Despite having dwelt exhaustively on the topic of stars — mainly our benefactor the mighty, yet fatherly, Sun — our knowledge of stars or universe on the whole is not complete unless we know about the other actors in the cast of the cosmic drama.These are binary stars (binaries), pulsating stars (pulsars), neutron stars, and quasars (quasi-stellar objects) — all of them emphatic and authentic actors in their own right. They have each played their part, and an important one at that, in giving the universe a colourful script. Some of them have been around since early universe when only the earliest galaxies and stars had begun to take shape (within the first billion years).

Above all, some have lent themselves well to deep and profound probing of our galaxy and universe. We shall see how fathers (in some cases the mothers) of astronomy in 19th and 20th centuries used these residents of deep space to discover the truths that, without their unflinching resolve and efforts, would have remained undiscovered for decades yet.

While going through the description of stars (or other objects) we shall keep in mind that everything in universe goes through metamorphosis in various stages of their existence: their birth, growth and development, death.

Metamorphosis is complete change in appearance or shape, form and characteristics — a baby grows into a young adult, then grows old and then....

When it comes to the issues of universe, the metamorphosis occurs at a leisurely pace consuming millions of years over any single stage. It proves that everything in universe is dynamic, subject to feverish activity and change. Nothing is static.

Let us finally consider binary stars. A binary is a part of two. Two stars that is. Two or more. These are stars that do not like to “live” alone, but in the company of another star (a companion star or two). Surprisingly, only about half of them live a lonely existence, all others do it in pairs. Most of them are created in pairs, triplets or clusters. When in pairs or more, they influence each other in many ways. They do a highly predictable gravitational dance around an invisible but perceptible point between them.

The “star pair” is never of the same size (mass) or heat. Often one of them is much dimmer than the other. Some of the apparent pairs just happen to lie in the observers’ line of sight. They are not pairs at all but only appear as such.William Herschel (1738-1822), the famous English astronomer who, together with his sister Caroline (1750- 1848) are regarded as pioneers of binaries, after years of research on erroneous line (with little hind sight to rely on), eventually correctly concluded that most of the stars that appear close together lie in each other’s gravitational field, that is, they are close (astronomically, of course), and massive enough to influence each other’s gravitational field. They revolve around a common point that lies on an imaginary line joining the pair (called their barycentre). By 1820, Hershchel had catalogued as many as 800 double stars. Astronomy was coming home to roost!

Binaries tell us a great deal about how they themselves and most of the other stars come into being and that their orbits hold a key to many of nature’s secrets. The one big question that took hold of the imagination of astronomers of the 19th century was: how and when did the stars of a binary system come into being? And exactly how?

Various conjectures (explanations) were put forward. But we shall take a look at the one that is most appealing, and scientifically plausible.

Earliest epochs in stars’ lives are within your knowledge already. That they start out from a few specks of dust and gasses. As their mass increases, so does their gravity with the passage of time. Then additional matter adds to both effects, called accretion. There comes a time when compaction and pressure lead to first, and earliest form of star called proto star, at which time nuclear reaction starts. Now, there is no stopping the activity!

It usually happens in a nebula — that cloud of dust and gasses — the cosmic debris, which is gradually turning into a star, (or many stars) though it is itself the remnant of an exploded star.

In one such nebula — visible to the naked eye — (Plaedies, or Surayyah) about 500 stars are coming into being. Clearly visible during winter nights it could have as many as 25 binaries! Then why not a binary anywhere you look? So, the birth of one star could be the birth of two or more stars from the same, common source. Now you know that it is not mere coincidence but a cosmic reality to have a sky full of binaries! When the nebula turns into stars, it usually is many stars that try to grab each other’s material and instead get trapped into their gravitational field and remain there forever, becoming a binary. With the universe being about 15 billion years old, the act of grabbing material has been going on for nearly that long, so binaries are not only numerous but are of many types and kinds.

Pulsars and many of their ilks remain to be looked into in the next issue!

The writer is a professional astronomer and a former head of PIA Planetaria. He can be reached at astronomerpreone@hotmail.com