Usually stars attract attention of viewers when they suddenly brighten up. That is the origin of the words nova and supernova. Interestingly some stars did get documented for suddenly becoming dim. One of them called Algol or the Devil’s Eye paved way for the important branch of the study of binary stars. The other called Mira baffled the observers of the previous centuries and is again in the news.

The first documentation of the sudden fading of Mira dates back to 1596 by David Fabricius. It almost vanished for a rather long time and became visible again after about seven months, after several short appearances in between.

Several observers also noted its frequent vanishing acts and the famous astronomer Johannes Hevelius of the seventeenth century named it Mira, meaning something astonishing. Since then it has been monitored regularly and its period of 333 days has been established. It is in the constellation of Cetus at a distance of about 350 light years. It has a number 68 attached to it and is called Omicron Ceti, based on its rank of brightness.

Spectroscopic studies have shown that it was a sunlike star and now bloated to almost 400 times the original size. Such stars, called giants, represent the final fate of stars. In other words, we are almost seeing a star on the deathbed.

Although we have several examples of stars in this category, there is something special about Mira. Although it looks like a single dot, it is a double. The bloated red giant Mira A, is gravitationally bound to another small star Mira B. This companion is believed to be a compact star, a white dwarf, to be precise. The orbital period is about 18 years.

A red giant
It is well known that a star in its final stages throws out most of the material which comprise oxygen, carbon and nitrogen. However, such winds from the stars quickly dissipate into the neighbourhood leaving no visible trace at least initially. Mira therefore, is considered to be a pulsating red giant in the usual sense losing mass comparable to the earth’s mass every year.

Earlier this year, in January 2007, a team of scientists reported a new phenomenon – the material thrown out from Mira A was assuming a disk like structure around Mira B, the tiny companion.

The researchers spotted Mira B's disk because the part of the disk facing Mira A glowed brightly in the infrared, heated by radiation from the red giant. That led to speculation on possible planetary disks around dead stars, something never heard before.

The estimated mass of the disk was comparable to that of Jupiter. Therefore, one wondered on the possibility of new class of planets – they would receive energy from two “suns”! Would they support life?

Another group of astronomers now turned GALEX (Galaxy Evolution Explorer) an orbiting space telescope, towards Mira to get a glimpse of the surroundings with ultraviolet eyes. What it reported in August was stunning!
There was a huge expanse of gas and dust extending to almost 13 light years, resembling the tail of a comet. It should be recalled here that the separation between the A and B components is about 100 AU (the earth – sun distance). Thus comet like tail of Mira was stretching to about 1000 times this distance.

The material mostly carbon, oxygen and nitrogen, has been blown off Mira recently in the last million year. It has been a gradual process – perhaps a strong puff was released roughly 30,000 years ago. The total mass in this “tail” also has been calculated. 3,000 future Earth-sized planets can be formed out of them.

The Mira pair is racing through at a fantastic speed of about 130km per second. Therefore the periodic puffing of gas and dust is trailing it in its journey in the Milky Way. This has generated a lot of interest because it is a demonstration of the recycling process prevalent in the universe. This processed material is rich in silicates and will eventually get added onto a new solar system – the right recipe for earth like planets that can nurture the type of life we know.

The writer is with the Jawaharlal Nehru Planetarium, Bangalore.