Can A Gas Giant Become A Star?

As we know, stars – like our Sun – are burning balls of gas. They burn as a result of thermonuclear reactions which occur deep in their cores.

There are theories that Jovian-class planets – large planets also referred to as gas giants – could be turned into a star. In our solar system alone there are four known gas planets: Jupiter, Saturn, Neptune, and Uranus.

However, astronomers now only refer to Jupiter and Saturn as gas planets, as Uranus and Neptune have different compositions which classifies them as ice giants.

With that being said, there are still questions as to whether these gas giants could ever become a star, but the answer is a little more complicated than you’d imagine.

If we use the Sun as an example, an object which has a mass that is less than 8% of the Sun’s total mass, is unable to ignite these significant thermonuclear reactions in its core. These objects are considered ‘failed’ stars, otherwise known as brown dwarfs.

Although brown dwarfs are able to generate some energy to create heat in their youth, older brown dwarfs only radiate a small amount of heat because of their slow contraction.

Stellification

Stellification is a theory that discusses the process of how a brown dwarf star or Jovian-class planet can turn into a star.

Stellification also discusses how the luminosity of dim stars can be magnified significantly, e.g. the star shines brighter.

Although this is a theoretical process, there are a few different methods of stellification. So, let’s take a look.

Luminosity Magnification

The fusion reaction which occurs in stars is heavily dependent on temperature. In our own Sun, the proton-proton reactions have a reaction rate with the fourth power of temperature – T4. For other reactions in the carbon-nitrogen-oxygen (CNO) cycle – where stars convert hydrogen to helium – the reaction rate can be as high as T20.

So, if we were to increase the temperature of a star – even by a small amount – then this would increase the power input which would also increase the temperature and luminosity of the said star.

One way that this could be achieved is by using reflective solar sails. A solar sail is basically a mirror attached to a spacecraft that could (in theory) reflect the Sun’s heat back onto itself.

Now we’ve looked at the part of stellification which increases the luminosity of a dim star, let’s look at how gas giants could theoretically transform into stars.

Thermonuclear Ignition

As we’ve mentioned, a star burns as a result of thermonuclear reactions which happen at its core. But is there a way in which these reactions could occur in a gas giant?

Well, Jovian-class planets typically consist of hydrogen and helium. It has been theorized that if the concentrations of these hydrogen and helium isotopes can be found at certain depths then it may be sufficient enough to support a fusion chain reaction.

If there is sufficient energy, then this might be enough to ignite the thermonuclear reaction. However, the gas giant would also need a layer with a large concentration of deuterium (heavy hydrogen) and ultra-high-speed.

Black Hole Seeding

As noted, gas giants and brown dwarf stars are not able to achieve sustained fusion in order to form a star. This is largely in part to the fact that they do not contain the sufficient amount of mass needed to gravitationally compress the reactants to the extent needed to initiate the reaction.

However, there is a way that the density of the gas giant or brown dwarf could be increased, allowing fusion to initiate.

This method is known as black hole seeding, with the aim to “seed” the body with a black hole. At first, the black hole would begin to swallow the body of the gas giant or brown dwarf, however, the huge amount of radiation that would be caused by this process would resist the flow of further material.

This infall would be bound by the Eddington Limit, which is the maximum luminosity that a body can achieve when there is a balance between the force of radiation acting outward and the force of gravity acting inward.

After being subjected to a black hole, the Eddington Limit will show in Watts that the luminosity of the resultant star would be equal to six times its mass (in kg).

But how would they be able to move a black hole directly towards the body of the gas giant or brown dwarf star?

Well, there is a suggestion that the black hole can be moved into the correct position by placing an asteroid in orbit around the black hole and using a mass driver (or electromagnetic catapult) to direct matter into it.

The black hole should be able to move as a result of the conservation of momentum, or by harnessing the power that has been generated.

Could Jupiter Ignite Into A Star?

As the largest planet in our solar system, and one of only two official gas giants, it’s natural to wonder whether Jupiter could ever turn into a star.

In terms of size, Jupiter’s diameter is actually larger than the smallest known star (140,000 kilometers vs 121,000 kilometers). However, when it comes to stars, it’s mass, not the size that matters.

This is because the mass determines the internal pressure. If it is sufficiently high enough, it is able to overcome the conversion of hydrogen nuclei into helium through nuclear fusion. This process emits a huge amount of energy, which is what makes stars “shine”.

If a large cloud of interstellar gas were to come near Jupiter, then there is a possibility that the planet would be able to gain enough extra mass in order to start the thermonuclear fusion.

However, as Jupiter’s mass would still not be enough, the fusion would be short-lived, and it would become a brown dwarf (midway between a planet and a star). However, if it were able to accumulate even more mass, it could be just enough in order for it to become a true star, but it would be a dim red dwarf.

Although true stars, red dwarfs are the smallest and coolest kind of stars and are the most common star found in the Milky Way. If Jupiter had the capacity to become a red dwarf, it wouldn’t look much different from how it looks now, and its radiation would barely affect us on Earth.

However, there would be significant worry that its increased mass would disrupt our solar system, and the temperature of the Sun would increase as it would capture most of the gas cloud that gave Jupiter its increased weight.

Although in theory, Jupiter could turn into a star, the likelihood of it happening is virtually impossible. It needs to be around 80 times as massive in order to turn into a small red dwarf star.

What is the Smallest Known Star?

As mentioned, small stars are commonly referred to as red dwarfs. They are smaller and colder in comparison to other stars.

Contrary to popular belief, the closer a star is to red, the colder it is. In comparison, the closer a star is to blue-purple, the hotter it is. This refers to the electromagnetic spectrum and visible light which the human eye can detect. For reference, our Sun is white in color, placing it somewhere in the middle of the spectrum.

The smallest known star is EBLM JO555-57Ab, and it is about 600 lightyears away from Earth. Although it is slightly smaller than Saturn, this star has a mass which is 6.4% of the mass of the Sun. It is also 70 times the mass of Jupiter.

Final Thoughts

So there you have it, all the theories surrounding whether or not gas giants are able to turn into stars.

As established, most gas giants don’t have the mass needed in order to withstand the thermonuclear reactions that occur in the center of stars, and even if they are able to begin the reaction, most fail and become brown dwarfs instead.

Within our own solar system, we have two gas giants. Jupiter, the larger of the two, needs to be at least 80 times as massive in order to turn into a small red dwarf star. So, the possibility of it happening in our own solar system is near impossible.