes on a dark, clear night. But on five occasions, in 1890, 1902, 1920, 1944 and 1967, this star brightened dramatically to magnitudes between 6.5 and 7 (a 1,000-fold increase in brightness in the most extreme case) making T Pyxidis just bright enough to be glimpsed without any optical aid. These eruptions came at an average of just over 19 years apart, and the longest stretch of time between them was 24 years.

But this month marks 40 years since the last outburst.

It was back on Dec. 7, 1966 that the most recent eruption was first noticed by New Zealand amateur astronomer, Albert Jones. The star had more than doubled in brightness to magnitude 12.9. Just two nights later it was almost four magnitudes brighter and after a month it was glowing at magnitude 6.3 before slowly fading back to normal.

Nobody knows exactly why T Pyxidis has remained quiet for so long, but the general consensus is that it may have accumulated an extra-thick coating of nuclear fuel on its surface over these past 20 years, which would make it appear extra bright when it finally blows its next surge of gaseous debris out into space.

Who knows? That night could be tonight!

Key vocabulary
  • Stargazer.
  • Outburst.
Analyse the text
  • What are astronomers expecting to happen and to what?
  • What is a nova?

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