Can stars become planets?
To the professional astronomers, the stars are part of a huge natural laboratory- one of enormous
extremes. Light years away, in the heart of the cosmos, stars provide a test bed to theories and
observations on behavior of matter, which cannot be comprehended through on- ground observations.
Our star, The Sun ,is no exception. It is halfway through its 10 billion lifespan,
and it too will fade away. There is still a lot of research ongoing as we speak about
stars and fates of stars. Are all stars similar? Do all of them have the same,
or seemingly same fate? What happens to stars when they die?
In today’s video, we are going to discuss a rather uncommon fate that some stars meet. Can Stars
become planets? Before we move on to this unusual topic, let's discuss more about stars and planets.
If you haven’t already watched our detailed video about stars, or how do stars die,
make sure to watch it till the end to completely comprehend this topic.
Let’s have a recap about planets, stars, and the fate of stars.
Before the space revolution, planets were hardly more than dots in the sky which revealed blurred
details when seen through a telescope.Now,thanks to surveys by diligent space probes, planets
are real "new worlds" with mountains , valleys , volcanoes , ring systems , and vast entourages of
moons. The temperature of the surface of planets can vary depending on its location from a star.
Planets are formed around newly formed stars when gasses and tiny particles come together,
spinning under the influence of their own gravity. The large planets further undergo
more collisions , throwing debris in space further forming more planets.
Stars, on the other hand, are giant balls made up of gas and dust which can have surface
temperatures varying to a large extent, depending upon the amount of gas utilized to form the star.
The hottest star category being Type O star and the coolest being Type M stars.
Stars are born inside a solar nebula, a large cloud of gas and dust. They are
formed in large numbers, and are initially called protostars, which further form a cluster of stars,
like the Tucane 47 globular cluster . The fate of a star varies depending upon its mass.
Stars, like our sun, belong to a category of stars known as main sequence stars. These stars continue
their fusion reactions in core for billions of years. During the end of their lives, they cool
down gradually and expand further to form giants and supergiants.They remain in the phase of giants
for about a billion year. During this time period,the star converts helium to lithium via
nuclear fusion reactions and further on converts lithium to beryllium and so on until iron.
When main sequence stars exhaust all of their fuel, they are left with a dense iron core.
Further, the gravity of the star weakens and they are unable to hold their outermost layers.
Hence they end up losing their outer layers in supernovas and form a “white dwarf” star
centered around the stellar remains of the dead star, WHite dwarfs are not ideal to be
classified as a planet. The main sequence Stars with mass greater than 1.4 times that of the sun,
end up in a supernova, which again, results in formation of planetary objects such as
black holes, neutron stars or white dwarfs. Such objects see no possibility of becoming a planet.
Now, the question arises. Can “ANY” star turn into a planet during any particular phase of its life,
As we couldn’t find the possibility of that happening throughout the lifecycle of an ideal
star. Or, are there possibly more classifications of stars? The answer to our questions is simple,
and lies within planetary nebulas, the birthplace of stars. Main sequence stars have no possibility
of turning into a planet by any means. However, there is another type of star, or better to say,
a failed star. The brown Dwarf. Many do not consider it as a star as it failed to sustain
a nuclear reaction . So what makes the brown dwarfs unique? Are brown Dwarfs habitable?
Not all protostars are able to become stars. Some blow away during their formation,
some are eaten away by other protostars, and some simply fail to start nuclear reactions.
Now imagine, what if, there was a massive protostar, which wasn’t massive enough compared
to other stars. Such a protostar wouldn’t be able to generate enough gravitational field at
its center to sustain nuclear fusions. Hence it simply stays as it is, unlike other protostars,
which compete against one another to become a star. Here, the brown dwarf comes .
Brown Dwarfs cannot fuse Hydrogen. The main fusion reaction supporting brown dwarfs is that of heavy
water, or deuterium, which is relatively very rare compared to abundance of hydrogen in space.
Hence, brown dwarfs exhaust their nuclear fuel early in their lives and cool down.
Such an object would simply radiate all of its energy into space, gradually cooling down over
billions of years and would then be dead rocky mass. In astronomical terms such objects are
referred to as brown dwarfs, the non igniting stars. Brown dwarfs are not actually brown in
color. They appear red through infrared imaging as they emit very low light rays. Brown dwarfs are
still massive enough to have planets around them in their orbits. Hence, Similar to a regular star,
planets revolve around brown dwarfs, making it look like a bunch of planets revolve around
a giant planet. An average Brown dwarf has a mass of 20 times that of jupiter.
In the early 20th century, a lot of research papers were being published on the discovery
of new stars and planets.In 1963, Dr. Shiv S Kumar, a professor at University of Virginia
predicted the presence of brown dwarfs or “black stars” as referred to by them. They made the
prediction based upon calculation of minimum mass required by a protostar to become a star.
However, it was not until 1995, that astronomers successfully detected the presence of brown
dwarfs. Brown dwarfs are difficult to observe as they emit very faint light and infrared
radiations, which were difficult to detect in early times. Hence, they remain cool and
undetectable throughout their life. Till date, only about 4000 brown dwarfs have been discovered.
But let's not forget the fact that brown Dwarfs are the “failed” stars. Hence,
even the smallest brown dwarf discovered was twice as massive as jupiter.
However, there's still a possibility of even white dwarfs becoming a planet. In fact, every star in
this universe, which will become a white dwarf in near future, will become a planet one day. Well,
don’t be surprised when i say, EVEN our SUN will become a planet, a real massive planet.
Although the gravity would still be extreme to such an extent that it won’t be habitable
for a living mechanism to survive, we still can classify it in the category of planets .
Let us go forward in the far future. After a septillion years, that is,
after ten billion trillion years, our universe will undergo an era known as the degenerate era.
The rate of expansion of the universe during this time would be faster than the speed of light,
hence making it impossible for light from one cosmological body to reach another
.As we know, the universe is expanding and will keep on expanding.
By this time, we all would have been flung apart in space in dark isolation from other
galaxies. All the presently existing stars would have been dead by that time, and the
newest generation of stars would have become white dwarfs. Even the white dwarfs would have
cooled down to such an extent in space that they could barely emit any more heat or light, ending
their lives by becoming a brown dwarf, a giant planetary object, radiating little to no heat.
There are endless possibilities to this question, awaiting more research and discoveries.
Well, we might not know the answer to these questions right now,
as we still have a long way to go. We may never even know the answers
to all questions, as the fate of our universe is the most mysterious amongst all.